GB2133157A - Electronic lung function analyser - Google Patents

Abstract

An electronic lung function analyser has an air flow tube through which a patient inhales or exhales, an air flow transducer associated with the air flow tube for providing an electrical output signal in response to inhaled or exhaled airflow in the tube, an electronic signal processor connected to a display device 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 for the manual input to the processor of data relating to the patient. The processor 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. <IMAGE>

Description

SPECIFICATION Portable lung function analyser This invention relates to portable lung function analysers, that is instruments which measure and provide analysis based upon respiratory parameters of lung function.

An object of the invention is to provide an electronic portable spirometer that gives three important measurements of lung functions together with their predicted normal patient (PNP) values:~ 1. 'Peak Flow Rate' (PFR) which is the maximum flow rate (litres/minute) that can be forcefully expired by a subject. The range of PFR is from zero to approximately 800 litres/minute.

2. 'Forced expiratory volume in one second' (FEV1) which, after the subject has fully inhaled, is the volume that can be forcefully expired during the time interval of one second. The range of FEV1 is from zero to approximately 7 litres.

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

The stored PNP values are utilised together with the measured parameters to provide other useful information or data using microprocessor or signal processing methods, for example, in the form of percentage of predicted normal patient values' (PPNP Values).

The present invention in broad terms provides an electronic portable spirometer for use in the measurement of lung function comprising an air flow transducer which provides an electrical output signal in response to inhaled or exhaled air and an electronic signal processing circuit which provides from the electrical output of the turbo-generator device an analogue electrical signal representative of the airflow rate.

Preferably the turbo-generator device provides a pulsed output which is converted to a frequency dependent output which is used to provide a digital read out of peak flow rate.

The turbo-generator device output, whether pulsed or analogue, can be integrated over a fixed time period and used to provide a digital output representative of the FEV1 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 done digitally by counting the pulses.

Provided a reversible turbo-generator device is employed, the spirometer of the invention can also be used to measure inhalation parameters as well as exhalation parameters.

The portable spirometer is described in two versions, that is, Version A and Version B. Version A is based on conventional digital electronic intergrated circuit components. Version A gives three measurements of lung function (PFR, VC, and FEV1). Version B is based on a microcomputer/microprocessor system and gives the three measurements of lung function together with their respective PNP and PPNP values. Version B gives both analysis and prediction of lung function parameters but may be simplified to give the measurements of lung function (PFR, VC, and FEV1 ) without their PNP or PPNP values.

To obtain the predicted normal patient values the operator is required to input into the spirometer information relating to the sex, height and age of the subject breathing into the instrument.

The predicted normal patient values are obtained by one of two methods described, these being designated as being of 'look-up table' and 'algorithm' form. 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, are permanently stored in an electronic memory device and the specific PNP value relevant to the lung function parameter under study is located 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 subject's height and age in the calculation of the relevant PNP value.

The three measurements and prediction of lung function parameters described here are by way of example only. This especially relates to the microcomputer/microprocessor version B which is suitable for increasing its sophistication and functionality as the electronic components on which it is based increase their operational capability due to technical improvements.

Some forms that the increased function of version B can embrace are given and include additional -lung function measurements together with appropriate PNP values. Also described are increased facilities relating to operator control, data processing, display and output options. Patient normal predicted values may take the race and whether the subject is a child or an adult into account, and instead of, or in addition to, providing the mean of the PNP value give the normal range within whose limits fall the majority of lung function values from normal subjects.

Although the spirometer described is portable, the invention can be powered by mains electricity and be of a non-portable form.

A spirometer instrument embodying the inventions is illustrated in the drawings by way of example only.

The spirometer instrument employs an air turbine generator as shown in figure 1 and 3 into which the subject breathes in the standard manner suitable for the acquisition of the lung function measurement selected.

INTRODUCTION This invention is described in two versions:~ VERSION A Portable Spirometer based on conventional digital i.c. components VERSION B Portable Spirometer based on a microcomputer/microprocessor system.

Although the portable spirometer described in Version B combines the analysis with the prediction of lung function parameters, a simpler version would provide analysis of the lung function parameters alone, without PNP or PPNP being given.

Portable instruments are described although a mains version based on similar principles would in both cases have less prohibitions, 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 version of the spirometers proposed could, for example, have the following characteristics:- 1. An alternative to the air turbine generator such a screen pneumotachograph.

2. An alternative to 4w segment LCD such as larger alphanumeric displays giving the lung function parameter, result, PNP values and unites perhaps based on LED or gas discharge displays, 3. Analysis of additional lung function parameters.

4. A greater selection of PNP values for: additional lung function parameter; adults and children; ethnic groups; and the range rather than the mean of the PNP values.

5. Write-out capability, for example: to a printer; X Y oscilloscope; X Y recorder; tape or disc storage system in magnetic form.

6. Calibration procedure.

VERSION A External appearance The air turbine generator is shown with a swivel-head in Figure 1 mounted on a polystyrene case.

There is a battery low indicator, for example, a red miniature light-emitting diode which only illuminates when there is a drop in battery voltage of approximately 10%. The lung function measurements are displayed in digital form on the liquid crystal display (LCD). There are four switches a, b and c being toggle switches and d, a momentary push button switch. The switches control of the internal electronics are as follows.~ a) Power off or on b) Modes 1) or 2) Mode 1) PFR alone Mode 2) FEV1 and VC c) Only applicable to mode 2) and displays on the LCD either FEV1 or VC d) Reset button Principles of circuitry A block diagram of the electronics contained within the instrument case is shown in figure 2.All the components apart from the air turbine generator and the pre-amplifier (Stage 2) are available from major suppliers of electronic components. All integrated circuits (i.c.) are C-MOS or alternatively other low power consuming components. The components are mounted in a conventional way such as on printed circuit boards.

The working of the electronics, as in figure 2 shall be described in four sections A, B1, B2 and C.

Sections A and C are common to both modes 1) and 2) while sections B1 and B2 are concerned with modes 1) and 2) respectively.

The three sections contain, in all, eighteen stages. Stages 5 and 10 are based on operational amplifiers whose circuits can be found in the handbooks of major semi-conductor manufactures. The majority of the other stages are based on i.c.s. that can be purchased from Radio Spares of London (RS) with the i.c. being utilized as described in their relevant RS data sheets.

The form of interfacing can be of different configurations, but in this instance binary coded decimal (B C D) outputs were obtained from stages 7, 13 and 14 with later stages being compatible with this form of output.

Section A The air turbine generator (Stage 1) and its pre-amplifier (Stage 2) give a pulsed electrical output where each pulse represents a given volume of air (for example 10 millilitres). The instrument is powered by small non-rechargeable or rechargeable batteries (Stage 3). A micropower sensor i.c. is employed as a battery low indicator (Stage 4). The pulses from the pre-amplifier are amplified to approximately 5 volts and shaped to a square wave form (Stage 5).

Stage 6 is a pulse multiplier based upon a tone burst generator circuit as shown in RS data sheet R121 13 and employs a C-MOS dual timer i.c. An alternative method, for example, is to use divider/multiplier logic i.c.s. A multiplication or division factor is necessary to enable each pulse received by the LCD decoder/driver i.c. (Stage 1 7) to be, for example, representative of one millilitre or ten millilitres of air volume. If we consider one pulse arriving at stage 1 7 representing one millilitre of air volume, then for one litre passing through the air turbine generator a 1,000 units will be displayed on the LCD. A decimal point can be introduced if required so that display represents litres of air volume, with 1.000 being displayed.

It must be noted that the calibration of the pulsed output as described here, using stage 6, need not take place at this particular place in circuit, for example, another option is for this to occur immediately prior to stage 17.

Section B1 This section only comes into operation when switch b is selected to Mode 1 which is the mode that gives the peak flow rate. To determine the PFR a frequency to voltage counter i.c. (Stage 7) is used to convert the pulsed input to an output which is a measure of the frequency of the pulses from Stage 6.

The choice of the accumulation time is important. It has been suggested that maintaining a peak flow for ten millisecond was sufficient for the original mechanical peak flow meter to respond accurately. The choice of the accumulation time can be made by comparison of the PFR results obtained from the spirometers described here with standard mechanical peak flow meters, such as these made by Wrights.

The divider i.c. of Stage 8 is optional and enables the pulsed output from Stage 7 to be converted to the traditional peak flow rate units of litres/minute, that is if required in preference to SI units of millilitres/second or litres/second.

Stage 9 detects the maximum frequency counter i.c. output and stores this value ready for when it is required to be displayed. Switch d operates the multiplexing of outputs from Sections B1 and 82 for interfacing their respective outputs with Stage 17.

Section B2 This section only comes into operation when switch b is selected to Mode 2 which is the mode that effectively counts the pulses for 1 second (FEV1) and for 6 seconds (VC) from the initial pulse detected. Six seconds is a long enough duration to collect the air volume for the VC and is the same time interval used on the 'Vitalograph' which is a standard spirometer used, for example, in respiratory hospital departments. The number of pulses counted being directly proportional to air volume passing through the turbine generator.

Stage 9 detects the first true pulse from the air turbine generator and is designed so that electronic noise will not activate the initial pulse detector. The method employed here was based on an operational amplifier i.c. employed as a comparator. This stage detects the first true pulse, rather than lower voltage electronic noise and triggers the comparator which drops from high voltage to ground and stays there so as to trigger, in their turn, the timers of Stages 10 and 1 The timers in this case, activate the FEV1 and VC counter i.c.s. (Stages 13 and 14) which begin counting the pulses received from Stage 6.The timers, Stages 13 and 14, upon reaching 1 second and 6 seconds respectively, activate the counter i.c.s. store facility so that the number of pulses received by them within their respective time limits are stored for output to Stage 17 via the multiplexing of Stage 1 5 which is controlled by switch c.

Section C Switch c decides which of the modes 1 or 2 is displayed. If mode 2 is selected the position of switch d selects which of the FEV1 or VC counter i.c. stored outputs is interfaced with Stage 1 7 for eventual display. The counter i.c. stored output selected is analysed by a digital panel meter i.c. (Stage 17) which incorporates decoders/drivers allowing a direct interface with a 7 segment, 421 digit, liquid crystal display (Stage 18).

VERSION B External appearance Figure 3 shows theportable version of this spirometer. The air turbine generator is shown with a swivel head mounted in a polystyrene case. There is a battery low indicator, for example, a miniature light emitting diode.

There are two switches:~ a) Power off/on b) Ready (allows reset/interrupts). Momentary push button switch.

The low profile keyboard allows for:~ 1) Selection of lung function parameters in combination with the ready/reset switch b.

2) Input of data, that is 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 #e low profile keyboard, miniature thumb wheel edge switches with B C D outputs could be employed.

Lung function measurements, PNP or PPNP values are displayed on a liquid crystal display (LCD).

Principles of internal hardware requirements The analysis of the digital output from the air turbine generator by the system proposed has the characteristics of a small computer or microprocessor based system. The heart of the system is the central processing unit (CPU). It is connected to a number of other peripheral devices/components as shown in figure 4.

1. Input Devices 1. Manual reset/interrupt button 2. Keyboard providing the user with the means to communicate with the CPU by typing in data and instructions.

3. An air-flow transducer, in this portable model, an air turbine generator giving a pulsed output.

2. Output Devices 1. Liquid Crystal Display 2. Battery Low Indicator (eg LED) 3. Central Processor Unit (CPU) All the data and instruction pass through the CPU. The execution of instructions from the memory (the program), one at a time, by the CPU, constitutes the functioning of the microprocessor device.

4. Clock generator It is based on an oscillator by means of which all actions of the CPU and the actions of the peripheral devices are synchronised and timed.

5. Memory Instructions controlling the CPU (the program) are found in the read only memory (ROM) which is needed to permanently store the program. ROM is also required to store the predicted normal patient values in the form of algorithms or look-up tables as shall be described later. Random access memory (RAM) is required for temporarily storing data collected from external devices, and the results of arithmetic operations.

6. Input/Output Ports The CPU communicates with the input devices and output devices via the input/output (I/O) ports.

I/O port control, multiplexing together with decoding/driving of I/O devices also takes place.

7. Power Supply A ground and positive DC voltage of approximately 5 volts are required. This can be provided by mains adapted supply or as described here, for a portable spirometer, by batteries of a chargeable or non-chargeable nature.

8. Store An option is for storage of information on a tape or disc system in magnetic form, with an output facility being on the exterior of the spirometer instrument case.

Internal hardware proposed A microprocessor/microcomputer system is proposed of the C-MOS type, or that of other low power components. A 4 bit machine provides a low cost, low power, low part count, intelligent hand held instrument. The microprocessor system may be configured on a single card.

Single chip microcomputer i.c.s. are available where many of components required are on one chip such as a processor, a ROM program, RAM memory and input/output control and communication with external devices. To enable the system to have a low part count preferred options of increased capability include:1. Programmable timers, so that there is less instruction counting.

2. External interrupts without the need for constant polling of an input.

3. Direct interfacing with keyboard and LCD display without the need for extra i.c.s. for decoding, drivers or multiplexing.

Two methods of obtaining predicted normal patient values are proposed. Extra memory in addition to that provided on the minimum microprocessor configuration may be required, this depending on the following options.~ 1. The number of lung function parameters analysed. Three are considered here as examples and also as being of prime importance, that is PFR, FEV1 and VC. Other possible parameters, for example, could include 'Peak Inspiratory Flow Rate', Flow at 25, 50 and 75% of Vital Capacity, Forced Inspiratory Volume in 1 second (FIVi) and Expiration Time.

2. Whether the PNP values are provided by 'look-up table' or 'algorithm' form as shall be described later.

Programming A series of instructions, or operations is proposed, whose main function, when executed by the CPU in a logical order will allow the operator to receive data and interrupts sent from the input ports; perform the appropriate analysis; select/calculate the PNP value; and output the results on the LCD.

The basis of the programming will be described in terms utilising the stages showing the functioning of the conventional electronic digital spirometer (Version A) as shown in figure 2 and as described earlier.

Operator input and display The operator inputs control instructions and data via the keyboard and the ready/reset interrupt button. A typical sequence of operation is as follows:~ 1. Power on 2. Ready/reset interrupt 3. Selection of Mode 1 (PFR alone) or Mode 2 (FEV1 & C) 4. Patient then breathes into the spirometer in the standard manner required for the mode selected 5. Displays on LCD either PFR (form Mode 1) or FEV1 (for Mode 2) If Mode 2 then ready/reset button allows VC to be displayed.

6. For PNP or PPNP values data is entered via the keyboard with appropriate 'data entered' interrupts a) Sex (male 1 or female 0) b) Age (years) c) Height (metres or centimetres) 7. Displayed on the LCD either the PNP or PPNP values for:~ PFR (for mode 1 ) FEV1 (for Mode 2) If Mode 2 then ready/reset button allows VC to be displayed.

On the keyboard shown in figure 3 the keys A-F may be labelled to facilitate keyboard entry.

Programming may be enhanced to facilitate data presentation by displaying on the 7 segment LCD prompts such as 7il- 7 ;,': E7 e " 1, 1 PFA,FEUI,UC,SEH,AGE@HT.

A useful addition to the three lung function parameters (PFR, FEV1 and VC) is the calculation and display of FEV1/VC x 100 together with its PNP or PPNP value.

Principles of the program analysis a) Lung function parameters The principles behind the analysis of the incoming pulses from the air turbine generator are basically the same as those employed for the conventional electronics version A whose functional stages of operation are shown in figure 2. The specific program employed will depend upon the number of stages shown in figure 2 that can be carried out by the microprocessor based configuration chosen.

For a low part count instrument, it is desirable for function to be carried out by software option rather than the additional use of external i.c.s. The functions of Version A stages 4, 6~17 are candidates for software application.

PFR The frequency of the pulses is required and can be found, for example, by repetitive accumulation times of 1 G milliseconds. It has been suggested that maintaining a peak flow for 10 ms was sufficient for the original peak flow meter to respond accurately (Wrights and McKerrow 1 959).

The maximum frequency is selected and stored.

FEV1 After the initial pulse has been identified, the FEV1 requires that the pulsed output is counted for 1 second.

VC After the initial pulse has been identified the VC requires that the pulsed output is counted for a fixed time spanning the total expiration period, with six seconds being that of the standard 'Vitalograph'.

As with Version A account has to be taken for calibrating the pulsed output from the air turbine generator to appropriate units for the display. Multiplication or division factors, equivalent to Version A stages 6 and 8 are necessary for the lung function parameters to be displayed in relevant units.

The software and additional components required, if any, for microprocessor forms of, for example, a battery low sensor (Version A stage 4) and peak hold frequency monitoring (Version A stages 7 and 9) are described in journals such as Electronics Engineering and New Electronics and can also be found in the 'Application Manuals' provided by the microprocessor manufactures.

b) Predicted normal patient values Upon receiving interrupts and data input of sex, height and age from the keyboard and ready/reset button, the PNP values are determined by one of two methods described here as with the lung function parameters the only PNP values described are for PFR, FEV1 and VC. These are by example only, being of prime importance, although PNP values for additional lung function parameters such as FEV1 x 100 - VC, FEV1 etc. 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 JE Cotes (3rd Edition) Blackwell Scientific Publication (Lung Function JE Cotes) 1. Look-up Tables An example of values to be found in the 'look-up table' are shown in table 1. Employing a keyboard with age and height inputs of 23 and 1.67 respectively, the software would first round up the inputs to 25 and 1.65 respectively then select the appropriate PNP value.The advantage of employing miniature thumbwheel edge switches instead of a keyboard is that one can be marked in year intervals, 20, 30, 40 etc. and another in height intervals (m) 1.60, 1.65, 1.70 etc with the operator selecting 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. The PNP values for children and races other than Europeans, using a combination of look-up tables and ~correction constant' is a possibility. Examples of 'correction constants' for applying to PNP values of European Descent for convertion to PNP values appropriate to those of African/lndian descent are to be found, for example, in "Lung Function" JE Cotes.

2. Algorithms The PNP values for each sex are obtained by this alternative 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 "Lung Function" JE Cotes. Table 2 is in two parts appliable to different ethnic groups.

Regressional relationships for PFR, FEV1 and VC for male and female adults and children of European descent.

Regressional relationships for PFR, FEV1 and VC for adults of African/lndian descent. These in effect being similar to those for adults of European descent with the subtraction of a constant value (correction constants).

These regressional relationships can be incorporated into the programming 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 input other than the sex, age and height.

c) Percentage of predicted normal patient values The PNP values are utilised together with the measured lung function parameters to provide other useful information or data using microprocessing or signal processing methods, for example, in the form of percentage predicted normal patient (PPNP) values.These are calculated for a particular lung function parameter as: subjects lung function parameter value subjects relevant PNP 100% PPNP relevant PNP value = subjects relevant PNP value TABLE 1 PNP VALUES IN 'LOOK-UP TABLE' FORM MALE FEMALE Height Age PFR FEV1 VC Height Age PFR FEV1 VC (m) (m) 1.60 20 580 3800 4300 1.50 20 410 2700 3080 30 560 3568. 4000 30 380 2500 2890 40 530 3200' 3700' 40 360 2200' 2710 50 510 2800' 3400 50 340 2000 2530 60 480 2500' 3100 60 320 1600' 2350 70 2200 ' 2800 70 1500 2170 1.65 20 600 3900 4620 1.55 20 420 2800 3340 30 570 3700 ' 4320 30 400 2600 3150 40 550 3300' 4020 40 380 2400 2970 50 530 3000 3720 50 360 2100 2790 60 50Qz' 2700' 3420 60 340 1700' 2610 70 2400 3120 70 1600 2430 1.70 20 620 4100' 4940 1.60 20 440 2900- 3600 30 590 3800 4640 30 420 2700 3410 40 570 3500 4350 40 400 2500- 3220 50 540 3200 4050 50 380 2200 3050 60 520 2900 3740 ' 60 360 1800 2870 70 2600 3440 70 1700' 2690 1.75 20 640 4300 5260 1.65 20 460 3100 3880 30 610 4000 4960 30 440 2800 3680 40 580 3700 4660 40 420 2600' 3500' 50 560 3400 4360 50 400 2300 3320 60 530 3100 - 4060 60 380 1900 3140 70 2800' 3760 70 1800' 2960 1.80 20 650 4500' 5580 1.70 20 480 3200 4130 30 630 4200' 5280 30 460 2900 3940 40 600 3900 4980 40 440 2700 3760 50 575 3600 4680 50 420 2400 3580 60 550 3300 4380 60 400 2000 3400 70 2900 4080 70 1900 3220 1.85 20 675 4700 5900 1.75 20 500 3300 4380 30 650 4300 5600 30 480 3000 4200 40 620 4100' 5300 40 460 2800 4020 50 590 3700 5000 50 440 2500 3840 60 570 3500 4700 60 420 210Q' 3660 70 3100- 4400' 70 2000 3380 PFR in jitres/minute FEV1 and VC in millilitres" TABLE 2 PNP VALUES IN ALGORITHM FORM

Status Function Height (m) Age (yrs) Constant Male PFR (I /s) hx -0.019a +6.58 Adults of FEV1 (l) 3.62h -0.031a -1.41 European Descent VO (I) 5.2h -0.022a 3.6 Female PFR 6.23h -0.035a +1.88 Adults of FEV1 3.29h -0.029a -1.42 European Descent VC 4.66h -0.029a -2.88 Male PFR 7.59h -5.53 Children of FEV1 0.812h European Descent VC 1.004h Female PFR 7.59h -5.53 Children of FEV1 0.788h European Descent VC 0.948h Male Adults of FEV1 3.B2h -0.031a 1.41 (0.45) African /Indian Descent VC 5.2h -0.022a -3.6(0.7) Female Adults of FEV1 3.29h African/lndian Descent VC 4.66h -0.029a 3.6(0.6)

Claims (13)

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 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.

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 (FEV,) and - (c) vital capacity (VC)

4. A lung function analyser according to any one of Claims 1 to 3, in which the signal processor and display device and manual data input means are housed in a hard-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 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 turbo-generator 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 FEV, 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.

1 1. A lung function analyser according to any one of the preceding claims, including means for computing from the measured parameters FEV, and VC the ratio FEV,/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.