US 2865365 A
Description (OCR text may contain errors)
Dec. 23, 1958 A. E. NEWLAND ET Ax. 2,855,355
SPHYGMOMETER Filed June ll, 1956 2. Sheets-Sheet 1 A rf/ 5c urz, E. MM f l l @50k/vara Dec. 23, 1958 A. E. NEWLAND x-:T A1. 2,865,355
sPHyGMoMEzTER Filed June 1l, 1956 2 Sheets-Sheet 2 T0 Cl/FF :ma =w @From/frs.
United States Patent 22,365,365 sPHYGMoMETER Arthur E. Newland, Bediord, Vand ,Arthur J. Schul/tz, vIndianapolis, lndgsaidshultz assignor `to said Newland Applicationgluue '11, 1956, Serial No. 590,579 1.3 Claims (Cl,- `1255-.--2-05) Ihisinventionrelates `to sphygrnometers andis particu- 4larly directedto a systemfor electrically indicating and/ or recording true systolic and diastolic blood pressures.
The usual .sphygmomanometen such as a column of mercury,`shows to `the operator -acontinually ,and more or less steadily changing pneumatic pressure within a cut strapped to a limb of the subject. lBy means `of a stethoscope, the operator `estimates from the sounds he hears the instant -the cuit pressure `passes through the systolic and diastolic blood pressure values. Usually readings are taken with decaying cuff pressure so `that the systolic and `diastolic values `are `read in that order. Because of the skill required insensing and interpreting the sounds picked up by thestethoscope, the time-consuming task of reading Vblood pressures has not heretofore been entrusted to unskilled labor. VInasmuch as accuracy of reading blood `pressure depends on the acuity and coordination of both the hearing and seeing senses of the operator, much `is left to be desired for uniform reliable results. The cumber- Vsome methods `of reading blood `pressure are particularly felt in ,the operating room where the anesthetists should ,have continual and directly observable information concerning the subjects blood pressure, yet his attentions are diverted by his many other important duties. Obviously, continual and directreading blood pressure meters would have important advantages at the operating table.
The object of this invention is to provide an improved sphygmometer. The sphygmometer of this invention is automatic in operation in that the device reads the required information directly from an outer surface of a limb of the subject, translates the information into electrical intelligence, and computes and indicates `the blood pressure values, all without the aid of an operator. The sphygmometer of this invention is so self-contained in its operation that an unskilled operator can safely operate it. In fact, it is contemplated in one embodiment of the invention that the subject can assemble the cui to himself,
`close a switch, including, for example, a coin-operated switch, and then read his own blood pressure from meters.
The objects of this invention are attained by applying a pressure transducer to the fluid system of the cui, either pneumatic or hydrostatic, to generate a voltage analogous to the pressure in the cuil. As this voltage is varied and `passes through values corresponding to the diastolic and systolic pressures, the voltage is momentarily sampled and applied to indicating and/or recording instruments. The sampling is under the control of a motion transducer or microphone with associated circuits. These circuits are capable of distinguishing and isolating voltage pulses corresponding to the systolic and diastolic waves at the constriction of a blood vessel, and of `momentarily opening a gate between the pressure transducer and the indicating instrument.
Other objectsand features `of this invention will become apparent to those skilled in the art by referring to the specific embodiments described in the following specification and shown in the accompanying drawings, in which:
Figs. 1, 2 and 3 are, respectively, cross sections of a 2,865,365 Patented Dec. 23, 1958 2 blood vessel with idealized mechanical means V for corn stricting the vessel to various stages of closure;
Fig. 4 is a graph of pulse waves heard. at various values of 'the constriction;
i Fig. 5 is a block diagram of one embodiment of the sphygmometer of this invention; and
' Fig. 6 is `a circuit diagram of one specic embodiment of the invention.
In Figs. l, 2 and 3, theblood vessel or artery 10 is shown in cross section and to represent the two extreme dilated and relaxed positions of the wall caused by the maximum and minimum pressures of a pressure wave originating at the heart. Because of the elasticity lof the vessel, let it be assumed that the wall `is in the position represented bythe dotted line 11 at the lowest point on thepressure wave and that the solid line 12 isthe position of the wall at the peak of the pressure wave. The pressures producing these two positions are called diastolic and systolic, respectively. Next, let it be assumed that `anexternal pressure Pe is applied, as by a piston, to the vessel to squeeze 4the vessel against a bone or solid structure of the body. lf the pressure is increased until the vessel is closed as in Fig. l, `no blood can flow. It will be perceived here that the walls of the vessel are rendered immobile and that no mechanical pulsing force is transmitted to the pressure device Pe. Now, if Pe is gradually `reduced, a minute opening through the constriction first appears and the vessel responds with limited ausculation. The internal and external pressures are equal at this instant. The A.first audible sound that can be heard with a stethoscope may be represented by the `pulse 15 on the pressure Vgraph of Fig. 4, and the pressure in this cuff `at this `instant is termed the systolic blood pressure. As the `external pressure Pe is further relaxed, the pliability of the vessel responds by increased amplitude of ausculation and the pulse amplitude heard graduallyincreases as shown in Fig. 4. The maximum mechanical pulse amplitude occurs, transmitted to the plunger Pe, as shown in Fig. 2, when the external pressure is just sufficient .to feel and follow the motion of the walls of the vessel throughout its travel from the fully relaxed to fully dilated diameters 11 and 12. Still further reduction in Pe causes the pressure device to lose Contact with the vessel and the pressure waves heard at the stethoscope or in the cuff suddenly cease.
According to this invention, a voltage analogous to the sphygmometer values is sampled and recorded at the instant the systolic pulse 15 appears and again immediately after the last diastolic pulse 16 appears. In Fig. 5, a pneumatic cuff Zi is shown, the most familiar type comprising a strong inelastic cloth band for encircling the forearm, wrist, finger, or other extremity of the subject. Inside the band is a pliable rubber tube or cavity communicating through the inilexible hose 21 to the pump 22. The pump 22 may, if desired, comprise the well known bulb with a 24 for inflating the cavity in the cuff and constricting the limb therein.` The specific structural details of the cuit and pump are immaterial to the understanding of this invention, the only requirement of the mechanical system being that sulcient pressure can be applied to the limb to completely throttle the flow of blood, and that there be a valve for controllably relieving the pressure. The pump, if desired, could be power-driven and of the reciprocating or steadydiow gear type with suitable pressure-safety devices. While a pneumatic or air system will be referred to hereinafter, incompressible liquids could, if desired, be employed.V
The pressure transducer 3i) communicates with lthe pneumatic system for translating the pneumatic pressure to its electrical analogue. The inertia of the pressure transducer will ordinarily be sufcient to mask minor noise` pulses as well as the heart pulses, resulting ina 3 steady output voltage completely under the control of the pump 22 and the relief valve 24. Accordingly, the output voltage from the pressure transducer in normal operation may be sawtooth in shape, with the slope of the wave decaying with time.
Also communicating with the pneumatic system is the motion transducer 40, the output of which are voltage waves corresponding to the pressure waves shown in Fig.` 4. The sensitivity of the motion transducer is adjusted and its output is so filtered at 41 that the heart pulses only are passed, devoid of spurious body and ambient electrical noises.
The gate 50 selectively passes an instantaneous sampled voltage from the transducer to the indicating instrument 60, through the isolation amplifier 61, this instantaneous value preferably being stored in the condenser-type memory device 62 to hold the needle deflection for sufficient time for reading or recording. The gate 50 is closed to isolate the pressure transducer from the meter and is opened to pass the transducer signal to the meter. Control of the gate is effected by the output of the motion transducer 40. 1n the particular system contemplated m Fig. 5, the filtered pulse of the motion transducer is amplified at 70, limited and shaped at S0, differentiated at 90, applied to the multivibrator 100, and then applied to the primary or control circuit of the gate 50. Once the-gate has opened, it is thereafter quickly closed by the multivibrator and locked out. Hence, the systolic pulse 15, Fig. 4, operates the gate so that the systolic pressure only is recorded at meter 60,
The gate 98 is thereafter opened to pass a signal from the pressure transducer to meter 60a when the motion transducer and its circuits recognize the diastolic pressure. Pulse 16 is characterized by the absence of any pulse, or by a vastly reduced pulse, immediately followlng pulse 16. By circuits which will be described in detail hereinafter, the output of the motion transducer 40 is filtered at 41 to eliminate all background or noise signals. The filtered pulses are amplified at 70a and again at amplifier 91. The `control bias of amplifier 91 may be adjusted by the threshold or limit set device 92 to establish the minimum pulse voltage which will pass the amplifiers. After rectification at 93, the pulse is passed through the RC time constant circuit 94 to theamplifier 96 and in parallel to the lockout amplifier 97. Amplifier 96 opens the gate 98 to pass the pressure transducer voltage to the indicating instrument 60a, while lockout amplifier 97 immediately thereafter closes the gate. As in the case of the systolic channel, the memory cell 62a stores the pressure transducer voltage of short t duration passed by the gate. Where the memory cell is a condenser, the isolation. amplifier 61a prevents discharge thereof and holds the meter reading at 60a for reading or recording.
Systolic keyer circuit The block diagram of Fig. is expanded in Fig. 6 to show one example of the principal circuits which may be used. The first feeble pulse 15, Fig. 4, detected as the cuff pressure reduces, is taken as an indication that this eX- ternal pressure is equal to the highest or systolic blood pressure. The pressure transducer may consist of an aneroid type bellows 31 mechanically coupled to the sliding Contact 32 of the potentiometer 33. The voltage at 32 is thus proportional to the pneumatic cuff pressure at all times. This voltage is applied to the meter 60 through the normally open contacts a of relay 50 which contacts are1 momentarily operated in response to the systolic pu se.
The motion transducer 40 may consist, for example, of a carbon button microphone held in contact with the cuff or with the line 21 communicating with the cuff. It is important, of course, that the line 21 be inflexible so that the impedance between the microphone and the cuff be at a minimum. Pulses detected by the motion 4 transducer are coupled by way of coupling condenser 42 and leak resistance 43, through rectifier 44 to the adjustable coupling potentiometer 45, and hence to the control grid of class C amplifier 70. Rectifier 44 is polarized to permit only a negative going signal to be applied to the grid of amplifier 70. Resistances 45 and 46 are the load for diode 44 which preferably is of the crystal type. Note that the mid-point of the load resistance 45-46 is connected to ground through normally closed contacts b' of relay 50. This connection makes amplifier 70 receptive to signals. Amplifier 70 is connected as a pentode limiter so that the output thereof is a positive going square wave across plate load 71. Adjustable resistance 45 of the coupling potentiometer permits setting the correct signal level to the amplifier. The square wave is differentiated by the circuit consisting of condenser 80a and resistance 80b causing a sharp positive going pulse to be applied to the grid of tube 102. Tubes 102 and 103 are intercoupled as a one-shot multivibrator, cathode-coupled. The multivibrator is monostable and in the embodiment shown, tube 102 is normally non-conducting while 103 is normally conducting so that the positive going pulse applied to 102 causes the multivibrator to generate a powerful positive square pulse in the anode circuit of 102. The duration of the pulse, as well known, may be controlled by appropriately adjusting the time constants of the RC circuits of the multivibrator and/or by the bias adjustments of the triodes.
Since 102 is normally at cut-off, the winding 51 of,
relay 50 is de-energized and the contacts thereof stand open. When the positive pulse is applied, 102 is made to conduct momentarily, the multivibrator cycling on and off quickly, and the contacts a and b positively close and open. Two things happen when contacts a and b close. First, the direct current analogue from the pressure transducer is connected to the memory capacitor 62 and to meter through contacts a. Second, contacts b cause relay 50a to cycle. l50a would immediately return to open condition but its contacts a cause the relay to lock in. Switch S1 has been closed by the operator at the beginning of the test. When 50a locks in, its contacts b open, removing the grounded connection to the center point of coupling potentiometer 45-46. This permits the high negative cut-off voltage 48 to be applied to the control grid of amplifier 70. Thus is cut off and will accept no more pulses, only the first feeble pulse being operative and the following pulses being cut off. This insures that the first pulse 15 only is recorded on meter 60.
The system is unlocked and restored to alert by opening switch S1. S1 may be opened, for example, by the operator or by a motor-driven cam, not shown. The motor for operating the primary pump coupled to the cuff may be used. When S1 opens, 50a unlocks, permitting a' to open, b to close and removal of the cut-off bias `on 70, thus making 70 again receptive of pulse signals from 40. The resistance 46 is to prevent shortcircuiting the bias supply 48 when contacts b are closed.
The grids and plates of 102 and 103 are RC crosscoupled as in ordinary multivibrators but coupling from the plate of 103 to the grid of 102 is omitted. Instead, the cathode resistor 104, common to both cathodes, couples the stages. 103 operates as a cathode follower so that changes in its grid voltage are repeated in the cathode circuit, thus affecting the cathode voltage of 102. While a multivibrator has been chosen for the purposes of illustration, it will occur to those skilled in the relay art that drop-out relays, annunciators, gas tubes, and the like may be employed alternatively.
Dastolz'c recording system It is now necessary to sample and record the voltage output from the pressure transducer at the time the pulse output of the motion transducer suddenly drops to zero or to a low level. The pulse signals from the motion transducer are received and fed to the grid of the amplifier 70a by way of a level control potentiometer 70b. The signal is amplified and fed into the grid of 91. Now, the grid of 91 is biased very negatively, by `potentiometer 92. When the input wave amplitude isbelow the bias level, no output signals are obtained. When, however, the input pulse becomes larger than the bias voltage, output pulses are obtained from the stage. The output pulses are negative going andare coupled to the crystal rectifier 93, so connected as to produce a negative charge on condenser 95, which charge is also applied to tube 96. As long as the grid of 96 holds the plate current of 96 down to zero or a low level, the winding 98 of the relay shown will not operate the contacts c, d and e. When the charge leaks off of 95 via resistance 110, the connected grid goes positive, plate current flows, and the relay operates. Contacts c close circuit and apply D. C. from the pressure transducers to `memory cell 62a. Contacts e also close and energize the winding of relay 111. Contacts d open and a cutoff bias voltage is applied to 96 whereupon the plate current of 96 drops suddenly to zero and winding 98 goes dormant.
When winding 111 energizes, contacts f open which continue to apply the cut-ofl bias to 96.` Contacts g, however, lock 111 in energized condition. Opening S2 restores the circuit.
It should be noted that at the very start of the above mentioned cycle, there is no negative voltage across 95, therefore tube 96 would draw high current and 98 would re immediately when S2 was closed. To prevent this, a third relay 112 is used. The grid of tube 113 is positive and the tube conducts, keeping winding 112 energized and its contacts h open to prevent plate voltage from bein'g applied to 96. Now let weak pulses to be applied from the motion transducer to the tube91. These pulses gradually increase in amplitude. When the amplitude of the pulses becomes greater than the bias on' 91, condenser '95 begins to charge up. Circuit voltage levels are so chosen that 96 is biased to cut off prior to the time when the grid voltage on tube 113 sets sufciently negative to all-ow 112 to go domant and close contacts h. In this manner, it is assured that 96 is cut olf prior to the application of its B-lvoltage. A condenser across winding 98 assures a smooth cycling action due to its holding the charge on 98 for a short period. lt should be noted that 112 will open after cessation of pulses and at the time the grid at 113 becomes positive, thereby to prevent too rapid an action of 112, and to assure that 112 will not open prematurely and disable the circuit. Condenser 1141 holds the charge on the grid of 113 for a time suicient for 98 to go through its cycle. A little later, the charge Ion 114 leaks off via 115, and 112 opens removing B-lfrom 96 after the cycle has been completed.
ln this system we have satisfied the requirement to identify the correct period when cycling should take place and eliminated the ambiguity caused by the two periods when the bias voltage on 96 is in a positive condition.
Re-set conditions As noted above, the switches S1 and S2 are employed in locking circuits which must be opened at the proper time to cause resetting of the system to a condition of rest, awaiting a next cycle of operation.
After the cuff has been adjusted to the arm or wrist of the subject, a start switch, not shown, is closed to start the motor for inflating the cuff. This start switch may be manual or coin-operated. During the first 15 second interval, say, the motor must elevate the pressure in the lines and cuff to approximately 200 mm. Hg. Switches S1 and S2 are then closed as by means of a cam driven by the motor. When the pressure is at maximum, a switch on the cam could open the bleeder valve a predetermined amount, unclutch the pump, and apply power to the recording circuits. The bleeder valve allows the air or fluid to escape from the cavity for a period, say, 30V sec onds. A highpressure relief valve acts as a safety device to prevent excessive pressure building up. As the Cpressure falls, the escaping lluid must be captured. A storage tank is provided for this purpose. A line from the tank returns to the input side of the pump anda check valve prevents Huid from entering on the high side of the pump. The safety valve also exhausts into the storage tank.
In' order to prevent blowing up the cavity excessively, a safety switch is `provided in the cuff or wrist fixture. The system will not start functioning until the arm or limb has been properly assembled, even though the coin or operate switch has been closed.
During `the thirty second period, while the pressure decays slowly, the systolic blood pressure `is measured first and the diastolic second. Provision is made to permit the systolic system to operate but the diastolic to be inoperative during this period. This control is due to the fact that the diastolic system is so designed, as by choice of voltages, time constants, et cetera, that it normally will not function on the first feeble pulses.
After the diastolic measurement has been made, the various switches restore the system to normal, bleed off all charges, resetting meters to zero and turning o circuit power supply. The heaters of the tubes are always on but the D. C. power load is always fully disconnected when the system is not in use. The 'heat from the tubes is used to keep the oil in the line above a cold viscous level.
Filters Because the pulse wave is made up of a multiplicity of sinusoidal wave forms and because it will vary from subp ject to subject due t-o several physical causes, the pulse must betcleaned up and shaped by means of a lter prior to use. Since the pulse rate may be as low as 50 P. P. M., it can be seen that `this frequency is less than one cycle per second. This is an extremely low frequency and is diicult to handle by conventional A. C. ampliers. 1f
esired, the pulse information may be chopped to facilitate amplification'.
While conventional radio tubes have been shown `in Fig. 6, it will appear that all of the amplifying functions could, with equal facility, be performed by transistors energized entirely by lightweight portable batteries. Accordingly, the sphygmometer of this invention could be packed in a carrying case about the size and weight `of the well known physicians blood testing kit.
lf the sphygmometer of this invention is coin-operated, it could be placed at the disposal of the public in general. In such a case, the pressure source for inflating the cuff would be a motor-driven pump as suggested above with suitable safety valves and of pre-set bleeder or relief` valve for predetermining the rate of decay of `pressure in the hydraulic art pneumatic system. The cui in such a machine would preferably be of a simple `type for partially encircling the wrist of the subject with a rubber or articulated plunger for pressing against :the 4radial artery of the wrist. Upon closure of a power switch, amplifier circuits are energized and the pump started. When the maximum pressure has been reached, the: motormay `be stopped by a cam-operated switch on the motor or by the pressure relief valve in the hydraulic system. Thereafter, the pressure starts to decay and the machine samples the pressure transducer voltages and feeds those voltages to the meters 6@ and 69a in response to the pulse signals from the microphone, as described.
By cycling the cuff pressure through its extreme range of pressures between, say, zero and 200 mm. of Hg, at regular intervals of about two minutes, and by holding the readings on the meters 6@ and 60a, the effect of continuous automatic blood pressure testing is obtained; this, without the disadvantages of co-nstricting the flow of blood for long periods of time, with attending .physio logical changes, in the limb below the constriction. The
advantages to the anesthetist at the operating table become obvious. g
Since the specific embodiments of this invention have been described for the sole purposes of demonstrating the principles of the invention involved, these specic embodiments are not to be construed as limitive of the invention.
The invention claimed is:
1. In combination in a sphygmometer, a cuff for encircling a limb of the body the blood pressure of which is to be measured, the cuff including a pneumatic or `hydraulic system for completely constricting and stopping the blood flow past the cuff, a motion transducer responsive to wave motion in the cuff for generating a voltage wave analogous to the Wave motion, a pressure transducer responsive to the pressure in said system for generating a voltage wave analogous to the pressure; a pump for inating the system to predetermined pressure, and a valve for linearly relieving said pressure; two meters, two normally open gates for instantaneously and selectively coupling said meters to the pressure transducer, and means responsive to voltage signals characteristic of systolic waves in the output of said pressure transducer for instantaneously closing one gate, and means responsive to voltage signals characteristic of diastolic waves in said output for instantaneously closing the other gate.
2. In combination in a sphygmometer, a pressure transducer for generating a voltage analogous to a fluid pressure which is in turn related to a constriction pressure on the body of a subject, an indicating meter, a
normally open gate for applying said voltage to said indicating meter; and a microphone responsive to said pressure, and means responsive to pulse information of the microphone for closing said gate.
3. In combination in a sphygmometer, a fluid operated cuff for constricting a limb of the subject to be tested and sensing blood pressure in the limb, a pressure-tovoltage transducer and a motion transducer coupled to the fluid system of said cuff, two meters, and gates for, respectively, applying two voltages to said meters in response to two characteristic signals from said transyducers.
4. In a sphygmometer, a pressure transducer, a motion transducer, an indicating instrument, a relay with a'secondary circuit coupled between the pressure transducer and said instrument, a multivibrator coupled to the primary circuit of said relay, the input of said multivibrator being coupled to said motion transducer.
5. In a sphygmometer, a motion transducer, a class-C amplifier coupled to said transducer, a grid bias source coupled to the control grid of said amplier, relay contacts for shorting said bias source, a gate, the control of the gate being coupled to the output of said amplifier, said short circuiting relay being responsive to said gate to operate the bias circuit and disable the amplier when y a single signal has been passed by the amplifier.
6. `In combination in a sphygmometer, a pressure transducer, a motion transducer, a voltmeter, a relay with contacts connected between the pressure transducer and said voltmeter; a pulse generator coupled to the winding of said relay, the input of said generator being coupled to and responsive to the pulse output of said motion transducer, and means for disabling said coupling immediately after activation of said generator.
7. In combination in a sphygmometer, a pressure-to voltage transducer, a motion-to-voltage transducer, voltage meter means, a first circuit means responsive to voltage pulses from said motion transducer characteristic of )systolic pressure waves, second circuit means responsive to voltage pulses characteristic of diastolic pressure waves, gate means with a controlled circuit coupled between said pressure transducer and said meter meansfor sampling pressure voltage and applying the sampled voltage to said meterkmeans, said first and second circuit means coupled between said motion transducer and the controlling circuit of said gate.
A 8. The sphygmometer dened in claim 7 further comprising a condenser for storing said sampled voltage, an isolation amplifier with high impedance input connected across said condenser, said meter means being connected to the output of said amplifier.
9. The sphygmometer defined in claim 8 further comprising a bridge circuit in the meter-to-amplifier coupling with the meter across one diagonal of the bridge so that J'the meter can be adjusted to zero for quiescent no-signal current in the ampliiier, and with the amplifier plate impedance in one arm of the bridge to unbalance the bridge.
l0. In combination in a sphygmometer, a pressure transducer, a motion transducer, meter means responsive to and calibrated in terms of diastolic pressure, a first amplifier biased to respond only to pulse voltages greater than a predetermined amplitude, a second amplifier normally conductive, a rectifier and a time-constant R. C. circuit `coupled between said first and second amplifier to block said second amplifier while pulses are applied and to unblock said amplifier when pulses cease, and a gate with a controlling circuit in the output of said second amplilier, the controlled circuit of the gate being connected between said meter and said pressure transducer.
11. The sphygmometer defined in claim 10 further comprising relay circuits responsive to the output of said second ampliiier coupled to the input of said second amplifier for blocking and locking out said second amplifier. l
12. In combination in a sphygmometer, a cuff for applying constriction pressure to the body of a subject, an indicating electrical meter operatively associated Withsaid cui for indicating pressure within said cuff, a microphone operatively associated with said cuff and responsive to pressure pulsations therein, and means operatively associated with said microphone and said meter selectively n operative to actuate said meter in response to systolic ypressure in said cuff.
13. In combination in a sphygmometer, a cuff for applying constriction pressure to the body of a subject, an indicating electrical meter operatively associated with said cuft for indicating pressure within said cur, a microphone operatively associated with said cui and responsive to pressure pulsations therein, and means operatively associated with said microphone and said meter selectively operative to actuate said meter in response to diastolic pressure in said cuff.
Gilford and Broida: Electronics, October 1955, pages -134 inclusive. (Copy in Division 55.)