FI94589B - Method and apparatus for measuring physical condition - Google Patents

Abstract

PCT No. PCT/FI93/00370 Sec. 371 Date Mar. 15, 1995 Sec. 102(e) Date Mar. 15, 1995 PCT Filed Sep. 15, 1993 PCT Pub. No. WO94/06348 PCT Pub. Date Mar. 31, 1994A method and an apparatus for measuring quantities relating to a person's cardiac activity, such as for example quantities proportional to heart rate, cardiac stroke volume and cardiac output. A person is positioned on a measuring support (S), so that a blood flow pulse caused by a stroke of heart is matched by a change in a person's weight (G). Said change of weight is recorded and the recorded changes of weight are used for deriving information about a person's cardiac activity, such as for example about stroke volume and cardiac output as well as heart rate.

Description

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METHOD AND APPARATUS FOR MEASURING PHYSICAL CONDITION

The invention relates to a method and an apparatus for measuring variables proportional to the heart rate and physical condition of a person, such as heart rate and weight, and to the volume and minute volume associated with the condition of the cardiovascular circulation and calculating a person's fitness index based on the measurement results.

The heart rate of the heart, i.e. the heart rate HR, whose unit is io beats per minute, measured in rest and various stress states, gives a picture of e.g. the physical condition of the subject. HR increases not only due to mental and physical exertion but also due to various medical conditions such as fever. At rest, the HR in good condition is typically lower than that in poor condition HR.

In assessing cardiac function, HR measurement provides only very superficial information. It is also important to know the heart rate SV, whose unit is liters, and the minute volume CO, whose units are liters per minute. CO is obtained, for example, by multiplying HR and the average SV.

It is known to measure HR by recording the electrical activity of the heart, the so-called ECG signal, from which, for example, the so-called QRS complexes are identified. HR is obtained by measuring the time between successive QRS complexes, the inverse of which gives 25 HR. Equipment based on this for athletes and fitness enthusiasts is manufactured, for example, by Polar Electro OY, Finland. The disadvantage of these devices is that they require electrodes to be attached to the body. The ECG signal also does not provide any information about SV or CO.

30 It is also known to measure HR by exploiting changes in the body's electrical impedance and light transmittance. Light transmittance can be measured e.g. earlobe and 2. 94589 from the finger. The HR measuring device for athletes based on light transmission is manufactured by e.g. Casio Computer Inc., Japan. The disadvantage of such methods is that the required sensor must be in good light contact with the body of the subject 5. In frail people or in a cold state, for example, the blood circulation in the finger or ear may be so poor that the required signal cannot be seen. Changes in light transmittance caused by distant circulation do not include information on SV or CO. Meters based on impedance change, in turn, require several electrodes to be attached to the body.

In ballocardiography equipment, the subject is lying on a sensitive surface and mechanical vibrations caused by heart activity are recorded. The SV and CO values can in principle be calculated from the amplitude of the oscillations. In practice, the absolute accuracy of the results has proven to be poor, but the different measurements of the same person are relatively well comparable. The difficulty of the method is e.g. arrange a sufficiently sensitive patient bed to make the measurement results sufficiently accurate.

It is also known to place a subject under the subject under whose piezoelectric signal or some other electrical quantity the person's HR can be measured. These measurements do not provide information on a person's CO or SV values.

25 Known methods and devices cannot simply measure HR, SV and CO values, nor can they generate simple indices to monitor a person's condition.

With the solution according to the invention, the shortcomings of the prior art can be eliminated and devices which, in addition to HR, provide information on SV and CO values and the person's weight G. The values measured by the methods and devices according to the invention can be used to generate index values R. To achieve this, the method 3 to 94589 according to the invention and the devices based thereon are characterized by what is set forth in the characterizing parts of the claims.

The most important advantages of the invention are the simplicity of use and the low cost of implementation, as well as in particular the information provided by the methods and similar devices according to the invention on a person's physical condition, weight and heart function.

The invention is illustrated by the accompanying drawings, in which - Figure 1 schematically shows the forces generated by cardiac function in the circulatory system - Figure 2 shows a block diagram of a device according to the invention - Figure 3 shows two different sensor solutions 15 - Figure 4 shows a block diagram of digital signal processing electronics top and side view of the device

Figure 1A schematically shows those parts of the human circulatory system which are essential for understanding the operation of the invention. The left ventricle of person P's heart H pumps a blood flow pulse to the aorta AO with each stroke, causing a change in blood flow BF. The blood flow is reversed in the aortic arch AC, which in turn causes a force FO directed towards the end of P as shown in Fig. 1B. Figure 1C shows graphically the changes in BF and the corresponding changes in weight G as a function of time t.

Figure 2 shows a device according to the invention, in which a person so P stands on a measuring platform S suspended by a sensor L, e.g. by springs, on a frame F. Transformation element means T, for example a strain gauge or a piezoelectric crystal, are recorded on the platform S, which registers S's movements. depend on the weight of P and the elasticity of L 4 94589. It should be noted that a similar signal is obtained if a person is positioned to sit on an S in which, for example, a chair-like stand is arranged. The sitting position is suitable for e.g. for frail or disabled people or 5 if you wish to make a long-term registration. The output signal of T is amplified by an amplifier A, the output of which thus depends on the weight G of P and can be displayed on the display D1. The output signal of A is applied to a derivative D, from the output signal of which a pulse modifier X generates a pulse corresponding to each rapid change in the weight of P io, which is applied to a counter C, the output of which gives the HR shown in the display D2. An X may also be connected to a detected pulse indicator, an audible signal or a light signal, or both. An arrangement is also conceivable in which the user can, if he wishes, select the quality and strength of the signal signal or switch it off completely. Integrating the changes in the output signal of A with integrator I gives a result proportional to the stroke volume SV and multiplying this by HR by a factor M gives a result proportional to the minute volume CO, which is shown in display D3.

T can consist of several separate sensors. With the help of several sensors, it is possible to reduce, for example, the variation caused by the jitter of a standing person. Equipment for examining a seated person may include a chair-like measuring platform 25 and below it four weight sensors, the signals of which are summed. It may further be advantageous to use • several sensors so that the first sensor registers mainly the weight of the person and the second sensor changes the weight of the person. Schematically, such sensor connections are illustrated in Figure 3. In the case of Figure 3a, a force G 'proportional to the patient's weight acts on a sensor element L to which a transformation element Ttt is attached, which may be, for example, a strain gauge sensor. Typically, such a sensor includes two elements whose resistance changes in the opposite direction as the sensing element L bends under the influence of the force G '. These elements are connected to an amplifier A „, the output signal Sw of which is proportional to the force G’. The current bathroom scales have a connection with -. 94589 5 The frequency of the oscillator is changed under the control of the lifting element Tw and this frequency is used to conduct the weight. Such a solution, both electrical and mechanical, is e.g. Hanson Hi-Tech (Bathroom scale, model 881) scale, val-5 from Hanson Industries Limited, Ireland. If such an implementation is to be maintained, it is advantageous to use other sensor means for recording changes in weight. These sensor means may be based on a different principle than the means for recording the average weight G. Such a second sensor solution is schematically shown in Figure 3b. For example, the sensor TB is placed on the measuring platform S in such a way that it is directly or indirectly affected by the weight G of the person. One preferred embodiment of the TB sensor is to use piezoelectric materials. Piezoelectric ceramic 15 components are manufactured e.g. N. V. Philips Gloeilampenfa-brieken, Eindhoven, The Netherlands. The applications of these have been described e.g. in Piezoelectric Ceramic, Designer's Guide, Philips Component Division 1989. The sensor TB is preferably implemented nun. using a piezoelectric bimorph consisting of two piezoelectric ceramic elements. Such an element has the advantage of relatively low electrical and mechanical impedance, which makes it particularly suitable for recording relatively low-frequency quantities. A piezoelectric sensor 25 as described can be placed in a flexible sensing element L as shown in Fig. 3a and the resulting signal is fed to an amplifier A „, the output signal SB of which is applied to the signal processing electronics.

Another way to use a piezoelectric material is to place a layer of piezoelectric material, such as a PVDF film, on a substrate S, such as e.g. Pennwalt Corp., PA, U.S.A. and markets it under the brand name Kynar Piezo Film.

Figure 2 shows only one block diagram of the device 35 according to the invention. For example, the relative magnitude of CO is obtained more accurately by averaging the values of SV and HR. In this case, the device must include the corresponding means β 94589 for this purpose. For example, in order to calculate an index reflecting the condition, the above-mentioned results can be converted into digital form and the desired index can be calculated from them with a microprocessor. In this case, the device must include the necessary means 5 for this purpose. The required A / D converters are manufactured, for example, by Motorola Inc., USA and Linear Technology Corp., USA, and suitable microprocessors e.g. Motorola Inc., USA and Intel Corp., USA. The result or results obtained can be stored in a memory and then used later as a reference when assessing the development of a person's condition. The storage medium can be, for example, a semiconductor memory or a magnetic, optical or magneto-optical disk, a magnetic tape or a so-called smart card or even a perforated card or tape. A suitable microprocessor set that is compatible with so-called IBM PC 15 devices is manufactured, for example, by Dover Electronics Manufacturing West, USA. The device type is ESP8680 and the necessary connection devices are available. Naturally, in series production, the device must be designed with its own solution, which is economically advantageous.

Instead of the implementation according to Figure 2, the invention can be implemented by utilizing the spectral information of the signal coming from the sensor. After the conversion means T and the amplifier A, the signal is converted to digital and converted, for example, using the FFT algorithm or the so-called autore-25 aggressive algorithms (autoregressive algorithms and other analysis methods • suitable for small sample samples): Kay et al. ai: Proceedings of IEEE, vol. 69, no. 11, 1981). This can be conveniently done in said PC 30 hardware, but dedicated signal processing circuits are also available. The resulting spectrum • includes a peak corresponding to a strong heart rate (i.e. HR) and multiples thereof. A simple program searches the appropriate HR range for a maximum, which is then the current HR-35. A suitable range of the spectrum is 0.5 to 4 Hz, which corresponds to beat rates of 30 to 240 beats / minute. This method is fast and is not easily disturbed by a person’s movements.

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The periodicity of the signal can also be examined using a correlation function. Such solutions have been used in the analysis of periodic signals and described e.g. in the following reference, Oppenheim and Schafer, paragraph: 11 5 "Fourier analysis of signals using the discrete Fourier Transform", including paragraph 11.7, "Spectrum analysis of random signals using estimates of the autocorrelation sequence".

Spectrum computing and signal processing issues 10 have been addressed in numerous publications, of which only Proakis J.G. and Manolakis D.G .: Introduction to Digital Signal Processing, Macmillan Publishing Company, New York, 1988, and Oppenheim A.V. and Schafer R.W .: Discrete-Time Signal Processing, Prentice-Hall International is Inc., Englewood Cliffs, New Jersey, 1989.

Many known solutions can be applied to the apparatus, the main principles of which are described, for example, in Tompkins W.J. and Webster J.G .: Design of microcomputer-based medical instrumentation, Prentice-Hall Inc, Englewood 20 Cliffs, New Jersey, 1981.

Figure 4 shows a block diagram for a device in which a signal STR from a sensor, amplified in a possible preamplifier, is fed to a filter F, then to an A / D-25 converter ADC and then to a processor DSP, the results of which are fed to a display DD. Filter F is a bandpass filter which, when analyzing the function of the heart, removes frequencies in which there is no significant information or in which there are, for example, interfering signals due to the oscillation of a person. In the experiments performed, the preferred frequency range has been found to be 6 to 15 Hz if it is desired to register HR. It is preferred that the filter removes low frequency (<0.5 Hz) components as efficiently as possible. The filter F may be implemented in analog or at least a portion of the filtering 35 may be performed digitally by the processor DSP.

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Many known principles can be applied in sensor solutions. Since the measurand is the person's weight G, which is mainly the force generated by the acceleration of the person's mass and the gravitational pull of the earth, changes in weight due to cardiac function can be recorded in several ways. Piezoelectric and piezoresistive sensor elements have mainly been described above. It is known to measure changes in force by means of sensing elements so that changes in the shape of the sensing elements (number of changes, rate of change) are measured by capacitive, inductive, optical and acoustic methods. These principles have been described e.g. in: Allocca J.A. and Stuart A .: Transducers: Theory and Application, Reston Publishing Company Inc., Reston, 1984 and Cobbold RSC: Transducers for 15 Biomedical Measurements, John Wiley & Sons, New York, 1974. By combining known sensor principles, the devices of the invention can be implemented in a variety of ways. way. The choice of sensor principles is influenced by e.g. manufacturing costs, accuracy requirements, and power consumption. In simple 20-so-called bathroom devices, it is quite probable that the most advantageous sensors are piezoresistive or piezoelectric. In the registration of changes in weight G, the Piet electroelectric sensor gives a strong signal, which on the other hand depends on e.g. ambient temperature. However, a solution may be advantageous if only HR is to be registered.

The results and the calculated indices or a summary of the results and the calculated indices can be printed on paper numerically as well as graphically in the form of curves and thus give 30 people an illustrative picture of his development. The device may also be provided with a signal, light or sound to indicate the detection of a heartbeat. This can be connected, as previously mentioned, to a pulse converter. The device may include or be connected to a necessary printing medium, for example a dot matrix or laser printer. Suitable printers are manufactured, for example, by Canon Inc, Japan.

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For example, to monitor the condition, e.g. indices R: R * c / (HR * G), or R * 1 / (HR * G) s calculated in the following ways, where c is a number proportional to the person's SV or CO derived from the measurement results. It is preferred to use the averages taken over several heartbeats as SV and CO, as well as HR. As a result of exercise, HR measured at rest in the heart decreases and SV rises relatively rapidly, but weight changes usually occur slowly. As the person's condition rises and the R calculated in the above-mentioned manner rises rapidly and shows the direction of development more sensitively than mere weight. R can thus be used to support weight loss diets and exercise programs. An index showing rapidly improving fitness significantly improves training and diet motivation.

Only one simple way of calculating an index R indicating the development of a condition from the measured quantities has been described above. For example, a target weight of 20 can be included in the formula of the index R, whereby the development and approach of the index R towards the target are clearly visible. Likewise, different weights can be given different weights depending on the goal of the exercise or weight loss program.

Depending on the versatility of the signal processing, the calculated indices R may be personal comparison figures, in which case the indices of different persons cannot be directly compared. If the signal processing is sufficiently versatile and the positioning of the person is done carefully, indices and measurement results can be derived that can be used for mutual comparison of different persons. The positioning can be aided, for example, by a chair-like measuring platform, the back of which can be tilted and thus the maximum weight change due to the action of the heart can be sought. This is because the direction of the aortic arc of 10,94589 different individuals is different.

The invention can be applied e.g. household (bathroom) scales. At its simplest, such a scale would show a person’s weight G and HR. For such a scale, 5 customer-specific integrated circuits can be developed. The displays do not have to be separate, but HR and weight can automatically alternate in the display or the display can be selected e.g. by a separate switch, remote control, etc. One such device is illustrated in Figure 5. In Figure 5a, the device is seen from above. Frame F has a measuring platform S. The sensor solution affects the implementation of the structure. The display DD has pointers for the displays HR and W, as shown. These can be, for example, light emitting diodes (LEDs). If, for example, the HR LED is lit, the display shows the heart rate HR. In Figure 15 5b the device is seen from the side. The mechanical implementation can be similar to the aforementioned Hanson scale. The advantages of such an alternative display are its low cost and space saving. The numbers on the display must be large enough to be easily read. The display can also be at the end of 20 arms or the information can be transmitted to a separate display unit wirelessly, e.g. using infrared or lower frequency electromagnetic waves (inductive or radio connection). Such a remote display may be advantageous because the person does not have to bend over while reading the display. Bending-25 changes the position of the chest and reduces any measurable SV and CO values.

The more advanced devices of the invention calculate a person's fitness indices and can display relative magnitudes of CO and SV. Such devices can be used by fitness enthusiasts, athletes and can be used in homes, spas, gyms, etc. Devices intended for public use can be equipped with a coin-operated device or, for example, a card reader to control use.

In more demanding use, more attention must be paid to the positioning of the subject 35 and a good solution is a chair-like measuring platform with more than one sensor (for example 3 or 4). The stand may have a reclining backrest and supports that repeatedly bring the person into the same position. The backrest and other supports 5 must have scales, etc., the readings of which are recorded or stored in the device's memory for future measurements. These supports can be motorized and the motors can be controlled by the computer of the device, for example on the basis of a personal identity number, to the measuring positions. io Naturally, the method according to the invention and similar devices can be used in all kinds of psychophysical tests, monitoring the treatment of diseases, etc.

Monitoring of cardiac SV and CO has been found to be advantageous e.g. monitoring the effect of atrial fibrillation treatment and bypass surgery. Similarly, changes in SV and CO may be thought to evaluate the treatment of heart failure. With the method according to the invention and the devices based on it, this is done effortlessly and advantageously.

Only some embodiments of the invention have been described above. It is possible to carry out many modifications of the invention within the scope of the inventive idea defined by the following claims.

Claims (31)

1. A method for measuring quantities associated with a person's condition and cardiac functions, such as, for example, weight (G), heart rate (HR), heart rate (SV) and 5 minute volume (CO) characterized by a person being placed on a measurement basis (S) such that the blood flow pulse caused by the heart beat corresponds to a change in the person's weight (G), which change is recorded and the recorded weight changes are derived from information about the person's cardiac functions, such as for example stroke and minute volume (SV, CO) and heart rate (HR). 2. A method according to claim 1, characterized in that a person relies on the measurement base (S). 3. A method according to claim 1, characterized in that a person sits on the measuring support (S). 4. A method according to any of the preceding claims, characterized in that the frequency spectrum of the weight changes is calculated (weight G). 5. A method according to any one of the preceding claims 20, characterized in that the correlation function of the weight changes is calculated (weight G). 6. A method according to any of the preceding claims characterized in that quantities are used proportional to the time integral of the weight changes (weight G) for calculating quantities proportional to heart rate (HR) and stroke (SV) and minute volume (CO). 7. A method according to any of the preceding claims, characterized in that a person's weight (G) is recorded. A method according to any of the preceding claims ice. 94589, characterized in that an index (R) describing a person's physical fitness is calculated by using measurement results. 9. A method according to claim 8, characterized in that the index (H), which describes a person's condition, contains a dependence on the person's weight (G). 10. A method according to claim 8 or 9, characterized in that the index (R) describing a person's condition contains a dependence on the person's heart rate (HR). 11. A method according to claims 8-10, characterized in that the index (R), which describes a person's condition, contains a dependence on the person's heartbeat volume. 12. An apparatus for measuring quantities associated with a person's fitness and cardiac functions, such as, for example, weight (G), heart rate (HR), heart rate (SV) and minute volume (CO), characterized in that it contains a measurement basis (S) on which a person is placed such that the blood flow pulse caused by the heart rate corresponds to a change in the person's weight (G), means for recording (T, L) of this weight change and means for deducing quantities, which are related to the person's cardiac functions, by utilizing the recorded weight change. 13. An apparatus according to claim 12, characterized in that it contains a measurement base (S) on which a person stands. 14. An apparatus according to claim 12, characterized in that it contains a measurement base (S) on which a person sits. An apparatus according to any of claims 12 - 14 19 - 94589 characterized in that the transformers (T) contain sensor means such as, for example, a so-called elongation strip, whose electrical impedance is affected by the weight (G) of the person and its changes. 16. An apparatus according to any one of claims 12 to 15, characterized in that the transformers (T) contain sensor means such as, for example, a so-called piezoelectric crystal or a piezoelectric plastic membrane, which generates an electromotive force whose size depends on the person's weight (G ). An apparatus according to any one of claims 12 to 16, characterized in that it comprises amplifier means (A) and filter means (F, FBP) for deriving a signal proportional to weight changes (weight G) in connection with the person's cardiac functions, of the output of the transformer (T). 18. An apparatus according to any one of claims 12 to 17, characterized in that it comprises means 20 (I, DSP) for calculating quantities proportional to the time integral of the weight changes (weight G). 19. An apparatus according to any of claims 12-18 characterized in that it contains means (DSP) for calculating the frequency spectrum 25 of the weight changes (weight G). An apparatus according to any of claims 12 to 19, characterized in that it contains means (DSP) for calculating the correlation function of the weight changes (weight G). An apparatus according to any of claims 12-20, characterized in that it contains means (DSP) for calculating an index (H), which describes a person's condition. 20 9 4 5 8 9 An apparatus according to any one of claims 12 to 21, characterized in that it contains means for storing measured values and calculated indexes (R), which describe a person's condition. 23. An apparatus according to any one of claims 12 to 22, characterized in that it contains means for printing in numerical or graphical form, for example on paper of measurement values and calculated index (R), which describes a person's condition. io An apparatus according to any one of claims 12-23 characterized in that the transformation means (T) contain several sensor means. 25. An apparatus according to claim 24, characterized in that a portion of the transducer means (G) of the transducing means 15 in particular records the weight (G) and a part of the transducer means in particular detects changes in the weight (G). 26. An apparatus according to any one of claims 12 to 25, characterized in that the sensor means, which separately record changes in weight (G), are so-called piezoelectric sensors, such as, for example, a piezoelectric crystal or a piezoelectric plastic membrane. . An apparatus according to any one of claims 12 to 26 characterized in that it contains display means (D1, D2, D3, DD) such as, for example, electroluminescence, light-emitting diode, liquid crystal or cathode ray display. 28. An apparatus according to claim 27 useful as a so-called bathroom path characterized by containing display means (D1, D2, DD) for displaying a person's weight (G) and heart rate (HR). 21. 94589 29. An apparatus according to any one of claims 12 to 28, characterized in that it contains means for controlling the use of the apparatus, such as, for example, a coin or card reader. 30. An apparatus according to any one of claims 12 to 29, characterized in that it contains means for indicating the registration of the changes in weight, such as, for example, an apparatus for light or sound signaling. 31. An apparatus according to any one of claims 12 to 30 characterized in that it contains means for improving the repeated identical placement of a person, such as, for example, back and arm rests.