WO1985001867A1

WO1985001867A1 - Electronic lung function analyser

Info

Publication number: WO1985001867A1
Application number: PCT/GB1983/000277
Authority: WO
Inventors: Richard Richardson
Original assignee: Richard Richardson
Priority date: 1983-10-31
Filing date: 1983-10-31
Publication date: 1985-05-09
Also published as: EP0159979A1

Abstract

An electronic lung function analyser has an air flow tube (2) through which a patient inhales or exhales, an air flow transducer (3) associated with the air flow tube for providing an electrical output signal in response to inhaled or exhaled air flow in the tube, an electronic signal processor (11) connected to a display device (6) to provide from the transducer output signals an analogue or digital display representative of selected parameters of the patient's lung function, and a keyboard (9) for the manual input to the processor of data relating to the patient. The processor (11) is programmed to compute from the input data predicted normal patient (PNP) values appropriate to the said lung function parameters for display selectively on the display device.

Description

Electronic Lung Function Analyser This invention relates to electronic lung function analysers, that is instruments which measure and provide analysis based upon respiratory parameters of lung function.

It is known to provide instruments known as "spirometers" which give three important measurements of lung functions:

1. 'Peak Flow Rate' (PFR) which is the maximum flow rate that can be forcefully expired by a patient. The range of PFR is from zero to approximately 800 litres/minute.

2. 'Forced expiratory volume in one second' (FEVl) which, after the patient has fully inhaled, is the volume that can be forcefully expired during the time interval of one second. The range of FEVl is from zero to approximately 7 litres.

3. 'Vital Capacity' (VC) which, after the subject has fully inhaled, is the total volume that the patient can expire. The range of VC is from zero to approximately 7 litres.

An example of such a known spirometer instrument is the model P251 lung function analyser manufactured by Paladin Kedical Products Limited.

An object of the present invention is to provide an electronic function analyser which allows a ready comparison to be made between the measured lung function parameters of a patient and the predicted normal values of those parameters for the patient.

According to the invention there is provided an electronic lung function analyser comprising an air flow tube through which a patient inhales or exhales, an air flow transducer operatively associated with the air flow tube for providing an electrical output signal in response to inhaled or exhaled air flow in the tube, an electronic signal processor connected to a display device for providing from the transducer output signals an analogue or digital display representative of selected parameters of the patient's lung function, and manual data input means for the input to the processor of data relating to the patient, the processor being programmed to compute from the input data predicted normal patient (PNP) values appropriate to the said lung function parameters, which PNP values can be displayed selectively on the display device.

The processor may utilise the computed PNP values and the measured values of a patient's lung function parameters to provide an output display of the ratio of these values, represented as percentage predicted normal patient (PPNP) values.

In a preferred embodiment the air flow transducer comprises a turbo-generator device housed in the air flow tube or a duct communicating therewith. Preferably the turbo-generator device provides a pulsed output which is passed to a frequency-to-voltage converter to provide a voltage analogue signal representative of the air flow measured by the turbo-generator device.

The turbo-generator device may be reversible, providing output signals representative of inhalation and exhalation parameters of a patient's lung function.

The turbo-generator device output, whether pulsed or analogue, can be integrated over a fixed time period and used to provide an output representative of the FSVl parameter (where said fixed time period is one second) or of the VC parameter (where the fixed time period spans the total exhalation period). Where the turbo-generator output is in the form of pulses, the integrating process can be effected digitally by counting the pulses.

The analyser according to the invention is preferably a portable instrument. Thus the signal processor and display device and manual data input means may be housed in a hand-portable casing upon which the air flow tube is mounted. To obtain the predicted normal patient values the operator is required to input into the instrument through the manual data input means information relating to the sex, height and age of the patient breathing into the instrument.

The predicted normal patient values may be obtained by means of a 'look-up table' or an 'algorithm' method. The predicted normal patient value is the mean value obtained from normal subjects for a particular lung function parameter. The PNP values in look-up table form axe permanently stored in an electronic memory device in the processor and the specific PNP value relevant to the lung function parameter under study is obtained by the input of data relating to the subject's sex, height or age. The algorithm form of PNP values relies on the calculation of regressional relationships for the prediction of lung function. Algorithms are provided separately for the males and females and require the patient's height and age for the computation of the relevant PNP value.

The three measurements and the prediction of corresponding PNP values of lung function parameters are given here by way of example only; further or alternative parameters may be measured. Other parameters which may be measured include, for example, 'Peak Inspiratory Flow Rats' , Flow at 25%, 50 % and 75% of Vital Capacity, Forced Inspiratory Volume in 1 second (FIVl) and the Expiration Time.

Patient normal predicted (PNP) values may take the race of the patient and whether the patient is a child or an adult into account, and instead of, or in addition to, providing a mean PNP value, may give the normal range within which the majority of lung function values from normal patients fall.

Although the analyser according to the invention is preferably portable, the analyser can be powered from a mains electricity supply and may be embodied in a non-portable form. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic plan view of a portable lung function analyser or spirometer according to one embodiment of the invention, and

Figure 2 is a block schematic diagram of a lung function analyser according to the invention.

The drawings illustrate a portable electronic lung function analyser or spirometer instrument 1 having an air flow tube 2 through which a patient breathes in the standard manner suitable for the acquisition of the lung function under test. The tube 2 incorporates a turbo-generator (not shown) which acts as a transducer 3 (Figure 2) providing an electrical output representative of the air flow in the tube 2. The tube 2 including the turbo-generator is carried by a swivel head 4 mounted upon a plastics hand-portable casing 5.

A liquid crystal display (LCD) 6 is mounted on the casing 5 for displaying lung function measurements, PNP or PPNP values as selected by the user.

The casing 5 carries two switches: a power off/on switch 7 and a ready/reset/interrupt push-button switch 8. The casing also carries a low profile keyboard 9 which enable the user to:

(a) select the lung function parameter to be examined, and

(b) input data, for example the sex, height and age of the patient, to enable the predicted normal patient (PNP) values or the percentage of predicted normal patient (PPNP) values to be displayed.

As an alternative to the low profile keyboard 9, miniature thumb wheel edge switches with digital outputs could be employed.

A 'battery-low' indicator 1C, for example, a light-emitting diode, is mounted in the casing5, adjacent the display 6. The hardware circuitry of the instrument is illustrated in block- schematic form in Figure 2. This includes a microprocessor or microcomputer having a central processing unit (CPU) 11, through which all the data and instructions pass. An oscillator 12 provides clock pulses which control the sequential actions of the CPU 11 and the actions of the peripheral devices connected thereto.

Pre-programmed instructions controlling the CPU 11 are stored in a read only memory (ROM) 13. The ROM 13 is also required to store the predicted normal patient (PNP) values in the form of algorithms or look-up tables as will be described later.

A random access memory (RAM) 14 is also connected to the CPU 11. The RAM 14 acts as a temporary store for data collected from external devices, and for the results of arithmetical operations.

The CPU 11 communicates with the input devices, that is, the transducer 3, the keyboard 9 and the push-button switch 8 and with the output devices that is, the LCD 6 and the indicator 10, through input/output (I/O) ports indicated generally 15, which may include multiplexing and decoding means.

The power supply indicated generally 16 is in this embodiment a battery source(chargeable or non-chargeable) of approximately 5 volts.

Additional storage of data/instructions may be provided, for example by a magnetic store 17, shown in broken outline, with connection to the CPU 11 through an output socket in the instrument casing 5.

The microprocessor/microcomputer system illustrated schematically in Figure 2 is of the C-KOS type, or another type having low power components. By employing a 4-bit system a low cost, low power, hand-held instrument can be designed, with the microprocessor system carried on a single printed circuit card.

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O PI The microprocessor/microcomputer is programmed so that the CPU 11 executes instructions or operations in a logical order allowing the operator to:receive data and interrupts sent from the input ports 15; perform the appropriate analysis of the selected lung function parameter; select and calentate the appropriate PNP value; and output the results on the LCD 6.

When using the instrument 1 the operator inputs control instructions and data via the keyboard 9 and the Ready/reset/interrupt push-button switch 8. A typical operating sequence is as follows:-

1. Switch power OK (switch 7) ;

2. Operate ready/reset/interrupt switch 8;

3. Select lung function parameter on keyboard 9, for example, PFR, FEV1 or VC;

4. Allow patient to breathe through the spirometer tube 2 in the standard manner required for the mode selected;

5. Display the measured parameter on the LCD 6;

6. Compute PNP or PPNP values, from data entered via the keyboard 9 with appropriate 'data entered' interrupts of the switch 8, including:

a) Sex (male 1 or female 0) b) Age (years) c) Height (metres or centimetres)

7. Display on the LCD 6 either the PNP or PPNP values for the selected lung function parameters.

A useful addition to the three lung function parameters referred to (PFR, FEVI and VC) is the calculation and display of the percentage ratio FEVl/VC x 100 together with its corresponding PNP or PPNP value.

The predicted normal patient (PNP) values are computed after effecting data inputs of sex, height and age via the keyboard 9 and ready/reset button switch 8. The PNP values may be determined by one of two methods described here. The only PNP values described are for the lung function parameters PFR, FEVl and VC. PNP values for additional lung function parameters such as FEVl x 100 - VC, F VI may be obtained by the 'look-up table' and 'algorithm' methods described later. In addition an evaluation of the range of normal values can be given, for example, by displaying the standard deviation, or the normal range limits of the lung function parameter being assessed. The PNP values, together with their standard deviation (allowing a determination of normal range) are to be found from published data such as that obtained from, for example, "Lung Function, Assessment and Application in Medicine" by J.E. Cotes (3rd Edition) published by Blackwell Scientific Publications.

Typical PNP values in 'look-up table' form areshown in Table 1. As an example, for a patient with age and height 23 years and 1.67 m respectively, the software upon input of the data via the keyboard 9 would round up the inputs to 25 and 1.65 respectively then select the appropriate PNP value. The advantage of employing miniature thumb wheel edge switches instead of a keyboard 9 is that one such switch can be marked in year intervals , 20 , 30, 40 etc. and another in height intervals (m) 1.60, 1.65, 1.70 etc., so that the operator can select the nearest appropriate values to those belonging to the subject under assessment.

Expansion of Table 1 to cover all possible keyboard inputs would require more ROM capacity. The PNP values for children and races other than Europeans, using a combination of look-up tables and a 'correction constant' is a possibility. Examples of 'correction constants' for applying tc PNP values of European descent for conversion to PNP values appropriate to those of African/Indian descent are to be found, for example, in the previously cited publication by J.E. Cotes.

The PNP values for each sex are obtained by the alternative algorithm method from regression relationships for the prediction of lung function from age and height. Table 2 shows examples of these regression relationships as found in the previously cited publication by J.E. Cotes. Table 2 is in two parts, applicableto different ethnic groups:

(a) Hegressional relationships for PFR, FEVl and VC for male and female adults and children of European descent.

(b) Eegressional relationships for PFR, FEVl and VC for adults of African/Indian descent, these being, in effect, similar to those for adults of European descent with the subtraction of a constant value (correction constant).

These regreseional relationships can be incorporated into the programiming as algorithms and together with the data input of sex, height and age, the appropriate PNP values can be calculated and displayed. Algorithms for other lung function parameters may require data inputs other than sex, age and height.

The PNP values may be utilised together with the measured lung function parameters to provide other useful information of data using microprocessing or signal processing methods, for example, in the form of percentage predicted normal patient (PPNI) values.

These are calculated for a particular lung function parameter as:-

PPNP value = subjects lung function parameter value subjects relevant PNP value x 100%

Although a portable instrument has been described a mains version based on similar principles would have fewer design constraints upon size, power requirements, the range of lung function parameters that are analysed and predicted, and the sophistication of the inputs and outputs. A mains-powered version of the spirometer device could, for example, have the following characteristies:-

1. An alternative to the air turbine generator such as a screen pneumotachograph.

2. An alternative to the 4½ segment LCD display such as larger alphanumeric LED displays identifying the lung function parameter, the measurement and PNP values.

3. Analysis of additional lung function parameters. 4. A greater selection of stored PNP values including additional lung function parameters for adults and children, different ethnic groups; and the range rather than the mean of the PNP values.

5. A write-out capaibility, for example: to a printer; an X-Y oscilloscope; X-Y recorder; or a magnetic tape or disc storage 6. A calibration procedure.

Claims

1. An electronic lung function analyser comprising an air flow tube through which a patient inhales or exhales, an air flow transducer operatively associated with the air flow tube for providing an electrical output signal in response to inhaled or exhaled air flow in the tube, an electronic signal processor connected t a display device for providing from the transducer output sign s an analogue or digital display representative of selected parameters of the patient's lung function, and manual data input means for the input to the processor of data relating to the patient, the processor being programmed to compute from the input data predicted normal patient (PNP) values appropriate to the said lung function parameters, which PNP values can be displayed selectively on the display device.

2. A lung function analyser according to Claim 1, in which the processor utilises the computed PNP values and the measured values of a patient's lung function parameters to provide an output display of the ratio of these values, represented as percentage predicted normal patient (PPNP) values.

3. A lung function analyser according to Claim 1 or Claim 2, in which the lung function parameters analysed include:

- (a) peak expiratory flow rate (PFR);

- (b) forced expiratory volume in one second (FEV₁) and

- (c) vital capacity (VC)

4. A lung function analyser according to any one of Claims 1 to 3, in vhich the signal processor and display device and manual data input means are housed in a hand-portable casing upon which the air flow tube is mounted.

5. A lung function analyser according to Claim 4, in which the electrical power supply for the analyser is provided by batteries housed in the casing.

6. A lung function analyser according to any one of the preceding claims, in which the air flow transducer comprises a turbo-generator device housed in the air flow tube or a duct communicating therewith.

7. A lung function analyser according to Claim 6, in which the turbo-generator device provides a pulsed output which is passed to a frequency-to-voltage converter to provide a voltage analogue signal representative of the air flow measured by the turbogenerator device.

8. A lung function analyser according to Claim 6 or Claim 7, in which the turbo-generator device is reversible, and provides output signals representative of inhalation and exhalation parameters of a patient's lung function.

9. A lung function analyser according to any one of the preceding claims, including means for integrating the output of the air flow transducer over a fixed time interval to obtain an output representative of the FEV₁ parameter or the VC parameter.

10. A lung function analyser according to Claim 9 in which the air flow transducer provides a pulsed output, and the integrating means comprise a pulse counter circuit or circuits associated with a timer or timers.

11. A lung function analyser according to any one of the preceding claims, including means for computing from the measured parameters FEV₁ and VC the ratio FEV₁/VC and for providing on the display device an indication of the said ratio.

12. A lung function analyser according to any one of the preceding claims, including a printer connected to the signal processor for providing a print-out of the display data.

13. A lung function analyser substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.