CA2026219A1 - Measurement of cardiac performance - Google Patents

Abstract

Abstract Cardiac performance is measured by measuring the left ventricular pressure, measuring the left ventricular volume, determining the product of the left ventricular pressure and the left ventricular volume as a function of time, determining the time derivative of said product; and determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index. In this invention, the left ventricular pressure is measured by measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values. Preferably, the largest number of pressure measurements is conducted in the interval during the early ejection phase. This method reliably measures cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index.

Description

MEA8~REMENT OF CARDIAC PERFORMANCE

Field of the Invention The present invention relates to cardiac monitors generally and more particularly to cardiac monitors which measure left ventricular performance.

Baokqround of the Invention Various cardiac monitors are known in the art. the known monitors typically utilize measurements taken invasively using cardiac catheterization or noninvasively.
The prior art is summarized in an article entitled "Method for Noninvasive Measurement of Central Aortic Systolic Pressure," by A. Marmor, et al., Clinical Cardioloqv, 1987, 10:215, and the references cited therein.
8ummarv of the Invention The present invention seeks to provide an improved cardiac monitor and method for cardiac monitoring.
There is thus provided in accordance with a preferred embodiment of the present invention a method for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index including the steps of:
measuring the left ventricular pressure;
measuring the left ventricular volume;
determining the product of the left ventricular pressure and the left ventricular volume as a function of time;

1 determining the time derivative of the product; and determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that the step of measuring the left ventricular pressure includes the step of:
measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially z set of optimized pressure values.
Further in accordance with an embodiment of the present invention the method is further characterized in that the step of measuring the left ventricular pressure also comprises the step of employing an optimization algorithm which concentrates the largest number of pressure measurements in the interval during the early ejection phase.
Additionally in accordance with a preferred embodiment of the present invention, the method is additionally characterized in that the step of measuring ~0 the left ventricular pressure also comprises the step of measuring the arrival times of cardiac pressure pulses at a given site during the time period during which the left ventricular pressure rises from 100% to 125% of the end-diastolic value.
The method may also comprise the step of displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.
There is also provide a method for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac powsr index including the steps of:
measuring the left ventricular pressure and the left ventricular volume;
determining the product of the l~ft ventricular pressure and the left ventricular volume as a function of time:
determining the time derivative of said product; and ., J 2 i ~

1 determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that it also includes the step of displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.
In accordance with a preferred emhodiment of the invention, the method is also characterized in that it includes the steps of displaying, simultaneously and together with said electrocardiogram and pressure wave forms, the calculated delayed left ventricle pressure values and the calculated corresponding left ventricular volumetric values.
Additionally in accordance with a preferred embodiment of the invention, the method is further characterized in that it comprises the step of measuring during one or more cardiac cycles, the arrival time for the given occlusive pressure, and storage of the measured times for each pressure.
Further in accordance with an embodiment of the present invention, the step of measuring the time of arrival includes the step of rejecting time values having unacceptable variance.
Additionally in accordance with a preferred embodiment of the invention, the step of measuring the time of arrival also includes the step of statistical averaging of several acceptable sample points to reduce the effects of beat-to-beat variance, artifactual signals and noise.
Further in accordance with an embodiment of the invention, the step of measuring left ventricular volume includes the steps of taking least one measurement within 15 msec of QRS.
Additionally in accordance with an embodiment of the invention, the step of measuring left ventricular volume includes the steps of carrying out multiple volume measurements within 40 msec of each other.

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1Further in accordance with an embodiment of the invention, the method is further characterized by the steps of measuring the systolic and diastolic blood pressure.
SIn accordance with a preferred embodiment of the invention, there is also provided the step of calculating the cardiac power index as the slope of the best least squares regression fit to an entire set of instantaneous power values up to a maximum power point, excluding points 10whose values lie outside the range of variance that is commensurate with the other points.
Another preferred embodiment of the inventive method relates to a method of measurement of the left ventricular pressure as a function of time, i.e., according to this 15embodiment not the cardiac power index based on the product of pressure and volume as a function of time is ascertained, rather the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially a set of optimized pressure values, are 20measured, and indices from said arrival times at sa~d plurality of pressure values are derived, including but not limited to the time derivative of the pressure. These indices can be taken or evaluated for the characterization of the cardiac performance.
25The measured arrival times are preferably used for fitting a curve, said curve estimating the time varying wave form of the left ventricular pressure. The slope of the curve is calculated and defines one of the preferred indices.
30An especially preferred embodiment of the inventive method resides in measuring the arrival times by measurement of Doppler signals of blood flow at the given site. For this a specific Doppler ultrasound sensor and processor are used which are described below.
35The inventive method has the advantage that cardiac performance can be reliably measured under exercise stress ' conditions of the patient. This is especially achieved h 1 by the Doppler blood flow measuring method used together with a very specific processing of the received Doppler signals which results in a clear and noise-free characterization of the cardiac performance, i.e., pressure and volume-time or pressure-time curves.
Additionally in accordance with an embodlment of the invention, there is provided an apparatus for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index comprising:
apparatus for measuring the left ventricular pressure;
apparatus for measuring the left ventricular volume;
apparatus for determining the product of the left ventricular pressure and the left ventricular volume as a function of time;
apparatus for determining the time derivative of said product; and apparatus for determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that the apparatus for measuring the left ventricular pressure comprises apparatus for measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially a set of optimized pressure values.
Further in accordance with an embodiment of the invention, the apparatus for measuring the left ventricular pressure also comprises apparatus for employing an optimization algorithm which concentrates the largest number of pressure measurements in the interval during the early ejection phase.
Additionally in accordance with an embodiment of the invention, the apparatus is additionally characterized in that the apparatus for measuring the left ventricular pressure also comprises means for measuring the arrival times of cardiac pressure pulses at a given site during the time 2~2~

1 period during which the left ventricular pressure rises from 100% to 125% of the end-diastolic value.
Additionally in accordance with an embodiment of the present invention, there is also provided apparatus for displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.
Further in accordance with an embodiment of the present invention, there is provided apparatus for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index comprising:
apparatus for measuring the left ventricular pressure and the left ventricular volume;
apparatus for determining the product of the left ventricular pressure and the left ventricular volume as a function of time;
apparat~s for determining the time derivative of said product; and apparatus for de~ermining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that it also includes apparatus for displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.
Additionally in accordance with a preferred embodiment of the present invention, the apparatus is also characterized in that it includes the apparatus for displaying, simultaneously and together with said electrocardiogram and brachial pressure wave forms, the calculated delayed left ventricle pressure values and the calculated corresponding left ventricular volumetric values.
Additionally in accordance with a preferred embodiment of the present invention, the apparatus is further characterized in that it comprises apparatus for measuring during one or more cardiac cycles, the arrival 2~ iisJi~

1time for the given occlusive pressure, and storage of the measured times for each pressure.
Further in accordance with a preferred e~bodiment of the present invention, the apparatus for measuring the 5time of arrival includes apparatus for rejecting time values lying outside the range of variance of the other values.
Further in accordance with an embodiment of the present invention, the apparatusfor measuring the time of 10arrival also includes apparatus for statistical averaging of several acceptable sample points to reduce the effects of beat-to-beat variance, artifactual signals and noise.
Additionally in accordance with a preferred embodiment of the present invention, the apparatus of 15measuring left ventricular volume includes apparatus for taking at least one measurement within 15 msec of QRS.
Further in accordance with a preferred embodiment of the present invention, the apparatus for measuring left ventricular volume includes the apparatus for carrying out 20multiple volume measurements within 40 msec of each other.
Additionally in accordance with a preferred embodiment of the present invention, there is also provided apparatus for measuring the systolic and diastolic blood pressure.
25Furthermore, the invention concerns an apparatus for carrying out the method according to one of the claims 14 or 15.
Additionally in accordance with a preferred embodiment of the present invention, there is also 30provided a pulse wave sensor and/or pulse wave processor with reduced motion artifact~effects.
Further in accordance with a preferred embodiment of the invention, the apparatus for detecting the arrival of the cardiac pressure waves at a given site, preferably at 35the brachial artery site, is a Doppler - ultrasound arterial wall motion sensor.

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1 According to an especially preferred embodiment of the inventive apparatus, the means for detecting the arrival of the cardiac pressure waves at a given site, preferably at the brachial artery site, is a Doppler ultrasound blood flow sensor. the sensor itself and a corresponding processing unit combined therewith allow the rejection of motion artifact effects.
The Doppler ultrasound sensor (transducer) is advantageously held by an armband mount comprising an adjustable transducer mount fixed to an adjustable attachment strap. The Doppler ultrasound sensor (transducer) is preferably formed as a flat package with Doppler crystals mounted so as to provide fixed angle of illumination, typically 30 to horizontal.
Said pulse wave processor preferably contains a high-pass filter separating the high frequencies from the audio signal and an RMS-amplitude-to-DC converter measuring the power of the high frequency spectrum by converting the total RMS (root mean square) into a proportional DC voltage.

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1rief Descripti~n of the Drawin~s The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in 5which:
FIG. 1 is a functional block diagram of the cardiac power index monitor (CPIM) constructed and operative in accordance with a preferred embodiment of the present invention;
10FIG. 2 illustrates a system implementation based on the embodiment of FIG. l;
FIGS. 3A, 3B and 3C illustrate the derivation of points on a pressure-time curve using a cuff, an ECG, and a distal pulse wave form sensor;
15FIGs. 4A, 4~ and 4C are a collection of idealized graphs of ECG, brachial arterial pressure and brachial arterial wall motion as a function of time, which are useful in understanding the operation of the apparatus of FIG. 1;
20FIG. 5 illustrates one possible version of a cuff pressure control algorithm for optimal decrementing of cuff pressure;
FIGS. 6A, 6B and 6C illustrate the acquisition and synchronization of composite volume and pressure curves, 25and the calculation of the resulting cardiac power curve, from which the cardiac power index (CPI) is derived;
FIG. 7 is a flow chart describing the operation of the apparatus shown in FIGS. 1-6:
FIG. 8 shows a specific embodiment of a pulse wave 30form sensor together with holding means;
FIG. 9 shown another embodiment of the holding means for the pulse wave form sensor;
FIG. 10 is a block diagram of a processor for the pulse wave form sensor;
35FIG. 11 is an exact circuit of the processor according to FIG. 10;

~ ~J U ~ IJ f-~ ~ 3 l FIG. 12 is a block diagram of a cuff pressure control unit; and FIG. 13 is an exact circuit of the cuff pressure control unit according to FIG. 12.

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1 Detailed Description of the Pre~ent Invention In an article entitled, "Noninvasive Assessment of Myocardial Performance," by A. Marmor, et al., published in the Journal of Nuclear Medicine, vol. 30, No. 10, Oct. 1989, and incorporated herein by reference as Annex A, the author defines a measure of cardiac performance known as the ejection rate of change of power, which is referred to herein as the cardiac power index or CPI. CPI represents the rate at which cardiac power changes during the period of ejection of blood from the heart, known as early systole, and is estimated from the cardiac power curve., The cardiac power curve is obtained by taking the time derivative of the product of the cardiac left ventricular pressure and volume during the early part of systole.
Reference is now made to FIG. 1 which illustrates, in block diagram form, a cardiac power index monitor, constructed and operative in accordance with the present invention. Reference is also made of FIG. 2, which illustrates a system implementation based on the embodiment of FIG. 1. the cardiac monitor, denoted by reference numeral 10, comprises a microcomputer 20, which is preferably IBM-PC compatible. the microcomputer 20 preferable controls all monitor functions and drives a physiological data display 22, such as an EGA graphics video monitor, and a cardiac power index (CPI) display 24, which may be provided by the same apparatus used for display 22. The microcomputer 20 also stores data in and retrieves data from a mass storage device 28, preferably a hard disk drive with at least 10 mbytes, and drives a hard copy device 26, preferably an Epson compatible dot-matrix printer.
The monitor of FIG. 1 also comprises noninvasive blood pressure measurement (NIBP)/cuff pressure controller (CPC) apparatus 30, such as a Bosch EBM 502 D, for measuring the brachial arterial pressure and heart rate, and which operates a sphygmomanometric cuff 38. Cuff 38 P ~

1 is preferably a wrap-around type such as that used in the PediSphyg system by CAS Medical, Inc. of Branford, Connecticut, U.S.A., or a Bosch cuff. The cuff pressure controller incorporates appropriate interface and con~rol circuitry and software to enable the operation of apparatus 30 in the mode of pressure control of cuff 38 instead of its conventional mode of operation for blood pressure measurement. A block diagram of the controller is shown in FIG. 12.
The monitor 10 also includes an ecg monitor 70 and an R-wave detector and trigger generator 72, both typically contained in standard ecg monitor systems such as a Mennen Horizon 2000 patient monitor.
Also included in ~onitor 10 is a pulse wave form sensor 40, namely, a Doppler ultrasound wall motion and blood flow detection sensor, such as MedaSonics model 94G, attached to the same arm as the cuff 38, and approximately 1-3 cm distal to lt. A pulse wave form processor 42 (shown in FIG. 10), preferably an analog and/or digital circuit whose input is the wave form from sensor 40, provides an analog output which is preferably proportional to the blood flow.
Alternatively, the output may be proportional to the wall motion or the velocity of wall motion. In either implementation, high-pass filters eliminate most of the influence of motion artifacts from the output signal to the A/D converter 44, whose digital data output is read by microcomputer 20.
A gamma camera 60, which may be a commercial field-of-view gamma camera, such as an Elscint Model APEX
and its associated CPU 62, receives a gating R-wave trigger either from an ECG monitor 70 or from its own internal ECG monitor. In response thereto, camera 60 records a plurality of frames of several milliseconds' duration at intervals of typically 25-40 milliseconds throughout each cardiac cycle, averaging together the frames from many (typically 300) cycles to obtain the h ~, t~ `3 1 averaged volumetric frame values along the time curve through the cardiac cycle.
A gamma camera CPU 62 communicates the resulting data values to microcomputer 20 via a digital link, preferably RS232 or Centronics parallel, or alternatively via disk transfer.
As illustrated in FIG. 2, cuff 38 is attached preferably above an elbow, and is controlled by microcomputer 20 via cuff pressure controller 30. An R-wave detector and trigger generator 72 senses the sharp spike-like wave of the ECG, known as the QRS complex, and provides a digital trigger pulse corresponding to the occurrence of the R-wave (the center of the QRS spike).
It is proposed in the article by A. Marmor, et al., ~5 of Annex A to measure a cardiac power curve and from it to calculate a cardiac power index. Cardiac power is defined as the time derivative of the product of cardiac volume and cardiac (or aortic) pressure with time. the cardiac power index is defined as the slope of the portion of the power versus time curve from onset of systole to the moment of maximal power.
Determination of the cardiac power curve and cardiac power index (CPI) using the cardiac monitor 10 is described hereinbelow.
E~timation of ~eft V~ntricular Pressure occlusion of brachial flow during most of the cardiac cycle creates a standing fluid column between the aorta and the brachial artery, such that the rising intra-aortic pressure wave form is transmitted to the brachial artery with minimal distortion. Accordingly, the pressure values obtained at the brachial artery very closely represent those in the left ventricle.
In order to enable later combination with left ventricular volume measurements made at the heart, the brachial pressure values must be shifted in time to account for the propagation of the cardiac pressure wave 1 from the heart to the brachial artery. The post-QRS time required for a cardiac pressure wave to travel from the heart to the brachial artery measurement si~e is known herein as the propagation time, as is discussed ~elow in conjunction with FIG. 5. The propagation time for a given patient during the examination period is presumed constant under all conditions of heart activity.
The operation of the cardiac monitor 10, including the calculation of the CPI, is described in the flow chart of FIG. 7. Patient preparations for gamma camera ventriculography are completed, and 3-4 ECG electrodes 41 are attached in standard thoracic montage, for input to ECG apparatus 70. While the patient is at rest, cuff 38 is applied just above an elbow, and the pulse wave form sensor40is attached 1-3 cm distal to the cuff on the same arm. The pulse wave form signal is acquired by microcomputer 20 from apparatus 42 and displayed together with the ECG, on the physiological data display 22, where the c~ality of both ECG and pulse wave form signals are used as visual feedback to verify proper signal acquisition or to guide any required adjustment.
FIG.S 3A, 3B and 3C illustrate the technique by which the sample points on the composite pressure-time curve are determined, through the relationship between brachial arterial pressure, cuff pressure, the ECG QRS complex, and the detection of a pulse wave form distal to the cuff.
Two simplified cardiac cycles are shown with representative parameter values in FIG.S 3A-3C. In the first cardiac cycle, systolic pressure is 110 and cuff pressure is set to 100 Torr, while in the second cycle, systolic pressure is 115 and cuff pressure isset to 90 Torr.
Shown in Fig- 3A are the brachial pressure wave form, the cuff pressure, and the ECG wave form, indicating the relative timing of the QRS complex o each cardiac cycle and the resulting brachial pressure wave form.
Point Al of cardiac cycle 1 occurs at the first instance during the cycle when brachial pressure exceeds i'~J~ J

1 cuff pressure. i~eferring to Fig. 3B, which depicts the pulse wave form produced by pulse wave form processor ~2, it is noted that tha pulse wave form abruptly rises at point Bl, whose occurrence coincides in time with point Al of FIG.
3A, as the blood pressure wave passes the cuff, i.e., breaks through, and causes arterial wall motion that is sensed by device 42.
The time delay from the QRS complex to the beginning of the abrupt rise of the pulse wave form, labeled Tl and having a value of 220 msec in FIG, 3B represents the time, after the QRS complex, when brachial arterial pressure reached 100 Torr. In FIG. 3C, which represents the composite pressure-time curve, point C1 has a pressure value of 100 Torr and a time of 220 msec, in accordance with the pressure and time values of points Al and Bl above. It is noted that the time scale of FIG. 2C is in msec, whereas that of both FIGS. 3A and 3B is in seconds.
In similar fashion, in cardiac cycle 2, where systolic pressure is shown as 115 Torr and cuff pressure is shown as 90 Torr, points A2 and B2 correspond to the time when the blood pressure wave breaks through the cuff, which occurs at 180 msec after the Q~S of cardiac cycle 2. In FIG. 3C, point C2 is shown at a pressure of 90 Torr and a time of 180 msec, in accordance with the pressure and time values of points A2 and B2 above. In actual implementation, each point on the composite pressure-time curve is determined by averaging together the delay times measured for a given cuff pressure maintained over a plurality of cardiac cycles.
While the patient is still in resting position, the operator causes the cardiac monitor 10 to commence measurement initialization. During initialization, prior to application of any pressure on cuff 38, the arterial pressure propagation time from heart to brachial artery iS estimated, and the pulse wave form is characterized.
Cardiac monitor 20 is operated to measure the maximum and minimum pulse wave form values. Pulse waveform values 1 MAX~MP and MINAMP are the respective average maximum and minimum values of the pulse wave form output of detector 42 during a plurality of cardiac cycles, preferably 10.
MAXAMP is preferably obtained by averaging together the maximum a~plitude value of the output of detector 42 from the aforementioned plurality of cardiac cycles, while MINAMP is preferably obtained by averaging together the minimum amplitude value of the output of detector 42 from each of the aforementioned plurality of cardiac cycles.
FIGURES 4A, 4B and 4C illustrate a method for calculating the propagation time, which is also used for calculating the breakthrough time referred to below and in Procedure ARRIVAL of FIG. 7. FIGURES 4A, 4B and 4C, respectively, show the ECG wave form, brachial arterial pressure wave form, and pulse wave form for two idealized cardiac cycles. The propagation time is calculated by first detecting the steep upswing of the pulse wave form shown in 4C.
A regression line, labeled S1 in the first cycle and S2 in the second cycle, is fitted to the early portion of the upswing, preferably to the samples from the first 30 milliseconds of the upswing. A second regression line, labeled D1 in the first cycle and D2 in the second cycle, is fitted to the last portion of the wave form prior to the upswing, preferably to the samples during the last 30 milliseconds prior to the upswing. The time interval T1, from the R-wave of QRS 1 until the intersection point Bl between lines S1 and Dl~ is the arrival time of the pulse wave of cardiac cycle 1 at the pulse wave form sensor 40.
Similarly, the time interval T2, from the R-wave of QRS
2 until point B2 is the arrival time of the pulse wave of cardiac cycle 2 at sensor 40. When determining propagation time, the above arrival times are preferably averaged together from a plurality of cardiac cycles, preferably 10 cycles.
The operator then causes the apparatus 30 to obtain the diastolic and systolic pressure values, and the heart ~3 1 rate, via microcomputer 20. A cuff pressure control algorithm, one embodiment of which illustrated in FIG. 5, uses the measured diastolic and systolic pressure values, and selects the pressures to which the cuff is to be inflated.
In a particularly important characteristic of the present invention, the series of pressure values to be implemented by the cuff 38 are defined such that the largest number of pressure measurements are concentrated during the early ejection phase, typically defined as the phase between 100-125% of the end-diastolic pressure. An example optimization algorithm for defining the pressure values is illustrated in FIG. 5, wherein the pressures P0 through P9 are set as follows:
for DP - Systolic pressure - Diastolic pressure P0 - 1.25 Systolic Pl - Systolic pressure P2 - Systolic - 0.25 DP
P3 - Systolic - 0.50 DP
P4 - Systolic - 0.65 DP
P5 - Systolic - 0.75 DP
P6 - Systolic - 0.85 DP
P7 - Systolic - 0.90 DP
P8 - Systolic - 0.95 DP
P9 - Diastolic pressure The number of points, and their precise dependence on systolic and dia~tolic pressure, may vary from the foregoing, so long as there are a plurality of points in the pressure ran~e from the end-diastolic point to midway up the systolic rise, i.e., from diastolic pressure to (systolic - 0.5 DP). In response to an operator instruction to monitor lOj cuff 38 is inflated to pressure P0, and the pulse detector output used to verify occlusion of flow by the cuff.

1 The threshold for confirmation of occlusion is when the output amplitude of pulse wave form detector 42 is less than a fraction of the difference between aforementioned MAXAMP and MINAMP, preferably 0.05 (MAXAMP-MINAMP). If the original cuff pressure P0 does not reduce the output of detector 42 per above, the value of P0 is increased, preferably by 10% of its previous value, and the confirmation procedure repeated. The above is repeated until occlusion is confirmed or until P0 reaches a maximum of 150% of systolic pressure. once occlusion is confirmed, the detected pulse wave form values are averaged together over a plurality of cardiac . cycles, typically 10, to obtain an average baseline value AI~P.
The operator then operates monitor 10 to commence the measurement of the pressure-time curve. Cuff pressure is reduced to value Pl, intended to allow breakthrough only near the systolic peak. Microcomputer 20 analyses the pressure wave form signal in real time during the current cardiac cycle to determine if and when breakthrough occurs. Breakthrough is typically defined as thepoint when the wave form value first rises significantly above the baseline, which in the preferred embodiment is defined as a rise of more than three standard deviations above the aforementioned baseline average value AMP.
If and when breakthrough is detected, the method described above in determining propagation time is used to estimate the breakthrough time. The above procedure is repeated during at least 2, typically 5-10, cardiac cycles for the same cuff pressure setting, providing at least 2, typically 5-10, estimates of the breakthrough - time for the pressure, from which mean and variance are calculated for said breakthrough time. Before proceeding to a new cuff pressure value, the set of breakthrough time estimates is reviewed, and outlying values (typically those lying more than three standard deviations from the mean) are excluded from the set, and a new final mean 1 value calculated. The final mean value is the one stored in the pressure-volume curve for the cuff pressure value used.
Once the final pressure-time point has been determined for a given cuff value, the cuff pressure is then reduced to the next value determined in the cuff pressure control algorithm, until the last value has been completed.
It will be appreciated from a consideration of FIG.

3 that at low pressures, such as those close to the diastolic pressure, the above-mentioned method may be unreliable as the required standing column of blood is not well established prior to the onset of systole.
Hence, the pressure-time value for onset of systole is taken to be the most recently measured diastolic pressure value and its time is taken to be the aforementioned propagation time determined when the patient was at rest.
The set of pressure values thus obtained is interpolated typically by a piecewise polynomial curve fit by least squares minimization to provide estimated pressure values at any desired time point during the systolic portion of the cardiac cycle. The pressure curve as shown in FIG. 6B, which typically comprises an average of pressure values recorded over a multiplicity of cardiac cycles as described hereinabove, is then shifted by the amount of the propagation delay, thereby producing an estimated left ventricular pressure curve.

Left Ventricular Volume Determination Reference is now made again to FIG. 1~ As noted above, in the preferred embodiment, the invention additionally comprises a field-of-view gamma camera 60, such one commercially available from Elscint of Haifa, Israel, and its associated CPU 62. The gamma camera 60 and CPU 62 measure the volume of the left ventricle using gated radionuclide ventriculography according to the count rate method as described in "Left Ventricular Pressure-Volume Diagrams and End-systolic Pressure-Volume - ~o -1 Relations in Human Beings," by McKay, R.G., et al., and published in Journal of the American Colleqe of Cardioloqy, vol. 3, 19~4.
In accordance with a preferred embodiment of the invention, the R-wave detector 72 detects the R-wave of the ECG signal. Alternatively, if gamma camera 72 incorporates an ECG apparatus and associated QRS or R-wave detector, the QRS or R-wave is detected by the detector of the gamma camera.
A predefined amount of time later, typically 10-20 msec, the gamma camera 60 counts the number of gamma rays coming from the left ventricle during a predefined time frame, typically 5-10 msec. The gamma camera 60 repeats the measurement every typically 20-50 ms, producing sampled points on a curve of the left ventricular volume with time. The volume curve thus produced is typically synchronized to the QRS complex via the R-wave detector, and is illustrated in FIG. 6A.
Typically, the volume curve will have only a few points and, thus, it is typically interpolated by least squares piecewise polynomial curve-fitting methods. Thus, an interpolated volume curve, illustrated in FIG. 6A, is calculated which has data at the same time points as the pressuxe curve calculated in accordance with the method described hereinabove. The cardiac power curve can thus be calculated from the volume curve and the pressure curve, as illustrated in FIGS. 6A, 6B and 6C.

Calculation of Cardiac Power Curve and CPI
At a plurality of points throughout systole, typically 32 points, the product of the corresponding pressure and volume values is calculated. The time derivative of the product is typically estimated using a second order central difference methodj to produce corresponding points on a cardiac power curve, illustrated in FIG. 6C. In the preferred embodiment, the CPI is calculated from the cardiac power curve values as follows:

1A linear regression line is fitted to the points of said power curve between the start of systole and up to and including its maximum value. Any data points whose value lies more than two standard deviations from the 5linear regression line are excluded. After having excluded the outlying points, a new regression line is calculated, and its slope is used as the final CPI value.
The entire sequence of operation of monitor 10, as described above, is summarized in FIG. 7.
10FIG. 8 shows a pulse wave form sensor 40 together with its mounting means. The sensor 40 is a Doppler ultrasound arterial blood flow sensor and comprises a Doppler ultrasound transducer 80 which is formed as a flat package. This enables a stable, compact mounting on the 15patient's arm. The Doppler crystals are mounted so as to provide a fixed angle of illumination, typically 30- to the horizontal.
The transducer is held by a transducer mount 81 which is adjustably supported in a bracket 85, the two legs of 20which serve for the attachment of a strap 83 which is put around the arm of a patient. The strap 83 can be fastened around the arm in a tight manner by an adhesive-free connection of its ends, for instance by means of Velcro material. At its inner side, the strap has a plurality 25of pieces 84 of a compressible material which serve for the absorption of shocks and movements.
After initial attachment of the transducer in approximate location, a fine adjustment of transducer position is made by an adjustment means including a screw 30shaft 82 extending through corresponding bores in the bracket 85 and the transducer mount 8i and through two retaining rings 87 on both sides of the bracket. The screw shaft can be manually operated by a ~nob 86 at its one end. By turning the knob 86, the mount 81 and then 35the transducer 80 is moved transversely with respect to the arm of the patient.

~332 ~3 1 This embodiment allows a reliable attachment to the arm without adhesives and maintenance of adequate pressure of transducer against the desired skin location.
Another embodiment of the mounting means for the transducer is shown in FIG. 9. The transducer 200 is identically shaped as in FIG. 8. It is also held by a transducer mount 201 having the shape of an inverted U.
According to this embodiment, the mount can be moved vertically in the drawing so that the pressure with which the transducer is pressed against the arm can be adjusted.
This is realized by means of an adjustment screw 203 which can be manually turned (at 204) and which extends through a screw bore in a bracket 202. Accordingly, by turning the screw, the distance between the mount 201 and the bracket 202 is varied and the transducer package is thus pressed against the arm.
As in the embodiment of FIG. 8, the two legs of the bracket 202 serve for the attachment of a strap 205 which can be put around a patient's arm. The strap can be fastened in a tight manner by means of a similar connection as shown in FIG. 8.
It is now referred to an embodiment of a pulse wave form processor 42 of which a block diagram is shown in FIG. 10. The processor has the following components:
120 BIDIRECTIONAL DOPPLER PROBE, model MEDASONICS P 94-A, is a 5 MHz Doppler blood flow transducer connected to the driving circuit.

121 PHASE SHIFT BOARD, MEDASONICS p.n. 109-0051-010, separates the sounds of the advancing blood flow, providing two high level audio outputs.

122 AUDIO BAND PASS, passes the frequencies between 70 Hz and 15,000 Hz, suppressing noise, especially the 50/60 Hz "hum".

2~ f' 1 123 POWER AMPLIFIER provides the speaker drive and volume control from the front panel.

124 HIGH-PASS FILTER separates the high frequencies from the audio signal. The blood break-through generates high frequencies (beyond 1400 Hz). This filter also attenuates the sound generated by the receding flow which has lower frequencies.

125 RMS to DC CONVERSION measures the power of the high frequency spectrum by converting the total RMS (root mean square) into a proportional DC voltage.

126 PROGRAMMABLE GAIN CONTROLLER, allows amplification of the RMS value under computer control. Three bits set eight levels of gain. The processed Doppler signal is available at the BNC output connector.

127 ISOLATION BUFFER, transfers the processed Doppler signal to the A/D converter which is isolated, according to patient safety standards.

According to this embodiment, the processor provides an analog output which is preferably proportional to the total rapid blood flow, i.e., the portion of the blood flow detected by sensor 40 which is flowing with significant velocity. The processor produces an output to an A/D converter which is proportional to the root mean square (RMS) amplitude of the Doppler audio shift frequencies above the smaller of 300 Hz or a frequency equal to the multiple of the Doppler carrier frequency and the factor 6 x 10 5.
FIGURE 11 shows an exact circuit of the processor according to FIG. 10.
FIGURE 12 is a block diagram of a cuff pressure control unit, i.e., of the pump controller 36 1 shown in FIG. 1. An exact circuit of this unit is shown in FIG. 13.
The cuff pressure controller has the following components:

101 PARALLEL INTERFACE, configured as an 8-bit parallel port, D-15 connector, receives the commands from the PC (Dell Computer). The available commands are:
- INFLATE
- STOP
- SLOW DEFLATION OF GIVEN RATE
- FAST DEFLATION

102 8 BIT LATCH stores the received command, controlled by STROBE pulse.

103 DIGITAL TO ANALOG CONVERTER uses the six most significant bits to generate 64 voltage steps(2.56 V
full scale, 40 mv per bit).
104 VOLTAGE CONTROLLED CURRENT SOURCE converts the constant voltage into constant current, according to:
current = input voltage/20k ohm which means 2 microamp per bit (126 microamp max).
105 CAPACIIOR DISCHARGER is a circuit capable of discharging a 1000 ~f capacitor, with constant current provided by block 104, in a floating mode (none of the terminals connected to the ground).
Due to the constant current discharge the voltage across the capacitor falls with a constant rate given by:
dv = l/c time current which gives a min of 2 mv/sec and a max of 126 3s mv/sec.

" . ~

1 106 COMMAND DECODER receives the two least significant bits of the received byte, decoding the four basic commands: inflate, stop, quic~ deflate and deflation of given rate.

107 CHARGE/DISCHARGE SWITCH connects the low leakage capacitor (used as sample & hold) to the charge or discharge circuit. The analog switch is DPDT type.

108 L0W LEAKAGE CAPACITOR, 1000 ~f, is used as a voltage memory. The voltage across the capacitor follows the actual cuff pressure value. Discharging it with a constant current generates a linear decreasing voltage.
109 CAPACITOR CHARGER & COMPARATOR, determines the voltage across the capacitor to follow the actual cuff pressure value. The value is received from the Bosch unit as 1 volt per 100 mm Hg pressure.
110 QUICK RELEASE CIRCUIT is a driver for the quick release valve of the Bosch unit. Quick deflation occurs upon receiving the corresponding command or when the pressure reaches the maximum allowed value (300 mm Hg).

111 OVER PRESSURE PROTECTION is an emergency circuit which completely deflates the cuff at 300 mm Hg pressure. This factory value can be changed by use of an internal potentiometer.

h 1~ 2 ~ f.~

1 112 VOLTAGE COMPARATOR is the feedback loop controlling the Bosch's deflation valve. During the slow deflation, the capacitor is discharged with a proqrammed constant current. The voltage across the capacitor is a linear descending ramp. The comparator compares this voltage with the actual pressure value. The amplified error value drives the deflation valve. As a result the pressure decreases at the programmed rate.
113 OFFSET CORRECTION, allows the calibration of analog pressure value against a standard manometer.
The cuff pressure controller has the following principle of operation: -Upon receiving (through the parallel port) the command INFLATE the pump is energized and inflates the cuff until the STOP command is received. During the inflation the capacitor is accurately charged to a voltage value equal to the actual pressure.
The SLOW DEFLATE command contains six bits which finally are converted into a constant current. This current discharges the capacitor generating an internal built-in linear voltage ramp. The comparator compares this voltage to the pressure value amplifying the difference. The error voltage drives the deflation valve forcing the pressure to follow the ramp. With the described values the minimum deflation rate is 0.2 mm Hg per sec and the maximum 12.6 mm Hg per sec.
The QUICK DEFLATION command deflates the cuff immediately.
The STOP command freezes the cuff pressure to the last value.
It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow.

-, --2 7 -- t `
~nn ~ ~ /4 __ _ ~ __ _ Radionuclide Ventriculography and Central Aorta Pressure Change in Noninvasive Assessment of Myocardial Performance Alon Marmor. Tali Shanr, Izhar Ben Shlomo, Rafael Beyar, Alex Frenkel, and Dov Front Depanmen~ o~Cardiology, Rebecca SieD ~ospital. Safed: Depanmen( of l~luclear .1Sedicine, Rambam llospi~a/, Haifa; Depanment of Biomedical Engineenng and Department of Cardiology, Rambam Medical Cemer: Technlon-llT, Far,~lly orl~edicine, Hai~a, Israel Systolic pressure-volume diagrams were obtained noninvasively by measunng the systo~ic eentral aonic pressure with a new devic~ and by combining the pressure measurements. thus obtained, with a~solute volume measurements obtained by radionuclide ventncu~ography during ejection. By dividing the peak power by the time elapsed from the beginning ot ejection to the peak power point, the ejectbn rate of change of power (ERCP) was calculated. The ability of this index to assess left ventncular function at rest and exercise was evaluated in ten healthy subjects. ERCP proved to be more sensitive than global left ventricular ejection f raebon increasing tivefold ~rom rest to exercise compared with only 2û% increase in global ejeetion fraction. ERCP inr,reased dramatically postexercise from 3411 ~ 2173 to 18 162 14 633 gm/secZ, median 12 750, 95% confidence interval 970û-29 600. in healthy, whil~ in pabents it increased twofold from 2637 + 824 to 5û62 ' 1897 gm/sec2, median 4û70. 95%
confidence interval 2800-7030, p < 0.001. ERCP had an excellent discriminative power in differentbting healthy subjects from patients. having 100% sensitivity, 9û% specifidty. 95%
aeeuraey, 95% positive prr,~dictive value, and 90% negative predicbve value. Thus, this noninvasive index seems to have a more comprehensive ability to evaluate changes in le~' ventrleulat ~unction and shows a promising potential lor elinieal applications.
J Nucl ~led 30:1657-1665.1989 Maior efforts were made in the last decades to powerandtheejectionr,lleofchangeofpower(ERCP) develop a reliable index to evaluate left ventricular to evaJuate left ventricular perforrnance. They demon-perfor,mance. These effons included the development strated the superiority of their inde~t jD animal studies of invasive indices obtained during cardiac catheteri- and in catheterization studies in patients. The invasive zation such as ma~dmal left ventricular DP/DT. as well nature of this method prevented it from becoming an as noninvasive indices such ns left ventricular ejection everyday clinically accepted diagoostic tool.
fraction at rest and during exercise. In recent studies In the present study an attempt was made to generate (1-3) pressure volume diagrams were generated for noniovasively the power indices described by Stein and diagnostic purposes for the evaluation of left ventric- Sabbah and to nssess their ability to evaluate leR ven-ular performance using radionuclide ventriculography tricular function in healthy subjects under varying con-for volume measurements and left ventricul~r intrlc:~v- ditions. The noninvasive measurementswere made pos-itary pressure recordings. In spite of their invasive na- sible by a new instrument allowing noninvasive meas-ture, these studies demonstrate the clinical importance urement of the central aorliC pressure (6). This method of pressure-volume loops and provide a new insight was found to yield a good correlation with the ascending into the leh ventticular fuDction. Stein ~nd Sabbah aor~ic pressure wave as measured by a Millar tipped (4,5) in a series of studies used left ventrtcular systolie manometer in p~tients during heart eatheterization. By combining this method with radionuclide measurement Received Dec.8,1988; rev~sion ~ccepted May 9,1989. of leh ventricular absolute volume, pressure-volume For reprinu contacc A. Mar~nor, MD, Dept. or Cardiology, curves were generated and the leR ventricular systolic RebeccasierrHosp~ srael l3loo~ work and power were calculated:.The mean ejection Volume 3û Number 10 October 1989 1 657 ~ _ - 2 8 - ~ ~ h ~

rate of ch tnge of power (ERCP) in early systole waS mean power, peak power. and the rate of change of power calculaled from the power-time curve. We attempted were compared with the change in global LVEF.
to deterrnine v~hether this index would be more sensi- The De~ice tive than other ejection indices (ejection fraction. mean The components and the theoretic pnnciple of the device power, tnd p~: tk power) in assessing leh ventricular and its elemems were reponed in a previous work (6) and are function tt rest and Ltfter exercise. brieflv summanzed here. The device is composed of four elements:
(a) a sundard sphygmomanometric cuff with an internal MFIl~ODS transducer measuring ~he imracuff pressure. The cuff is pro-vjded with an automDtic dellecting device controlled by a Patient Populsltion microprocessor allowing gradual and constant delllation;
The study was performed in nine male patients 3 to 6 mo (b) an addiuonal narrow sphygmomanometer cuff con aher an acute myocardial infarction (Ml), mean age 56 + 5 nected to a high sensitivity pressure transducer placed 1-3 cm yr (patients) and ten healthy subjects (male, mean age 56 + below the occlusive cuff:
12 yr). The patients were included if they had a documemed (c) a sundard ECG monitoring svstem: and Ml by elevation of total CK above 120 IU/I (>90 IU normal (d) all three elements are connected through an analog to value), and CK-MB fraction above 4~O. and had a normal or digital convener to a censral processinr unit ICPU) consisting near normal ejection fraction (>44%). There were six padents of an INTEL 8088 micro-processor. The output is displayed with an inferior Ml and three patients wjth a non-Q wave Ml. on a monitor screen (Fig. I ).
mean total CPK being 655 + 160 IU with 6 + 2L/-o CK-MB. The method is based on the creation of a sunding fluid Global left ventncular ejection fraction ~LVEF) measured by column from the aona to the occluded brtchial anery during radionuclide ven~riculogrtpny was 57.11 1 9.3%. ranging theentireprrJcessofpressuremeasurements.Bvapplyingan between 44% to 73%. No regional wall abnormalities were occlusive pressure on the brachial anerv dunng systole using detected in any of the patients. an intlauble cuff. 3 temporarv sunding IIuid column is created The nommal group included ten subjects wjth no symptoms in which the nsing intraaonic pressure is transmined to the of angina pectoris. Mean global LVEF in the healthy subjects periphery with minimaJ distonion. The time intervals needed was 61.1 ~: 7%. rangjng from Sl% to 75%, p = N.S.. when for the aonic pressure wave to overcome a ,iven occlusive compared to the study group, All subjects underwent supine brachial pressure applied bv the inll tuble cuff on the ann are exercise radionuclide ventrieulography which WaS stopped equal to the time intervals needed to reach the same pressure aher 3 min at 100 W. The increase in heart rate and blood in the central aonu plus the propag~tion tirne to the brachial pressure are summarized in Tlble 1. None of the subjects point, which is constant in the same patient throughout the experienced chest pain, trrhythmias. or ST-T wave chmges. measurements. Time inter als are measured from the onst Three patients eomplained of fatigue and shonness of breath. of depolarization ~QRS comple~ servin~r IS I reference s-stem ~
Measurements were uken before (at rest~ and immediately to the detection of the pressure wave b: an extemal transducer aher exercise. Absolute LV volumes were measured b,v the at the brachial anery level. Application ot muhiple. successive, count rate methods ts descrioed (3). At the same time. non- occlusive pressures on Ihe brachial aQerv decreasing sequen-invasive measurements of central aonic pressure were made tially from peak svstolic to diastolic pressures. and plotting by the device developed by us (6) which is described brieny their values ag~unst Ihe above described time intervals results in the following paragraphs. Pressure-volume-time systolic in the reconstruction of the central aonic pressure curve.
curves were generated and the initial systolic work and power The validity of the noninvasive method waS documented were calculated for the rlrst half of the stroke volume, The by two different approaches (6).
rate of change of power was calculated by dividing the peak 1. The pressure values measured by the device were super.
power by the time elapscd from the beginning of ejection to imposcd on the simultaneously measured central intraaonic the peak power point. The changcs, from rat to exercise. in pressure wava in patients undergoing cardiac catheterization Blood Pressure and Heart Rate at Rest and Postexercise in Normals and in Patients' Rest Postexerdse Doubb Doubb HR beats/sec BP mm/HgproductHB beats/secBP mm/Hg product _ . . ..
Normals 70 + 10 102 + 17 7140 121 + 5 124 + 16 15 004 nD10 PaUents 70+8103~:97210 114 1 8 128+19 14592 n-9 P value NS NS NS NS NS NS

Note: Thsre was no significant di~terer~ h the postexerdse response ot heart rate. blood preSSure and doubb product betweer the heatthy and the patients.

1658 Marmor, Sharir, Shlomo et al The Joumal d Nudear Mediane 1 ~
~1_ ~ ~
7- f~J
~ _ __ _ _____ ~
I '~' \
, , Schematic representation of the nomnvasive pressure device A. Sphygmornanometer cuff with intemal transducler measuring the inlracuft pressure. 2. Narrow cuff connected to a high sensltivity pressure transducer. ECG and computer are also schematically represented.

using Millar micromanometers. The tvpicai invasive prcssure :n~is to cotrect for the time lag between the pressure and time curvc was generated from _10 cycles. and the mean s.d. volume curves. The beginning of lhe imfial pressure nse was curvcs were calcul3ted. All vrtlues measurcd by lhe dcvice l'cll aligned with the beginning of lhe decrease in left ventricular within I s.d. ~rom lhe cenlml inlr~ortlc recordings in 1-1 om volume ( ncgalive DV/DT) when lhe inhial end diaslolic poiDl of the 15 patients studied. signifiles the beginning of ejec~ion. In ordemo eliminate errors 2. Using linear regression analvsis. ~n e:tcellent correlation resulting Irom changes in heart rate during acquisiuon of data of r = 0.97 was found in e tch palienl (in a mtal group of 15 lhe study was aboned and lhe palicnts were e.~cluded when patients) between the invasive tnd noninvasive digitized pres- changes of 5 bpm or more were l'ound. The pressure curves sure values. obtained in lhe s tme pafient for the same fime rccordcd by the device and lhc lime-acuvily curves obtained intervals. by the 8amma camera were ploncd agunst each other and systolic pr~ssure-volume diagrams wcre generated. As the peak Genera~ion of S~slolic Pressure ~olume Curves and Power power occurs early in ejection (4), and as we were interes~ed Crlculation . in dcriving indices on the initial phase of ejecuon, only the Absolu~e venuicular volumes were dclcrmincd by Ba~ed first haJf of the ejection phase (in ~erms of suroke volume) was radionuclide ventnculography aCCordinK lO ~he coun~ r;t~e genera~ed. namely. the portion of ~he diagram dunng the first me~hod (3). Using red blood cells laoelcd in vivo wi~h ~0 mCi halr of the ventncular emptying~ Leh ventricuiar work at half of techne~ium-99m (~9mTc), a standard field-of-view gamma s~roke volume, mean power, pe~k power, ;tnd ERCP were camera was inler~aced to a dedicatcd minicomputer with a dcnved according ~o ~he following formulas:
low-encrgy, medium resolu~ion, par~llel hole collima~or. Data v_v~-"~sv werecollec~edin45-1ehantenoroblique(LAO)positionwi~hW = 0.0136 J~ p-dv tl)a 15- caudal anguhtion. The cardlac cycle was dtvldcd ID~O _v"
20 frames. A ~otal of 5 million counts were collected. Time-activity curves were generated for the left ventricle. Aher the p _ (2) aquisilion of leh ventricutar volume points a smoothing ~1- T
gorithm was applied using a fast f~ourier regression analysis pp wi~h 16 harmonics. The ejection flow was oalculated ~s IheERCP = Tl ~ (3) first denvative of the above dcscribed Founer fit. Aner the simultaneous acquisition of pressure and volume points thcv where W = systolic work, V0~ = the end diastolic volume in were aligned in such a way that for every pressure poin~ a milliliters, SV = stroke volume in milliliters, p D instanta-corresponding volume point was found from the Founer fit. neous pressure in millili~ers of mercury and 0.0136 is constant All prtssure points were moved lehward on the htorizontal ~o e~press the work in gram'meter, P - the mean pow in ., Vdume 30 ~ Number 10 October 1989 1659 r~ ~) h ;.

g-m/sec. PP = Fleak power, T = time in milliseconds, Tl - of ~ spccific lest using multiplc Ih~esholds lo dislin~uish lim~ ~o peak po-v~r in seconds, and ERCP = eJection ra~e of belween normal and abnormal ~roups. RO(: :~n~lvsis was change Or power in g'm/sec^, done to tesl Ihe sensilivily. specificily. accuracv and prediclive A new ind~ lomhe assessmenl of rate or chanpe of pow~r values of each or Ihc methods sludied. The Ihrcshold with Ihe was d~veloped. In ord~r to calculal~ Ihis index. pcak pow~r highest accuracy was selcc~ed to represent the best possible was divided by Ihe limC to peak power, namely we calculalcd Ihreshold dclincaling normal from palholo~ic~l response. The the slopc of the line connecung the power at Ihc beginning of rollowing indices wcre dcrived ~ccording lo the following cjeclion to the peak power (Fig. 2). The reason ror the gen~r- equalion: -ation of this index is that it ~enectS an average eslimase of rale of change o~ power, unaffecl~d by the vanabilily associaled senslllvlly (%) s Irue poslllve/true posltlve + ralse nceative wilh measurements of the instantaneous power values. A x 100 possible noisiness in the instantaneous power measurements specificitv (Co) = true negati~e/lru~ ne~aDve + ralse posiuve may result from the MUGA technique of measunng relatively x 100 few volume values. This inde~ is independent of instantaneous prcssure and nOw variabiLity, prediaive accuracy of a posiuve test (~0) = Iruc positive/true posiliVe + ralsc posilive x 100 Ststtisticlll Ar~lysis The ability of Ihe subjects to perforrn and to inaease the predictive accuracy of a negative test ( 5) = Irue ne~aUve/lrue ejection power is dependem on their physical condilion, es- negative + ralse negauve x 100.
p~cially in thc healthy subjects (sedentar,v and physically trained subjects participaled in Ihe sludy). The populauon RESUL
thus disphyed a skeved dislribuuon. Ihe Irained subjec s TS
outstanding in Iheit perforrnance. Thaefore Ihe melhod of calculaingconfidence imervals fora populalion median waS All subjects pcrformed supme exercise stress tests applied rather thati a parametric approach with t-tests and starting with 75 W with an increment of '5 W ever,v 3 standard deviation. Aher calculaling a 95'0 confidence inler- min and reaching 100 W in atl subjects. glob~l ejection val the nonparametnc rank test. Mann-Whilney. was applied. fraction increasing in the health,v subjects from 61.1 This apptoach is recommend~d in m~dicat studie5 deaLing 7% to 66 1 7%, p = N.S., tnd in the patients t'rom 57.1 wjth small and nonhomo~en~ous populalions ( 7.S). For the ~ 9,~0 to 58 1 6%. p = N.S, Pv using ~5~o conRdence purpose of presentation and compalison ~ith ejection fraction interva~ and nonparametric r~nk test. resttng ejection mean and stand;lrd d~viation were calculated. althou~h these fraction in healthY subjects had a medi~n value of 63,o parameters were not used in the statistical anal~sls. as the population is not normally dismbuled. wnh a confidence mtervat of 52-65~o. It Increased aher Receivcr operator charaaerislic (ROC) tn3.1ysis stands lor exerQse to a medtan value of 67,b, 95 o confidence receiver operator charactenstic curves and it is denvcd from Interval of 59-71 C~o. p < 0.03. In patients the median a graph in which the sensitivily is ploued versus l-specificilv was 59% at rest (95æ confidence imenal ~7-685o), while tfter e:cercise the median waS 60to (95~o confi-~300 dence interval 48-70%), p = N.S. When the t~o groups PE~K POYER~PP) were compared there was an overlapping in the confi-,_ ~ ~~- dence in~en~als, rank test showing non significtnt dif-~n ro~ /~/ --1~ , ference between the groups. The indices of m,vocardial ~ // ~ ~ performance in the control group (health,v subjects) and a: /~/ ' in the patient group are detailed in Tables 2,3. Mean .. // power increased in the healthy from 297 + 169 g''m/
~ 5Do ~/ ERCP-PP/TI sec to 695 + '~79 g~m/sec, while in Ihe patients from 3 // ~ 245 + 67 to 441 + 147 g m/sec. In the patients the ;~ 5~ I ~~ peak power increased only slightly from 346 + 78 to I ~ ",~ ~ A ~ 561 + 129 g~mlsec. The ejection rate of change of InO~ ~-.~ . . .. 130 lilO power (ERCP) increased in the healthy fivefold from TIME (MSEC) 3411 + 2173 to 18 162 + 14633 g~m/sec' (Table 2), t T l t median 12750 (95% confidence interval 9700-29 600) while in the patients it increased twofold from 2637 +
FIGURE 2 824 to 5062 + 1897 g~mlsec2 (Table 3), median 4070 Schematic representation of calculation of ERCP from the (95% confidence interval 2800 7030). As shown, the power time curve at rest and after exercise in a healthy two confidence intervals are completely different, p <
subject. A: Power-time curve at rest. P: Power-time curve O.oO I . To funher demonstrate the discriminative power postexercise. ERCP as shown ~n the tigure is calculated Of this parameter the percent change from rest to effon by dividing the peak power by the tlme needed to reach peak power in early systole, and represents the slope Of was calculated: ERCP mcreased m the healthy group the line connecting the power at the beginning ot the by 376% (95% confidence interval 304-625%) while in ejection and peak power. the patients it increased only by 84% (95% confidence :
1 660 Mamlor, Sharir, Shlomo et al TheJoumal d Nuclear Medidne ~ iJ h t My dial Per1onT ancc Indices at Rest and aner a 1 00W Exercise in Healthy Subjects A. Rest Work LVEFPower Peak power ERCP
Subject no lgml [%IIg m/secl~g-m/secl ~g-mlsec~

3 32 S3 203 354 _2360 r~. Postexerase Pat~ent no.

4 107 ~1 1071 1402 5a417 ~5 77 372 604 7550 AVG 55 6~ 696 1027 18163 STD 24 6 2~8 453 14634 interval 67-21 7~o). The individual changes in ejecdon ficity was found. its poshive predicti- e v~lue being 88C~o fraction and in the ejection rate of change of power in ~nd the neg~tive predictive value being 90~0 (Fig. j).
both groups are summnnzed in Tables 2. 3. Note that the change in ejection fraction was relatively small in both groups while the chnnge in ERCP waS mnrkedty DISCUSSION
higha in the normal group compared to the patient group. ROC analysis of the studied indices showed that The function of the left ventricle ~s a pump is best LVEF at rest had a low sensitivity and a low negntive nssessed during ejection. when simultaneous changes in predictive value (Table 4, Fig. 3). Mean power. peak pressure and volume with respect ~o time take place.
power, and ERCP also hnd low discriminative power nt Most of the methods devised to measure left ventricular rest, but ERCP showed m e~cellent discrtminntive function are bnsed on chnnges of one pnrameter, either power at e~ercise with a 100% sensitivity: 90~O specific- volume (circumferentinl fiber shonening, ejection f~ae-ity; 90% positive predictive power and 100% negative tion) or pressure (dp/dt) ns a function of time. These predictive power (Table 5, Fig. ~). This contrasted with methods give an incomplete information. each of them the ejection fraction which showed 675 sensitivity, 70% nssessing only one aspect of the leR ventricular pçrforrn-speeificity with positive and nega~ive predictive powerS nnce. ignoring the simultnneous chnnges in the other of 62% and 63%, respecdvely (Figs. 3, 4). As illustrated pn~meter. An index taking into account end-systolie in Flgure 4, ERCP a~fter exercise separates accurately pressure-volume relationship hns been used more re-the healthy from the patients, while ejection fraction nt cently as a relnlively load independent and sensitive rest and nher e~ercise and ERCP at rest were unsuc- measure of ventricular contractile state ( 9~. However, cessful in differentiating between the two groups. Even this inde~c, mensured invnsively, was shown to be rela-when the chnnge in ejection frnction was considered tively insensitive to chnnges in the inotropie state (10).
(Flg. 5), its specifici~y reached only 60% and its posidve The only systolie inde~c bæd on nll three parameters predictivè vatue only 40%. In contrnst. when the change (pressure, volume, and time) is the leh ventrieular in ERCP was used. a 100g'o sensitivity and 90% speci- power. In ~hysicnl terms the power is the most impor-.
Volume 3û Number 10 ~ October 1989 1661 Myocar~ial Performance Indices at Rest and After a 100W Exercise In Patients A. Rest Work LVEFPower Peak power ERCP
Sub~ectno lgml [%llg m/secl Ig m/secl lg m/sec' 'l 32 49 266 429 3900 2 28 52 178 303 2c20 ~3 32 47 262 3~8 3180 34 73 306 361 2asa 7 16 59 91 150 a82 8 44 63 315 420 2a1s 9 3s 59 292 346 2662 AVG 32 57 246 346 263a STD 7 9 68 78 a25 B. Postexercse Patient no.
36 50 400 59~ 7035 2 36 60 3~8 s42 3613 3 42 4~ 410 626 6260 6 35 70 29s 514 4283 9 54 6s ss7 835 8789 tant parameter which describes the function of a pump. ischemia during exercise tests. In the present studv we The left ventricular powcr is an expression of the rate present a noninvasive method of measuring vemncular at which the left ventricle does work, and it was used power as the product of aonic pressure and the r~le of before to characterize the performance of the left ven- change of left ventricular oiume durin~ ejection. We tricle in dogs ( I I ) and in man ( 1'-15 ). It was measured recently described a method to measure the ascending invasively and calculated as the product of the aortic limb of thc aortic pressure noninvasively (6). The pres-pressure and flow (13-15). Another invasive mcthod sure wave of the ascending aorta during e rly ejection that was used to calculate left ventricular power was the phase represents the pressure wave of the leh ventricle product of aortic pressure and the rate of ch tnge of left in the absence of aonic stenosis. We utilized this ventricular volume during ejection (l6). method together with the absolu~e ventricular volume The reason ejection power did not become popular curve obtained by radio-entriculogram to obtain ven.
as an index of leh ventricularcont}actility is its invasive tricular instantaneous power during ejection. The leh nature and therefore the inability to use it in a clinical ventricular power increases rapidly during early ejec-setting for the measurement of myocardial reserve or tion, reaches a peak volume and then declines, therefore . ' ROC Analysis at Rest in ~he 19 Subjects .
LVEFMeanpower Peak power EPCP
SensiUvity 33 89- 100- 100-Speci~aty loo 30- 30- 30.
Accu-acv - 68 58 63 63 Threshd~ 50 31 459 3957 Posi~ivepredictivev~ue 100 3s- 63' 63-Negat~vepredictiveva~e 63 65 100- 100-Stabsticallv sbnificant ~p ~ 0.05).

1 662 Marmor, Sharir, Shlomo et al The Journal ot Nudear Medicine 3 3 - ~ ~J t~

REST EXERCISE
,_ r~o~TIrHTS ~ o ~TIEIITS HaLTHY
e ~~ ~ sT uaUE
" ` 60 _~ . I z ~: ., ~ ~_ z 40 ~: 40 1~: z Z o20 ~ Q 20 _ u. ~ v, FIGURE 3 Discnminative power of ejection frac-3 _ tionat rest ana exercise.

we considered the eslrlv ejection period only (till the The noninvnsive nature of our method enables us to volume reached half the end diastolic volume. Fig. '). use this index in ambulator,v pttients ~nd to measure In order to nssess myocardi~l reserve we mensured the chslnges in ERCP at rest and exerc~se. in order to nssess lefs ventriculnr power a~ rest and postexercise. myocnrdial performance and myocardi31 resene.
The inde.~c developed in the present stud,v (the slope Ejecsion R~te of Change of Power of the line connecting the power at the be~inning of We csllculated the mean rnte of ch3nge of power ~jection so peak power. Fig- ~) constilUtes ~n 3vernge during enrly ejectiOn by dividing the peak power to the estim;~te of the r;tte of ch~nge of power during c y time from beginning of ejection to peak power- Math- ejection This index is simihr to the inde~ me3sured by ematicallY. the rstte of chsmge of power is the firsl Stein ;Ir;d Sslbbnh (4,5~1he pe3k r~te ol changc of derivative of power ;tnd the second derivat~Ve of work power--both ~ssessing the r;tte of ch3nge of power-with respect to time. Physiologic311Y. the r3te of ch~nge However. our indc.x represents ~n ~-crnge estim3te of of powerduringejectionm~ansthe3cceler3tlonolwork the rate of ch3nge of power ~nd no~ ~ singlc v31ue of generated by the left ventricle during ejectiOn- A simil,3r r3te of change of power sls Stcin ~nd S~bb3h s inde-~-index had stlready been mestsured invasivc!y by Stcln Another difTcrcnce bctween our mclhod and the in-and S3bb3h (~.5). It was shown to be sensttl-e to dru~- dex me3surcd by Stcin ~nd Sabbah is thc nonin-~35il~e induced ch;tng~s of the inotroPiC st3te in dogs. while 3nd indircc~ nature of our mcthod- The nonin~35iVc affected little by ~llter3tions in prelold or ~ftcrlo~d. in ;~ppro;~ch h3s inherent difficultics ~nd ~rrors in me~
contrast to othcr cjcction indiccs (ejectiOn fr~ction- urements ol' instantsmeous volume 3nd prcssure- The circumferentisll fiber shonening. ventnculslr vork ~nd pressure meslsurementS were v~id~led in-~si-~ly (6)-etc) which arc m3rliedly influenced by los~din8 The rstdionuclide technique was chosen tor olu conditionS (~). The ejeclion r3te of change of power me$lsuremeDts because it is free of geometric ~sump-was also shown to separ3te psltients with abnorm3l ~nd tions ;md was extensivelY validated in the p;tst ( 17-20)-normal ventricuhr pertformance (categonzed on the basis of the ejection frstction. me3n velocity of circum- Palien~ Selection and E.Yerr;ise Tcsffng ferential fiber shortening and left ventricul~r end dia- The aim of this study was to assesc the usefulness of stolic volume inde:t) with no overlap of values between power and ERCP indices in the evaluation of leR ven-categories of p3tients (p c 0.001) (5). tricular perform3nce. P~tientc after Ml ith preserved ROC Analysis Postexercise in the Studied Population LVEFMean power Peak powar EP~CP
( /o)~0~ (o~O) ~0/o) Senslovity 67 67 56 too-Speclhrity ~o 80 100- so~
Arxuracy 68 74 79 95 PosiOvepredir,~tivev~6e 62 ~s loo ga-l,, Negaove preair,tive value 63 62 71 100 Thresho~ vaiue 63489 g~m/sec 564 g-m/sec 8970 g-m/ser, StaOsOc~ly sigmflcanl (p < 0.05;.
.
Vdume 30 Number 10 October 1989 1663 --3 4-- ~ ~j f.; `~3 ~ ~ ~

REST EXERCISE
~RTIENTS HEP~LTHY PaTlENTS H~

I
.. ~o ~ X~O
~, T u~LUE ; ~ zoooo .

giscriminative power of ERCP at rest O . (n ~ j and exercise. 0 0 or slightly reduced left ventricular function (as judged 1897 g~m/sec in the patient group (Tables B and 3B), by the ejection fraction at rest) were chosen. We delib- and it differentiated the two groups ~lth 100~0 sensiliv-erately chose these patients, who in spile of bçing aher ity. 90% specificity. 90~ accuracv and had a erv small documented myocardial injury were diagnosed as overlap of values (Tables 5. Fig. ~). Using ~5~c conl;
healthy by LVEF at rcst~and at çxercise. failing to dence interval a clear differenlialion between ~he differentiate between them and the heaJlhv subjects healthv subjects and the palients was obt~ined. ERCP
(Fig. 3, Tables 2A. 3A. and 4). LVEF increased from increasing in Ihe healthy bv 376 c. 95C,~o confidence 61 7%to66+6.2%inthehealthvsubjects(Table2) in~erval 30~6'5% while in the patients it increased and from 57 l 9% to 58 9,8% ir; pa~ients. p = N.S. onlv b,v 84æ (95% confidence intenal 67- 1, 0).
(Table 3). Ejection fraction did not differentiale be- The difference in ERCP from rest to exercise also tween healthy subjects and p~tients as shown by the separ;tted Ihe IwO groups whh hi~h sensili h- and spec-ranktestand~he95oconfidenceinten~als. w hichwere ificily (lOO~o and 90%. respectively) (Fig. j). h in-almost identical in the two groups at rest and after creased fivefold in the healthy group while less Ihan exercise. In this respect. this group of pttients v.ith twofold in the patients.minimal myocardial damage served as the reference We conclude that ERCP is a useful index of m-ocar-system when comparing left ventricular ejeaion rrac dial performance. It cm be measured nonin~ el . Ils tion performance to ERCP performance in discrimi- physiologic meaning is the accelerttion of energy ex-nating the healthy from the diseased. These patients pended upon the production of usetul work b- the had myocardial damage ~documented enzvmatic in- entricle during ejection. It was shov.n to be sensitive farction). Peak power, mean power. and ERCP did not to change in contraaile state. while relati-ely independ-separate the two groups at rest. We concluded that the ent of loading conditions (5). It increases markedly myocardial damage was too small to affect ejection during exercise. and has a hi~h sensitivit,V ~nd specificity indices at basal conditions. . for detecting mvocardial reserve. In order to assess its ERCP at the postexercise measurement was 18162 clinical importance as an indicator of leh ventricular + 14 633 g~m/sec- in the healthy group and 5062 I pertormance or as a detector of myocardial ischemia EXERC I SE
a"".~r~ ms o , . ~,' ~ oo ~ ~ -Discrim~native power ot the change ~ ~ ~ ~ ;
in ejection tractlon and in ERCP atter ~ ~t exerclse. 0 1664 Murnor, Shuir, Shlomo et al The Joumal ot Nucleu Medicine ~ ~. r~ j J ~ J

funher s~uclics in different groups of patients with is- K, Sag3v~a K, Compar3~i~e inlluencc o~' 1O3d ~ersus chemic hean disease h tve to be pert^ormed. inotroplc st3tes on mde.~es o,' ~entncul~r contractlhts:
e.~penmen~al and ~heorenc~l an~lvs~s based on pres-sure-volume rei3~ionships. Circulailon I Y87: 76:14"-REFERE,~CES 1436.
I l. Chapman CB~ B3kcr O. ~itchell JH. Lcft ventncul~r 1. McKav RG. Spe~rs JR. Aroesty J.~/l. ct al. Instant3- runction at rest 3nd dunng e.~ercise. J Clin In~est neous rrle3surement of left ~nd nght ventncular stroke 1959: 38:1'01.
volume and pressure-volume relationships wjth an 1~. Bunncl IL. Grant C. Greene DG, Thc me~surcment impedancec1theter. Circula~ion 198~: 69:703-710, of le~ cn~ncular pov~er 3nd ~ cnslon in m3n.
2. M~gon3n DJ. Shafrer P, Bush CA. et ~1. Assessment Phnsiol 196': 5:115.
of lelt entncular pressure-volume rel3tions using 13. Hernandez RR, Greenfield JC Jr, .~lcCall B~V. Pres-gated radionuclide ~ngiographv, echocardiography sure-~low studics in h~penrophic subaomc stenosis. J
andmicromanometerpressurerécordings. Circula~ion ClinIn-es~ 1964: 13:iOI, 1983: 67:844-853. 14. Greent;eld JC Jr. Harlev A. Thompson H~. et ~1.
3. MclCa~ RG. Aroes~,v IM. Heller GV. et ~1. Left en- Pressure-llow studics in rn3n dunng a~nal l;brillation.
tricular pressure--volume dia~ms and end-systolic J Clin In-es~ 1968: ~7:'411.
pressure--volume relations in human beings. J .~m 15. Snell RE. Luchsinger PC. Dctermination ot` the e!ner-Coll Cardiol 1984: 3:301. nal v~ork 3nd po~er ot' the lett ventrlcle in int3ct man.
4. Stein PD. Sabbah H~l. Rate of ch~nges of ventncular ,Im ~ean J 1965: 69:539.
power an indicator of ventncular pertormance dunng 16. Russell RO Jr. ~IcGavock PC. Frumer .~. Dod~e HT.
ejection.. ~mHeanJ1976:91:819. Leh ~entncul3r power in man. .~m Hear~ J 1971;

5. Stein PD, S3bbah H;`l. Ventncular performance me~ 81:799.
ured during ejection: studies iA pauents of the rate ot' 17. Veran~ S. Gaeta J. LcBlanc AD. et ~1. V3lidation of changeol'-entricul3rpower.. ~mHear~JI976:91:599. Ieft~cnlncullr~olumemelsuremenlsbvr3dionuclide 6. Marmor AT. Blondh.lm DS. Gozlan ~. et al. I~lethod an~o@~ph,v, J .~'ucl .lled IY85: '6:1394-1-101.
for nonin-asi-e measurcmentofcentrDI aonic s-stolic 18. :~aSsle B. ~. Kramer BL. Gcnz E~'. Hcnderson SG.
pressure. ClinCardiol 1987: 10:'15. Radionuclidemcasurementol'lelt-entricular~olume:

7. Campbell ~IJ. Gardner .MJ. Calcul3ting confidence comp~nson ol' ~comelnc and COuDt5 bascd method.
interval for some non-parDmetnc aml-ses. 8r .tled J Circuia~ n I Y8~: 65:7'5- ~ ~0.
1988: '96:1454-1456. 19. Dchmer GJ. Finh BG. Hillis LD. .~I'icod P. Willerson 8. Gardner MJ. Altman DG. Confidence inter~al rDther JT. Lcwls SE. :Nonieomc~nc delermination of right than P ~alues: es~imation rDther than h.spothesis tes~- ventncular olumes from equillibnum blood pool ing. 8r .ll~dJ 1986: '9~:746-750. sc~ns. . Im J Cardu~l 198~: IY:7g-~ 1, 9. Suga H. S~g3wa K. Shoukas AA. Load independence '0. Swling .~,iR. Dell'lUJi~ LJ. :~us-nowiu ~IL. Walsh of the instantaneous pressure-volume r;ttio ol the ca- RA. Little WC. Benedetto AR. Estimates ot' Icft en-nine leh entricle and elrects of epinephrine and heart tricular volume5 bv equlllibr.um radionuclide angiog-rate on the ratio. Circ Rcs 19?3: 3':31~. raph~: imponance of attenuallon correcllon. J .~ IIC

10. KassDA.. ~augh3nWL.GuoZ~l.KonoA.Sunagawa .~le/l IY84: '5:14-'0.

Volume 30 Number 10 October 1989 1665

Claims (38)

1. A method for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index including the steps of:
measuring the left ventricular pressure;
measuring the left ventricular volume;
determining the product of the left ventricular pressure and the left ventricular volume as a function of time;
determining the time derivative of said product;
and determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that the step of measuring the left ventricular pressure comprises the step of:
measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially a set of optimized pressure values.

2. A method according to claim 1 and further characterized in that the step of measuring the left ventricular pressure also comprises the step of:
employing an optimization algorithm which concentrates the largest number of pressure measurements in the interval during the early ejection phase.

3. A method according to claim 1 or claim 2 and additionally characterized in that the step of measuring the left ventricular pressure also comprises the step of measuring the arrival times of cardiac pressure pulses at a given site during the time period during which the left ventricular pressure rises from 100% to 125% of the end-diastolic value.

4. A method according to any of claims 1-3 and also comprising the step of displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.

5. A method for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index including the steps of:
measuring the left ventricular pressure and the left ventricular volume;
determining the product of the left ventricular pressure and the left ventricular volume as a function of time:
determining the time derivative of said product;
and determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that it also includes the step of displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.

6. A method according to either of claims 4 and 5 and also characterized in that it includes the steps of displaying simultaneously and together with said electrocardiogram and brachial pressure wave forms, the calculated delayed left ventricle pressure values and the calculated corresponding left ventricular volumetric values.

7. A method according to any of the preceding claims and further characterized in that it comprises the step of measuring during one or more cardiac cycles, of the arrival time for the given occlusive pressure, and storage of the measured times for each pressure.

8. A method according to any of the preceding claims 1-4 and wherein the step of measuring the time of arrival includes the step of rejecting time values having unacceptable variance.

9. A method according to any of the preceding claims 1-4 and 8 and wherein the step of measuring the time of arrival also includes the step of statistical averaging of several acceptable sample points to reduce the effects of beat-to-beat variance, artifactual signals and noise.

10. A method according to any of the preceding claims and wherein said step of measuring left ventricular volume includes the steps of taking at least one measurement taken within 15 msec of QRS.

11. A method according to claim 10 and wherein said step of measuring left ventricular volume includes the steps of carrying out multiple volume measurements within 40 msec of each other.

12. A method according to any of the preceding claims and further characterized by the steps of measuring the systolic and diastolic blood pressure.

13. A method according to any of the preceding claims and also comprising the step of calculating the cardiac power index as the slope of the best least squares regression fit to an entire set of instantaneous power values up to a maximum power point, excluding points whose values lie outside the range of variance that is commensurate with the other points.

14. A method for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the left ventricular pressure as a function of time by measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially a set of optimized pressure values, and deriving indices from said arrival times at said plurality of pressure values, including but not limited to the time derivative of the pressure.

15. A method according to claim 14, characterized by fitting a curve to said arrival times at said plurality of pressure values, said curve estimating the time varying wave form of the left ventricular pressure.

16. A method according to any of the preceding claims, characterized by measuring the arrival times of cardiac pressure pulses by measuring the Doppler signals of blood flow at the given site.

17. A method according to any of the preceding claims, characterized by measuring the arrival times of cardiac pressure pulses under exercise stress conditions.

18. Apparatus for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index comprising:
means for measuring the left ventricular pressure;
means for measuring the left ventricular volume;
means for determining the product of the left ventricular pressure and the left ventricular volume as a function of time;
means for determining the time derivative os said product; and means for determining the slope of the time derivative, as it rises thereby to provide an indication of the cardiac power index, characterized in that the means for measuring the left ventricular pressure comprises means for measuring the arrival times of cardiac pressure pulses at a given site at a plurality of pressure values, especially a set of optimized pressure values.

19. Apparatus according to claim 18 and further characterized in that the means for measuring the left ventricular pressure also comprises mans for employing an optimization algorithm which concentrates the largest number of pressure measurements in the interval during the early ejection phase.

20. Apparatus according to claim 18 or claim 19 and additionally characterized in that the means for measuring the left ventricular pressure also comprises means for measuring the arrival times of cardiac pressure pulses at a given site during the time period during which the left ventricular pressure rises from 100% to 125% of the end-diastolic value.

21. Apparatus according to any of claims 18-20 and also comprising means for displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.

22. Apparatus for reliably measuring cardiac performance under resting and/or exercise stress conditions to enable measurement of the cardiac power index comprising:
means for measuring the left ventricular pressure and the left ventricular volume;
means for determining the product of the left ventricular pressure and the left ventricular volume as a function to time;
means for determining the time derivative of said product; and means for determining the slope of the time derivative as it rises thereby to provide an indication of the cardiac power index, characterized in that it also includes means for displaying real-time electrocardiogram and blood pressure wave forms on a continuously updated basis.

23. Apparatus according to any of claims 21 or 22 and also characterized in that it includes the means for displaying, simultaneously and together with said electrocardiogram and brachial pressure wave forms, the calculated delayed left ventricle pressure values and the calculated corresponding left ventricular volumetric values.

24. Apparatus according to any of the preceding claims 18-23 and further characterized in that it comprises means of measuring during one or more cardiac cycles, of the arrival time for the given occlusive pressure, and storage of the measured times for each pressure.

25. Apparatus according to any of the preceding claim 18-24 and wherein the means for measuring the time of arrival includes means for rejecting time values having unacceptable variance.

26. Apparatus according to any of the preceding claims 18-25 and wherein the means of measuring the time of arrival also includes means for statistical averaging of several acceptable sample points to reduce the effects of beat-to-beat variance, artifactual signals and noise.

27. Apparatus according to any of the preceding claims 18-26 and wherein said means of measuring left ventricular volume includes means for taking at least one measurement within 15 msec of QRS.

28. Apparatus according to claim 27 and wherein said means for measuring left ventricular volume includes the means for carrying out multiple volume measurements within 40 msec of each other.

29. Apparatus according to any of the preceding claims 18-28 and further characterized by including means for measuring the systolic and diastolic blood pressure.

30. Apparatus according to any of the preceding claims 18-29 and also comprising means for calculating the cardiac power index as the slope of the best least squares regression fit to an entire set of instantaneous power values up to a maximum power point, excluding points whose variance is not commensurate with the other points.

31. Apparatus for carrying out the method according to one of the claims 14 or 15.

32. Apparatus according to any of the preceding claims 18-31 and also comprising a pulse wave sensor and a pulse wave processor 42 operative to reject motion artifact.

33. Apparatus according to claim 32 and wherein said means for detecting the arrival of the cardiac pressure wave at a given side, preferably at the brachial artery site is a Doppler ultrasound arterial wall motion sensor.

34. Apparatus according to claim 32, wherein said means for detecting the arrival of the cardiac pressure wave at a given site, preferably at the brachial artery site, is a Doppler ultrasound blood flow sensor.

35. Apparatus according to any of the preceding claims 18-34, characterized by means for rejecting motion artifact, said means comprising Doppler sensor holder and means for rejecting low frequencies from the Doppler audio shift spectrum.

36. Apparatus according to claim 34, wherein said Doppler ultrasound sensor (transducer) 80, 200 is held by an armband mount comprising an adjustable transducer mount 81, 201 fixed to an adjustable attachment strap 83, 205.

37. Apparatus according to claim 34, wherein said Doppler ultrasound sensor (transducer) 80, 200 is formed as a flat package with Doppler crystals mounted so as to provide fixed angle of illumination, typically 30° to horizontal.

38. Apparatus according to claim 32, wherein said pulse wave processor 42 includes a high-pass filters 124 separating the high frequencies from the audio signal and a RMS-amplitude-to-DC-converter 125 measuring the power of the high frequency spectrum by converting the total RMS (root mean square) into a proportional DC voltage.