US3771515A

US3771515A - Automatic recording sphygmomanometer

Info

Publication number: US3771515A
Application number: US00177405A
Authority: US
Inventors: M Hurwitz
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-09-02
Filing date: 1971-09-02
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13
Also published as: JPS4835689A; DE2226652A1; FR2141150A5; GB1384306A; CA952339A

Abstract

An automatic blood pressure recording apparatus which eliminates or minimizes substantially all known sources of human error in sphygmomanometry. A uni-directional micorphone maximally sensitive to Korotkoff sounds is contained within the cuff donned by the subject. Analog signals from the microphone are amplified, and digitalized by an electronic circuit whose digital output pulses occur in synchronism with the Korotkoff sounds. Each output pulse actuates a printing stylus which produces a mark on a stationary record chart resulting in a series of marks. The stylus position is controlled by cuff pressure. Thus, the positions of the first and last marks indicate systolic and diastolic pressures.

Description

[ Nov. 13, 1973 11/1971 Saba 128/205 Q ABSTRACT 0 United States Patent [191 Hurwitz AUTOMATIC RECORDING SPHYGMOMANOMETER [76] lnventor: Mathew Hurwitz, 63 Oakland Ave.,

Auburndale, Mass. 02166 [22 Filed: Sept. 2, 1971 [211 Appl. No.: 177,405

US. Cl... 128/2.05 G, 128/205 M, 128/205 0 [51] Int. A61b 5/02 128/205 G, 2.05 A, 128/205 M, 205 Q, 2.05 P

References Cited UNITED STATES PATENTS [58] Field of Search..................

cord chart resulting in a series of marks. The stylus position is controlled by cuff pressure. Thus, the positions of the first and last marks indicate systolic and I diastolic pressures.

10 Claims, 13 Drawing Figures 3,349,763 Clements, Jr. et al. 2,980,107 4/1961 Hurley et a1. 3,444,856 5/1969 Settler et al.... 3,651,798 3/1972 Egli et al. 3,117,570 1/1964 Halasz et al.... 3,557,779 1/1971 Weinstein 3,146,777 9/1964 PATENTEDnuv 13 1913 SHEET 10F 5 1% w H ark ./-W 7 D 5 l E m :r m m m S H W m R M -/Mnw 5 L 5 UM w B M W .v 5 .T 2 m M R 0 G M m M0 H R 2 7 E K F P 2) g m L mm w A T. w a

PATENTED NOV 13 I875 3711.515 SHEUEUF 5 PATENTED "UV 1 3 1973 SHEETRDF 5 FIGS I FIG, 7

PATENTED am 1 31915 SHEET 5 OF 5 "IIIIIIIIIIIIA.

-l 70 FIG, 11

FIG, 15 v BACKGROUND OF THE INVENTION This invention relates to an indirect, automatic, blood pressure recording apparatus which is accurate, simple to use, low in cost, and which eliminates or greatly reduces substantially all of the known sources of sphygmomanometer error due to operator technique and observer skill, acuity, and bias. It is based upon the universally accepted Riva-Rocci/Korotkoff technique familiar to all practitioners skilled in the art.

The Riva-Rocci/Korotkoff technique for the indirect measurement of blood pressure, as standardized by the American Heart Association, is practiced with an instrument known as the sphygmomanometer.

This instrument consists of an inflatable rubber bladder within a non-stretchable fabric cuff, an inflating.

bulb with a venting valve, a pressure meter (either a mercury column or aneroid gauge) to register the pressure within the rubber bladder, and a stethescope with which the operator listens to characteristic sounds which come from the artery during the course of the measurement. The sounds are known as Korotkoff sounds, named for the Russian scientist who discovered them in 1905. The method of listening for Korotkoff sounds is universally accepted as providing an accurate indication of the systolic and diastolic blood pressure for most people.

The technique for indirect measurement of blood pressure by the conventional sphygmomanometer requires an operator having good hearing and a fair measure of skill. A properly fitted. cuff is wrapped snugly about the upper arm of the subject in such a manner that the bladder is centered over the brachial artery and the edge of the cuff is disposed about one inch above the anticubital space. The operator then inflates the cuff rapidly until the pressure in the cuff is sufficient to-compress the arm and stop the flow of blood. The artery is now said to be occluded. The operator next places the stethescope at the anticubital space over the brachial artery just below the cuff. Initially, of course, no sounds are to be heard because the artery is occluded and no blood is flowing through the artery. The operator then opens the venting valve and adjusts it so that the pressure in the cuff falls gradually, at a rate of 2 to 3 mmHg 'per second. When the pressure within the cuff reaches the systolic pressure blood begins to flow through the artery and the operator hears a tapping sound (Phase 1 Korotkoff sound) through his stethescope. Simultaneously, he observes the reading on the pressure gauge. This pressure is the systolic blood pressure. As the pressure continues to fall, the operator will hear sounds diminish in intensity (Phase 2 Korotkoff sound) then the sounds become crisper and louder (Phase 3 Korotkoff sound), subsequently the sounds become muffled, as if an obstruction had been placed in the stethescope (Phase 4 Korotkoff sound), and finally the sounds disappear (Phase 5 K- rotkoff). There is some controversy as to whether Phase 4 or indicates diastolic pressure; some practitioners use Phase 4 and others use Phase 5. It is generally agreed, however, that the differences are not highly critical and good results can be obtained using either phase providing care is exercised in all other aspects of the measurement. Having noted the diastolic pressure, by whichever criterion he prefers, the operator vents the remaining pressure and may either remove the cuff or, after allowing the subject to rest for a reasonable period, usually 2l/2-3minutes, he may repeat the measurements. It is well known that the accurate measurement of blood pressure, according to conventional indirect methods, demands good hearing, skill, and painstaking attention to such details as the snugness and proper fit of the cuff, the control of the vent valve, the recognition of the sometimes subtle changes in the K0- rotkoff sounds, and an ability to read a moving, pressure gauge- SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide-an improved apparatus for the accurate determination of blood pressure by which the systolic and diastolic pressures are automatically sensed and recorded with a high degree of precision.

Another object of this invention is the provision of an automatic recording apparatus for the accurate determination of blood pressure which is simple to use and requires no special skill or acuity, even. to the extent that a patient may measure his own blood pressure with the same accuracy as that achieved by a skilled practitioner using the same apparatus.

Stillanother object of this invention is the provision of an apparatus of the foregoing type which may be economically manufactured.

A further object of this invention is the provision of an apparatus which functions according to well known accepted principles and procedures, so that it should readily gain wide acceptance among physicians and other practitioners skilled in the art.

lniaccordance with my invention, auscultation is carried out electronically by means of a specially designed contact type microphone which is located within a pocketin the cuff. The microphone is connected to an electronic circuit which amplifies the analog signal from the microphone and interprets the signal to determinewhether the sounds being detected by themicrophone are of sufficient intensity to be characterized as being within the range of systolic pressure (Phase 1 K0- rotkoff) and diastolic pressure (Phase 4 or 5 Korotkoff). The circuit then digitalizes those amplified microphone signals which satisfy the amplitude criteria and produces digital output pulses (actually square waves) whose amplitude (voltage) and duration are constant, independent of the strength of the analog signals which gave rise to them. These pulses occur in synchronism with the heartbeats of the patient or subject under measurement, beginning with the first of the Phase 1 Korotkoff sound and terminating with the last of the Phase 4 or 5 Korotkoff sounds. The recorder includes a movable printing stylus, whose position is determined by direct pneumatico-mechanical means controlled by the pressure within the cuff. Output pulses from the electronic auscultation means are used to activate the stylus or printing means and the position of the printing means at any point during a measurement cycle is governed by the cuff pressure which is caused to slowly decrease under the control of a fixed orifice valve, at a rate of 2 to 3 mmHg/second, according to accepted practice.

A stationary record chart is positioned to cooperate with the moving stylus to produce a record which consists of a series, or train, of marks. The position of the first mark in the series denotes the pressure at which the incipience of Phase 1 Korotkoff sounds was detected. This is the systolic blood pressure. The position of the last mark in the series denotes the pressure at which the last of the Phase 4 or Korotkoff sounds was detected. This is the diastolic blood pressure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of an apparatus, in accordance with my invention.

FIG. 2 is a block diagram illustrating the circuit logic of my invention.

FIG. 3 is a more or less exploded view illustrating the components of my invention in connected relationship.

FIG. 4 is a side elevational view showing the working components of the apparatus illustrated in FIGS. 1 and 3 mounted on a chassis.

FIG. 5 is a cross-sectional view taken substantially on line 5--5 of FIG. 4.

, FIG. 6 is a cross-sectional view taken substantially on line 66 of FIG. 5.

FIG. 7 is a cross-sectional view taken substantially on line 7-7 of FIG. 4.

FIG. 8 is a top plan view taken substantially on line 88 of FIG. 7.

FIG. 9 is a bottom plan view taken substantially on line 99 of FIG. 7.

FIG. 10 is a cross-sectional view, on an enlarged scale, of the valve assembly taken substantially on line I0-10 of FIG. 11.

FIG. 11 is a cross-sectional view taken substantially on line ll-ll of FIG. 10.

FIG. 12 is a cross-sectional view taken substantially on line l2--l2 of FIG. 10; and

FIG. 13 is a cross-sectional view taken substantially on line 13-13 of FIG. 10.

BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT The apparatus of my invention includes an inflatable compression fabric band or cuff 25 which is adapted to be wrapped or applied about a limb having an artery for the testing of blood pressure. The cuff 25 is shown and described in greater detail in my co-pending US. Pat. application, Ser. No. 26,283, filed Apr. 7, 1970 now US. Pat. No. 3,669,096, issued June 13, 1972, and briefly, comprises an elastic panel 26 attached to one end of the body portion of the cuff and provided with a pair of snap fasteners 27 which cooperate with a series of cooperating fasteners 28 disposed along the edges of the body portion, medially thereof. The cuff is intended to be formed into a closed loop, closely approximating the size of the limb, prior to being pulled thereon and is securely in proper alignment by wrapping the body portion about the loop in the usual manner. The cuff includes a pocket to receive a contact microphone 29 so disposed that its contact surface may be located over the brachial artery, in the case of an arm, when the cuff is applied thereto. The microphone is connected to an electrical circuit, hereinafter to be described. However, briefly, the circuit includes an amplifier and a gate which has a threshold so adjusted that the circuit produces output pulses only when it receives signals resulting from Korotkoff sounds of sufficient intensity to be classified within the range of Phase I and Phase 4 or 5 Korotkoff.

The cuff 25 is inflated by an inflation bulb 31 connected by a flexible conduit 32 to a manifold 33. The

cuff is connected to one side of said manifold by a flexible conduit 34 and to the opposite side of said manifold are connected two flexible conduits 36 and 37, conduit 36 leading to a bellows assembly 38 constituting part of a recording mechanism, indicated generally by the numeral 39 and hereinafter to be more fullydescribed. The conduit 37 is connected to a valve switch assembly, indicated generally by the numeral 41. and hereinafter to be more fully described. The valve of the assembly 41 affords means for the controlled venting of air pressure from within the cuff 25.

The recorder mechanism (FIG. 3), indicated generally by the numeral 39, comprises a low cost hydroformed metal bellows 42, (FIG. 4) the head of which is arranged to engage against one end of a shaft 43 supported for axial movement in an arm 44 and a nylon sleeve 45 positioned axially by a threaded adjustable jam nut 45a having a slotted end. The round shaft 43 has machined on it an intermediate gear rack portion, (shown end-on in FIG. 7), which meshes with a pinion 46a, machined onto the vertical shaft 46 (FIG. 7). The shaft is journaled for rotation in an insulating block 48 having integral hollow threaded

bosses

62, 62 in which the sleeve 45 and nut 45a are received, the block being supported on a pair of bracket members 49. The lower end of the shaft 46 is machined to a conical shape 47 (FIG. 7) which is engaged by a resilient electrical contact arm 51 secured to one of the brackets 49. A rotor arm 52 formed of insulating material is mounted on the upper end of shaft 46 and is secured thereto for rotation therewith. Supported at one end of the rotor arm 52 is a push type solenoid 53 having a plunger, the upper end of which is typically machined to a frustoconical or spherical point to enable it to make visible impressions on a stationary pressure-sensitive record tape, as will be hereinafter explained. It will, of course, be understood that other suitable stylus means and record media may be employed in place of the solenoid arrangement hereinabove described. For example, an electro-magnetically actuated ink pen may conveniently be used for recording on a paper tape of the type used in conventional adding machines or a blinking light may be used to record on photosensitive record paper. The opposite end of the rotor arm 52 is provided with a shallowdepression to receive a counter-weight 57. The rotor arm 52 carries an upstanding stop pin 56 which constitutes an abutment member for engaging an adjustable dial/stop, hereinafter to be described. A metal strap 50 lying on the top surface of rotor arm 52 is in contact with one terminal of solenoid 53 and pin 56 and provides a ground conductor through shaft 46. The other terminal of solenoid 53 is connected through a section of conductive tape 55 attached to the underside of rotor arm 52, to a conductor in the form of a hair spring 58, the inner end of which is attached to an insulating sleeve 60 circumposed about shaft 46. The hair spring thus serves both as an electrical conductor and as an anti-backlash spring for the rack and pinion. The outer end of spring 58 is connected to a lug 59 mounted on block 48. A compression spring 61 is circumposed about shaft 43 and one end of the spring abuts sleeve 45 which is supported in threaded hollow bosses 62 integral with block 48.. The sleeve 45 is axially adjustable by means of a screw driver inserted in the slot of jam nut 45a. The shaft 43 is drilled laterally and threaded to receive a screw 63, the head of which is arranged to engage two adjacent coils of the spring 61 thereby to fix the spring in a position of adjustment. It will be apparent that the spring rate of spring 61 may be adjusted for purposes of calibration by increasing or decreasing the number of active coils between the end of sleeve 45 andscrew 63. The spring 61 serves to urge the shaft 43 to the left, as viewed in FIG. 4, to maintain the left hand of the shaft 43 in engagement with the head of the bellows 42. Thus the spring 61 normally urges the rotor arm 52 in a counter-clockwise direction, as viewed in FIG. 3, to assume a normal non-operative position.

The housing of the apparatus is shaped substantially as illustrated in FIG. 1 and includes a top panel 66 (best seen in FIGS. 3, 7, and 9) having an arcuately formed opening 67 concentric with the axis of s'haft'46. As shown in FIG. 7 the opening 67 is in registration with the path of travel of the plunger 54 as it revolves about the axis of shaft 46. It will be understood that when the solenoid 53 is energized the point of plunger 54 will pass through the arcuate slot 67 and impinge on a tape 78 lying on the surface of the panel 66.

A dial/stop 68, shaped substantially as illustrated in FIGS. 3 and 9, is mounted for rotation below the panel 66 coaxially with shaft 46. The dial/stop is provided on its periphery with a series of uniformly spaced notches 69 and carries a series of numerals or indicia on its upper face which are visible through a window opening 71 provided in the panel 66. The dial/stop 68 is supported by an integral arm 72 which is notched along one edge, as at 73, to engage the stop pin 56, as will be hereinafter explained.

A portion of panel 66 is cut away, as at 66a (FIG. 9) to expose an edge portion of dial/stop 68 so that it may be rotated, as with a finger, to position the arm 72 in a desired angular disposition to provide a stop for pin 56. It will be understood that the indicia on the dial/- stop 68 is related to the position of arm 72 so that a particular indicium visible through the window 71-will indicate a particular cuff inflation pressure value.

A spring biased metal detent 130 (FIG. 3) supported in an insulated case suitably mounted in the housing 70 is arranged to contact the periphery of dial/stop 68 and to engage one of the notches 69 to releasably retain the dial/stop 68 in a position of adjustment. The detent element is electrically connected to signal lamp 125 by conductor 13].

Referring to FIG. 4, the housing 70 includes a well 77 to receive a supply roll of a suitable pressure-sensitive record paper 78 on which the measurements are recorded. The record paper is adapted to be manually drawn over the panel 66 between edge guides 75 (FIG. 7). A transparent plate 79 bearing dial indicia in units of pressure is superposed over the panel 66 resting on the guides 75 so as to accommodate the record paper 78 in the space therebetw'een. The plate 79 has a circular transparent window 80 (FIGS. 1 and 3) superposed over the arcuate slot 67. In addition, plate 79 is pro vided with a transparent window 81 in registration with the opening 71 (FIG. 3) and also includes an additional window 82 in registration with the well 77 so as to afford to the operator a view of the record paper supply roll 78. In addition, an aperture 83 exposes a portion of therecord paper 78 so that pertinent information concerning a particular blood pressure measurement may be written on to the tape by the operator, as with a pen or pencil.

The housing includes a well 77 for storing the cuff I 25 when not in service. A signal lamp 125 is mounted on panel 66 for indicating when the cuff has been inflated to a pressure pre-set by dial 68.

The valve and switch assembly, indicated generally by the numeral 41, is shown more particularly in FIGS. 5,6 and 10 through 13 inclusive.

The valve, indicated generally by the numeral 84, includes a body 86, shaped substantially as shown, and having two cylindrical bores 87 and 88 respectively, and an intermediate bore 89 in which is joumaled an operating shaft 91. An opening 37a is provided in the flange of the body 86 to receive one end of conduit 37. Received in the bore 87 is a valve element 92 having a longitudinally extending passage 93 communicating with a vent aperture 94 controlled by a needle valve 96. The passage 93'is threaded for a portion of its length to accommodate a conventional tire valve core 97. Received in the bore 88 is,a valve element 98 which includes a threaded longitudinally extending passage 99 in which is received a conventional tire valve core 101. The passage 99 extends through the element 98 and vents directly to the atmosphere. Each of the

valve elements

92 and 98 has an enlarged chamber in which are received the

balls

102 and 103, respectively. The valve 84 includes a rotor element 104 which is keyed to shaft 91 for rotation therewith. The rotor element includes two circular.

recesses

106 and 107 respectively, and an arcuately shaped recess 108. Additionally, the rotor element is provided with three apertures 109, 110 and 111 which insure a free flow of air from opening 37a to valve chamber 116 within the valve body. It will be noted that the centers of each of the recesses and apertures are located on a circle, the center of which coincides with the axis of shaft 91. A cover member 112 shaped to receive the rotor element 104 and having an annular groove to accommodate a sealing O-ring 113 is secured to the valve body 84, as with screws 114. O- ring 113a effects a seal between shaft 91 and bore 89.

The opposite end of shaft 91 is connected to a rotary switch 117 which is in circuit with the electrical components, hereinafter to be described. An actuating lever 118 fixed to the shaft 91 extends through a slot in the panel 66 and terminates in a knob 119 which may be readily engaged by the operator. It is noted that the valve 86 and switch 117 are connected for synchronous operation, as will be hereinafter explained.

Power to operate the apparatus is derived from a plurality of dry cell batteries 121 (9 volts) contained in a suitable housing 122.

A circuit board 123, preferably positioned at the rear of the housing of the apparatus, carries substantially all of the electrical components shown in the block diagram illustrated in FIG. 2. Said components and their functions'are well known in the art and will be described hereinafter, briefly, in relation to their functions in the operation of the apparatus of my invention.

OPERATION The cuff is applied to the subjects limb and the operator moves the control lever 118 to its initial position corresponding to inflate position, as indicated by a legend on panel 66. Prior to inflating the cuff 25, the operator rotates the dial/stop 68 to a point where the indicia visible through the openings 71 and 81 should indicate a pressure approximately 30 mml-Ig higher than the anticipated systolic pressure. It will be understood that the arm 72 of dial/stop 68 thereby has been rotated to a specific angular position related to the pressure indicated.

In inflate position, the valve rotor element 104 is disposed in the position illustrated in FIG. 11, with shoulder 120 abutting stop 121 of the body 86. Ball 103 is disposed in recess 108 and ball 102 is disposed in recess 107. Neither of the valve cores 97 or 101 now is engaged by a respective ball hence, both valves are closed to venting of any air. Air may pass freely from bulb 31, through manifold 33, to cuff 25, valve 86 and bellows 42.

As cuff 25 is inflated, air pressure entering bellows 42 effects rotation of shaft 46 and rotor arm 52 to the point where pin 56 engages in notch 73 thereby closing an electrical circuit to energize signal lamp 125 which indicates to the operator that the pressure in the cuff is high enough to occlude the artery and that he may now begin the recording cycle. The lamp 125 is energized by current which flows from batteries 121 through conductor 133, switch 117, conductor 134, lamp 125, conductor 131, detent 130, dial 68, arm 72, pin 56, strap 50, shaft 46, arm 51 to a ground connected by conductor 136 to the other battery terminal.

The operator now moves the lever 118 to record position which conditions the switch 1 17 to extinguish the signal lamp 125 and simultaneously to switch the circuit output to solenoid 53. Correspondingly, the ball 102 is now caused to be cammed out of the conical recess 107 and to rest on the surface intermediate the

recesses

106 and 107, thereby engaging valve core 97 and venting the system through vent aperture 94. The rate of fall of cuff pressure is not constant but is roughly proportional to cuff pressure. Nevertheless, it is possible to adjust the needle 96 so that the cuff pressure falls at a rate between 1.5 to 3.5 mmI-Ig/sec over that portion of the pressure range (170 to 70 mmHg) where most adult blood pressures lie. This rate deviates by an acceptable margin from the vent rate range of 2-3 mmI-Ig recommended by the American Heart Association. Ball 103 remains in recess 108 out of engagement with valve core 101 which remains closed.

As the pressure in the cuff diminishes a point is reached wherein Korotkoff sounds are detected by the microphone. The microphone transduces these sounds to voltage waves which are fed into the circuit which amplifies the analog signal from the microphone and interprets the signal to determine whether the sounds being detected by the microphone are of sufficient intensity to be classified in the range of systolic and diastolic pressures. When the first Phase I Korotkoff sound is detected which satisfies the amplitude criterion of the circuit, the circuit produces a digital output pulse, preferably a square wave, which causes the solenoid 53 to be energized thereby activating the plunger 54 to produce a dot on the pressure sensitive record paper 78. These output pulses whose amplitude and duration are constant occur in synchronism with the heart beats of the subject, one dot for each heart beat, until Phase IV or V Korotkoff is reached, at which point the amplifled microphone signal is no longer of sufficient ampli- I pressure so that the angular position of the rotor member 52 and solenoid 53 will vary in accordance with such pressure. Thus, the record produced on the tape 78 comprises a series of dots arranged in an arc, with the position of the first dot in the series denoting the pressure at which the Phase I Korotkoff sound was detected, (systolic blood pressure) and the position of the last dot in the series denoting the pressure at which the last of the Phase IV or V Korotkoff sounds was detected, (diastolic blood pressure).

In the final step, the lever 118 is moved to the off position wherein shoulder 122 abuts stop 121. The switch 117 is conditioned to open the circuit to the batteries 121. The valve rotor 104 is positioned so that the ball 103 is cammed out of the recess 108 to come to rest on the flat surface of the rotor element wherein it engages the valve core 101 to open the passage 99 and rapidly vent the air from the system to the atmosphere. Ball 102 is received in recess 106, closing valve core 97.

After a measurement has been taken and recorded, as above described, the series of dots on the record paper is interpreted with reference to the dial indicia carried on the transparent plate 79 and the reading may be written directly on the record paper preferably in the area provided by the aperture 83. The record paper may then be advanced manually and the portion bearing the record torn off and saved for future reference. Since the transparent plate is part of the apparatus, the record paper need not be printed with a scale, nor need it be carefully oriented or positioned for rcthreading. Thus, the usual costly paper transport mechanism required in many types of data recording apparatus is eliminated. i

In the operation of the circuit embodied in my invention the signal developed in the microphone 29 by the subjects Korotkoff sounds is applied to a field effect transistor operated in a source follower mode. The signal passes through a gain control 151 into the amplifier 152 which increases the amplitude of the signal to a level suitable for usage in the remainder of the circuitry. The output from the amplifier is applied to a band pass filter 153 which allows only frequencies between predetermined limits to pass and which provides some additional amplification to the signal which is then applied to the emitter follower 154 which produces a low impedance output which follows the input signal. This output is applied to a gate 155 which discriminates the signals in accordance with their amplitude. Only a signal of sufficient amplitude can cause the gate to emit an output signal. The output signal from the gate 155 triggers a monostable multivibrator 156 to generate a square wave which is applied to the driver 157, the output of which actuates switch 158 which controls the circuit to solenoid 53. A feedback circuit 159 in parallel with the gate, multivibrator and driver, locks out random noise signals so that they will not produce signals to actuate the switch 158. A ,failsafe circuit 160 associated with the driver 157 senses low battery voltage and inhibits the driver 157 from actuating the switch 158 when. the battery voltage is below 5.8 volts to prevent the solenoid 53 from pulsing under such conditions wherein it might otherwise record a measurement erroneously.

It is to be understood that my invention anticipates other forms than the preferred embodiment described.

For example, the stylus may be translated linearly rather than being moved through an arc. The resulting embodiment produces a record consisting of a linear train of marks on the record medium which are then interpreted against a linear scale rather than the circular dial described.

It should also be clear that although the record medium in my preferred embodiment bears no scale (interpretation being expedited by the stationary dial on the instrument itself), my invention anticipates embodiments in which the record medium carries a pressure scale imprinted thereon so that interpretation may be made both by reference to the dial on the instrument and by the scale imprinted on said record medium.

Various changes coming within the spirit of my invention may suggest themselves to those skilled in the art; hence, I do not wish to be limited to the specific embodiments shown and described or uses mentioned, but intend the same to be merely exemplary, the scope of my invention being limited only by the appended claims. 1

I claim:

1. An apparatus for measuring and recording blood pressure comprising:

a. an inflatable cuff adapted to be applied to the upper third of a limb and having inflating means for inflating said cuff for selectively occluding the flow of blood to the limb;

b. a microphone positioned within said cuff capable of detecting Korotkoff sounds occurring within the limb as the pressure in said cuff is reduced;

0. electronic circuit means mounted in a housing and connected electrically to said microphone for amplifying and discriminating the signals emanating from said microphone for emitting a digital output signal for each Korotkoff sound;

d. a recording device having a stationary record medium and stylus means which is operable therewith, said recording device being electrically connected to said circuit means, and said stylus means being operable upon actuation by the digital pulses emanating from said circuit means for imprinting a single mark on said stationary record medium for each Korotkoff sound;

means mechanically coupled with said stylus means for moving e. stylus means relative to said record medium in synchronism with falling cuff pressure such that the position of said stylus means is specifically determined by the pressure in said cuff;

f. an adjustable indicating means for indicating inflation of said cuff to -a pre-determined pressure above the anticipated systolic blood pressure, said adjustable indicating means being mounted in said housing and connected to said means for moving said stylus means;

g. multi-position pneumatic bleed valve means selectively conditionable in a ontrolled-slow-leak mode for venting of said cuff during the measurement, in a gross venting mode for releasing the pressure from said cuff when the measurement is completed, and in a sealed mode during inflation of said cuff, said valve means being mounted in said housing and connected pneumatically to said cuff;

h. multi-position electrical switch means selectively conditionable in a first mode for actuating said indicating means to indicate when the predetermined cuff inflation pressure has been at tained while preventing said stylus means from being actuated, in a second mode to deactivate the said indicating means, and to permit said stylus means to imprint a record of said medium, and a third mode to deactivate said circuit means and said indicating means to disconnect all electrical functions, said switch means being mounted in said housing and connected to said circuit means and to said indicating means; and

i. a stationary dial graduated in units of pressure mounted adjacent said record medium to permit interpretation of the marks recorded on said record medium.

2. The invention as defined in claim 1 in which said stylus means comprises a solenoid having a plunger stylus arranged to produce visible marks on said record medium.

3. The invention as defined in claim 1 in which said means for moving said stylus means comprises pneumatico-mechanical means in pneumatic communication with said cuff.

4. The invention as defined in claim 1 in which said circuit means is adapted to digitalize only those microphone signals which are within a predetermined range of amplitudes which includes the amplitudes of Korotkoff sounds. v

5. An apparatus for measuring blood pressure as defined in claim 1 comprising,

a. a rotatable vertical shaft journaled in said housing;

and 1 b. a rotor arm supported on said shaft;

0. said stylus means comprising a solenoid having a plunger stylus arranged to make impressions on said record medium and supported on said rotor arm; r

(1. said means for moving said stylus means comprising bellows connected by a conduit to said cuff and operable in' response to variations of pressure in said cuff, and p e. means operatively connected to said shaft and being engaged with said bellows for effecting rotation of said shaft;

f. whereby movement of said bellows will effect rotation of said shaft to move said solenoid in synchronism with the variations in said cuff pressure 6. The invention as defined in claim 5 including moveable abutment means mounted adjacent said rotor arm and arranged to be selectively positioned within the range of movement of said rotor arm in relation to different predetermined pressures, and stop means carried on said rotor arm and engagable with said abutment means for limiting the movement of said rotor arm, said indicating means being operable upon contact of said stop means with said abutment means to indicate when a predetermined cuff inflation pressure has been reached.

7. The invention as defined in claim 5 wherein said indicating means for indicating when a predetermined cuff pressure has been reached includes a lamp.

8. The invention as defined in claim 1 in which said stationary record medium is pressure sensitive paper.

9. The invention as defined in claim 5 including spring means mounted adjacent said bellows and said means for effecting rotation of said shaft for acting against the movement of said bellows and including means for adjusting the spring rate of said spring means.

10. The invention as defined in claim 1 wherein said multi-position switch means is operable to control the operation of said circuit means, and is connected to said multi-position pneumatic bleed valve means to permit the use of a single actuator to control both means and thereby control the electrical and pneumatic functions of the apparatus.

Claims

1. An apparatus for measuring and recording blood pressure comprising: a. an inflatable cuff adapted to be applied to the upper third of a limb and having inflating means for inflating said cuff for selectively occluding the flow of blood to the limb; b. a microphone positioned within said cuff capable of detecting Korotkoff sounds occurring within the limb as the pressure in said cuff is reduced; c. electronic circuit means mounted in a housing and connected electrically to said microphone for amplifying and discriminating the signals emanating from said microphone for emitting a digital output signal for each Korotkoff sound; d. a recording device having a stationary record medium and stylus means which is operable therewith, said recording device being electrically connected to said circuit means, and said stylus means being operable upon actuation by the digital pulses emanating from said circuit means for imprinting a single mark on said stationary record medium for each Korotkoff sound; means mechanically coupled with said stylus means for moving e. stylus means relative to said record medium in synchronism with falling cuff pressure such that the position of said stylus means is specifically determined by the pressure in said cuff; f. an adjustable indicating means for indicating inflation of said cuff to a pre-determined pressure above the anticipated systolic blood pressure, said adjustable indicating means being mounted in said housing and connected to said means for moving said stylus means; g. multi-position pneumatic bleed valve means selectively conditionable in a ontrolled-sLow-leak mode for venting of said cuff during the measurement, in a gross venting mode for releasing the pressure from said cuff when the measurement is completed, and in a sealed mode during inflation of said cuff, said valve means being mounted in said housing and connected pneumatically to said cuff; h. multi-position electrical switch means selectively conditionable in a first mode for actuating said indicating means to indicate when the pre-determined cuff inflation pressure has been attained while preventing said stylus means from being actuated, in a second mode to deactivate the said indicating means, and to permit said stylus means to imprint a record of said medium, and a third mode to deactivate said circuit means and said indicating means to disconnect all electrical functions, said switch means being mounted in said housing and connected to said circuit means and to said indicating means; and i. a stationary dial graduated in units of pressure mounted adjacent said record medium to permit interpretation of the marks recorded on said record medium.

4. The invention as defined in claim 1 in which said circuit means is adapted to digitalize only those microphone signals which are within a predetermined range of amplitudes which includes the amplitudes of Korotkoff sounds.

5. An apparatus for measuring blood pressure as defined in claim 1 comprising, a. a rotatable vertical shaft journaled in said housing; and b. a rotor arm supported on said shaft; c. said stylus means comprising a solenoid having a plunger stylus arranged to make impressions on said record medium and supported on said rotor arm; d. said means for moving said stylus means comprising bellows connected by a conduit to said cuff and operable in response to variations of pressure in said cuff, and e. means operatively connected to said shaft and being engaged with said bellows for effecting rotation of said shaft; f. whereby movement of said bellows will effect rotation of said shaft to move said solenoid in synchronism with the variations in said cuff pressure

6. The invention as defined in claim 5 including moveable abutment means mounted adjacent said rotor arm and arranged to be selectively positioned within the range of movement of said rotor arm in relation to different predetermined pressures, and stop means carried on said rotor arm and engagable with said abutment means for limiting the movement of said rotor arm, said indicating means being operable upon contact of said stop means with said abutment means to indicate when a predetermined cuff inflation pressure has been reached.