Indirect blood pressure recorder
US 2989051 A
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Description (OCR text may contain errors)
June 20, 1961 G. D. zuxDEMA ET AL 2,989,051
INDIRECT BLooD PRESSURE RECORDER 3 Sheets-Sheet 1 Filed May 29, 1956 -Nlml IN V EN TORJ.
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June 20, 1961 G. D. zulDEMA ETAL 2,989,051
INDIRECT BLOOD PRESSURE RECORDER 5 Sheets-Sheet 3 Filed May 29, 1956 limite Ohio Filed May 29, 1956, Ser. No. 588,195
1 Claim. (Cl. 12S-2.05) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to us of any royalty thereon.
This invention relates to an indirect blood pressure recorder and more particularly to an improved means and method for taking and recording blood pressure, as Well as pulse rate changes and the like.
The indirect taking and the recording of blood pressure readings by the inated cuff method is Well estabh lished. In a usual procedure an inflatable cult is applied over an artery in a mans arm, the cuff is inflated to a pressure in excess of the mans systolic blood pressure and gradually deflated over a period of about seconds, during which time the blood llow approaches normal for that individual. Sounds made by the blood in the artery during the described procedure are commonly detected 'by the use of a stethoscope. Of particular interest are the sounds at the systolic or peak blood pressure and at the diastolic or minimal blood pressure during the described procedures.
In practicing the above described method the cuff may be made of fabric, rubber, a flexible plastic or the like and may belinated with air, Water or other desired fluid to a predetermined measured and controlled pressure. 'The pressure within the cut is commonly measured with a mercury or an aneroid manometer. The deation of the cul'Ir is commonly accomplished by the manual control of the escape valve during which the sound from the stethoscope is commonly depended upon for indicating the blood pressure at the systolic and at the diastolic pressure extremes. The manual control of the escape valve is characterized by the limitation of a nonuniform linear cui deation, which is desirable.
During the cardiac cycle it lis of particular importance to detect or to identify that instant at which the artery obstruction which is introduced by the inflated cuff just opens at the systolic pressure and the instant at which the dropping arterial pressure just reaches the diastolic pressure. The sounds of blood ow through the artery during the cardiac cycle as the artery undergoes compression yand decompression by the operation of the inflated cuff, both when detected by the stethoscope or recorded, are important sources of information to the experimenter.
The nature of the present invention is the supplying of records of blood pressure which are usable as a basis for the study of cardiovascular responses from circulatory functions, inclusive of heart action. The substance of the present invention is an adaptation of an inated cuif technique by means of a pump or a bulb for iniiating the cuif with a mercury manometer indicating controlled pressure and inclusive of a first pressure transducer connected with a recording oscillograph for recording the pressure within the inatable cui. A pressure sensitive device is positioned between the inatable cuff and a skin surface overlying an artery from which mechanical data is to be derived and a second pressure transducer picks up and converts the arterial pulse into an electrical signal which is applied preferably through a capacitor to the same recording oscillograph where a tape is printed. The tape produced by the recording oscillo States Patent graph shows on a time basis, both the cuff pressure and the arterial pressure rise and fall accurately and perma nently recorded.
As the terms are used herein systolic pressure is dened as the point at which systemic arterial pressure is just suliicient to overcome the pressure within the inflated cui. In analyzing the recorded pulse waves which are produced by the apparatus contemplated hereby, the first abrupt increase of the amplitude of the pulse wave, together with its change in shape, is taken as the point of systolic pressure and the point of diastolic pressure is recognized by its form change and by its decrease in amplitude. At the systolic pressure point the pulse also is characterized by a Wider separation of the ascending and the descending strokes of the curve. A pressure sensitive device overlying the brachial artery in the arm and beneath the inflatable culi permits the detection of pulses as they appear and disappear with pressure alterations within the cuff.
The blood pressure recorded which is contemplated hereby is used on human subjects in studies of the heart and the circulation. It has been used successfully by the Armed Forces in supplying recordings taken from subjects on the human centrifuge, in high altitude pressure chambers and the like.
An object of the present invention is the collection andk the preservation of records indicating the cardiovascular status of a subject, particularly during the changes of acceleration and during high altitude tlight Where cardiovascular responses are all important. The records so pro vided are a graphic presentation of arterial blood pressure and pulse rate for purposes of study, comparison, and illustration.
This device provides for the automatic recording of blood pressure, and pulse rate changes using the generally accepted, recognized and well established inflated arm cuff method.
In practicing the present invention preferably an electric motor operated pump is used to inflate the cuff sufciently to occlude the brachial artery in the human arm. The motor may be replaced by a rubber bulb if desired. The cuff is then allowed to deflate slowly preferably at a substantially linear, uniform rate during which the pressure changes with time are made a permanent record in a recording oscillograph.
An illustrative embodiment of the present invention is shown in the accompanying drawings wherein:
FIG. 1 is a diagram of an apparatus contemplated hereby as installed on a human arm;
FIG. 2 is a reproduction of an oscillograph recording of an actual pulse wave above a cuff pressure curve on time-pressure coordinates using the equipment shown in FIG. 1;
FIG. 3 is a reproduction of another oscillograph recording Where an actual pulse Wave above a cuff pressure curve is presented on coordinates of time in seconds along the abscissa and of pressure in millimeters of mercury along the ordinate; and
FIG. 4 is a modil'ication of the invention substituting a strain gage for an inatable balloon shown in FIG. l of the drawings.
The equipment embodying the present invention and represented in FIG. l of the present drawings comprises a preferably automatic pump 1 which supplies under pressure a fluid such as air, Water or the like through a hollow tube 2 to an inilatablecuif 3. The cuif 3 is shown encircling a member or an extremity such as a human arm 4 to which blood pressure pulses are conducted through a brachial artery 5. Magnitudes of pressure within the cuff 3 and within the hollow tube 2 preferably are made directly visually observable by means of a glass walled merculy manometer 6. The manometer 6 has one leg 7 opening directly into the pressure tube 2 and has a second leg 8 which is sealed at its end remote from the tube 2. The mercury meniscus of the manometer is read directly projected against a scale 9, in indicating the magnitude of pressure within the cuff 3. The manometer 6 is used both in calibrating the system and in providing direct readings during experimentation upon a subject. A first pressure transducer 10 has a blood pressure receiving end which opens directly into the pressure tube 2 and an output end from which an electrical lead 11 extends. The lirst pressure transducer output electrical lead 11 is connected to a recording oscillograph 12. The first pressure transducer output signals cuff pressure curves 13 and 13 which are reproduced in FIGS. 2 and 3, respectively, of the accompanying drawings.
The pressure system of the pump 1, the pressure tube 2, the cuff 3, the manometer 6 and the pressure end of the transducer 10, preferably has a safe pressure range up to at least 250 mms. of mercury. The pump 1 which is contemplated hereby is the subject matter of a patent application now being prosecuted in the interest of the H. L. Klein Manufacturing Company of 481 East 11th Avenue, Columbus, Ohio. The pump 1 control, not shown, is adjusted to perform automatically within l or 2 seconds the inflation of the cuff 3 and then to shut off automatically upon reaching a desired pressure of illustratively 240 mms. of mercury, as indicated by the manometer 6. Pump control then automatically allows theY fluid pressure within the system to subside along the curves 13 and 13 to ambient over the next 22 to 24 seconds of a full time cycle, which illustratively is 25 seconds long. The entire cycle of 25 seconds duration in time is repeated continuously until the procedure iS terminated by the operator.
The lirst pressure transducer 10 illustratively may be a Gauer-Wetterer miniature manometer, which is described in the publications: the journal Science, for October 6, 1950, page 404, and in the journal Circulation, volume 3, page 390; a pressure transducer manufactured by and commercially available from Statham Laboratories, Inc., Los Angeles, California under Patent Nos. 2,036,458 and 2,059,549; or the like. The Gauer- Wetterer pressure transducer described herein has a rubber diaphragm over a piston head at the fluid pressure end of the transducer for the purpose of confining fluid at the input end of the transducer.
The pressure values picked up by the rst transducer 10 are conducted by the transducer electrical output lead 11 to the recording oscillograph 12, where they are recorded on a tape produced by the oscillograph as the cuff pressure curves 13 and 13', along with the pulse wave curves 14 and 14', respectively, in FIGS. 2 and 3 of the drawings. The recording oscillograph 12 illustratively may contain a 7-215 galvanometer 15, which has a sensitivity of 13 microamperes for each inch of the tape, or a galvanometer of similar sensitivity, The recording oscillograph 12 illustratively may be made by the Consolidated Engineering Corporation, or by Wm. Miller Instruments, Inc., both of Pasadena, California.
Interposed between the cuff 3 and skin overlying the brachial artery 5 of the arm 4, is an inflatable iiuid filled balloon or bladder 16. Preferably a thin rigid plate 16 is interposed between the bladder 16 and the cuff 3. The plate 16 reduces the elasticity of the system and provides a more accurate response on the tape produced by the oscillograph 12. The balloon or bladder 16 is shown as connected by a hollow tube 17 with a second pressure transducer 18. The second pressure transducer 18 has an electrical output signal lead 19 preferably capacitively coupled through a series connected condenser 21, with the recording oscillograph 12. The oscillograph 12 also contains a 7-239 galvanometer 20 with the sensitivity of 4 microamps `per inch of tape.
The bladder 16 and the hollow tube 17 preferably may be made of a polyethylene plastic, rubber or the like, and preferably contain an incompressible uid, of which boiled water is a satisfactory example and which uid provides a direct hydraulic ram between the skin overlying the brachial artery 5 and the thin sheet rubber diaphragm which covers the piston head within the transducer 18. The direct current component of the electrical signal output from the transducer 18 preferably is blocked by the condenser 21, which may have an illustrative capacitance of 200 microfarads. The use of a condenser of a range of from 200 to 1,000 microfarads, connected in series between the transducer 18 and the oscillograph 12, is preferred. In the event a miniature manometer is used, a preferred type is backA loaded through a constriction so that only the alternating current component of theV blood pressure signal is transformed into movements of the diaphragm, since a carrier wave is not blocked by a condenser.
Pulse waves of arterial blood surging in the brachial artery 5 a-re transmitted by direct mechanical conduction to the hydraulic fluid which is confined within the balloon 16 and within the tube 17. The pulse waves in turn are applied to the pressure transducer 18 and produce displacements of the transducer diaphragm. Displacements of the transducer diaphragm initiate electrical signals which are conducted between the electrical conductor 19 and into the oscillograph 12, for presentation upon the tape produced by the oscillograph. The pulse waves appear on the oscillograph tape as shown in the curves 14 and 14 of FIGS. 2 and 3 of the accompanying drawings.
The tube 17 may be omitted, if preferred, from be tween the balloon 16 and the fluid pressure end of the transducer 18 for short coupling and for simplifying this arrangement, with the rubber diaphragm closed input tube end of the transducer 18 inserted directly through the Wall of the balloon 16. The resultant structure combines directly the balloon 16 and the transducer 18 in a single unit which is easily and conveniently attached to individual subjects. The short-coupled form of the invention is immediately and accurately responsive in sense and in magnitude to minute pressure changes which are passed from the brachial 4artery tothe Huid within the balloon y16.
Further simplication of the assembly results in building the balloon 16 into the wall of the inflatable culf 3, or attaching the balloon 16 directly to the Wall of the inflatable cuff against the skin overlying the brachial artery S. The resultant structure provides a single assembly whether the transducer 18 is directly attached to the bladder or is attached to the bladder through a tube 17, as preferred.
In many of the above arrangements, pressure within the cuff 3 is lapplied directly to the thin diaphragm of the transducer 10, and displaces it. The resulting electrical output signal is conducted by the electrical conductor 11 to the oscillograph 12, where the cuff pressure recordings are applied to -the oscillograph tape simultaneously with the recording of balloon or bladder pressure pulse wave recordings.
The use of the condenser 21, of from 200 to 1,000 microfarads capacity, connected in series in the pulse Wave recording output from the transducer 18, serves to pass alternating current and to block the passage of direct current and thereby to atten out fluctuations in the base lines 14 and 14 of the graphs shown in FIGS. 2 and 3 of the drawings. The presence in circuit of the condenser 21 eliminates the large relatively slow drop in pressure within the cuif 3, while preserving the smaller pulse wave displacements from within the balloon 16, as indicated in the upper curves 14 and l14 of FIGS. 2 and 3, respectively, of the accompanying drawings.
The arrows 25 and 26 appearing in FIG. 3 of the drawings indicate respectively the systolic and the diastolic configurations of the arterial blood pulse force patterns of the brachial artery 5, as they appear on the tape of the oscillograph 12 from which readings in pressure in millimeters of mercury may be taken from the ordinate and time in seconds may be taken from the abscissa.
Modifications of the above described means for taking and for recording arterial blood pressures which are contemplated herein, and some of which have been used lsuccessfully experimentally in the laboratory, include a metal strain gage 30. The strain gage 30 is enclosed in a substantially fla-t envelope 31 of rubber, plastic or metal. The strain gage device provides a substantially flat unit for replacing the `balloon 16 between the brachial artery 5 and the inatable cuffv 3, both when the balloon 16 is separate from t-he cui and when it is made integral therewith. Output leads 32 from the strain gage 30 conduct their electrical output to an amplier 33, from which leads 19 conduct signal through the capacitor |21 to the oscillograph 12, as in the earlier disclosed embodiments of the present invention.
A modiication of the strain gage concept, where the strain gage is mounted directly into and to be integral with the cu 3 toi overlie the brachial artery 5, has the advantage of providing a single assembled cui unit with a built-in indicator which provides simplified handling, uniformity of arm mountings, a minimizing of connections and -a minimum of error arising from manipulations and connections.
The oscillograph numbers 7-215 and 7-239 `are Consolidated Engineering Corporation part numbers.
A preferred form of the invention which is disclosed herein and which has been used experimentally as an automatic recording device, has been compared with auscultatory measurements made by trained and experienced physicians with favorable results. In both methods at least 20 seconds were allowed for enough pulse beats to come through for clear detection for both systolic and for diastolic pressures. In making the auscultatory measurements the diastolic pressure was noted in the muling of sounds `and at the disappearance of sounds. Systolic pressure was taken as the point at which the pulse sound was irst heard.
It is to be understood that the cuff and bladder arrangement shown in FIG. l of the accompanying drawings is an experimentally successful method of operation of the present invention and that changes and modifications described and explained herein may be made without departing from the scope of the present invention.
What we claim is:
An indirect blood pressure recorder for recording blood pressure and pulse rate changes of blood circulating in an artery of an appendage comprising an inflatable cuff positioned around a `source of pressure change, cui inflation means for controlling the extent of cuff inflation, means indicating the extent of cuff inflation, an incompressible Huid-filled hydraulic pressure sensitive ram device overlying the source of pressure change and beneath the inatable cuif, pressure transducer means receiving its input from the pressure sensitive ram device as changes in hydraulic prsure and converting its received input into electrical signal output sensitive in time and in magnitude, an electrical signal recording means receiving the electrical signal output Vfrom the pressure transducer means and recording in time and in amplitude the lpressure changes to which the hydraulic pressure sensitive device is subjected, and a single piece thin rigid pressure distributing plate interposed between the pressure sensitive ram device and the cuff for uniformly sustaining pressure throughout its area and thereby modifying the elasticity of the system.
References Cited in the tile of this patent UNITED STATES PATENTS 1,043,521 Hoob'ler Nov. 5, 1912 2,076,642 Hubbard et al Apr. 13, 1937 2,272,836 Gerdien Feb. 10, 1942 2,354,818 Lippitt Aug. 1, 1944 2,447,018 Keinath Aug. 17, 1948 2,536,527 Appel Ian. 2, 1951 2,555,422 Scott et al. June 5, 1951 2,615,940 Williams Oct. 28, 1952 2,634,721 Greenwood Apr. 14, 1953 2,648,328 Hathaway et -al Aug. 11, 1953 2,755,796 Boucke July 24, 1956 2,826,191 Burns Mar. 1l, 1958 2,837,082 Elliott et al. June 3, 1958 FOREIGN PATENTS 723,402 Germany Aug. 4, 1942