US3308811A - Sphygmometer - Google Patents

Description

March 14, 1967 F. N. GILLETTE ET AL 3,308,811

SPHYGMOMETER Filed March 30, 1964 5 Sheets-Sheet 2 37 38 39 PUMP UP SYSTOLE DIASTOLE FIG; 2

SI 52 53 54 55 58 59 46W 14w Mr SHAPER SMOOTHER FF FF FROM 7 7 AMP. 29

62 W F/ 6 3 OUTPUTS PUMP uP QUIET SYSTOLE DIASTOLE F IG. 4

INVENTORS FRANK N. GILLETTE JOHN w. GRAY BY ARVID w. JACOBSON ATTORNEY.

March 14, 1967 Filed March 30, 1964 F. N. GILLETTE E l.

SPHYGMOMETER 5 Sheets-Sheet 5- ATTORNEY.

March 14, 1967 GlLLETTE ET AL 3,308,811

SPHYGMOMETER' Filed March 30, 1964 5 Sheets-Sheet 4 r. L FROM Ldclc CKT 32 ISI I 34 INVENTORS FRANK N. GILLETTE JOHN w. GRAY BY ARVID w. JACOBSON ATTORNEY.

March 14, 1967 F. N. GILLETTE ET AL 3,308,811

SPHYGMOMETER 5 Sheets-Sheet 5 Filed March 30, 1964 N? .56 JOmkZOo 20mm mm C6 5528 205 EN EMILE 20mm INVENTORS FRANK N. GILLETTE JOHN W. GRAY BY ARVID W. JACOBSON ATTORNEY.

United States Patent 3,308,811 SPHYGMOMETER Frank N. Gillette and John W. Gray, Pleasantville, and Arvid W. Jacobson, Millwood, N.Y., assignors, by mesne assignments, to Smith Kline & French Laboratories, Philadelphia, Pa, a corporation of Pennsylvania Filed Mar. 30, 1964, Ser. No. 355,610 10 Claims. (Ql. 1282.05)

This invention relates to apparatus for automatically determining the systolic and diastolic blood pressure of a human subject.

It is well known that arterial blood pressure varies during the cycle of each heart beat between a maximum value called the systolic pressure and a minimum value called the diastolic pressure. In the most common present technique -for determining blood pressure the physician wraps a pressure cuff around the patients upper arm and raises the pressure in the cufl to a level above the systolic blood pressure of the patient thereby cutting oil the flow of blood completely. He then allows the pressure to diminish slowly and as it diminishes listens with a stethoscope to the sounds originating in the artery below the point of cutoil. At the same time he observes pressure on a manometer or other suitable gauge connected to the cuif. At the highest pressure there is no blood fiow through the artery and there is no sound. When the pressure falls below the systolic blood pressure level, blood flows through the constriction at the maxima of the heart pressure pulses. As the pressure reduces further, blood flows throughout a larger and larger portion of the pressure cycle. Finally, when the pressure is lower than the diastolic blood pressure the artery is open through the entire cycle and blood flow is uninhibited.

During this pressure cycle the physician hears nothing at all above the systolic level. He hears pulses which vary in amplitude and character when the pressure lies between systolic and diastolic levels. He again hears nothing when the pressure is below the diastolic point.

At a pressure level a few millimeters above the diastolic pressure the sound changes in character acquiring a mufiled characteristic that is easily detectable by a skilled physician. The pressure at which this Occurs is generally termed the onset of muflling.

According to all common practice the pressure level at which the first sound is heard is called the systolic pressure. The diastolic point is defined either as the cessation of sound or as the onset of mufiling depending upon the conviction of the physician taking the readings.

Machines have been made in the past to read blood pressure automatically. In general, they have included the usual cuff and-a manual or automatic pump which inflates the cuff to occlude the artery. A typical machine includes two pressure gauges to monitor the pressure in the cuff, each including a valve which may be closed at an appropriate time to hold the indicator constant. The stethoscope is replaced by a microphone which generates pulse signals as blood passes through the stoppage. The output of the microphone is amplified, passed through a filter to minimize extraneous sounds such as the rustling of clothing, and passed to a control circuit. The latter circuit responds to the occurrence of the first pulse to close the valve to the systolic guage and responds to a cessation of pulses to close the valve to the diastolic 3,398,811 Patented Mar. 14, 1967 gauge. The difficulty with a machine of this kind is that it responds solely to cessation of sound rather than to the onset of muflling and correspondingly no combination of amplifier gain and threshold setting provides correct results for all subjects.

It is a general object of the present invention to provide an improved sphygmometer for detecting systolic and diastolic pressurer Another object is to provide a sphygmometer which consistently gives the same results as obtained by a physician even when operated by a technician.

A more specific object of the invention is to determine by automatic means the pressure corresponding to the onset of mufiling and to present this as the diastolic pressure.

Briefly stated, the invention is based on the discovery that the sounds indicative of systolic and diastolic pressures lie in different frequency bands. Accordingly, the invention includes the usual pump, cuif and microphone for monitoring sounds. The output of the microphone is passed through a filter which passes a first band of frequencies until the systolic point is determined whereupon the characteristics are changed so as to pass a second band of frequencies which enables the diastolic point to be determined more accurately. Additionally, if the sound level is unusually high, as it is for some patients, the gain of the system is automatically reduced after the systolic point has been passed.

For a clearer understanding of the invention reference may be made to the following detailed description and the accompanying drawing in which:

FIGURE 1 is a schematic block diagram of the apparatus in accordance with the invention;

FIGURE 2 is a diagram useful in explaining the invention;

FIGURE 3 is a schematic block diagram of the logic circuit shown in FIGURE 1;

FIGURE 4 is a table showing the operation of the logic circuit;

FIGURE 5 is a schematic diagram of the logic circuit shown in FIGURES 1 and 3;

FIGURE 6 is a schematic diagram of the high pass filter and control circuit; and

FIGURE 7 is a schematic diagram of the amplifier and control circuit.

Preliminary investigation of the problem has shown that the sound of interest lies in a band of frequencies from 30 to c.p.s. Detection of the systolic pressure is comparatively easy because the sounds represent the difference between no noise and some noise. The diastolic pressure is more difiicult to detect because it is not a sharply defined point. The only criterion for operation is that the machine shall give the same result as is obtained by a physician. A more thorough investigation has led to the following observations:

(1) All of the energy of interest for the determination of both the systolic and diastolic points is transmitted through a sharp cutoff filter with its normal end points at 30 and 100 c.p.s.

(2) The diastolic point is the pressure at the onset of muffiing and after the onset of mufiling the energy that would pass through a sharp cutoff filter .with the end points lying at 50 and 100 c.p.s. is very small. There remains significant energy below 50 c.p.s. and it is this which must be ignored by a machine to detect the onset.

of mufiling.

(3) At the systolic point the pulses have not enough energy in the narrower band for dependable detection. The total energy down to the 30 c.p.s. cutoff is required.

(4) Some individuals have a very high sound level. For these, the energy passing through the narrow filter after the onset of mufiling may still be enough to fool the machine. For such subjects a reduction in system gain appears desirable.

Some persons develop a very low signal level for quite a while after the systolic point. All of the energy in the pulse is required for dependable operation in this region.

From the above observations it has been concluded that a satisfactory machine must operate in the following manner:

(1) There must be a narrow band filter having its upper end point at 100 c.p.s.

(2) ,The filter must have two end points at the low end, one at 30 c.p.s., the other at 50 c.p.s., with means for switching between them.

(3) The machine must have fairly high gain to work reliably with low input levels.

(4) There must be means for reducing the gain in the presence of a very high level input.

, (5) At the start of a reading the gain must be high and the filter must be set to the 30 c.p.s. end point.

(6') When the systolic point is reached the filter end point must shift to 50 c.p.s., but after a delay sufiicient to cover the period of low signal level mentioned above.

(7) If a high amplitude signal appears and holds for two or three pulses the gain must switch to a level perhaps one-third or one-half of maximum and must stay at the low level until the diastolic point has been detected.

Referring now to FIGURE 1 there is shown the usual cuff 11 wrapped around the arm 12 of a patient. Positioned within the cuff beyond the point of occlusion is a microphone 13 which monitors the sounds of blood through the artery and generates signals indicative thereof. A pipe 14 connects the cuff to a suitable pump such as the usual bulb 15 used to inflate the cuff. A relief valve 16 may be opened after full pressure has been attained so as to release the pressure at a uniform rate. Also connected to the pipe 14 is a pressure responsive actuator 17 which is connected to two switches 18 and 19. When the pressure rises to a low value such as 15 low pass filter 26 having a cutoff frequency f in the range from eighty to one-hundred twenty cycles per second, which is preferably 100 c.p.s. The filter 26 is connected to a high pass filter 27 the cutoff point of which is normally at a frequency f in the range from twenty to forty cycles per second, preferably about 30 c.p.s. but which may be switched by application of a suitable signal from a control circuit 28 to have a cutoff frequency of f in the range from forty to sixty cycles per second, preferably about 50 c.p.s. The output of the filter 27 is connected to an amplifier 29 the gain of which may be switched from a high value to a low value upon application of a suitable signal from a control circuit 31. The amplifier 29 is connected to a logic circuit 32 which generates suitable output signals on the conductor 33, 34, 35 and 36 as will be more fully explained.

Referring now to FIGURE 2 there is shown schematically the sequence of operations. When the pump 15 is operated the microphone 13 generates signals shown by the waveform 37 due to the fiow of air into the cuff and these signals continue until the end of pump-up when a period of quiet follows, indicated by the line 38. The relief valve 16 is opened at this time allowing the pressure to fall gradually until a point is reached in which blood spurts through the stoppage. The pressure at this point is the systolic pressure. Flow continues in spurts as the pressure is further decreased causing additional signals to be generated as shown by the waveform 39 until a point is reached at which the sounds, irf heard in a stethoscope, would begin to be muffled. The pressure at this time is the diastolic pressure.

Referring again to FIGURE 1, as soon as power is applied by the operation of the pump 15, the actuator 17 and the switches 18 and 19, a warning lamp 41 is illuminated. At the end of pump-up the logic circuit 32 generates a signal on the conductor 33 which actuates a lamp control circuit 42 which extinguishes the lamp 41 and also generates a signal on a conductor 43 which is passed to the control circuit 31. When the systolic point is reached the logic circuit 32 generates two signals, one on conductor 34 and one on conductor 35 indicative of this point. It would be possible to utilize but a single control signal but in the particular circuit being described millimeters of mercury, the actuator 17 closes the switches 18 and 19 thereby connecting the batteries 21 and 22 into the circuit to activate the machine.

Two pressure gauges 23 and 24 are also connected to the pipe 14 and are provided to indicate systolic and diastolic pressure respectively. Each of these gauges is of the kind whose indication may be locked at any time upon the application of suitable signals. One suitable kind is described in the copending application of John W. Gray, Arthur F. Hayek and Arvid W. Jacobson, Jr., Ser. No. 313,351, filed Oct. 2, 1963, for Lockable Meter, which application is assigned to the same assignee as is the instant application. Briefly, the cited application describes a pressure gauge provided with an electromagnet which attracts a magnetic disk fastened to the pointer shaft and clamps it to the frame thereby locking the indicator. Such an arrangement is illustrated schematically in FIG. I wherein electromagnets 23' and 34' are shown mechanically connected to the gauges 23 and 24 respectively.

The microphone 13 is connected to an amplifier 25 the principal purpose of which is to provide a. low impedance source for the signals generated by the microphone 13. The amplifier 25 is connected to a bandpass filter which passes a band of frequencies extending from either one of two lowfrequency limitsto a highfrequency limit. As shown in FIGURE 1 the bandpass filter comprises a two complementary signals have been found to be con-.

venient and accordingly two are shown. The signal on the conductor 35 operates a drive circuit 44 which controls the electromagnet 23 which in turn locks the systolic gauge 23. The systolic signal on conductor 34 is delayed by about five seconds by a time delay circuit 45 after Which a signal is passed by a conductor 46 to the control circuit 28. Upon receipt of this signal the control circuit 28 actuates a switching mechanism in the filter 27 which changes the cutoff point from f to f that is, from 30 to 50 c.p.s. Additionally the control circuit 28 gencrates an enabling signal on the conductor 47 which is passed to the control circuit 31. The control circuit 31 is inactive until it has received signals from both the conductor 43 and the conductor 47 whereupon it becomes active. The output of the gain control amplifier 29 is: also connected to the control circuit 31, and, if the signal exceeds a predetermined amplitude, a switching circuit within the amplifier 29 is operated so as to reduce the gain by a factor of two.

At this point the systolic pressure has been indicated, the cutoff point of the filter 27 has been switched and, it the signal is at a high level, the gain of the amplifier 29 has been reduced. Signals continue to flow to the logic circuit until the diastolic point has been reached whereupon a signal on the conductor 36 operates a drive circuit 49 which controls the electromagnet 24' which in turn locks the diastolic pressure gauge 24.

FIGURE 3 shows the logic circuit in block diagram form. The signals from the amplifier 29 are irregular in form as indicated by the waveform 51. These signals are applied to a shaping circuit 52 the function of which is to generate a series of pulses of uniform width and uniform amplitude as indicated at 53. The circuit 52 may be a conventional monostable multivibrator in which each of the irregular pulses 51 triggers the circuit to its unstable state. The circuit reverts to its stable state after a time delay determined by the constants of the circuit which in this case may be approximately one-quarter of a second. Such a multivibrator circuit is well known and need not further be described.

The pulses 53 are applied to a smoothing circuit 54 the function of which is to generate a single long pulse such as the pulse 55 as long as the train of pulses 53 continues and which ends upon an interruption in the train of pulses 53. This circuit will be more fully described. The pulses 51, 53 and 55 occur during pump-up and similar pulses also occur during the period between the systolic and diastolic point.

The pulse 55 is applied to a flip-flop circuit 58 which is triggered to one of its states by the leading edge of the pulse 55 and is triggered to its opposite state by the trailing edge of the pulse 55. The flip-flop 58 is connected to a second flip-flop 59 and triggers this second flip-flop only upon the completion of a full cycle of operation of the flip-flop 58.

FIGURE 4 indicates the condition of the flip- flops 58 and 59 at various steps of operation. The flip-flop 58 initially has outputs 0, 1 on conductors 61 and 62 respectively and this condition continues until the end of pumpup whereupon conditions are reversed. The condition of the flip-flop 58 again reverses at the systolic point and yet again at the diastolic point as indicated in FIGURE 4. The flip-flop 59 has outputs of 0 and 1 on conductors 63 and 64 respectively during both the pump-up and quiet periods. At the systolic point the conditions reverse and the conductors 63 and 64 carry outputs of 1 and 0 respectively for the remainder of the cycle as indicated in FIGURE 4.

Referring now to FIGURE 5, there is shown the shaping circuit 52 the output of which is coupled by a capacitor 71 to the smoothing circuit which consists essentially of the transistors 72 and 73 and their associated circuitry. The collector of the transistor 72 is connected through a resistor 74 to the negative source; the base is connected through a resistor 75 to the positive source; and the emitter is connected through a resistor 76 to the positive source. The collector of the transistor 73 is connected through a resistor 78 to the negative source; its base is connected directly to the collector of the transistor 72 and its emitter is grounded. A capacitor 79 couples the emitter of the transistor 72 to the base of the transistor 73. An auxiliary transistor 81 has its collector and emitter connected respectively to the collector and emitter of the transistor 73. The transistor 81 is normally nonconductive and consideration of its operation will be deferred.

When the power is first turned on the transistor 72 would be nonconductive except that at the same time a negative-going signal from the shaping circuit 52 turns the transistor 72 on. The collector 72 is near ground potential and the transistor 73 is nonconductive. The capacitor 79, being short circuited through the transistor 72, is discharged. Upon the passage of the first pulse 53 and before the next pulse arrives the transistor 72 becomes nonconductive and the capacitor 79 starts to charge. However, the parameters of the circuit are selected so that the capacitor 79 does not charge sufficiently to turn on the transistor 73 before the arrival of the next pulse at which time the capacitor 79 is again discharged through the transistor 72. Thus the collector of the transistor 73 remains at a negative potential as long as the pulses 53 continue to arrive. Thus a long pulse waveform 55 is generated. However, interruption in the train of pulses 53 allOWs the capacitor 79 to charge sufiiciently to render transistor 73 conductive thereby terminating the pulse 55.

The pulse 55 is coupled by a capacitor 82 to the flipfiop circuit 58 which consists essentially of the transistors 83 and 84 and their associated circuitry. These transistors are connected as a conventional flip-flop circuit. The leading edge of the pulse 55 turns 011? the transistor 83 and turns on the transistor 84. The two previously mentioned output conductors 61 and 62 are connected to the collectors of the transistors 83 and 84 respectively.

The flip-flop 59 consists of the transistors 86 and 87 and their associated circuitry. These transistors are also connected in a conventional flip-flop circuit. However there is an auxiliary transistor 88 the collector of which is connected to the collector of the transistor 86 and the emitter of which is connected to the emitter of the transistor 86. The base of the transistor 88 is connected through serially connected resistors 91 and 92 to a source of positive potential. The junction of the resistors 91 and 92 is connected through a capacitor 93 to a source of negative potential. When power is first applied the resulting transient is passed through the capacitor 93 to the base of the transistor 88 thereby turning it on. Since the collector of the transistor 88 is connected to the collector of the transistor 86 which is coupled to the base of the transistor 87 the transistor 86 is also initially turned on while the transistor 87 is initially cut oft". This condition is indicated in FIGURE 4.

Returning to FIGURE 5 the collector of the transistor 83 is coupled by a capacitor 94 to the anodes of two diodes 35 and 06 the cathodes of which are connected to the collectors of the transistors 86 and 87 respectively. By this well known connection a negative-going change in the potential of the collector of transistor 83 has no effect While a positive-going change flips the transistors 86 and 87 to the opposite state. Such a positive-going change occurs at the systolic point as indicated in FIG- URE 4. The previously mentioned output conductors 63 and 64 are connected to the collectors of the transistors 86 and 87 respectively.

The first output signal required of the logic circuit is that required to turn off the lamp 41 (FIGURE 1). The conductors 62 and 64 are connected to the anodes of diodes 101 and 102 respectively the cathodes of which are connected together and through a resistor 103 to the negative source. It is obvious that as long as both the conductor 62 and the conductor 64 are negative no current will flow through the resistor 103 and the potential of the conductor 33 will be negative. When either one of the conductors 62 or 64 becomes positive (in the present case the conductor 22 becomes positive) current will flow through the resistor 103 thereby placing a positive potential on the conductor 33 which operates through the lamp control circuit 42 to turn off the lamp.

The next signal required of the logic circuit is the systolic signal. This occurs when the conductors 63 and 64 change their polarity conditions. The conductor 64 is connected directly to the conductor 35 and generates a positive-going signal at the systolic point which operates through the drive circuit 44 to lock the systolic gauge. The conductor 63 is connected directly to the conductor 34 and provides a negative-going signal which is passed to the time delay circuit 45.

The next signal required is the diastolic signal and this occurs when the conductors 62 and 64 both become positive. The conductors 62 and 64 are connected to the cathodes of diodes 104 and 105 respectively the anodes of which are connected together and through serially connected resistors 106 and 107 to a source of positive potential. The conductor 36 is connected to the junction of resistors 106 and 107. It is obvious that as long as either one of the conductors 62 and 64 is negative, cur rent will flow through the resistors 107 and 106 causing low potential to appear on the conductor 36. However, when both of the conductors 62 and 64 become positive, current flow ceases and a positive-going signal appears on the conductor 36 which is applied to the drive circuit 49 which in turn locks the diastolic gauge.

Finally, the logic circuit generates another signal at the diastolic point which is the complement of the just described signal and is obtained from the conductors 61 and 63. These conductors are connected to the anodes of the diodes 108 and 109 respectively the cathodes of which are connected together and through a resistor 111 to a source of negative potential. A capacitor 112 is connected to the cathodes of the diodes 103 and 199 and to a source of positive potential. It is obvious that as long as one of the conductors 61 or 63 is positive, current will flow through the resistor 111 making the potential of the conductor 113 at or slightly above ground potential. However, when both the conductor 61 and the conductor 63 are negative, current fiow ceases and a negative signal is applied to the conductor 113 which is connected to the base of the transistor 81 thereby rendering this transistor conductive, short-circuiting the transistor 73 and preventing passage of any further pulses.

Referring now to FIGURE 6 the high pass filter 27 is shown as one type of active filter, that is, a filter including an amplifier with frequency selective feedback. The amplifier comprises the transistors 121 and 122. Input signals from the low pass filter 26 are coupled through capacitors 123 and 124 to the base of the transistor 121, the collector of which is connected through a resistor 125 to a source of negative potential. The base of the transistor 121 is connected through a resistor 126 to ground; the emitter is connected through a resistor 127 to ground. The collector of the transistor 121 is connected directly to the base of the transistor 122 the emitter of which is grounded. A voltage divider comprising serially connected resistors 128, 129 and 131 is connected between a source of negative potential and a source of positive po tential. The collector of the transistor 122 is connected to the junction of resistors 128 and 129. The collector of transistor 122 is also coupled by a capacitor 132 to the amplifier 29. A resistor 133 is connected between the collector of transistor 122 and the junction of capacitors 123 and 124. The cutoff frequency of the filter may be changed by altering the values of the resistors 133 and 126. This is accomplished in effect by means of a resistor 134 which has one terminal connected to the lower end of the resistor 133 and the other terminal connected to the collector of transistor 135 the emitter of which is connected to the upper end of the resistor 133. In a similar fashion, a resistor 136 is connected to the upper terminal of the resistor 126 and to the collector of the transistor 137 the emitter of which is connected to the lower terminal of the resistor 126. When the transistors 135 and 137 are nonconductive the resistors 126 and 133 alone are in the circuit while when these transistors are conductive the resistors 133 and 126 are effectively reduced in value by having the resistors 134 and 136 respectively connected in shunt with them. The transistors 135 and 137 are normally nonconductive and the cutoff frequency of the filter is 30 c.p.s. When these transistors are made conductive the cutoff frequency is shifted to 50 c.p.s.

The conductivity of the transistors 135 and 137 is controlled by the condition of a flip-flop circuit comprising the transistors 141 and 142. The collector of the transistor 141 is connected through a resistor 143 to ground while the collector of transistor 142 is connected through a resistor 144 to the source of negative potential. The emitters are connected together and through resistor 145 to a source of positive potential. The base of the transistor 141 is returned to the positive source through a resistor 146 while the base of the transistor 142 is connected through a resistor 147 to the positive source. The collector of the transistor 141 is coupled by a resistor 148 to the base of the transistor 142. v

The conductor 34 from the logic circuit 32 carries a negative-going signal when the systolic point is reached.

8 This signal is delayed in time by the time delay circuit 45 which consists of a resistor 151 and capacitor 152 serially connected from the conductor 34 to the source of positive potential. The output conductor 46 of the time delay circuit is connected to the junction of the aforesaid resistor and capacitor. Prior to the systolic point, the conductor 46 carries a positive potential which is applied to the base oi the transistor 141 rendering this transistor nonconductive and rendering the transistor 142 conductive. Accordingly, the collector of the transistor 142 is at or slightly above ground potential therefrom maintaining the transistors and 137 nonconductive. When the systolic point is reached, the negative-going signal of the conductor 34 starts to charge the capacitor 152 so that the potential of the conductor 46 starts to fall. circuit is large so that the potential of conductor 46 does not become sufficiently negative to turn on the transistor 141 for approximately five seconds after the systolic point has been reached. Then the transistor 141 is made conductive and the transistor 142 is made nonconductive; the potential of the collector 142 becomes negative; and the transistors 135 and 137 are made conductive thereby inserting the resistors 134 and 126 into the circuit and changing the cutofi point of the filter from 30 c.p.s. to 50 c.p.s. The collector of the transistor 142 is also connected to the conductor 47 so that a negative-going signal is passed to the control circuit 31.

Referring now to FIGURE 7, there is shown a schematic diagram of the control amplifier 29 and the control circuit 31. The amplifier comprises essentially the transistor 161, the base of which is coupled by the capacity 132 to the output of the filter 27. The base of the transistor 161 is returned to ground through a resistor 162 while the emitter is connected through a resistor 163 to a source of negative potential. The collector is also connected directly to the base of the transistor 164 which acts as emitter follower. The collector is connected directly to the source of negative potential while the emitter is connected through a resistor 165 to a source of positive potential. A capacitor 166 is connected between the base of the transistor 164 and ground. The emitter of transistor 164 is coupled by a capacitor 167 to the logic circuit 32.

The gain of the transistor 161 is controlled by the amount of degeneration caused by unbypassed emitter resistors. More specifically, the emitter of the transistor 161 is connected through a resistor 168 to the positive potential source. The emitter is also connected through the serial combination of a capacitor 171 and a resistor 172 to ground. A resistor 173 has one terminal connect- 7 ed to the junction of capacitor 171 and the resistor 172 and the other terminal connected to the collector of atransistor 174 the emitter of which is grounded. The base of the transistor 174 is connected through a resistor 175 to asource of positive potential. The transistor 174 is normally conductive thereby effectively shunting the resistor 172 with the resistor 173. The resistors 168, 172 and 173 are all in the emitter circuit of the transistor 161 and are unbypassed thereby causing degeneration. When the transistor 174 is made nonconductive the resistor 173 is removed from the circuit thereby increasing the amount of resistance in the emitter circuit, increasing the degeneration and thereby decreasing the gain of the stage.

The control circuit 31 consists essentially of two transistors 181 and 182 connected as a conventional flip-flop circuit. At the end of the pump-up period a negativegoing signal on conductor 43 from the control circuit 42 is applied through resistor 183 to the base of the transistor 182 thereby rendering this transistor conductive. The transistor 181 is thereby rendered nonconductive and its collector is at a negative potential which potential is passed by a resistor 184 to the base of the transistor 174 thereby rendering the latter transistor conductive and holding thegain of the amplifier to its higher value.

As previously mentioned the amplifier gain should be increased five seconds after the-passage of the systolic The time constant of thepoint provided that the signal level is above a predetermined magnitude at this time. This is accomplished by applying the signal to a summing point 185. The junction 185 is connected through a resistor 186 to a source of positive potential and is also connected to the cathode of a diode 187 the anode of which is connected to the base of the transistor 181. The negative-going signal on the conductor 47 from the control circuit 28 occurs approximately five seconds after the systolic point is reached and is passed through a resistor 188 to the summing point 185. Additionally, a signal from the output of the amplifier is coupled by a capacitor 189 to the summing point 185. In the absence of the negative-going signal on the conductor 47 the amplifier output can never be of sufficient amplitude to pass through the diode 187 to the base of the transistor 181 to such an extent as to render the transistor 181 conductive. However, the signal from the control circuit 28 lowers the potential of the summing point 185 sufficiently so that if the output of the amplifier exceeds a predetermined magnitude the potential of the junction 185 can become sutficiently negative to pass through the diode 187 to the base of the transistor 181 thereby rendering this transistor conductive. When this occurs the collector of the transistor 181 rises in potential and this rise is passed to the base of the transistor 174 thereby turning it off, removing the resistor 173 from the circuit and decreasing the gain of the amplifier by a factor of two.

The signal from the lamp control circuit 42 prepares the circuit for operation by turning onthe transistor 182. Thereafter, five seconds after the passage of the systolic point as indicated by the signal from the control circuit 28, the gain of the amplifier can be reduced provided the signal level exceeds a predetermined magnitude.

From the foregoing description it is apparent that applicants have provided a novel and effective sphygmometer. The energy of the signals from the microphone contained in a first band of frequencies, from about 30 c.p.s. to about 100 c.p.s., is used to determine the systolic pressure. Since some individuals exhibit a low signal level for a while after the systolic point has been reached, this first band is utilized for several seconds thereafter, whereupon the frequencies utilized are limited to a second band from approximately 50 c.p.s. to approximately 100 c.p.s. The diastolic point is determined as the pressure existing at the onset of mufiling which is manifested by the absence of energy in this second, more limited band. More specifically, the absence of energy in this limited band (not the complete absence of output from the microphone 13) causes an interruption of the pulses 53 which in turn terminates the long pulse 55 thereby triggering the flip-flop 58 to its final condition. Additionally, if the patient is one of those individuals who exhibit very high level signals, the gain of the amplifier is reduced.

Apparatus according to the invention has been built and tested on many different persons and has been found to give results in close agreement with the results obtained by a physician using a stethoscope.

Although a specific embodiment of the invention has been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

What is claimed is:

1. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone for monitoring the sounds of arterial flow past said cuff and generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normally passing a first band of fre- It? quencies in the range of from thirty to one-hundred cycles per second and selectively actuable to pass a second band of frequencies in the range of from fifty to one-hundred cycles per second,

means responsive to the first occurrence of a signal passing through said filter means as the pressure in said cufi is reduced for recording the pressure then existing in said cuif and for actuating said filter to pass said second band of frequencies, and

means responsive to a subsequent interruption of the signal passing through said filter for recording the pressure then existing in said cuff.

2. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial flow past said cuff and for generating electrical signals in response thereto, and

a filter receiving signals generated by said microphone for normally passing a first band of frequencies in the range of from thirty to one hundred cycles per second and selectively actuable to pass a second band of frequencies in the range of from fifty to one-hundred cycles per second, 7

a control circuit connected to the output of said filter,

said circuit including means responsive to the first occurrence of a signal passing through said filter as the pressure in said cuff is reduced for recording the pressure then existing in said cuff and for actuating said filter to pass said second band of frequencies,

said circuit also including means responsive to a subsequent interruption of the signal passing through said filter for recording the pressure then existing in said cuff.

3. A sphygmometer, comprising:

a cutf for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial flow past said cuff, where-by as the pressure is reduced said microphone generates a first series of electrical pulses each indicative of a spurt of blood passing through said artery,

filter means receiving signals generated by said microphone, whereby the output of said filter means is a second series of electrical pulses,

said filter means normally passing a first band of frequencies in the range of from thirty to one hundred cycles per second and being selectively actuable to pass a second band of frequencies in the range of from fifty to one-hundred cycles per second, and

a control circuit connected to the output of said filter means,

said circuit including means responsive to the occurrence of the first pulse of said second series of pulses for recording the pressure then existing in said cuff and for actuating said filter means to pass said second hand of frequencies,

said circuit also including means responsive to a subsequent interruption in said second series of pulses for recording the pressure then existing in said cuff.

4. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial flow past said cuff and for generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normally passing a band of frequencies between a first predetermined lower frequency below which there is no sound energyof interest and a predetermined upper frequency above which there is no sound energy of interest and being selectively actuable to raise said first predetermined lower frequency representative of the onset of mufiling to a second predetermined lower frequency, and

a control circuit connected to the output of said filter means,

said circuit including means responsive to the first occurrence of a signal passing through said filter means as the pressure in said cuif is reduced for recording the pressure then existing in said cult and for actuating said filter to pass said second band of frequencies,

said circuit also including means responsive to a subsequent interruption of the signal passing through said filter means for recording the pressure then existing in said cuff.

5. Apparatus according to claim 4 in which said first predetermined lower frequency is in the range from twenty to forty cycles per second, said second predetermined lower frequency is in the range from forty to sixty cycles per second, and said predetermined upper frequency is in the range from eighty to one hundred and twenty cycles per second. i

6, Apparatus according to claim 4 in which said first predetermined lower frequency is approximately thirty i cycles per second, said second predetermined lower frequency is approximately fifty cycles per second, and said predetermined upper frequency is approximately one hundred cycles per second.

7. A sphygmometer, comprising: a cuif for encircling a portion of the human body, means for inflating said cuff to occlude an artery, means for reducing the pressure in said cuff slowly, a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial flow past said cuff and for generating electrical signals in response thereto, filter means receiving signals generated by said microphone for normally passing a first band of frequencies in the range of from thirty to one-hundred cycles per second and selectively actuable to pass a second hand of frequencies in the range of from fifty to one-hundred cycles per second, a control circuit connected to the output of said fiiter means, saidcircuit including means responsive to the first occurrence of a signal passing through said filter means as the pressure in said cutf isredu-ced for generating a first control signal, means responsive to said first control signal for recording the pressure then existing in'said cuff, means for delaying said first control signal, means responsive to the signal so delayed for actuating said filter means to pass said second band of frequencies, said control circuit also including means responsive to a subsequent interruption of the signal passing through said filter means for generating a second control signal, and means responsive to said second control signal for recording the pressure then existing in said cuff. 8. A sphygmometer, comprising: a end for encircling a portion of the human body, means for inflating said cud to occlude an artery, means for reducing the pressure in said cuff slowly, a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial flow past said cuff and for generating electrical signals in response thereto, filter means receiving signals generated by said microphone for normally passing a first band of frequencies'which passes all sound energy of interest and selectively actuable to pass a second band of frequencies which excludes sound energy below that frequency required to detect the onset of mufiiing. an amplifier connected to the output of said filter means, normally inactive means for reducing the gain of said amplifier when the output thereof exceeds a predetermined magnitude,

means responsive to the first occurrence of a signal passing through said amplifier as the pressure in said cufi is reduced for the triple purpose of recording the pressure then existing in said cuff, for actuating said filter means to pass said second hand of frequencies, and for activating said normally inactive means, and

means responsive to a subsequent interruption of the signal passing through said amplifier for recording the pressure then existing in said cuff.

9. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuif slowly,

a microphone positioned adjacent to said artery downstream from the point of occlusion for monitoring the sounds of arterial fiow past said cult and for generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normally passing a first band of frequencies which passes all sound'energy of interest and selectively actuable to pass a second band of frequencies which excludes sound energy below that frequency required to detect the onset of mufiiing.

an amplifier including switch means operable to reduce the gain thereof connected to the output of said filter means,

a control circuit connected to the output of said amplifier,

said circuit including means responsive to the first occurrence of a signal passing through said amplifier as the pressure in said cuff is reduced for generating a first control signal,

means responsive to said first control signal for recording the pressure then existing in said cuff.

means for delaying said first control signal to generate a secondcontrol signal,

means responsive to said second control signal for actuating said filter to pass said second hand of frequencies,

means jointly responsive to said second control signal and to the output of said amplifier in excess of a predetermined magnitude for operating said switch means,

said control circuit also including means responsive to a subsequent interruption of the signal passing through said amplifier for generating a third control signal, and means responsive to said third control signal for recording the pressure then existing in said cuff.

10. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for selectively inflating said cufi to occlude an artery,

means for relieving the pressure in said cufi slowly,

first and second pressure gauges each for indicating the pressure within said cuff,

each of said gauges including means for locking its indication despite subsequent pressure changes,

a microphone for monitoring the sounds of arterial flow past said cuif, whereby as the pressure is relieved said microphone generates a first series of electrical pulses each indicative of a spurt of blood passing through said artery, 7

a bandpass filter operatively connected to the output of said mircophone, whereby the output of said filter is-a second series of electrical pulses.

said filter having characteristics normally pasing a band means responsive to an interruption in said second of frequencies between a first predetermined lower series of pulses for locking said second gauge. frequency below which there is no sound energy of interest and a predetermined upper frequency above References Cited by the Exammel which there is no sound energy of interest and in- 5 UNITED STATES A S 3112125235!Z5 2$223325? iliimifiiiiwii $101,082 8/1963 Seen at 128-105 fre uenc to d d t (11 f 3,140,710 7/1964 Glassner et a1. l282.05

q y e representative of the onset of mufiling, means responsive to the occurrence of the first pulse of 10 ROBERT MORGAN Acting Primary Examiner.

said second series of pulses for locking said first gauge and for actuating said selectively actuable SIMON BRODER Exammermeans, and

Claims (1)

1. A SPHYGMOMETER, COMPRISING: A CUFF FOR ENCIRCLING A PORTION OF THE HUMAN BODY, MEANS FOR INFLATING SAID CUFF TO OCCLUDE AN ARTERY, MEANS FOR REDUCING THE PRESSURE IN SAID CUFF SLOWLY, A MICROPHONE FOR MONITORING THE SOUNDS OF ARTERIAL FLOW PAST SAID CUFF AND GENERATING ELECTRICAL SIGNALS IN RESPONSE THERETO, FILTER MEANS RECEIVING SIGNALS GENERATED BY SAID MICROPHONE FOR NORMALLY PASSING A FIRST BAND OF FREQUENCIES IN THE RANGE OF FROM THIRTY TO ONE-HUNDRED CYCLES PER SECOND AND SELECTIVELY ACTUABLE TO PASS A SECOND BAND OF FREQUENCIES IN THE RANGE OF FROM FIFTY TO ONE-HUNDRED CYCLES PER SECOND, MEANS RESPONSIVE TO THE FIRST OCCURRENCE OF A SIGNAL PASSING THROUGH SAID FILTER MEANS AS THE PRESSURE IN SAID CUFF IS REDUCED FOR RECORDING THE PRESSURE THEN EXISTING IN SAID CUFF AND FOR ACTUATING SAID FILTER TO PASS SAID SECOND BAND OF FREQUENCIES, AND MEANS RESPONSIVE TO A SUBSEQUENT INTERRUPTION OF THE SIGNAL PASSING THROUGH SAID FILTER FOR RECORDING THE PRESSURE THEN EXISTING IN SAID CUFF.

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