WO1992003966A1 - Procede et appareil de mesure de la pression arterielle - Google Patents

Procede et appareil de mesure de la pression arterielle Download PDF

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Publication number
WO1992003966A1
WO1992003966A1 PCT/US1991/006191 US9106191W WO9203966A1 WO 1992003966 A1 WO1992003966 A1 WO 1992003966A1 US 9106191 W US9106191 W US 9106191W WO 9203966 A1 WO9203966 A1 WO 9203966A1
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WIPO (PCT)
Prior art keywords
signals
neural network
blood pressure
input
physiological parameter
Prior art date
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PCT/US1991/006191
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English (en)
Inventor
Phillip D. Baker
Joseph A. Orr
Dwayne R. Westenskow
Timothy P. Egbert
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University Of Utah
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Publication date
Application filed by University Of Utah filed Critical University Of Utah
Priority to JP3516262A priority Critical patent/JPH06505886A/ja
Publication of WO1992003966A1 publication Critical patent/WO1992003966A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/022—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
    • A61B5/02225—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers using the oscillometric method
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/0215—Measuring pressure in heart or blood vessels by means inserted into the body
    • A61B5/02156—Calibration means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/022—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7264—Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems
    • A61B5/7267—Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems involving training the classification device
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7221—Determining signal validity, reliability or quality
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7239—Details of waveform analysis using differentiation including higher order derivatives
    • G—PHYSICS
    • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
    • G16H—HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA
    • G16H50/00—ICT specially adapted for medical diagnosis, medical simulation or medical data mining; ICT specially adapted for detecting, monitoring or modelling epidemics or pandemics
    • G16H50/70—ICT specially adapted for medical diagnosis, medical simulation or medical data mining; ICT specially adapted for detecting, monitoring or modelling epidemics or pandemics for mining of medical data, e.g. analysing previous cases of other patients

Definitions

  • Present invention relates to a device and method for indirect estimation of variable physiological parameters such as blood pressure utilizing a neural network. More particularly, the present invention relates to a method for training a neural network to recognize and interpolate blood pressure values based on an oscillometric waveform generated by an external blood pressure cuff.
  • Prior Art Blood pressure has become one of the primary physiological measurements used to access the condition of a patients cardiovascular system. During acute care, as is provided in the operating room and intensive care unit, blood pressure measurements are routinely used to monitor and manage the condition of patients.
  • noninvasive methods of estimating blood pressure are generally atraumatic and present little risk to the patient, they are often used instead of the invasive method, which requires that a catheter or needle be inserted into an artery.
  • a major disadvantage associated with noninvasive methods has been their lack of close agreement with actual blood pressure as would be measured by an invasive method.
  • lack of close agreement also exists between different noninvasive methods, further adding to the uncertainty of any particular reading derived by noninvasive methods.
  • Oscillometry has become the most common method used for automatic, noninvasive blood pressure monitoring. It is estimated that there are we'll over 150,000 automatic oscillometric noninvasive blood pressure devices in the United States alone.
  • One advantage of the oscillometric method over other noninvasive methods is its ability to estimate not only diastolic and systolic pressures, but also mean pressure.
  • Conventional oscillometric blood pressure monitors use an inflatable air filled occlusive cuff that is placed around a limb, usually the upper arm.
  • the minimum cuff pressure at which the oscillations reach their maximum provides a reasonable estimate of mean blood pressure.
  • the maximum amplitude criteria however, apparently underestimates true mean blood pressure and is dependent for accuracy on such factors as the magnitude of the intraarterial pulse pressure.
  • blood pressure monitoring as represented by amplitude oscillometry processed by conventional algorithms merely generalizes relationships which are based on minimum cuff pressure versus maximum oscillation for mean blood pressure and some empirical percentage under the fixed ratio amplitude criteria for estimating systolic and diastolic pressures.
  • oscillometric waveforms are susceptible to artifacts and noise from a variety of sources. Typical algorithms are not capable of dealing with artifacts, common noise and other variations which may be reflected in the oscillometric waveform.
  • mi3t conventional oscillometric algorithms are based either directly or indirectly on the assumption that blood pressure remains constant during the recording period, which may last as much as ten to thirty seconds. It is apparent that the processing of artifacts and noise interferring with quality signals degenerates the accuracy of any estimation of blood pressure.
  • a still further object of the present invention is to provide a method and device for determining the values of physiological parameters despite occurrence of artifacts, noise and other corrupting signal influences.
  • Another object of the present invention is to provide a device and method for determining blood pressure and other similar physiological parameters without a need for reliance upon generalizing assumptions which undermine system accuracy.
  • the method comprises the steps of (i) identifying the physiological parameter to be quantitatively monitored and estimated; (ii) generating a sequence of signals which are quantitatively dependent upon the variable physiological parameter, but which are not suitable for providing a direct quantitative readout based on direct measurement of the parameter; (iii) transmitting the signals to and processing such signals within a computer system including input nodes of a neural network supported by the computer system, which neural network is capable of generating at least one output signal for the combined input signals as an estimated value for the physiological parameter; (iv) determining an actual, true value for the physiological parameter concurrent with the previous steps; (v) making adjustments within the neural network which modify the value of the output signal to match the true value of the physiological parameter determined in the previous step; recording as training data within memory of the computer system the input signals, adjustments, and true Values associated with the sequence of signals generated under step ii; and sequentially repeating the previous steps sufficient to train the neural network to recognize relevant input signals and estimate the value of the physiological parameter based on association of on-line input signals with trained output signals
  • a device for implementing the above inventive method, as well as specific adaptations with respect to systolic, mean and diastolic blood pressure. Also disclosed is a neural network for pre- classifying waveforms and for disregarding noise and artifact signals.
  • FIG. 1 is a graphic representation of components making up a conventional oscillometric monitoring system for blood pressure.
  • Figure 2 comprises a graphic plot of the derivative of transducer bladder pressure (dp/dt) as actually recorded from a superficial temporal artery of a patient in a thoracic intensive care unit, as the bladder was inflated from approximately 0 to 90 torr (P cuff) .
  • Figure 3 is a graphic representation of the oscillometric waveform reconstructed from the derivative of the transducer bladder pressure signal represented in Figure 2.
  • Figure 4 shows a conventional oscillometric amplitude waveform in graphic display corresponding to the pressure readings represented in Figures 2 and 3.
  • Figure 5 is a graphic display of a three layer neural network as is used in the preferred embodiment disclosed herein.
  • Figure 6 is a graphic representation of a node input/output function.
  • Figure 7 provides a graphic illustration of a normalized oscillometric amplitude waveform developed from a sampling of signals at 4 torr increments.
  • Figure 8 represents a block diagram illustrating the training phase and methodology for applying a neural network for determining physiological parameters in accordance with the present invention.
  • Figure 9 represents a diagnostic (nontraining phase) application of the present invention operable to generate output values estimating the physiological parameter.
  • Figures 10a, 10b and 10c provide graphic representations of neural network learning curves generated with respect to testing.
  • Figures 11a, lib and lie provide graphic representation of performance curves as generated with respect to the test animals.
  • Figures 12a, 12b and 12c provide a graphic representation of neural network performance after-50, 250 and 1,500 passes through the training data plotted against the number of hidden layer nodes.
  • the neural network performance in these graphs is evaluated in terms of mean difference between invasive measurement and neural network estimates.
  • Figures 13a, 13b and 13c provide similar graphic representations as represented in Figures 12a, 12b and 12c, except that the performance is evaluated in terms of standard deviation of the differnces between invasive measurements and neural network estimates.
  • Figure 14 illustrate numerical data and corresponding graph data comparing the conventional algorithm processes, neural network proccesses of the present invention and invasive measurements for diastolic, mean and systolic blood pressure.
  • Figure 15 graphically compares a clean signal with a superimposed signed including randon noise.
  • Figure lis illustrates in block diagram a neural network adapted for pre classification and rejection of artifacts.
  • FIG. 1 illustrates a block diagram of a blood pressure monitor and processing system constructed in accordance with principles of the present invention.
  • This includes a blood pressure cuff 20 which is adapted with suitable hardware necessary to pressurize the cuff in accordance with conventional practice.
  • This cuff 20 may be a banded configuration typically applied to limbs or extremities of a patient or may be a superficial temporal artery blood pressure monitor as applied to the patients head.
  • a temporal artery blood pressure pad is disclosed.
  • a conventional occlusive blood pressure cuff could likewise be substituted in application of the present inventive principles.
  • the cuff 20 interfaces at a pulse side of the patient to generate noninvasive, oscillometric blood pressure data which is processed in a computer 21 the computer is connected through a parallel interface card 22 to a satellite box 23 which contains the hardware necessary to inflate and measure the pressure in a transducer bladder of the cuff 20.
  • a software controlled direct current Romega 80 air pump is used to inflate the transducer bladder.
  • the transducer bladder of the superficial temporal artery blood pressure pad is connected to the output of the needle valve 24 through an air line 25 approximately 1.5 meters long with an inside diameter of approximately 1.5 milimeters.
  • a secondary line is connected from the output of the needle valve 24 to a pressure transducer and a software controlled solenoid valve.
  • the pressure transducer is used to record the inflation ramp and oscillometric waveform from the superficial temporal artery blood pressure pad transducer bladder.
  • the solenoid valve serves as a dump valve to release the pressure in the transducer bladder following each blood pressure determination.
  • the satellite box 23 houses the pump and pneumatic circuit, pressure transducer, analog amplifier/filter, 12 bit a/d converter and parallel port. This combined hardware services the inflation needs of the cuff 20, and provides initial filtering and processing of signals. Digital signals are then transmitted over connecting line 27 to the computer interface card 22. Software within the computer 21 controls subsequent data collection, processing and data display.
  • the oscillometric waveform comprises transducer bladder pressure oscillations plotted as a function of transducer bladder pressure and is constructed by software using the derivative of the transducer bladder pressure signal.
  • the derivative of the transducer bladder pressure is the sum of the changes in pressure due to the inflation ramp and of the changes in pressure due to volume oscillations transmitted from the underlying artery.
  • the goal in reconstructing the oscillometric waveform is to isolate the component of the derivative signal corresponding to the volume oscillations from the derivative signal and then integrate the resulting signal beat-to-beat to recover the original pressure oscillations.
  • Figures 2 and 3 contain an oscillometric recording from the superficial temporal artery.
  • Figure 2 is the derivative of the transducer bladder pressure as the transducer bladder was inflated from approximately 0 to 90 torr. The positive offset or bias in the derivative signal corresponds to the slope of the inflation ramp.
  • Figure 3 is of the oscillometric waveform constructed from the derivative of the transducer bladder pressure signal. Further refinement of the oscillometric waveform is carried out by noting that a single oscillation or beat should start and return to nearly the same diastolic pressure level. Consequently, the sum of the derivative signal over a beat should be zero. Any non-zero sum is assumed to be part of the ramp signal and is subtracted from the derivative signal over the period of the beat. The adjusted derivative signal is integrated over the period of the beat to obtain a more accurate reconstruction of the oscillation or beat.
  • the reconstructed oscillometric waveform is shown in Figure 4 in its conventional form.
  • Neural networks are based on models of the nervous system and employ adaptive signal processing techniques to develop training data which facilitates recognition of previously observed conditions. Once a neural network is trained, it provides a means of transforming a given input signal into an appropriate output signal. Training sets of data are used to modify the neural network weights as applied to various nodes making up the network until the network is optimized in a statistical sense to provide the appropriate output for a given input.
  • the present invention introduces an application of neural networks for identification or estimation of physiological parameters which can be estimated by indirect measurements made with respect to the patients body. Such indirect measurements are feasible where a physiological event can be monitored noninvasively based on generation of a sequence of signals which are quantitatively dependent upon the variable physiological parameter.
  • blood pressure is a prime example of such noninvasive estimation, based on monitoring signals generated in oscillometry.
  • the neural network can be trained to transform noninvasive oscillometric signals into estimates of intraarterial blood pressure. Because the network process of the entire oscillometric signal rather than trying to identify a single occurrence, such as the point of maximum oscillation, the network is inherently more robust (less sensitive to noise and artifact) than standard oscillometric algorithms. Furthermore, unlike standard algorithms whose accuracy varies with factors such as blood pressure and pulse pressure, the network can provide nonlinear processing of the input signal and thus be relatively consistent over a wide range of pressures.
  • a neural network may be specified in terms of its architecture. This includes the number of nodes and the interconnection relationships between them, node characteristics such as input/output functions, and learning or training rules which define the method by which the node interconnection are adapted during training.
  • the power of a neural network arises in part from the use of nonlinear functions to process node inputs and the use of parallel distributed processing wherein a given piece of information is not restricted to a single node but may appear as input to many nodes which may operate on the network inputs concurrently.
  • a three layer, feed forward neural network was designed to process oscillometric amplitude waveforms with the present invention as shown in Figure 5.
  • the three layer system includes an input layer 30, one hidden layer 31 and an output layer 32.
  • each hidden layer node 34 is in turn connected through a weighted link 35 to the single output layer node 36.
  • forty input nodes 37 were provided for the neural network and adapted to receive forty incremental signal samples of a normalized oscillometric amplitude waveform (cuff pressure oscillation amplitude versus cuff pressure) . These samples were taken over evenly spaced increments of 4 torr over a cuff pressure ranging from 20 to 176 torr.
  • These forty input samples were stored in computer memory and then concurrently transmitted to the forty input nodes of the input layer 30. In other words, the first sample was transmitted to P(n), the second sample to P(n-l), etc. This total transmitted set of sample signals is concurrently received at the input layer 30 and represents a sample view of the waveform which represents a single diagnostic test procedure.
  • This input signal is processed through one or more hidden layers 31 with application of weighting factors at interconnecting nodes to establish an internode relation between the input signals 38 and a desired output signal 39.
  • This processing includes adjustments made within the neural network which at the weighting links 33 and 35 which modify the value of the output signal 39 to match the particular value of the blood pressure or other physiological parameter which it to be determined. This is accomplished in a training sequence wherein the output value 39 is a known value which is generated by virtue of the adjustments made to the input signals 38 as the signals are processed through the network.
  • the process of training the neural network to accomplish this result involves initially establishing appropriate weighting factors within the weighting links 33 and 35 such that upon occurrence of a similar set of input signals 38 in a future diagnostic test, the neural network will associate such input data with the desired output signal 39 by reason of applied waiting factors within the links 33 and 35 which have been saved in memory. This procedure will be outlined in greater detail hereafter.
  • Nodes are commonly characterized by an internal threshold or offset and the type of nonlinearity through which the node inputs are passed.
  • the internal thresholds and offsets of the hidden layer nodes 31 are determined adaptively utilizing a well known back propagation algorithm and which is a generalization of the Widrow-Hoff Delta Rule.
  • the backward error propagation algorithm is a gradient descent algorithm designed to minimize the mean square error between the desired output and the actual output of the network. In order to generate an error term, the data set used to train the network must contain not only network inputs, but also the desired output which is specified in supervised training.
  • Input data is processed forward through the network to generate an output.
  • An error term is computed using the difference between the desired output and the actual network output.
  • the error term is propagated back through the network to modify the internode connection weights and node thresholds so as to minimize the mean square error.
  • Steps 1 and 2 are repeated with new input data in an interactive adaptive process. Commonly, adaptation is halted and the connection weights are saved after the network has reached some specified level of convergence, such as when the error has dropped to 10 percent of the desired output.
  • the following is a representative listing of the equations and steps used in implementing the back propagation algorithm for oscillometric waveform processing.
  • Wj j (n) is the weight from hidden node i to an output node or from an input node i to a hidden node j at time n.
  • x ; (n) is either the output of node i or is an input.
  • the weight of the sum of the inputs 33, 33a, 33b, 33c and 33d were passed through a sigmoid nonlinearity of the form shown in
  • the input of the forty samples to the network input node layer 30 is represented by a normalized oscillometric amplitude waveform as shown in Figure 7.
  • This amplitude waveform is part of the inventive process wherein the sequence of signals generated by the cuff and pressure transducer are sampled at 4 torr intervals to supply a set of forty-plus sample signals representing the total range of pressures covered by the diagnostic test procedure. With respect to each sample signal, a feature is identified which constitutes the maximum amplitude of that sample signal. This same procedure could be applied to other diagnostic tests which involve oscillatory signals having an amplitude feature.
  • This feature is then utilized to develop the referenced waveform in Figure 7 wherein the respective sample amplitude values form ⁇ * locus of points representing the amplitude of cuf ⁇ pressure over the diagnostic test.
  • This waveform is the image or pattern corresponding to an actual blood pressure value as it is represented at the forty input nodes of the neural network.
  • the neural network is trained to recognize the actual blood pressure value to assign to this waveform and is trained to generate this value at the output layer upon receipt of a simillar set of input signals.
  • the device includes a sensing means 20 for indirectly detecting changes in a physiological parameter which is to be quantitatively monitored and estimated. Selection of the sensing means will depend on the nature of the parameter and will generally be a conventional diagnostic device which is already being used to attempt such estimations.
  • a blood pressure cuff which currently generates oscillometric signals forms the sensing means for the blood pressure application.
  • Pulse oximetry is another procedure which may be adapted for processing with a neural network. In this case, an estimation of blood oxygen saturation is transmitted through or reflected from body tissues.
  • a third area of application is generally referred to as dilution cardiac output. This procedure estimates cardiac output or blood flow by processing the time dependent concentration or temperature signal produced by injection of a dye or thermal solution into the vascular system. Obviously, in the latter two cases different sensing devices will be utilized, and an appropriate signal, which is quantitatively dependent upon the variable physiological parameter, but which is not suitable for providing direct quantitative readout based on direct measurement of that parameter.
  • the sensing means and an associated signal generating means 23 together cooperate to produce the required set of signals to be applied at input nodes in the neural network.
  • the neural network includes a supporting computer system 21 coupled to the generating means and operates to control data collection, processing and display. It will be apparent to those skilled in the art that reference to the computer system would include other data processing devices such as hardware analog circuits or integrated circuits which could be specifically designed to implement a neural network without a separate computer system.
  • the neural network has been described in one preferred embodiment, and can generally be described as including (i) a series of input nodes for receiving signals from the generating means, (ii) a series of hidden nodes coupled individually to each of their respective input nodes, and (iii) at least one output node which is coupled to each of the respective hidden nodes for supplying a desired output value.
  • the neural network includes means for generating the single output signal from the signals received at the input nodes wherein the output signal provides the trained estimated value of the physiological parameter.
  • the computer system also operates as a data storage means for storing training data generated within the neural network with respect to relationships between the input signals and desired values for the physiological parameter to be designated during such training and supplied as an output.
  • the computer system may also provide a readout means for indicating the estimated value of physiological parameter based on the output signals from the neural network.
  • the present invention When used as part of a training system, the present invention also includes invasive detection means which are coupled to the computer system and adapted with means for determining an actual, true value for the physiological parameter. This invasive detection means is applied concurrent with receipt of sample signals received from the generating means.
  • Memory storage means is provided in the computer system for storing parameter true values in association with corresponding input signals fed to the neural network. These related values and signals are subject to future recall and association upon recurrence of a similar set of input signals to the input nodes of the neural network.
  • the number of input nodes will vary depending on the number of input * signals to be processed, or at least two input nodes are required to establish a minimum statistical image.
  • hidden nodes will differ in number and in levels. A single hidden layer will generally be adequate and will usually include at least five nodes making up the single hidden layer between the input nodes and the single output node. Where additional boundary conditions within the neural network are required, multiple hidden layers may be applied.
  • the computer also provides a selection control means for sampling periodic signals generated from the generating means. As indicated in the previous example, forty sample signals were taken over the diagnostic test procedure pressure range and were placed in memory for subsequent transmission on a concurrent basis to the input nodes of the neural network. Generally, at least one feature will be identified within these sample signals, which feature can be processed through the neural network as a feature signal having a dependent relationship with respect to the physiological parameter.
  • a portion of computer memory or other memory means is set aside to store training data including weighting factors and parameter values which can be used to generate a value for the physiological parameter including mean intraarterial blood pressure, systolic intraarterial blood pressure and diastolic intraarterial blood pressure.
  • the invention need not include connection with the invasive detection means required for determining true value for the physiological parameter. Instead, the device need only include the neural network and recorded training data necessary to develop association with on-line data input.
  • the device may include three separate neural netwo'rks respectively configured and trained to determine the named blood pressure attributes, or may be a single neural network with - three outputs configured to generate the same result. Further detail with respect to technical implementation of the neural network in accordance with the teachings of this invention is unnecessary in view of current knowledge of those skilled in the art with respect to neural network systems generally.
  • Figure 8 represents the general procedural steps associated with the present invention in its broader terms. The first step involves identifying the physiological parameter to be quantitatively monitored and estimated.
  • Item 41 represents a blood pressure cuff and the associated physiological parameters of diastolic, mean and systolic blood pressure.
  • the cuff 41 also represents the associated hardware to support operation of the cuff in its conventional manner.
  • the next step involves generating a sequence of signals 42 which are quantitatively dependent upon the variable physiological parameter, but which are not suitable for providing a direct quantitative readout based on direct measurement of the parameter.
  • the third step comprises transmitting these signals to and processing such signals within a computer system 44, including input nodes 45 of a neural network 46 supported by the computer system 44 is similar to that described previously and provides capability of generating a single output signal 47 for the combined input signals 43.
  • This output signal 47 provides the estimated value of the physiological parameter corresponding to the referenced input signals 43.
  • the device represented by Figure 8 includes steps for determining the actual, true value of the physiological parameter concurrent with the generation of signals as represented by item 42.
  • This procedure is represented by an intravenous device 49 which is invasively positioned withi the patient to directly readout actual blood pressure values for transmission along line 50 and to the computer system 44. • This true value for the parameter is processed by the computer system and stored as training data 51. This value is transmitted via line 52 as the desired output value 47. Adjustments are then made within the neural network 46 which modify the value of the signal transmitted from the output nodes 53 to a value which equals the desired output value 47 transmitted from training data 51. Typically this is accomplished by applying weighting factors at interconnecting nodes within the neural network between the input nodes and hidden layer of nodes 54 and between the hidden layer of nodes 54 and the output node 53.
  • the input signals 42 are saved as training data 51, along with the adjustments or weighting factors required to modify the input signal through the hidden layer to reach an output value equal to the output value generated by the invasive measurement 49. These data are collectively recorded as training data 51 for use in actual diagnostic measurements on-line with a patient in the absence of the invasive measurement.
  • This series of steps is repeated a sufficient number of times to train the neural network to recognize relevant input signals and estimate the value of the desired physiological parameter based on association of on-line input signals at some future time.
  • this method is particularly applicable with respect to oscillatory signals which generate a waveform corresponding to a single diagnostic test procedure.
  • this diagnostic test procedure is represented by the sequence of a blood pressure cuff and implementing conventional oscillometry to generate the desired sequence of signals.
  • the oscillatory signals be changing in amplitude or frequency in a dependent relationship with respect to the physiological parameter. This enables the neural network to learn the various relationships through actual training wherein the true value of the parameter is taught to the neural network in association with the input signals received.
  • an additional value of utilizing a neural network is its ability to analyze and interpolate from several sample signals and generate an accurate estimation of the parameter value without having the need to process the full sequence of signals originally generated 42.
  • the computer system or other form of selection control means selects a plurality of sample signals from the sequence of signals 42 which may be received directly through line 55.
  • the computer system identifies at least one feature, such as signal amplitude, within the sample signals which can be processed through the neural network as a feature signal.
  • the normalized oscillometric amplitude waveform illustrated in Figure 7 demonstrates how 40 signals selected at 4 torr increments can generate a typical waveform without the need for processing all signals as is represented in the waveform illustrated in Figures 3 and 4.
  • the subject inventors have successfully developed accurate results in a blood pressure monitoring system by selecting only 3 sample signals and by processing those sample signals through the neural network in accordance with the teachings of this invention. Obviously, at least two sample signals will be required to generate a meaningful waveform, depending upon the training capacity of the neural network with respect to the desired parameter. Accordingly, the neural network system provides a much improved efficiency in that the processing and association steps of analysis can be accomplished with several signals, rather than the full range of designated signals. Generally the selected number of sample signals determining the minimum number of input nodes required with respect to the neural network.
  • the specific method of practice involves developing a waveform for each single diagnostic test procedure wherein the predetermined number of sample signals corresponds approximately to the number of input nodes in the network.
  • the sequential signals are stored in memory and are collectively and concurrently transmitted to the input nodes of the neural network as a representative waveform.
  • Application of the inventive steps represented in Figure 8 to a specific training session for generating blood pressure training data is accomplished in the following specific format. Specifically, a sequence of oscillometric signals are generated from a pressure sensing means. This means, represented by the blood pressure cuff 41 of Figure 8, is coupled externally to a patients anatomy in a sensing proximity to a heart pulsing sensing location.
  • the computer system 44 is adapted to identify a set of sample signals at defined increments wherein the primary feature of the oscillometric signal constitutes pulse amplitude.
  • the process continues by measuring and recording pressure values within the pressure sensing means, along with the corresponding pulse amplitude signals described in the previous step.
  • invasive blood pressure measurements are made concurrent with the generation of the oscillometric signals representing heart pulse. This true value is transmitted to the computer system for recording as part of the training data 51.
  • the sample feature signals representing pulse amplitude are transmitted to the input nodes 45 for processing through the neural network. Appropriate adjustments are made with application of weighting factors to force the output signal of the network to match the output value determined invasively.
  • the neural network is capable of recognizing sets of input signals and determining accurate estimates of blood pressure values.
  • the typical range of measuring and recording pressure values extends over defined increments from approximately 20 to 200 torr.
  • the subject inventors have found an appropriate increment to be 4 torr, representing approximately 40 to 45 sample signals.
  • the present system was tested with respect to five dogs.
  • a total of 425 recordings of oscillometric amplitude waveforms, along with simultaneous invasive measurements of arterial diastolic, mean and systolic blood pressures were obtained (approximately 85 recordings per dog) .
  • Three separate neural networks were utilized, one each for estimating diastolic, mean or systolic blood pressure. These systems were trained utilizing the back propagation algorithm as previously discussed.
  • the networks were trained and tested using a trained - on-4/test-on-l procedure. Following training of the network on data from 4 of the dogs, adaptation of the internal hidden layer thresholds and network internode connection weights was halted and data from the fifth dog was processed forward through the network to obtain estimates of either arterial diastolic, mean or systolic blood pressure. The protocol was repeated five times such that data from each dog was tested on a network trained using data from the other four dogs.
  • Training data was passed adaptively through each network a total of 1,500 times. Following each adaptive pass, the training data (340 oscillometric readings from 4 dogs, 85 readings per dog) was processed forward through the neural network to evaluate the level of convergence. The test data from the fifth dog (85 oscillometric recordings) was then processed forward through the network to evaluate neural network performance at different levels of convergence. The convergence coefficient, and total number of passes through the training data were selected to yield reasonable rates of convergence, final convergence levels, and steady state oscillations.
  • the level of convergence was quantified in terms of the mean error, the standard deviation of the errors and the mean square error.
  • the error was computed as the difference between the desired (invasive arterial blood pressure measurement) and the actual network output (noninvasive estimate) .
  • the mean square error is the variable which the back propagation algorithm is attempting to minimize and this serves as an appropriate measure of the level of convergence.
  • this method of quantitative estimation of the variable physiological parameter is practiced by identifying the parameter to be estimated, generating a sequence of on ⁇ line signals which are quantitatively dependent upon the variable parameter, and transmitting those signals to the input nodes of the neural network.
  • the neural network has been appropriately trained and includes within its memory training data which will be used to identify the closest parameter value based on comparison with signals received at the input nodes as well as weighting factors which have been saved as part of the training data.
  • Figures, 10a, 10b and 10c disclose examples of learning curves obtained by processing the training data forward through the network after each adaptive pass. This data corresponds to a network having three hidden layer nodes.
  • Figures 11. 11a, lib and lie contain corresponding performance curves obtained by processing the test data forward through a neural network having 63 hidden layer nodes.
  • These figures represent training data which was presented within the network a total of 5,000 times, as opposed to the earlier mentioned 1,500 presentations.
  • the mean error learning curves change rapidly at first, sometimes changing sign and then begin a slow noisy ascent or descent toward 0. Both a standard deviation of the error and the mean square error are characterized by noisy decaying exponentials.
  • the convergence patterns vary depending on the number of hidden layer nodes and the number of passes through the training set, the different neural network architectures all successfully converged.
  • increasing the number of hidden layer of nodes was associated with a higher level of convergence on the training data and improved performance on the test data in the form of decaying exponentials.
  • Increasing the number of hidden layer nodes was also associated with smaller steady state oscillations in both the learning and performance curves.
  • Increasing the number of passes through the training data was associated with a higher level of convergence; however, this did not always translate into an increase in performance on test data, particularly after prolonged testing.
  • the price for improved performance is an increase in the number of interconnections and thus the amount of time required to train or process data through the network.
  • Figures 12a, 12b, 12c and 13a, 13b, 13c show, respectively, the differences and the standard deviation of the differences between the invasive measurements and the noninvasive neural network estimates arterial blood pressure plotted against the number of hidden layer nodes.
  • the network's performance was evaluated at different levels of training by processing test data forward through the networks after 50, 250 and 1,500 adaptive passes through the training data.
  • Both the mean difference and the standard difference Figures 12a, 12b and 12c and the standard deviation Figures 13a, 13b and 13c of the differences tended to decrease as the number of hidden layers was increased.
  • the improvement in performance was in the form of a noisy decaying exponential. As previously noted, increased training did not necessarily ensure better performance.
  • the best performance (minimum standard deviation of the differences) in estimating diastolic, mean or systolic blood pressure was achieved using networks with 63 hidden layer nodes (the maximum number of hidden layer nodes tested) .
  • the best performance was achieved after 422 training passes; for mean estimates, after 18 training passes; and for systolic after 548 training passes.
  • the neural network oscillometric blood pressure estimator performed as well or better based on data obtained from the 5 dogs.
  • the neural network approach for estimating blood pressure and other physiological parameters provides a potentially powerful alternative to the conventional algorithmic processing of oscillometric amplitude waveforms.
  • neural networks are very simple to implement. Once the neural network is appropriately trained, it can readily respond with generation of appropriate parameter estimations.
  • the neural network system has a natural robustness in that it is not as sensitive to artifact and noise as conventional algorithmic processes. Unlike conventional algorithms, which usually depend on the identification of a single event (e.g., the lowest cuff pressure at which maximum oscillations occur) , the entire oscillometric waveform can be processed by the neural network to obtain an estimate of the desired blood pressure attributes.
  • Figure 14 discloses a table of values comparing invasive measurements with conventional algorithm techniques, as well as the neural network system of the present invention.
  • the first row in the table contains the mean differences, plus or minus the standard deviation between invasive measurements and noninvasive conventional algorithm and neural network estimates of blood pressure. These statistics were computed using the data generated with respect to the test animals previously desribed.
  • the second row contains the average of the means and standard deviations separately for each dog, providing an improved measure of intrasubject variations.
  • the attendant graph provides a more dramatic example of how the accuracy of the conventional algorithm decreases with increasing blood pressure while the accuracy of the neural network remains relatively constant.
  • the neural network may also be utilized as part of a pre-classification system for identifying the nature of certain input signals. For example, when a set of input signals arrives at the input nodes of a neural network, certain patterns may be readily detectable which are unique to a child as opposed to a adult patient. Such a pre-classification application is useful for identifying various patient conditions which fall in broad categories generally identified as patient induced conditions. Age, body size, disease conditions and other conditions falling within other unique classifications can be detected by certain patterns which are reproduced at the input nodes of the neural network.
  • the neural network can then reduce the processing of such information by restricting the selective training data to that applicable for the selected classification.
  • a neural network may be trained to recognize blood pressure attributes as they relate to pediatric patients. By using a pre-classifier, the neural network can immediately recognize that the input signals have a pediatric pattern, thereby limiting comparison of input data with training * data specifically developed for pediatric patients. Similar applications of the neural network can be utilized in this pre ⁇ classification rule for equipment induced conditions that may represent a malfunction. Reference to training data which enables the neural network to recognize certain common malfunction conditions for diagnostic equipment can lead to more timely alert of attending medical personnel for equipment correction or maintenance.
  • the neural network of the present invention can be trained to recognize noise and artifact input received at the input nodes of the neural network.
  • This technique was specifically applied with respect to measurement of test animals as previously described. These specific procedures involved a initial determination of the oscillometric waveform quality based on human observation of the waveform graph. This was accomplished by observing the waveform and noting the occurrence of noise or artifact signal and then assigning a "quality 11 factor such as "excellent", "good” or "artifact”. Training samples from a total of 245 waveforms were selected and processed through a neural network having 60 input nodes, 15 intermediate hidden nodes and a single output.
  • This network was trained using a supervised stochastic method to calculate a "quality" number at the output node based on this goodness indicator.
  • the numbers selected were 500 representing an excellent waveform, 0 representing a good waveform and -500 indicating an artifact.
  • the network was consistently able to calculate lower numbers for the artifact waveform and higher numbers for the good and excellent waveforms. It was thus able to distinguish the worst quality waveforms from the better ones, enabling the network to thereby distinguish and reject artifact and noise signals. This held true for both the training data set and the nontraining data set of signals. It was also noticed that when this procedure was tested on the nontraining data set, the network properly classified a few waveforms which had been misclassified during the initial human classification process.
  • Figure 15 presents a graph which illustrates normal oscillometric pulse amplitude versus cuff pressure.
  • the quality or clean signal is represented by the small square box point indicators, whereas the random noise or artifact signal is superimposed and indicated with + signs. Processing of these respective signals confirms the ability of the neural network to distinguish and reject inappropriate signals and record and process quality signals.
  • the selected parameter is a blood pressure value generated by use of an oscillometric system represented by a cuff 60.
  • a sequence of signals are generated 61 and transmitted to a pre-classification neural network 62.
  • the pre-classification network is trained to recognize signals which are corrupted by extraneous noise and to classify these as artifacts 63 which will be rejected or stored as training data for future recognition. All other signals are considered quality signals 65 and are transmitted to the neural network as previously described 66 for processing and estimation of blood pressure as an output signal 67.
  • Development of training data is accomplished in a procedure similar to that outlined with respect to training of the neural network to recognize certain blood pressure parameter values.
  • the signal input is classified as corrupted or artifact and weighting factors are applied at interconnecting nodes within the neural network 62 to establish an internode relationship between the corrupted signal received at the input nodes and a desired output * signal which is defined to be an artifact 63.
  • These relationships and values are saved in computer memory for a future association with respect to signal input which is not predefined with respect to quality.
  • the pre-classification neural network 62 may be useful for identifying and discarding noise and artifact signals such that these are not saved as part of training data. This operates to enhance the accuracy of the training data stored as much as all artifact and noise signals are pre-classified and rejected.
  • training data which is being coordinated with the output signal of the blood pressure neural network 66 is of pure value, overcoming a major cause of error in conventional algorithm processing which comprehends both quality and artifact signals on an equal basis.

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Abstract

Le procédé et le dispositif décrits permettent d'estimer indirectement de façon quantitative les caractéristiques de la pression artérielle d'un sujet et des paramètres physiologiques variables similaires, grâce à l'utilisation de techniques indirectes non invasives. Ce procédé consiste: (i) à générer une séquence de signaux dont le caractère quantitatif dépend du paramètre variable; (ii) à transmettre et à traiter ces signaux à l'intérieur d'un système d'ordinateur et d'un réseau neuronal associé capables de générer un signal de sortie unique pour les signaux d'entrée combinés; (iii) à déterminer de façon invasive une valeur effective pour le paramètre conjointement à la génération non invasive de signaux des étapes précédentes; (iv) à appliquer des facteurs de pondération à l'intérieur du réseau neuronal au niveau des n÷uds d'interconnexion, pour obliger le signal de sortie du réseau neuronal à correspondre à la vraie valeur du paramètre tel qu'il a été déterminé de façon invasive; (v) à enregistrer les signaux d'entrée, les facteurs de pondération et la vraie valeur sous la forme de données d'apprentissage à l'intérieur de la mémoire de l'ordinateur; et (vi) à répéter les étapes précédentes jusqu'à constituer suffisamment de données d'apprentissage pour permettre au réseau neuronal d'estimer avec précision la valeur des paramètres lors de la réception ultérieure de signaux d'entrée en ligne. On décrit également des techniques permettant la classification préalable de signaux et le rejet des artéfacts. Grâce à l'apprentissage fait au niveau du réseau neuronal, toute mesure invasive ultérieure est superflue et le système est prêt pour les applications diagnostiques et pour l'estimation non invasive des valeurs des paramètres.
PCT/US1991/006191 1990-08-31 1991-08-29 Procede et appareil de mesure de la pression arterielle WO1992003966A1 (fr)

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WO1995018564A1 (fr) * 1994-01-05 1995-07-13 Vital Insite, Inc. Appareil et procede pour la mesure non invasive de la pression sanguine
EP0765630A1 (fr) * 1995-09-28 1997-04-02 Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO Méthode et dispositif pour déterminer l'onde de pression d'une artère brachiale? en fonction de la mesure non-invasive d'une onde de pression sanguine digitale
US5752919A (en) * 1996-12-17 1998-05-19 Johnson & Johnson Medical, Inc. Mitigation of respiratory artifact in blood pressure signal using line segment smoothing
EP0997103A1 (fr) * 1998-10-29 2000-05-03 Colin Corporation Dispositif de la mesure non-invasive et continue de la pression sanguine
WO2000076393A2 (fr) * 1999-06-09 2000-12-21 Vsm Technology Inc. Procede et appareil pour mesurer des valeurs de parametres physiologiques
WO2002069798A1 (fr) * 2001-02-28 2002-09-12 University Of Technology, Sydney Methode et dispositif non invasifs permettant de determiner l'apparition d'etats physiologiques
AU2002233052B2 (en) * 2001-02-28 2004-06-10 University Of Technology, Sydney A non-invasive method and apparatus for determining onset of physiological conditions
EP1848321A2 (fr) * 2004-10-05 2007-10-31 Optical Vitals, LLC Appareils et procedes pour le controle non invasif de parametres sanguins
WO2019025427A1 (fr) * 2017-07-31 2019-02-07 Redwave Medical GmbH Procédé permettant de faire fonctionner un dispositif de mesure de la tension artérielle et ensemble permettant de mesurer la pression dans un vaisseau sanguin

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Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995018564A1 (fr) * 1994-01-05 1995-07-13 Vital Insite, Inc. Appareil et procede pour la mesure non invasive de la pression sanguine
EP0765630A1 (fr) * 1995-09-28 1997-04-02 Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO Méthode et dispositif pour déterminer l'onde de pression d'une artère brachiale? en fonction de la mesure non-invasive d'une onde de pression sanguine digitale
NL1001309C2 (nl) * 1995-09-28 1997-04-03 Tno Werkwijze en inrichting voor de bepaling van brachiale arteriedrukgolf op basis van nietinvasief gemeten vingerbloeddrukgolf.
US5746698A (en) * 1995-09-28 1998-05-05 Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno Method and device for determining brachial arterial pressure wave on the basis of nonivasively measured finger blood pressure wave
US5752919A (en) * 1996-12-17 1998-05-19 Johnson & Johnson Medical, Inc. Mitigation of respiratory artifact in blood pressure signal using line segment smoothing
EP0997103A1 (fr) * 1998-10-29 2000-05-03 Colin Corporation Dispositif de la mesure non-invasive et continue de la pression sanguine
WO2000076393A2 (fr) * 1999-06-09 2000-12-21 Vsm Technology Inc. Procede et appareil pour mesurer des valeurs de parametres physiologiques
WO2000076393A3 (fr) * 1999-06-09 2001-03-15 Vsm Technology Inc Procede et appareil pour mesurer des valeurs de parametres physiologiques
WO2002069798A1 (fr) * 2001-02-28 2002-09-12 University Of Technology, Sydney Methode et dispositif non invasifs permettant de determiner l'apparition d'etats physiologiques
AU2002233052B2 (en) * 2001-02-28 2004-06-10 University Of Technology, Sydney A non-invasive method and apparatus for determining onset of physiological conditions
US7450986B2 (en) 2001-02-28 2008-11-11 Aimedics Pty Limited Non-invasive method and apparatus for determining onset of physiological conditions
EP1848321A2 (fr) * 2004-10-05 2007-10-31 Optical Vitals, LLC Appareils et procedes pour le controle non invasif de parametres sanguins
EP1848321A4 (fr) * 2004-10-05 2011-03-02 Optical Vitals Llc Appareils et procedes pour le controle non invasif de parametres sanguins
US9380951B2 (en) 2004-10-05 2016-07-05 Covidien Lp Non-invasively monitoring blood parameters
WO2019025427A1 (fr) * 2017-07-31 2019-02-07 Redwave Medical GmbH Procédé permettant de faire fonctionner un dispositif de mesure de la tension artérielle et ensemble permettant de mesurer la pression dans un vaisseau sanguin
CN110996779A (zh) * 2017-07-31 2020-04-10 雷德韦医疗有限公司 用于运行血压测量设备的方法和用于测量血管中的压力的设备

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EP0546098A1 (fr) 1993-06-16
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JPH06505886A (ja) 1994-07-07
AU8645291A (en) 1992-03-30

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