US3905353A - Blood pressure apparatus - Google Patents

Abstract

A closed air system includes a reservoir and inflatable cuff arranged to block off blood flow in a portion of a person''s circulatory system when inflated by air from the reservoir. An outlet tube connected to a pump passes air from the reservoir to the inflatable cuff and a single valve in a return tube from the cuff to the reservoir permits pressure to be gradually decreased. A pressure transducer provides a feedback signal to the valve to control the rate of pressure drop and maintain it substantially constant all to the end that a doctor can more quickly and accurately take a patient''s blood pressure.

Description

United States Patent 11] 3,905,353 1451 Sept. 16, 1975 Lichowsky BLOOD PRESSURE APPARATUS 3,654,915 4/1972 Sanctuary l28/2.05 M M 128 2. M [75] Inventor: Abraham Lichowsky, Los Angeles, 37792 12/1973 urphy Jr et al 05 C l'f.

a 1 Primary Examiner-Kyle L. Howell [73] Assignee: Medical Monitors, Inc., Los Attorney, Agent, or FirmRalph B. Pastoriza Angeles, Calif.

[22] Filed: Feb. 28, 1974 [57] ABSTRACT 2 App] 44 754 A closed air system includes a reservoir and inflatable cuff arranged to block off blood flow in a portion of a persons circulatory system when inflated by air from [52] US. Cl.2 l28/2.05 G; 128/205 M the reservoir An Outlet tube connected to a pump [51] hit. Cl. passes air from the reservoir to the inflatable cuff and [58] Field of Search..... 128/205 A, 2.05 C, 2.05 G, a Single valve in a return tube from the cuff to the 128/205 Z ervoir permits pressure to be gradually decreased. A pressure transducer provides a feedback signal to the [56] References cued valve to control the rate of pressure drop and maintain NITED T T PATENTS it substantially constant all to the end that a doctor 3,508,537 4/1970 Kahn et a1. 128/205 A can more quickly and accurately take a patients 3,527,204 9/1970 Lem 128/205 A blood pressure. 3,550,582 12/1970 Wilhelmson.... 128/205 A 3,552,381 1 1971 Bums et al 128 205A 5 Claims, 2 Drawing Flgures \w '8 7 Pressure Display 23 s l9 Pressure A Transducer 7 I6 ll 1 Reservoir Power Supply I4 2 ,1 l Valve W P =5; 29 @l I A D L [y i r 2 Diff. Diff. A AlTlp.a a I Control t 1 27 1 BLOOD PRESSURE APPARATUS This invention relates generally to blood pressure measurements and more particularly to a semiautomated apparatus for aiding a doctor or other professional to quickly and accurately take a persons blood pressure.

BACKGROUND OF THE INVENTION The systolic blood pressure of a patient or person is a measure of the peak or maximum pressure in the patients circulatory system whereas the diastolic blood pressure is a measure of the average pressure of blood flowing through the circulatory system. The conventional apparatus for determining these pressures includes an inflatable cuff arranged to be wrapped about a patients arm, for example, and inflated by a squeeze bulb to thereby close off the circulatory system in the arm. Normally, a manometer or other pressure indicating device connects to the tube from the squeeze bulb to the inflatable cuff to indicate pressure in the cuff.

After the cuff is inflated sufficiently to close off circulation, this point being determined by the absence of acoustic pulses in a stethoscope, the doctor or nurse will gradually release the pressure in the cuff and carefully listen with the stethoscope for the start of blood flow to the lower portion of the arm. At the instant a first acoustic pulse is detected in the stethoscope, a reading of the manometer or other pressure indicating device is taken, this reading indicating the systolic blood pressure. The pressure is gradually decreased further until such time as there is an absence of pronounced acoustic pulses detected by the doctor listening in the stethoscope. At this point, another pressure reading is taken which serves to indicate the diastolic blood pressure.

The gradual decreasing of the pressure is accomplished by a small screw-type bleeder valve usually disposed close to the squeeze bulb so that the doctor can control the flow of air from the inflated cuff in such a manner as to decrease the pressure at a constant rate.

While the foregoing apparatus is fairly simple and relatively inexpensive, it demands a certain amount of skill in its use particularly if consistent results are to be obtained. Thus, the doctor or other professional must be able to detect the absence of acoustic pulses in his stethoscope while simultaneously squeezing the squeeze bulb to build up the pressure in the cuff. Moreover, this pressure build up should be fairly rapid and should occur at a fairly consistent rate if consistent results are to be achieved. Similarly, in gradually decreasing the pressure, the doctor must simultaneously manually manipulate the small screw bleeder valve, which is subject to particles and moisture in the air, listen for acoustic pulses or the absence of acoustic pulses, and observe the manometer or other pressure indicating device.

The acoustic pulses, called Korotkoff sounds in the medical profession, are divided into five phases based on changes in the characteristics of the sound as cuff pressure is decreased. Phase IV is a muffled sound relative to the first three phases. Phase V is silent. There is some disagreement on whether the end of Phase III or Phase IV more accurately represents the true diastolic pressure. It can be appreciated, accordingly, that any arrangement which will relieve the doctor of various operations now necessary in taking the blood pressure so that he can concentrate primarily on the proper detection of the acoustic pulses or the absence of the same, will greatly improve the overall operation of obtaining consistent results.

BRIEF DESCRIPTION OF THE PRESENT INVENTION With the foregoing in mind, the present invention contemplates an improved blood pressure taking apparatus wherein proper pressure build up rate in a cuff and the gradual decreasing of the pressure is effected in a consistent manner substantially automatically so that the doctor or other person taking the blood pres sure is relieved of the necessity to manipulate a squeeze bulb and subsequently control the opening in a relief or bleeder type valve.

In accord with the invention, a pneumatically sealed reservoir having outlet and inlet tubes communicating with its interior is provided. These tubes connect to an inflatable pressure means, such as acuff, exterior of the reservoir arranged to block off blood flow in a portion of a persons circulatory system when inflated to a given pressure. A pump means is connected to the outlet tube for pumping air from the reservoir into the inflatable pressure means when energized. Preferably, this pump means is incorporated in the reservoir itself so that it is shielded against dirt and dust and also any sounds from the pump are muffled.

A single electrically controlled valve connects to the inlet tube for the reservoir to pass air from the inflatable pressure means back into the reservoir in a con trolled manner. Actual control of the valve is effected by a pressure transducer means responsive to pressure in the inflated pressure means for generating an analog signal constituting a function of the pressure, this analog signal being fed back through a suitable feedback means for controlling the action of the valve to provide a given constant rate of pressure decrease from the inflatable pressure means.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention will be had by now referring to the accompanying drawings in which:

FIG. 1 is a diagram partly in block form showing the basic components of the blood pressure apparatus in accord with the invention; and

FIG. 2 shows a series of wave forms occurring at correspondingly lettered points in FIG. 1 useful in explaining the operation of the apparatus.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. I there is shown in the central portion of the drawing a pneumatically sealedreservoir 10 having outlet andinlet tubes 11 and 12 connecting to an inflatable pressure means 13 such as the usual type cuff employed in conventional blood pressure taking apparatus. As shown, the pressure inflatable means 13 is wrapped about a persons arm to close off blood flow in this portion of his circulatory system.

A pump means 14 is connected to the outlet tube 11 and in accord with a preferred embodiment of the invention, the pump is incorporated within the pneumatically sealedreservoir 10. By positioning the pump within the reservoir, it is not only protected from dust and moisture but any sounds generated by the pump are muffled.

As shown, thepump 14 is arranged to be energized by power leads 15 from any suitable power supply such as indicated at 16, upon depression of a push button switch SW-l. Operation of the pump will transfer air from thereservoir 10 to theinflatable means 13 as indicated by the arrows.

An electrically controlledvalve 17 is shown in thereservoir inlet tube 12. When this valve is cracked open slightly, the compressed air in thecuff 13 passes back into thereservoir 10.

From the foregoing, it will be appreciated that the apparatus comprises a closed air system, the same air being used again and again to operate the inflatable pressure means 13. The air is thus kept dry and free of particles.

As shown in the upper portion of the drawing, there is provided apressure transducer 18 connected to the outlet tube 11 and thus responsive to the pressure in theinflatable cuff 13. This pressure transducer generates an analog signal constituting a function of the pressure at all times within theinflatable means 13.

Afeedback line 19 passes from thepressure transducer 18 to a differentiatingcircuit 20, the output of which connects to one side of adifferential amplifier 21. The other sideof the differential amplifier receives a reference voltage signal indicated at 22. Any difference in these signals gives rise to an error signal passed to the electrically controlledvalve 17 by thedifferential amplifier 21. The valve is controlled to provide a constant rate of pressure decrease in thecuff 13. A visual display of the pressure also derived from thepressure transducer 18 may be provided as at 23.

Also shown in FIG. 1 is a conventional stethoscope including the usualacoustic tube 24 terminating at one end in a pick up 25 and at its other end inear inserts 26. An operator such as a doctor or nurse or other professional is represented by thebox 27 and this person will manually operate the switch SW-l as indicated by thedashed line 28.

With respect to the foregoing, in the simplest embodiment of the present invention, the stethoscope would be used by the person taking the blood pressure and the push button switch SW-l operated manually. It should be understood, however, that detection of acoustic pulses could be accomplished electronically and automatic controls actuated to record the pressure displayed at 23 at the initiation and termination of acoustic pulses thereby recording the systolic and diastolic pressures. In a completely automated device, the same controls could be utilized to terminate operation of thepump 14 by opening of the switch SW-l when the desired given pressure sufiicient to assure complete block-off of blood flow is achieved. Such a completely automated blood pressure measuring system is shown and described in my copending patent application Ser. No. 443,442 filed Feb. 19, 1974 and entitled BLOOD PRESSURE MEASURING SYSTEM, assigned to the same assignee as the present invention. In other words, the present invention could be utilized in such a system as shown and described in this referred-to copending application or it may be used by itself in conjunction with a stethoscope as depicted in FIG. 1.

With respect to the foregoing, it should be understood that the present invention is concerned solely with the closed air system and feedback control for respectively inflating the cuff l3 and controlling the rate of decrease of pressure in the cuff in a consistent, constant manner.

It will be noted in FIG. 1, that when the push button SW-l is operated, it will supply energy from thepower supply 16 to the pump and will also actuate a closure means 29 connected to theleads 15 which functions to hold thevalve 17 closed whenever thepump 14 is energized. When the pump is de-energized by opening of the switch SW-l, theclosure control 29 is also released so that the valve is then under control of the signal from thedifferential amplifier 21.

Referring now to FIG. 2, the analog signal from thepressure transducer 18 is indicated at A in the top diagram. It will be noted that the pressure build up when the pump is energized is quite rapid as indicated by therise line 30. This rate may be, for example, 50 millimeters per second. The remaining portion of the analog curve indicated at 31 represents the gradual decreasing of the pressure in the cuff at a constant rate.

Diagram B indicates the output of the differentiatingcircuit 20 of FIG. 1 and this output constitutes a constantnegative voltage signal 32 depicting the constant negative slope of the decreasingpressure curve portion 31 in diagram A.

Diagram C shows the reference negative voltage at 33 fed to the other side of thedifferential amplifier 21. Adjustment of the negative magnitude of the voltage C will control the rate of discharge of the air through thevalve 17 of FIG. 1.

Finally, the signal from the differential amplifier is shown in diagram D at 34, which signal serves to maintain the pressure decrease constant.

OPERATION In operation, the doctor or other professional need only position the inflatable means in the form of thecuff 13 about the patients arm in the usual manner and position the pick up 25 of the stethoscope at a lower portion downstream of the circulatory system to be blocked off. While listening to the stethoscope, the doctor will then simply press the push button switch SW-l which will energize thepump 14 to rapidly inflate thecuff 13. As mentioned heretofore, theclosure con trol 29 is also energized upon closing of the switch SW-l so that thevalve 17 is closed and pressure can build up in thecuff 13. The air utilized to inflate thecuff 13 is simply drawn from the reservoir so that the reservoir pressure decreases.

The doctor will maintain the switch button SW-l depressed until he no longer detects acoustic pulses in the stethoscope the same as he does when operating a squeeze bulb. Releasing of the push button then deenergizes thepump 14 and simultaneously removes thevalve closure control 29. The valve will then automatically be cracked the correct amount to cause a gradual decrease of the pressure in the cuff as defined by theanalog signal portion 31 in FIG. 2. As mentioned, this rate of decrease is controlled by the value of the reference voltage set into thedifferential amplifier 21 and normally would be at a rate of two millimeters of mercury per second.

As an example of the feedback control to assure that the gradual decrease in pressure takes place in accord with the desired constant rate, assume that for some reason there is a sudden pressure fluctuation in thecuff 13 such as would cause an increase in the drop rate. Such a sudden increase in the drop rate is indicated at 31 in FIG. 2 in greatly exaggerated form. This fluctuation in the pressure will give rise to a change in the output signal from the differentiating circuit as indicated at 32. Thus the initial increase in the drop rate will cause an initial increase in the negative voltage from the differentiatingcircuit 20. Since the referencenegative voltage 33 is constant, there will develop an error signal as indicated at 34' which will close down the valve initially to decrease the rate, this action being reflected in the pressure transducer and feeding back through the differentiating circuit to give rise to the remaining portion of the error signal which functions to adjust thevalve 17 in a proper direction so that the output of the differentiatingcircuit 20 matches precisely the reference. When this matching or equality is achieved, there will no longer be an error signal deviation from thesignal 34 so that the valve will return to its set position so long as the rate of decrease remains constant as determined bysignal 34.

It will thus be evident that the doctor need not be concerned with controlling manually a bleeder type relief valve but can devote his entire attention to detecting acoustic pulses while observing the pressure displayed at 23.

The recording of the systolic and diastolic blood pressure is done by the doctor in the same manner as is conventionally done, the doctor simply recording the pressure reading at the initiation of the acoustic pulses to provide the systolic pressure and at the termination of the acoustic pulses to provide the diastolic pressure.

From the foregoing, it will be appreciated that a completely closed air system provides the necessary pressure control. As a consequence, the air is free of particles and moisture and consistent and reliable opertion of the valve is thus insured. Heretofore, the presence of moisture and particles in the air could clog the bleeder type relief valves necessitating constant corrective activity on the part of the doctor.

While air has been described as the pressure supplying fluid, any other gas or fluid could be used if desired.

What is claimed is:

l. A blood pressure apparatus comprising, in combination:

a. a pneumatically sealed reservoir having outlet and inlet tubes communicating with its interior;

b. inflatable pressure means exterior of said reservoir connected to said tubes and arranged to block off blood flow in a portion of a persons circulatory system when inflated to a given pressure;

c. pump means connected to the outlet tube for pumping air from said reservoir into said inflatable pressure means when energized;

01. means for energizing said pump means;

e. an electrically controlled valve connected to said inlet tube for passing air from said inflatable pressure means back into said reservoir in a controlled manner after said given pressure is reached to cause a continuous gradual decrease in the pressure;

f. pressure transducer means responsive to pressure in said inflatable pressure means for generating an analog signal constituting a function of said pressure; and

g. feedback means connected between said pressure transducer means and said electrically controlled valve, said feedback means including:

1. means responsive to said analog signal to provide a a singal level proportional to the slope of the analog signal generated in response to said gradual decrease in pressure;

a reference signal level generating means; and,

3. means for generating an error signal in response to any difference in said signal level proportional to the slope of said analog signal, and said reference signal level, for controlling the action of said valve to correct any deviation in said slope from a desired constant value to thereby provide a given constant rate of pressure drop in said inflatable pressure means, whereby'a doctor can energize said pump means to close off said blood flow when said given pressure is attained and then listen to acoustic pulses with a stethoscope to determine systolic and diastolic blood pressure with assurance that the rate of pressure decrease in said inflatable pressure means remains contant.

2. An apparatus according to claim 1, in which said pump means is positioned within said reservoir so that it is protected from dirt and sound therefrom is muffled.

3. An apparatus according to claim 1, including pressure display means for visually indicating the pressure in said inflatable pressure means.

4. An apparatus according to claim 1, in which said pump means includes means, when energized, to build up pressure at a desired rate.

5. An apparatus according to claim 1, including means connected to said electrically controlled valve and responsive to energization of said pump means to automatically hold said valve closed while said pump means is energized.

Claims (7)

1. A blood pressure apparatus comprising, in combination: a. a pneumatically sealed reservoir having outlet and inlet tubes communicating with its interior; b. inflatable pressure means exterior of said reservoir connected to said tubes and arranged to block off blood flow in a portion of a person''s circulatory system when inflated to a given pressure; c. pump means connected to the outlet tube for pumping air from said reservoir into said inflatable pressure means when energized; d. means for energizing said pump means; e. an electrically controlled valve connected to said inlet tube for passing air from said inflatable pressure means back into said reservoir in a controlled manner after said given pressure is reached to cause a continuous gradual decrease in the pressure; f. pressure transducer means responsive to pressure in said inflatable pressure means for generating an analog signal constituting a function of said pressure; and g. feedback means connected between said pressure transducer means and said electrically controlled valve, said feedback means including: 1. means responsive to said analog signal to provide a a singal level proportional to the slope of the analog signal generated in response to said gradual decrease in pressure; 2. a reference signal level generating means; and, 3. means for generating an error signal in response to any difference in said signal level proportional to the slope of said analog signal, and said reference signal level, for controlling the action of said valve to correct any deviation in said slope from a desired constant value to thereby provide a given constant rate of pressure drop in said inflatable pressure means, whereby a doctor can energize said pump means to close off said blood flow when said given pressure is attained and then listen to acoustic pulses with a stethoscope to determine systolic and diastolic blood pressure with assurance that the rate of pressure decrease in said inflatable pressure means remains contant.

2. a reference signal level generating means; and,

2. An apparatus according to claim 1, in which said pump means is positioned within said reservoir so that it is protected from dirt and sound therefrom is muffled.

3. means for generating an error signal in response to any difference in said signal level proportional to the slope of said analog signal, and said reference signal level, for controlling the action of said valve to correct any deviation in said slope from a desired constant value to thereby provide a given constant rate of pressure drop in said inflatable pressure means, whereby a doctor can energize said pump means to close off said blood flow when said given pressure is attained and then listen to acoustic pulses with a stethoscope to determine systolic and diastolic blood pressure with assurance that the rate of pressure decrease in said inflatable pressure means remains contant.

3. An apparatus according to claim 1, including pressure display means for visually indicating the pressure in said inflatable pressure means.

4. An apparatus according to claim 1, in which said pump means includes means, when energized, to build up pressure at a desired rate.

5. An apparatus according to claim 1, including means connected to said electrically controlled valve and responsive to energization of said pump means to automatically hold said valve closed while said pump means is energized.

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