Blood pressure measurement apparatus

Claims

We claim:

1. Blood pressure measurement apparatus using an inflatable cuff which constricts an appendage of a subject whose blood pressure is to be measured, said apparatus comprising means for changing the pressure in the cuff, means for sensing the auscultatory sounds from the appendage while the pressure in the cuff is changing, means for producing a signal having an amplitude which corresponds with the pressure in the cuff, valve means for modulating the pressure in the cuff as the pressure changes during the sensing of said auscultatory sounds, and means for controlling said valve means to linearize the change in pressure in said cuff which comprises means for generating a reference, linear ramp signal, which starts prior to the sensing of said auscultatory sounds, means for comparing said reference signal with said pressure signal to produce a first output corresponding to the difference in amplitude therebetween, means for generating a train of repetitive triangular waves each having a period much less than the duration of said ramp signal, means for comparing such repetitive triangular waves with said first output to produce a train of pulses, the durations of the pulses varying in accordance with the magnitude and sense of deviation of said pressure signal from said linear ramp signal, and means for applying said variable duration pulses to said valve means for opening and closing said valve means in accordance with the duration of the pulses in said pulse train such that the pressure in said cuff changes linearly in amplitude, correspondingly with said ramp signal.

2. The invention as set forth in claim 1 further comprising blood pressure measurement cycle control means for initiating and controlling cycles during each of which said auscultatory sounds are sensed, means in said cycle control means for operating said ramp generating means to start said ramp signal, said means for changing the pressure in said cuff including a pump, and means in said cycle control means for operating said pump.

3. The invention as set forth in claim 2 further comprising means responsive to said pressure signal for detecting when said cuff pressure has reached a first predetermined high pressure for operating said pump operating means and said cycle control means to stop said pump from increasing the pressure in said cuff.

4. The invention as set forth in claim 3 further comprising means in said cycle control means responsive to the initiation thereby of a measurement cycle for operating said pump operating means to stop said pump from increasing the pressure in said cuff a predetermined period of time after the initiation of each of said cycles.

5. The invention as set forth in claim 2 further comprising means included in said cycle control means for inhibiting the application of said pulses which vary in duration to said valve means except when said ramp signal is being generated.

6. The invention as set forth in claim 2 further comprising a second valve adapted to be in communication with said cuff, and means in said cycle control means for opening said second valve to release any pressure in said cuff except when any of said pump operating means is operating to increase the pressure in said cuff and said ramp signal generating means is operative to generate said ramp signal.

7. The invention as set forth in claim 1 further comprising means for detecting the pressure in said cuff and providing at least a first signal when said pressure is a certain relatively high pressure and a second signal when said pressure is a certain relatively low pressure, recorder means responsive to said sensing means for recording signals corresponding to said auscultatory sounds, and means for recording said first and second signals with said auscultatory sound signals to provide a scale of pressure which corresponds in linearity to said ramp signal for indicating the pressures corresponding to said auscultatory sounds.

8. The invention as set forth in claim 7 further comprising blood pressure measurement cycle control means for initiating cycles during each of which said auscultatory sounds are sensed, said means for changing the pressure in said cuff being a pump, means in said cycle control means for starting said pump and said recorder means, means in said pressure detecting means for providing an output when said cuff pressure reaches a certain pressure which is sufficiently above the higher systolic pressure of said subject to enable an auscultatory sound corresponding to said systolic pressure to be sensed, means in said cycle control means responsive to said above-systolic pressure output from said pressure detecting means for stopping said pump without stopping said recorder means and initiating said ramp signal whereby said modulating valve means is operated by said modulating valve control means to provide a linearly decreasing pressure in said cuff while said auscultatory sounds are recorded.

9. The invention as set forth in claim 8 further comprising means manually operable by the subject for providing first output commands to initiate a measurement cycle, means for providing successive second output commands automatically at selected intervals of time, said second output commands also to initiate automatic measurement cycles, means in said measurement cycle control means responsive to said first and second output commands for starting said pump and said recording means and controlling a measurement cycle.

10. The invention as set forth in claim 9 further comprising means responsive to each of said first output commands for generating a signal indicative of said manual measurement cycle and applying said manual measurement cycle signal to said recording means for recording said signal to distinguish recordings of manual and automatic measurement cycles.

11. The invention as set forth in claim 9 further comprising means included in said measurement cycle control means for inhibiting the initiation of a manual measurement cycle in response to said first output commands if they occur with greater than a certain frequency.

12. The invention as set forth in claim 11 wherein said means in said measurement cycle control means for inhibiting the initiation of said manual measurement cycle comprises means operated by said automatic second output commands for inhibiting said manual first output commands from initiating a measurement cycle unless one of said automatic second output commands has preceded said one of said first output commands and initiated an automatic cycle immediately before the initiation of a manual cycle.

13. The invention as set forth in claim 12 wherein said measurement cycle control means further comprises means for inhibiting the initiation of a measurement cycle in response to said first output commands when a prior measurement cycle is in progress.

14. The invention as set forth in claim 1 wherein said ramp generating means comprises a capacitor, means for charging said capacitor to a voltage corresponding in amplitude to a pressure in said cuff above the systolic pressure of said subject, a current source circuit connected to said capacitor, means operative for switching current from said capacitor to said current source to generate the linear reference ramp signal, wherein said means for comparing said ramp signal with said pressure signal comprises a first difference amplifier which produces a first output, and wherein said means for comparing said triangular waves with said first output comprises a second difference amplifier which produces said variable duration pulses for opening and closing said modulator valve means to produce linearly decreasing pressure in said cuff while said auscultatory sounds are sensed.

15. The invention as set forth in claim 14 wherein said triangular wave generating means is a sawtooth signal oscillator.

16. Longterm, portable blood pressure monitoring apparatus, for use with an inflatable cuff which is applied to the appendage of the subject whose blood pressure is to be measured, said apparatus comprising means including a pump for inflating said cuff, transducer means for sensing the pressure in said cuff, means for detecting auscultatory sounds from the appendage to which said cuff is applied, means for recording said sounds, means for producing successive first commands at predetermined periods of time for initiating automatically blood pressure measurement cycles at predetermined intervals, means operable manually by the subject for producing upon each operation a second command for initiating manually a blood pressure measurement cycle, means for controlling said blood pressure measurement cycle by operating said pump until the pressure in said cuff reaches a predetermined pressure above the systolic pressure of the subject, said pump being started at the beginning of said cycle and said cuff being deflated below the diastolic pressure of the subject at the end of said cycle, and for operating said recording means during said cycle, means in said cycle control means for producing a measurement cycle upon occurrence of each of said first commands, and means in said cycle control means for producing a measurement cycle upon occurrence of said second command which do not recur with more than a certain frequency.

17. The invention as set forth in claim 16 wherein said means for producing a measurement cycle in response to said second command include means responsive to said first commands for inhibiting said second command from producing a measurement cycle unless a first command occurs between successive second commands.

18. The invention as set forth in claim 17 wherein valve means are provided for controlling the pressure in said pump and said measurement cycle control means comprises three flip flops, a first of said flip flops being coupled to said pump, a second of said flip flops being coupled to control said valve means, and a third of said flip flops being included in said means for inhibiting the production of said manual cycle upon occurrence of said second command, said means for inhibiting said production of manual measurement cycles including a gate circuit, means responsive to said first commands for conditioning said first and third flip flops into one of their two alternate states which causes the operation of said pump and enables said gate circuit, means responsive to the pressure in said cuff reaching said predetermined pressure for conditioning said first flip flop into the other of its alternate states to stop said pump, means coupling said first flip flop to said second flip flop to condition said second flip flop into the one of its alternate states which causes operation of said valve means, means for conditioning said second flip flop into the other of its alternate states when the pressure in said cuff reaches said pressure below diastolic pressure of the subject, and means connecting said first and second flip flops to said gate circuit for inhibiting said gate circuit when said first flip flop or said second flip flop is in said one of said alternate states thereof, and said gate circuit being connected to said first flip flop for conditioning said first flip flop into said one state thereof upon occurrence of said second command when said gate circuit is enabled.

19. The invention as set forth in claim 18 further comprising gated latch means for conditioning said first and third flip flops into said one of said alternate states thereof upon occurrence of said first command.

20. The invention as set forth in claim 17 further comprising means for generating a manual control signal and means controlled by said manual control signal generating means in said cycle control means for producing a measurement cycle for applying a marker signal to said recording means only upon occurrence of said manual control signal to distinguish automatically and manually initiated blood pressure measurement cycles from each other on the recording produced by said recording means.

21. The invention as set forth in claim 16 wherein said means for producing a measurement cycle in response to said second command includes means operative when a measurement cycle is in progress for preventing said second command from producing a measurement cycle.

DESCRIPTION

The present invention relates to blood pressure measurement apparatus and particularly to apparatus for making a number of successive blood pressure measurements over a long period of time automatically or when such measurements are called for by the subject or patient whose blood pressure is being measured.

The invention is especially suitable for use in providing long-term ambulatory blood pressure measurement in apparatus which is portable and can be worn by the subject for many hours, say 12 or 24 hours, during the patient's normal activities and recording the auscultatory (Korotkoff) sounds obtained from a sensor which is coupled to an appendage, such as the arm, of the subject which is constricted by an inflatable cuff on the subject's arm.

The need for long-term measurement of blood pressure levels has been recognized, and portable apparatus has been proposed for the purpose of long-term ambulatory blood pressure measurement (see Schneider, Kimmell, and Meter, Journal of Applied Physiology, 37, 5, 776 (1974) and U.S. Pat. No. 4,216,779 issued Aug. 12, 1980 and U.S. Pat. No. 3,712,297.) The need still exists for long-term blood pressure measuring apparatus which provides accurate blood pressure data from the auscultatory sounds accompanying the constriction of the patient's arm. The problem of providing accurate data is complicated by the need to maintain portability and long-term operation of the apparatus, for example about 80 measurements without attention to the apparatus. Another need is to provide for measurements automatically at certain intervals, for example every 30 minutes, as well as when the patient is concerned with his or her condition, for example under stressful situations. The blood pressure measurement involves the constriction of the arm and the artery. Too many cuff inflations can be harmful. Each inflation draws power from the portable power source, for example a battery, and can prevent long-term operation. The measurement data from closely successive manually activated measurements is not advantageous in that it may not provide additional significant medical information, and much inconvenience and potential harm may result to the subject.

Accordingly, it is an object of the present invention to provide improved blood pressure measurement apparatus.

It is another object of the invention to provide improved apparatus for a long-term measurement of blood pressure which makes a large number of blood pressure measurements over a long period of time, such as over a 12 or 24 hour period.

It is a further object of the present invention to provide improved apparatus for monitoring the blood pressure of the subject over a long period of time and which may be portable and worn by the subject and used to record the blood pressure measurements which are made during measurement cycles which recur automatically or when activated by the patient while the patient engages his or her normal daily activity.

It is a still further object of the present invention to provide improved long-term blood pressure measurement apparatus which senses and may record and indicate data which accurately reflect the blood pressure of the subject during each of many measurements which may occur over the long term.

It is a still further object of the present invention to provide improved long-term blood pressure measurement apparatus which may be activated automatically at predetermined intervals of time or manually by the subject, but with a frequency which reduces the possibility of harm to the subject and conserves power so as to adapt the apparatus for portable operation.

Briefly described, blood pressure measuring apparatus embodying the invention uses an inflatable cuff which constricts an appendage of a subject whose blood pressure is to be measured. Means such as the pump is provided for changing the pressure in the cuff, for example inflating the cuff and then stopping so as to permit a valve associated with the cuff to deflate the cuff. Means, such as a microphone held by the cuff on the appendage, senses the auscultatory sounds from the appendage while the pressure in the cuff is changing. It is preferable to utilize the change in pressure upon deflation of the cuff in order to reduce the effect of noise produced by the pump while inflating the cuff. A recorder may be used to record the auscultatory sounds. The pressure in the cuff is also monitored and a signal having an amplitude which corresponds to the cuff pressure is generated. Means for controlling the valve are operative to linearize the change in pressure in the cuff while the auscultatory sounds are being produced and recorded. A reference linear ramp signal generator, a source of triangular waves which repeat at a high rate (such that many occur during the period of the ramp signal), and circuits for comparing the ramp signal with the signal representing the pressure in the cuff to produce an output which is compared with the triangular wave result in pulses having a width which varies with the deviation from the linear ramp of the pressure signal from the cuff. These pulses are applied to the valve so as to control the cuff pressure and provide a linear pressure change. The auscultatory sounds therefore occur along a linear time base and indicate accurately the subject's blood pressure.

The apparatus also includes means for controlling each blood pressure measurement cycle in response to commands for the initiation of each cycle. A command may be produced automatically at predetermined intervals, so as to initiate automatic measurement cycles, or by the subject, manually. The measurement cycle control means has means for controlling the frequency of the manually activated cycle. When a manual cycle is initiated, information as to the occurrence of the manual cycle is stored and used to inhibit subsequent manual cycles unless there is an automatic cycle between successive manual cycles. Also the measurement cycle control means is operative to prevent a measurement cycle from being manually activated while a blood pressure measurement cycle is in progress.

The foregoing and other objects, features and advantages of the invention as well as the presently preferred embodiment thereof will become more apparent from a reading of the following description in connection with the accompanying drawing in which:

FIG. 1 is a block diagram of blood pressure measurement apparatus in accordance with the invention which is adopted for the long-term recording of blood pressure data by being worn or carried by the subject whose blood pressure is being measured;

FIG. 2 is a diagram showing the measurement cycle control circuits of the apparatus illustrated in FIG. 1 in greater detail; and

FIG. 3 is a diagram showing the pressure ramp linearization and modulator valve control circuits of the apparatus shown in FIG. 1 in greater detail.

Referring first to FIG. 1 there is shown a cuff 10 having a bladder to which connections are made by two tubes 12 and 14. The cuff is adapted to be wrapped around an appendage, such as the arm, of the subject, such as the patient, whose blood pressure is to be measured at intervals over a long period of time of several hours, say from 6 to 24 hours. The cuff is designed from thin walled material which will not withstand sustained pressure which might harm the patient due to arm constriction (e.g. 300 mm Hg.). There is a safety feature of the apparatus in that the tubes 12 & 14 are desirably connected to the apparatus via a quick disconnect coupling which immediately drops the cuff pressure, thereby avoiding potential harm in case of excessive pressures & cuff constriction. The blood pressure measurements are made by sensing the auscultatory or Korotkoff sounds issued by the artery of the patient as it is constricted by the cuff or while the constriction is released. A sensor which may be a crystal microphone 16 is held to the arm by the cuff and detects the auscultatory sounds. Also detected are the vibrations coupled to the arm as the cuff is inflated. The inflation vibrations may be used as a marker to indicate the beginning of a blood pressure masurement cycle. A pressure transducer 20, which may be a body of PZT or a strain gauge element coupled to a diaphragm is connected via the tube 14 to the cuff to sense the cuff pressure. The transducer 20 is indicated in the drawing as P.sub.TR and is located in the lower part of a small manifold 22 which distributes the pressure over the diaphragm of the transducer 20. A signal having an amplitude corresponding to the pressure in the cuff 10 is produced by the transducer 20 and applied to cuff pressure detecting circuits 24.

The tube 12, which may be a flexible, somewhat elongated tube, for adding compliance to damp or isolate vibrations generated during inflation and deflation of the cuff, is connected to a manifold 26. A pump 28, which may be a diaphragm pump driven by a brushless, low noise motor 30 and vented on the return side thereof by a tube 32 to the atmosphere, is connected to the manifold 36. Also connected to the manifold are two solenoid operated valves 34 and 36. The valve 34 indicated as V.sub.M, is a modulating valve. The opening and closing of this valve 34 modulates the pressure in the cuff in the course of the deflate portion of the cycle, during the sensing of the auscultatory sounds and the recording thereof by a recorder 38, which may be a miniature magnetic tape cassette recorder. The other valve 36 is indicated in the drawing as a V.sub.D, and is operated as a dump valve to open the manifold to the atmosphere and dump or maintain the pressure in the cuff 10 at atmospheric pressure between measurement cycles.

It is preferred to use the modulating valve 34 to control and linearize the change in pressure of the cuff to a linearly decreasing pressure during the deflation portion of the cycle, while the constriction is released and when the auscultatory sounds are detected and recorded. It will be appreciated that the inflation cycle may also be used, in which case the ramp is linearized by modulating the cuff pressure as the pump inflates the cuff. Inasmuch as vibrations are generated during "pump-up" or inflation of the cuff which may mask the auscultatory sounds or be considered as artifacts (erroneous auscultatory sounds), the deflation portion of the cycle is used in accordance with this preferred embodiment of the invention. The pressure transducer 20 may also be used