US3444856A - Blood pressure monitor - Google Patents

Description

y 1969 M; SETTLER ET BLOOD PRES SURE MONITOR Sheet L 0:2

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BLOOD PRESSURE MONITOR Sheet of2 Filed June 24, 1965 Fig.6

United States Patent 3,444,856 BLOOD PRESSURE MONITOR Morris Settler and Bert Settler, Winnipeg, Manitoba, Canada, assignors to Harco Electronics Ltd., Winnipeg, Manitoba, Canada Filed June 24, 1965, Ser. No. 466,602 Int. Cl. A61b 5/10 US. Cl. 128--2.05 2 Claims ABSTRACT OF THE DISCLOSURE An occluding culf having a transducer connected to preamplifier and multi-vibrator circuits to produce impulses for actuating systolic and diastolic aneroid gauges. The gauges have electro-mechanical means for locking the same at systolic and diastolic pressures as a function of the generated impulses.

This invention relates to new and useful improvements in blood pressure monitoring instruments, particularly instruments adapted to be used in conjunction with a conventional occluding cuff.

The conventional method of taking blood pressure of a patient consists of strapping the occluding cuff around the brachial artery area of the patients arm, inflating the cuff to a pressure sufiicient to close off the artery, and then bleeding the pressure from the cuff slowly and at the same time listening adjacent the brachial artery with a stethoscope. As soon as the pressure in the cuif is reduced to a point where the artery may open with the heart pulse, a sound is heard in the stethoscope known as a Korotkoff sound and the pressure reading is taken from one manometer connected to the cuff.

This gives the systolic blood pressure and as the cuff continues bleeding, thus reducing the pressure therein, the Korotkofr" sounds are heard with each systolic heart movement until the artery is fully opened at which time the sounds cease.

At this point the pressure is read on the manometer and this pressure is known as the diastolic blood pressure.

Taking blood pressure readings frequently over long periods requires accuracy, repeatability, and freedom from fatigue.

The present techniques employed in taking a patients blood pressure may be auscultatory, palpatory or oscillometry (indirect methods) and produce variable and inconsistent results which can be attributed to human variability in the listening, recording, bleeding of the occluding cuff, predetermined prejudices, and to the many other areas in the techniques which contribute to the inconsistency of readings.

As mentioned previously, the most common method of taking a patients blood pressure is the auscultatory method using an occluding cuff and stethoscope which requires the operator to listen to the blood pressure sounds, relating them to a falling mercury column or aneroid, make a mental record of the first and last blood pressure sound or Korotkoff sound in relation to mercury column readings and then make a written record of these readings.

This technique can introduce many variables which often differ from one person to another taking the blood pressure readings of the same patient.

The present invention overcomes the disadvantages inherent in the present methods by providing a blood pressure monitor which can be used with an occluding cuff and a transducer in the distal part of the cuff and in which the pulse rather than the Korotkoff sound is utilized. The present method therefore becomes a fifth method of taking the blood pressure.

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Using the occluding cuff and stethoscope, the pressure is supplied to the brachial artery until this artery closes off completely against the systole action of the heart. As the pressure is bled slowly from the cuff, the pressure constricting the brachial artery gradually lessens until the systole impulse from the heart opens the artery momentarily and permits a small quantity of blood to pass through the constriction at which time the artery immediately closes.

It is this passage of the blood through the constricted artery which causes the well known Korotkolf sound. However, it will be appreciated that there is a mechanical distension of the artery and it is this mechanical movement which is picked up by the transducer of the present device.

As the pressure is gradually reduced, the arterial wall is distended with each systole action and the Korotkofi sound is heard until such time as the constriction on the arterial wall is removed completely, at which time, of course, no further Korotkoff sounds are heard. With the stethoscope, this last Korotkoff sound gives the diastolic pressure but in actual fact, the pressure continues to drop gradually until the restriction of the occluding cufl? is removed completely. However, at this point, it will be appreciated that the blood is still under pressure within the artery and that the artery expands slightly upon each systole movement. This relatively small expansion cannot be detected by the stethoscope and is in effect what is known as the threshold pulse. We believe that the threshold pulse pressure and the diastolic pressure are theoretically the same but in actual practice the diastolic pressure is normally read at a slightly higher level due to the lack of instrumentation sensitive enough to detect the movements of the artery between the last detected Korotkoff sound and the threshold pulse pressure.

We therefore believe that our device permits a far more accurate indication of diastolic pressure to be obtained.

This device, which is electronic in structure, monitors blood pressure both visually and aurally and furthermore, when used with the visual embodiment, records and locks the systolic and diastolic pressure on separate aneroid guages automatically so that the readings can be read off or recorded at leisure.

With this present device, the operator is not required to listen or relate sounds to aneroid or mercury levels, neither is he required to mentally record the systolic and diastolic readings. Furthermore, he is not required to make a Written record and is not required to bleed the occluding cuif at an optimum rate as this is preset and automatic in the present device.

The operator can also check his visual readings by employing the aural technique incorporated into the device to confirm the visual readings.

One of the difficulties in the design of a blood pressure monitor is the technique for establishing the proper gain level setting for each individual in order to distinguish between the pulse level of the last blood pressure pulse and the resting or threshold pulse. By employing the aural embodiment of the present device, to establish the level of gain at which the resting or threshold pulse over the brachial artery first fades out, the operator can overcome the problem in question. This setting of the gain level, once established, should be maintained for that particular patient as long as he or she is being monitored visually or aurally.

Another problem relating to blood pressure phenomena is the presence of false signals, spurious noises, or artifacts which the operator or blood pressure monitor may accept as a blood pressure pulse.

In order to minimize the effects of these artifacts,

and the like, a three position step switch is provided which permits the operator to use the blood pressure monitor remote from the instrument and the patient.

Also the step switch permits the operator to energize the machine only during the interval between just beyond the subjects systolic pressure and his diastolic pressure and a little beyond the latter, after which the operator can immediately lock up the readings and not be concerned about spurious or additional noises, false signals, and the like, which would have made the machine give a false reading.

The three position step switch is preferably enclosed within a plastic holder to which is attached the inflating bulb and preset release valve for the occluding culf. With this switch, the operator can abort any false readings that might occur during the critical interval and immediately repeat the inflate, deflate and lock up cycle.

In the inflate position, the cuff is inflated by the bulb beyond systolic pressure. In the deflate position, the machine is energized and awaiting the blood pressure pulses. At the end of the blood pressure pulses, the step switch is manually moved to the lock up position and the readings are locked on the manometers, and remain locked until the step switch is moved to the inflate position and the cycle repeated.

Also incorporated in the present device is a relatively simple method for the locking of the aneroids or manometers. This method does not in any way disturb the operation of the aneroids and it is relatively easy to incorporate a Vernier adjustment so that individual aneroids can be set for positive locking and unlocking.

The aneroid pressure gauges can be recalibrated and adjusted without interfering with the locking mechanism and furthermore, the aneroid gauges can be removed and replaced from the case of the instrument leaving the locking device intact.

Summarizing, the blood pressure monitor and the associated equipment provide means so that the weakest blood pressure pulses can be picked up, amplified, the systolic pressure can be distinguished from diastolic pressure and these pressures can automatically be locked upon the aneroid gauges operated from the blood pressure pulses.

With the foregoing in view, and all those objects, purposes, or advantages which may become apparent from consideration of this disclosure and specification, the present invention consists of the inventive concept embodied in the method, process, construction, arrangement of parts, or new use of the same, as herein particularly exemplified to one or more specific embodiments of such concept, reference being had to the accompanying figures in which:

FIGURE 1 is a Wiring diagram of the electronic circuitry associated with the device.

FIGURE 2 is a fragmentary top view of the step switch, inflated bulb and bleed valve.

FIGURE 3 is a side view of FIGURE 2 sectioned in part to show the interior thereof.

FIGURE 4 is a schematic front view of the instrument within the case showing the aneroid gauges utilized.

FIGURE 5 is an enlarged cross sectional view of the bleed valve per se.

FIGURE 6 is a side elevation of one of the aneroid gauges showing the lock up mechanism.

FIGURE 7 is a fragmentary front elevation of an occluding cuff showing the location of the trandsucer.

FIGURE 8 is a sectional view substantially along the line 88 of FIGURE 7.

In the drawings like characters of reference indicate corresponding parts in the different figures.

The occluding cufI 1 used consists briefly of a band 2 adapted to be wrapped around the patients arm and to be clipped into position in the usual way.

Within the band is an inflatable bladder 3 having an inlet 4 and an outlet 5. Adjacent the outlet 5 is formed a .4 small pocket 6 between one fabric face 7 of the cuff and one side 8 of the bladder 3. This is formed by the stitching across the pocket 6, a piece of elasticized material 9 upon the inner surface of the material 7 as shown in FIGURE 8.

The inlet 4 is connected by means of a flexible rubber hose or tubing 10 to a conventional inflating bulb 11.

The outlet 5 of the bladder is connected to a similar length of hose or rubber tubing to a conduit connection 12 upon the instrument case 13 and is thence connected by internal conduits (not illustrated) to the two aneroid pressure gauges 14 and 15 contained within the casing and having the faces of the gauges showing in the front panel thereof.

A bleed valve 16 is situated between the inflating bulb 11 and the tubing 10 and is shown in detail in FIGURE 5.

It consists of a cylindrical barrel 17 having a drilling 18 extending therethrough and being connected by one end thereof to the bulb, and by the other end thereof to the tubing 10.

A drilling 19 extends through the cylindrical barrel 17 from a shoulder portion 20 to the drilling 18 and the base of this drilling is formed With a conical seat 21 as shown. An air bleed hole 22 extends through the shoulder 20 to the drilling 19 and an adjustable needle valve 23 is screw threadably engaged within the shoulder so that the valve end 24 is situated adjacent the conical seat 21.

By adjusting this needle valve within the shoulder, a constant rate of bleed may be attained from the conduit 18 through the drilling 19 and through the bleed hole 22.

It has been found desirable that a bleed rate of approximately mm. of pressure per 20 secs. is satisfactory. This bleed rate established at between a pressure of m./m. and 75 m./m. on the aneroid gauge.

Once the bleed rate has been set, the needle valve 23 may be sealed within the shoulder so that this constant bleed rate is maintained under all conditions.

It is also desirable to have a quick release valve for relieving discomfort of the patient after the readings have been taken and this is also incorporated within the portion 16.

A further drilling 25 extends through the Wall of the cylindrical portion 17 and reverse conical seating 26 is provided at the inner end thereof. A conical headed valve 27 extends through drilling 25 and the valve normally is seated upon the conical seat 26 by means of the spring 28 thus sealing off this drilling 25.

However, when it is desired to release the pressure rapidly, the head 29 of the valve is depressed thus permitting the air to exhaust from the cuff, back through the tubing 10 and out through the drilling 25.

Also secured to the valve assembly 16 is a three position step switch collectively designated 30 and contained within a plastic block 31. The details of this step switch will be described hereinafter.

The transducer 32 is placed within the aforementioned pocket 6 on the cuff and the cuff is wrapped around the arm so that the transducer is within the brachial artery area. It is then capable of picking up the blood pressure pulses and converting same to electrical energy which is conveyed via a cable 32 to the input 33 of the preamplifier circuit 34 shown in FIGURE 1.

In this connection it is essential that the transducer be placed on the lower side of the occluded portion of the brachial artery otherwise the transducer will pick up the pulse movements of the blood within the brachial artery above the occluded portion. In other words, the transducer should be placed on the side of the occluding portion of the brachial artery remote from the heart.

This pre-amplifier circuit is conventional and utilizes solid state circuitry or transistors.

From the pre-amplifier, the pulses are fed to the multivibrator circuit, collectively designated 34, which produces a train of square pulses. Note should be made of the K resistor situated between the base of the second transistor of the multi-vibrator and B- and also the 1 mf. condenser situated between the collector of the first transistor and the base of the second transistor of this circuit. The choice of values of these two components determine the time constant of the pulse width and we have chosen these values to give a pulse width of approximately 200 milli-seconds.

At this point, the operator has the choice of utilizing this train of square pulses from the multi-vibrator either to the visual portion collectively designated 35 or the aural portion collectively designated 36, the choice being made by the operation of the switch 37.

Dealing first with the aural portion, the signal is fed to the aural driver collectively designated 37 which is conventional in structure and thence to the output amplifier and 1000 cycle oscillator circuit collectively designated 38 which is also conventional.

The resultant amplified output then passes to the output transformer 39 and to either a loud speaker 40 or car phones (not shown) connected at 41 so that the operator can hear the blood pressure pulses and can adjust the intensity thereof by means of the variable resistance 42 in the normal manner.

Dealing next with the visual portion 35, the train of square wave pulses is fed to the diastolic driver portion collectively designated 43 and the systolic driver portion collectively designated 44. In this connection note should be made of the 100 mf. condenser and the 100 ohm re sistor both of which are situated in the emitter portion of the circuitry from the diastolic transistor. These are inserted in order to overcome feedback within the circuit.

The operation of this portion of the circuitry is controlled by the aforementioned step switch which is situated adjacent the inflating bulb 11 and held within the hand of the operator remote from the patient.

The step switch shown in detail in FIGURE 3, consists of a lever 45 pivoted by one end thereof as at 46, to the block 31. A disc 47 moves with the lever and contains an arcuate connecting strip 48 thereon and a contact 49. This contact 49 either connects a common feed 50 to electrical conductors 51, 52 or 53 depending upon the position of the switch. In FIG. 3, the full line position (position 1) shows the electrical conductors 50 and 51 connected together. In the position shown in phantom (position 2) the conduit 50 is connected to conduit 52 and in the phantom position (position 3) the common conductor 50 is connected to conductor 53.

A cable 54 extends from the switch to a male socket 55 shown in FIGURE 1 which can be plugged into the casing in a corresponding female socket 56.

The aforementioned conduit 32 from the transducer 32 is also connected to the socket 56, terminals 5 and 6 being connected to this cable. Internally, terminals 5 and 6 of the female socket 56 connect to the aforementioned input 33.

When the switch is in the inflate position (position 1) and the main switch 57 is in the on position thus con necting the source of power 58 to the circuit, the preamplifier portion 34 and the multi-vibrator portion 34 are in circuit together with the aural section of the device, provided switch 37 is switched to the aural circuit.

However, if it is switched to the visual circuit 35, then the drivers 43 and 44 are open.

When the switch is moved to position 2, terminals 3 and 4 of the socket 56 are connected thus closing the circuit to the systolic driver 44.

As soon as the first impulse is detected from the transducer, the pulse energizes the systolic relay 58. It closes contacts 60 on the systolic relay 58 which places full battery voltage across the systolic relay locking it, also closing the emitter circuit of the diastolic driver closing the diastolic relay 59.

Succeeding pulses do not effect the systolic relay 58 due to the fact that it is held by the full battery voltage by virtue of contacts 60. However, succeeding pulses do momentarily unlock the diastolic relay 59 due to the circuitry connecting same to the diastolic transistor. This unlocking is momentarily only and as soon as the pulse ceases, the relay 59 relocks so that when the last blood pressure pulse is detected, this relay 59 unlocks and subsequently locks at the end of the last pulse, this being equivalent to the diastolic pressure.

At this time, the switch is moved to position 3 thus connecting terminals 1 and 2 of the socket 56 and placing the 4.7K resistor in circuit with the base of the diastolic transistor thus preventing further pulses or spurious noises from unlocking this relay 59.

At this point both the systolic and diastolic relays are locked and will remain locked until the switch is moved to position 1.

The relays 58 and 59 are secured to the aneroid gauges 15 and 14 respectively and the details of this connection are shown in FIGURE 6.

Inasmuch as both relays and gauges operate in a similar manner, only one will be described.

The gauge 15 is contained within a casing 62 having a face plate 63 in the normal manner.

The aneroid pressure responsive portion is not shown as it is conventional. However, this aneroid bellows operates the sector plate 64 carrying indicating needle 65 thereon.

The relay 58 is secured to the back 66 of the casing and the movable plate 67 is hinged to post 68 in the conventional manner.

The movable plate 67 is provided with an extension 69 through which is screw threadably engageable, a finger or plunger 70. The distal end 71 of this plunger passes through an aperture within the back 66 of the aneroid case and this end 71 is normally clear of the sector plate 64 with the movable leaf 67 of the relay in the non-activating position.

However, as soon as the relay 58 is energized, the movable leaf 67 moves downwardly with respect to FIGURE 6 thus permitting the end 7-1 of the plunger or finger 70 to contact the sector plate 64 frictionally and prevent further rotation thereof.

Referring back therefore to previous description, as soon as the first blood pressure pulse is detected by the transducer, the systolic aneroid gauge which has been dropping responsive to the bleed off of the pressure, is locked by the frictional contact of finger 70 to the sector plate 64 thereof.

At the same time a similar result occurs with the diastolic aneroid gauge.

With the diastolic gauge, the relay 59 is being energized and de-energizcd with each pulse so that the needle 65 of the diastolic gauge gradually drops responsive to the drop in pressure from the cuff until the last pulse occurs at which time it remains in the locked position.

By moving the aforementioned switch to the lock (position 3) both gauges remain locked against further pulses which might be caused by spurious noises and the like.

It will be appreciated, of course, that both aneroid gauges are calibrated prior to installation so that they read the blood pressure direction in the normal manner.

However, with the automatic locking mechanism, hereinbefore described, both the systolic and diastolic pressures are shown by the gauges in the locked position.

By maintaining a constant rate of bleed, the blood pressures shown by this instrument will always be relatively accurate and consistent.

Recapitulating the operation of this portion of the device, blood pressure pulses are picked up by the transducer 32 in the cuff placed on the brachial artery. The pulses are changed to electrical signals which are fed into the transistorized amplifier which in turn triggers the multi-vibrator section 34' to produce a pulse train of equal amplitude signals of a square wave nature, so that there is a definite time interval and width allocated to each pulse.

A pulse train is now available, the first pulse occurring at the time the systolic pressure is in the bladder of the 7 culf and the last pulse occurring when the diastolic pressure is in the bladder.

The detection of the systolic pressure is relatively simple inasmuch as the first pulse from the multi-vibrator section 34 energizes the relay 58 thus stopping the movement of the needle of the systolic aneroid 15. This relay remains locked due to contact '60 being closed at the same time so that further pulses from the one shot multivibrator section 34 will not effect this relay.

The detection of the last or diastolic pulse is more difficult and the diastolic pressure is recorded by sampling the pressure in the cuff every time a pulse appears. The di astolic pointer or needle of the diastolic manometer 14 is also locked up when contact 60 is closed by the first pulse.

However, when succeeding pulses appear, the diastolic relay 59 opens releasing the needle 65 of the aneroid gauge 14 so that the needle moves to the new bladder pressure. At the end of the pulse, this relay 59 locks up again due to contact 60 still being closed and waits for the next pulse to unlock it so that the needle may fall to the next pressure. With every succeeding pulse, relay 59 opens and locks up at the end of the pulse so that the last blood pressure pulse unlocks relay 59 and the needle falls to the new bladder pressure and then locks up at the end of the pulse and waits for the next pulse to unlock it. But as no more pulses are present, the diastolic pressure remains locked in this gauge 14. We have also found that it is necessary to establish the proper level of gain for different subjects so that the aural section of the device is used initially. The resting or threshold pulse of the patient is detected by the transducer and the gain control 42 is set back until the resting or threshold pulse just disappears. This gain control consists of a potentiometer situated within the collector circuit of the second stage pre-amplifier transistor. This is the correct level for proceeding with the measurement of the blood pressure. In this connection, note should also be made of the two rnicrofarad condenser in the collector circuit of the second pre-amplifier stage and connected to ground which cuts down the frequency response of the pre-amplifier to approximately 400 cycles per second thus eliminating all extraneous noises such as speech, machinery, and the like which might otherwise affect the operation of the device.

We have found that the device is far more sensitive if the polarity of the coil in the transducer is matched with the transistor used in the first stage of the preamplifier section 34.

In other words, the coil of the transducer should be connected to the input so that a positive signal occurs first if an NPN transistor is used or negative signal if a PNP transistor is used.

The present device is compact, light weight and portable and has been found to be extremely consistent in the taking of blood pressure readings.

The blood pressure monitor has also been found extremely useful in open heart surgery. In normal open heart surgery, the heart is stopped and the blood is supplied to the patient through a machine which circulates the blood at the required temperature and pressure.

Under these circumstances there is insuificient pressure available in the brachial artery to enable the blood pressure to be taken by the conventional method of occluding cuff and stethoscope. Furthermore the ambient noise is normally quite high under these circumstances due to the machinery being utilized in such an operation.

Therefore even if the Korotkoif sounds were present, it is extremely difficult if not impossible to detect same by means of the stethoscope.

By contrast, the present device can detect the pulses without the interference of extraneous noise and the like.

Since various modifications can be made to the invention herein described within the scope of the inventive concept disclosed, it is not intended that protection of the said invention should be interpreted as restricted to the modification or modifications or known parts of such concept as have been particularly described, defined, or exemplified, since this disclosure is intended to explain the construction and operation of such concept, and not for the purpose of limiting protection to any specific embodiment or details thereof.

What we claim as our invention is:

1. In a blood pressure monitoring apparatus, the combination of an occluding cuff including an inflatable bladder and a cover thereon, said cuff being provided between said bladder and said cover with a pocket disposed so that when the cufl? is used the pocket is located on that side of the occluded region of a brachial artery which is remote from the heart, an air pump, a flexible conduit connecting said pump to said bladder for inflating the same, a bleeder valve provided on said conduit for releasing air from the bladder, an instrument casing separate from said cutf, systolic and diastolic aneroid gauges in said casing, a second flexible conduit communicating said bladder with said gauges, a transducer positioned in said pocket of the cuff, an electronic pulse amplifier circuit provided in said casing and connected to said transducer, and electro-mechanical means in the casing responsive to said electronic circuit for locking said gauges at systolic and diastolic pressures, each of said gauges including a rotatable plate, and said electro-mechanical locking means comprising a relay in said amplifier circuit, said relay including a movable contact portion, and a finger connected to said movable contact portion for movement of the finger toward and away from said rotatable plate of the associated gauge, said finger frictionally engaging and locking said plate against rotation when said relay is energized.

2. The apparatus as defined in claim 1 wherein said bleeder valve comprises a valve body provided with a longitudinal bore which communicates at one end thereof with said air pump and at the other end thereof with the first mentioned of said conduits, said valve body also being provided with first and second lateral bores having valve ports at their inner ends in communication with an intermediate portion of said longitudinal bore, the first lateral bore having an orifice vented to the atmosphere, an adjustable valve member provided in the first lateral bore and coacting with the valve port at the inner end of the first lateral bore to discharge air through said orifice at a predetermined restricted rate, a manually operable valve stem slidable in and projecting outwardly from the second lateral passage, and resilient means biasing said valve stem to -a position wherein it normally closes the valve port at the inner end of the second lateral bore, said Valve stem being manually operable against the action of said resilient means to open the last mentioned valve port for quick discharge of air through the second lateral bore to the atmosphere.

References Cited UNITED STATES PATENTS 3,067,617 12/1962 Buck 73-411 3,137,292 6/1964 Richter et a1. 128-2.05 3,148,677 9/1964 Smith 128-2.05 3,188,645 6/1965 Trumpy et a1. 346-33 3,213,688 10/1965- Huston 73-411 2,379,573 7/1945 Gilson 128-205 WILLIAM E. KAMM, Primary Examiner.

US. Cl. X.R. 73-410

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