WO1995000070A1

WO1995000070A1 - A device for measuring quantities related to blood circulation

Info

Publication number: WO1995000070A1
Application number: PCT/FI1994/000277
Authority: WO
Inventors: Raimo Erik Sepponen
Original assignee: Increa Oy
Priority date: 1993-06-22
Filing date: 1994-06-21
Publication date: 1995-01-05
Also published as: FI932881A; FI932881A0

Abstract

The invention concerns an apparatus for registration of the human blood pressure and other quantities belonging to the blood circulation system. The apparatus contains a bracelet (WB) having first cuff means (MA) to load the wrist artery and means (PA) for registration of pressure variations (MPP) and pressure (MP) in the first cuff means (MA). The apparatus contains also second cuff means (MB) to load the wrist in an area beside the first cuff means. The apparatus may also contain a wrist unit (WU) with electrode means (RE, BPE) to registrate an EKG-signal, means (CPU) for analysing the registrated signals and a display (DD) for indicating the results.

Description

A DEVICE FOR MEASURING QUANTITIES RELATED TO BLOOD CIRCULATION

This invention relates to a device for measurement of blood pressure and other quantities related to the vascular system of a human body.

One significant risk factor for cardiovascular diseases is a high blood pressure. On the other hand a blood pressure which is lower than normal may lead a weakness of the blood circulation in the brain and a degeneration of brain tissue. Blood pressure may be highly variable due to e.g. a physical or mental stress. Because of this a person may feel dizziness and other symptoms. Changes in the blood pressure are very individual. The blood pressure may be elevated or lowered through medication but these drugs have significant side effects. The medication may be adjusted to a proper level through a continuous or frequent measurement of the blood pressure and in this way a under or over medication may be avoided.

The methods for blood pressure measurements may be roughly divided in direct and indirect measurement methods. These have been described among others in the reference John G.

Webster (ed), Medical Instrumentation - Application and design, Houghton Mifflin Company, Boston 1978 and in the later editions of this book. In the direct methods one measures the pressure inside a vessel either by with a fluid filled catheter or with a transducer in the tip of a catheter. An use of the direct methods involves the obvious risks - a rupture of a blood vessel and an infection - this limits the use only in hospitals and in some special scientific research settings.

The most commonly used indirect method is the auscultatory method which is based on the so called Korotkoff sounds. Another widely exploited method is the so called oscillatory method, which is based on the oscillations in the cuff. Other methods are among others the methods which are based on the changes in the electrical impedance under the cuff. One method which is based on the changes in the impedance is described in the reference Sepponen R. E.: FI application 780615 and in the corresponding patent publication. Further in respect to the background information about blood pressure measurements the publications Sepponen R.E.: Epasuoran verenpaineen mittausmenetelman kehittaminen (A development of a method for indirect measurements of blood pressure), Master of Science thesis, Technical University of Helsinki, 1974 and Sepponen R.E.: Eras diagnostiseen kayttόon soveltuva verenpaineen mittausmenetelma (One method of indirect measurements of blood pressure suitable for diagnostic use). Thesis for the degree of Licenciate of technology, Technical University of Helsinki, 1979. Devices which are based on indirect methods are manufactured by several companies: among others Nihon Kohden (Japan), Omron (Japan), Minolta (Japan), Hewlett Packard (USA) and Datex/Instrumentarium Inc. (Finland). Casio manufactures a device which is similar than a wrist watch and which measures the values of the heart rate (HR) and the blood pressure (BP): This device is based on a measurement of the period (Pulse Transit Time, PTT) between the optically detected blood pulse at the tip of a finger and the QRS- complex of an EKG-signal detected with an electrode which is in a contact with another finger and an electrode in the back of the watch. It has been demonstrated that the changes in PTT correlates well with the changes in the systolic values of BP of a person, BPS, but not so well with the changes in the diastolic values, BPD of BP. This method has been discussed in the reference Obrist P.A. et al: Pulse transit time: Relationship to blood pressure and myocardial performance. Psychophysiology; vol. 16, pp. 292- 301, 1979. In the reference Sepponen R.E.: FI application 932728 the method based on the measurement of PTT has been further developed. One possible application for BP measurements described in the reference is the utilization of ballistocardiographical BCG detection and detection of peripheral pulse in e.g. the leg. In this way one improves the accuracy of the method based on the measurements of PTT. This is because the registration avoids the errors generated by the alternations in the electro-mechanical function of the heart.

Devices which measure the heart rate based on measurements of EKG signals and which include a wrist unit are manufactured by Polar Electro Oy, Finland.

By using the known methods and devices it is very difficult to arrange the measurement of BP in such a way that a person could as he will to check his or her BP. By using the known methods it is not possible to identify the most common arrhythmia's of the heart, because all the equipment's needed are large, difficult to use and expensive. Additionally the alternations in the blood pressure and arrhythmia's with adjunct symptoms (among others dizziness) show up sporadically e.g. after a meal, during an exercise, with some fever diseases etc.. With the help of the conclusions based on the results derived from the registrations of these situations one may observe the changes in the health status of a person, control the medication, avoid the functional disorders of the heart generated by stress conditions etc..

With the devices of the invention one may avoid the drawbacks of prior art and perform registrations and measurements of quantities essential for the cardiovascular function of a person without difficulties. From the results one may derive indices which may be used in follow up of the physical condition of a person. Among others additional features of the invention are simplicity of the use, low cost, and reliability of the devices. To the foregoing ends the devices of the invention are characterized by what is set forth in the characterizing sections of the annexed claims .

The invention will now be described in more detail with reference made to the accompanying drawings, in which:

- Fig. 1 shows one device of the invention attached to a wrist and an axial cut of a wrist

- Fig. 2 shows the behavior of the pressure inside the cuff for pressure measurements during the measurement procedure and the blood pressure values estimated from the oscillations in the pressure of the cuff using criteria's of the oscillometric method

- Fig. 3 shows one device of the invention attached to a wrist and an axial cut of a wrist

- Fig. 4 shows the mutual relationship of oscillations of the pressure inside the cuff and the EKG signal in the case of a regular rhythm and in the case of an extra systole

- Fig. 5 shows a front view of a wrist unit of a device of the invention

- Fig. 6 shows a back view of a wrist unit of a device of the invention

- Fig 7 shows third device of the invention attached to a wrist and an axial cut of a wrist

- Fig. 8 shows one device of the invention where the wrist unit is connected with an analyzing unit by using e.g. a serial link

- Fig. 9 shows one possible block diagram of a wrist unit of a device of the invention

- Fig. 10 shows a block diagram of an another device of the invention. Explanations for the symbols in the figures: AB: Buzzer, AU: Analyzing unit, BBA: Breast belt, BBT: Time period between successive heart beats, BE: Breast electrodes, BEA: Amplifier for signals from breast electrodes, , BPD: Diastolic blood pressure, BPE: Back plate electrode, BPF: Band pass filter, BPM: Means blood pressure, BPS: Systolic blood pressure, DD: Display, CB: Control buttons, CPU: Central processor, EA: EKG preamplifier, EAD: EKG analog to digital converter, EKG: Electrocardiogram, ES: Extrasystole, H: Hinges, IA: Amplifier for inductive or radio signals, IAD: Analog to digital converter for inductive or radio signals, M: Modulator, MA: Cuff for pressure measurements, MAP: Pressure bellows, MB: Compression cuff, MP: Pressure inside cuff, MPP: Pressure oscillations in cuff, OSC: Oscillator, PA: Amplifier for pressure signal, PAD: Analog to digital converter for pressure signal, PAP: Compression plate, PTT: Pulse transit time, PT: Pressure transducer, QRS: QRS complex, RA: Artery radialis, RADIUS: Radius, RA: : Memory, RE: Electrode for EKG registration, RIA: Means for reception of inductive or radio signals, SCL: Communication bus, SOT: Serial communication connector, TIA: Means for transmission of inductive or radio signals, TIME: Time, TMA: End stage of transmitter, TS: Wrist tendons, ULNA: Ulnar bone, VS: Valve, WB: Wrist band, WU: Wrist unit.

Figure 1 shows a device of the invention attached to a wrist. The external main components of the device are the wrist unit WU which includes a major part of the electronics of the device and which is fixed on the wrist with the wrist band WB. In the figure there are also visible schematically the radius bone RADIUS and ulnar bone ULNAR of the bone structure of the wrist. The radial artery is RA, which is parallel to the tendons TS in the wrist. On WU there is a compression plate PAP which is fixed with hinges H, on PAP there are cuff means with two sections, the sections are a compression cuff MB and pressure measurement cuff MA. The use of the device includes following steps: The user lifts PAP away from the wrist in the position shown in the Figure. During this MA and MB will be filled with air via unidirectional valve of PAP. The user press PAP with his/her another hand towards the wrist. During this MB compresses at first TS against RADIUS and after that MA compresses RA against RADIUS.

With this arrangement one important benefit may be gained: RA cannot move under TS along RADIUS. This new construction of the device improves considerably the reliability of the measurements of blood pressure using arteries in the wrist. Another essential improvement gained with the construction is that one do not need battery or other energy sources for pressurization of the cuff loading RA.

The natural grip of the user during the use of the device is as follows: The device is fixed on the left wrist. The right hand is positioned so that the palm is set on WU and one press PAP towards wrist with the fingers.

The user press PAP so fast that MAP will be elevated fast so high that RA will be closed. After this the pressure will be lowered slowly and MAP will be lowered. After MAP has been lowered below the systolic value of BP which is BPS oscillations MPP in MAP will be detected as the pressure pulse proceeds under the cuff. The maximum amplitude of MPP indicates that MAP corresponds to the mean blood pressure BPM. The diastolic value may be detected as e.g. the amplitude of oscillations of MPP has decreased 20% from the maximum amplitude.

The lowering of the pressure inside the cuff may also be effected by using special flow resistance through which the air escapes from the cuff. The maximum pressure may be determined so that the volume of air used to fill the cuffs is controlled. This may be effected by adjusting the filling degree of the cuffs. Obviously the cuffs may be pressurized by using a pump which is powered by hand or a motor, by heating liquid or gas, carbondioxide vessel, carbondioxid generated from calsiumcarbide and water mixture etc.. Figure 7 shows an alternative where hand powered bellows MAP are connected to MA via a valve arrangement. The pressurization of MA is effected by pumping MAP with a hand. VS will decrease the pressure of MA in a controlled manner after the pumping.

Figure 9 shows one possible block diagram of a device of the invention. The pressure in MA is measured by a pressure transducer PT, whose output signal is amplified by pressure signal amplifier PA and the amplified signal will be converted in a digital form by using the A/D converter PAD. The digitized pressure signal will be analyzed by the central processor CPU. The start of the measurement procedure is effected by using the control buttons CB for signaling that to CPU. The signal from PT may also control the measurement procedure: An elevation of the pressure over a given threshold starts automatically the pressure measurement procedure in CPU.

By using an arrangement of the invention one may also detect the EKG signal generated by the electrical function of the heart. In this case the back plate BPE of WU serves as an electrode which makes a contact with the wrist (of the left hand) and on the front side there is another electrode RE which makes a contact with e.g. the palm of the hand (the right hand) pressing PAP. RE may also situate in the frame of the display DD of WU. This kind of construction is illustrated in Fig. 3. Fig. 9 shows the blocks needed for a detection of EKG, like the amplifier EA of the signals from the electrodes RE and BPE, and the signal from EA is conducted to the band pass filter BPF, which eliminates low frequency interference's generated by power lines and interference's generated by function of muscles. A proper band width for BPF is e.g. 0.3 - 30 Hz. The signal from BPF is conducted to an A/D-converter EAD, whose digital output is connected to CPU. A signal sound device AB e.g. a piezoelectric buzzer emits a sound signal for each detected changes in MPP or EKG corresponding to a contraction of the heart. AB may obviously also serve as a source of an alarm signal as WU serves as a conventional digital watch. AB may also give a signal as a sign for the time when e.g. a blood pressure measurement should be done.

The simultaneous registration of EKG and MPP makes it possible to perform among others following measurements: The time period PTT between the QRS-complex of the EKG signal and the corresponding oscillation of MPP correlates well to the systolic value of BP of a person. This may be exploited in a determination of the systolic pressure value BPS. A peak of EKG corresponding to an extrasystole has not a corresponding oscillation of MPP which may be exploited in detection of ES. The shape of ES differs from the shape of QRS so the stored EKG signal may be useful in diagnostics. EKG and MPP with the measurement results may be stored in the memory RAM of WU, from where they may be transferred e.g. via the serial communication port through the contact means SCL to an external analyzing unit AU as is shown in Fig. 8. The connection may be effected also capacitively, inductively, via radio waves or optically in each case the necessary means are included by SOT.

CPU may determine the heart rate HR of a person by measuring the period BBT between successive beats from one or more pairs of beats. For this purpose one may utilize either MPP or EKG signals or both signals.

Fig. 5 shows a front view of one device of the invention. In the display DD of WU time information and measurement results are visible. By using CB one may modify the functions of WU e.g. from a conventional watch to a watch for time measurements and to a measurement device. The known functions of a conventional digital watch may be programmed in CPU. Fig. 6 shows a back view of a device of the invention. Fig. 6 does not show the arrangements of pressure cuffs which are connected to the wrist band WB.

Fig. 10 shows an alternative way to convey the EKG signal to WU. In this alternative the EKG electrodes BE are attached to the breast belt BBA. BE are also connected to an amplifier BEA whose signal is connected via modulator M to the end stage of a transmitter TMA, to which an optional carrier frequency is fed from an oscillator OSC. TMA is connected to antenna means TIA, which may include an induction loop or a ferrite bar. The signal emitted by TIA is received by RIA, receiver antenna means of WU, and amplified by an amplifier IA, detected by a detector ID and converted to digital form with an A/D converter IAD. The receiver antenna means RIA and the receiver means adjunct to them may receive other external signals like e.g. time signals at radio frequency in order to calibrate the time information displayed by WU. The means in WU (CPU) may also be programmed to count various indices in order to check the cardiovascular condition of a person. One useful index among others is a product of HR and BPS: If a person suffers from cardiac dysfunction this product does not rise during an exercise. This index may be used among others in adjustment of the medication of cardiac dysfunction (often digitalis medication) .

Because one essential feature of the device is the portability it is obvious that a battery is utilized as a power source. A lithium battery is one good choice due to its long life and reliability. If one utilizes electrical pumping means for pressurization of the cuff means it may be beneficial to use rechargeable batteries as nickel- cadmium accumulators or nickel anhydride accumulators. A part of power may also be taken from a light cell. As examples of the use of the device may be following situations:

A person is known to suffer from a high blood pressure. For prescription of medication he measures his blood pressure and HR with the device at various times during a working day. The readings are stored in RAM from where they may be brought to the display DD with the time information. The medication for the high blood pressure may be adjusted so that the values of BP are kept within the given guide values. The guide values may also be stored in RAM in order to make the comparison easier. A long term registration of BP may be send via SOT to AU and printed as a curve on a paper. The printing may take place in a health center because AU may be a general purpose PC device (manufactured e.g. by IBM, USA or Apple Computers, USA) As a printer may be e.g. a matrix or laser printer (manufactured e.g. Canon Inc., Japan).

A person feels occasionally dizziness and numbness of hands. In order to assess the situation the person performs a blood pressure measurement and simultaneously WU detects EKG. The measurements reveal that dizziness is due to a decrease of BP and to a simultaneous increase of HR. The person may identify the situations in which the phenomenon occurs at most often and changes his habits so that avoid those situations. Alternatively it could be possible that one had detected repeated extra systoles or that the symptoms are not due to any heart related condition.

In addition to the example cases people have an increasing need to assess objectively their own health. The changes in the health of aging persons need to be detected as early as possible, so that one is able to start treatment operations as soon as possible. The number of brain infarctions may be reduced via monitoring the condition of vascular system individually and by this way save markedly the costs for the society. The invention is not limited to the above embodiments but also other embodiments are conceivable within the scope of the invention as described by the annexed claims.

Claims

1. A device for measurements of blood pressure, heart rate, and other quantities related to the vascular system of a human body including wrist unit (WU), wrist band (WB) c h a r a c t e r i z e d in that the wrist band includes the first cuff means (MA) for loading wrist artery (RA).

2. A device as set forth in claim 1 c h a r a c t e r ¬ i z e d in that pressure transducer (PA) means are connected to the first cuff means (MA) in order to measure pressure inside said cuff means (MA) and to detect oscillations of pressure (MPP) generated by artery (RA).

3. A device as set forth in any of the claims above c h a r a c t e r i z e d in that it includes second cuff means (MB) in order to load wrist on the area beside cuff means (MA).

4. A device as set forth in claim 3 c h a r a c t e r - i z e d in that said second cuff means (MB) are pressurized before said first cuff means (MA).

5. A device as set forth in any of the claims above c h a r a c t e r i z e d in that it includes compression plate (PAP) attached to wristband (WB) with hinge means (H).

6. A device as set forth in claim l c h a r a c t e r - i z e d in that said cuff means (MA, MB) are pressurized by pressing compression plate (PAP) with hand.

7. A device as set forth in any of the claims 1 - 4 c h a r a c t e r i z e d in that said cuff means are pressurized via valve means (VS) by using pumping means (MAP).

8. A device as set forth in claim 7 c h a r a c t e r - i z e d in that pumping means (MAP) are driven by hand.

9. A device as set forth in claim 7 c h a r a c t e r - i z e d in that pumping means (MAP) include a vessel, in which there is pressurized gas or two materials as calciumcarbid and water, which via mutual reaction generate gas or in which one heats gas or liquid.

10. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes means (CPU) to analyze the signal of pressure oscillations (MPP) .

11. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes display means (DD).

12. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes control means (CB) for changing operation conditions and settings of device.

13. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes sound signaling means (AB).

14 A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes memory means (RAM) .

15. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes connection means (SOT) for transferring information stored in memory means (RAM) in external device (AU).

16. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes electrode means (BPE, RE) for detection of electrical function of heart (EKG) .

17. A device as set forth in claim 16 c h a r a c t e r ¬ i z e d in that some (BPE) of the said electrode means (BPE, RE) are that part of wrist unit (WU) which is against wrist during an sue of the device.

18. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) -includes also antenna means (RIA) for detection of external signal.

19. A device as set forth in claim 16 c h a r a c t e r ¬ i z e d in that said external signal is EKG signal detected with breast electrode means (BE) attached to breast belt (BBA) and send via transmitter means (TIA).

20. A device as set forth in any of the claims 16 - 19 c h a r a c t e r i z e d in that wrist unit (WU) includes means (CPU) for measuring the time difference (PTT) between the appearance times of QRS complexes of (EKG) signal due to electrical function of heart and pressure oscillation signal (MPP) of cuff means.

21. A device as set forth in any of the claims 16 - 20 c h a r a c t e r i z e d in that wrist unit (WU) includes means (CPU) for comparison of QRS complexes of (EKG) signal due to electrical function of heart and pressure oscillation signal (MPP) of cuff means and for detection of extra systoles (ES) based on comparison.

22. A device as set forth in any of the claims 16 - 21 c h a r a c t e r i z e d in that using control means (CB) means (CPU) inclusive to wrist unit (WU) store detected events in memory means (RAM) from where they may be transferred via connection means (SOT) to external means (AU).

23. A device as set forth in any of the claims above c h a r a c t e r i z e d in that wrist unit (WU) includes means (CPU) for calculating various indices from measurement results.

24. A device as set forth in claim 23 c h a r a c t e r ¬ i z e d in that said index includes measured values of heart rate (HR) and systolic blood pressure (BPS) .

25. A device as set forth in any of the claims above c h a r a c t e r i z e d in that means included in wrist unit (WU) have at least a part of their operating energy from battery as lithium battery, nickel cadmium or nickel anhydrid accumulator.