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BACKGROUND OF THE INVENTION
In order to take blood pressure it is conventional practice for a doctor
(or nurse or other trained operator) to wrap the cuff of a
sphygmomanometer around a patient's arm. He then utilizes one hand to
inflate the cuff by means of a squeeze bulb to impede the flow of blood to
the arm, while with his other hand he holds the sensor of a stethoscope on
the patient's arm to monitor heart pulses acoustically. Using his first
hand, the doctor then slowly bleeds air from the cuff to gradually
decrease the pressure in the cuff while carefully observing the pressure
gauge (aneroid or mercury column) of the sphygmomanometer. As the pressure
in the cuff decreases he observes and mentally retains the pressure gauge
readings at which the first heart pulse is heard (systolic pressure) and
at which the heart pulses cease to be heard (diastolic pressure). It is
common for the doctor or operator to repeat this process one or more times
either to confirm the initial readings in the event that he may not have
been able to clearly detect the systolic and diastolic pressure points, or
to minimize the ambiguity of this type of measuring system, or to average
the results, or to re-affirm the results in the event of loss of trend of
concentration or failure to recall one or both of the observed readings.
It is also clear that owing to the inherent lack of precision with this
type of medical measurement system, the results vary significantly from
operator to operator. Additionally, as conventionally configured and
utilized, this instrument is slow, necessitates much subjective judgement
in interpreting the results, is cumbersome to use, and does not easily
adapt itself for use by an average patient in taking his own blood
pressure.
SUMMARY OF THE INVENTION
The digital sphygmomanometer herein, in conjunction with an inflatable arm
cuff, pump, and bleed valve provides a cuff pressure sensor which through
optical and electronic devices transforms decreasing cuff pressure into
three digit systolic and diastolic pressure readouts in mm. of Hg with
countdowm to systolic pressure on the systolic readout and with countdown
from systolic pressure to diastolic pressure on the diastolic readout.
A principal object of the present invention is to provide an apparatus and
method for automatically measuring blood pressure without the need for
conventional manometers or stethoscopes.
Another object of this invention is to provide a simple apparatus which is
easy to set up and use by an operator or by the patient himself to rapidly
and accurately monitor blood pressure independently of operator or patient
skill and without requiring operator or patient judgement on the
interpretation of the results.
Other objects and advantages will appear from the ensuing description.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view showing the digital syphgmomanometer herein in
use;
FIGS. 2 and 3 are schematic diagrams showing successive components of the
present invention from the cuff to the incremental logic device (FIG. 2),
and from the up-down counter and down-up detector which receive the
encoder output pulses and encoder direction pulses to the systolic and
diastolic displays (FIG. 3);
FIG. 4 depicts the sine/cosine wave pattern output of the encoder, the
signal shaping, and the sequential encoder pulse outputs as a function of
encoder displacment;
FIG. 5 is a cross-section view of the pneumatic sensor and encoder portions
of the present invention; and
FIG. 6 is a block diagram illustrating a system for concurrent automatic
multi-monitoring of blood pressure data of numerous patients.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawings, and especially to FIGS. 1 and 5, apparatus 1
automatically detects and records blood pressure from a conventional
inflatable cuff 2. The cuff 2 is wrapped around the patient's arm and is
pumped up or inflated by means of hand pump or squeeze bulb 3. The cuff
pressure is transmitted by means of a flexible tube 4 into cavity 5 of
apparatus 1 through pressure port 6. A pneumatic sensor in the form of a
metal bellows 7 deflects upward against its own natural spring constant as
a result of the force created by the air pressure unbalance existing
between cavity 5 and cavity 8. Cavities 5 and 8 are isolated from each
other by means of the bellows 7 and the O-rings 9. Cavity 8 is vented to
atmosphere through vent port 10.
The cuff pressure and, consequently, the pressure in cavity 5 is increased
by pump 3 until the bellows 7 contacts the adjustable terminal post 11. At
that point an electrical circuit is completed comprising contact post 11,
metal disk 12 brazed to the conducting bellows 7, and contact post 13
which extends through the non-conducting pneumatic sensor block 14 to
contact bellows 7 at the peripheral of the flange 15 thereof. This signal
may be used: (1) to indicate to the operator that he may stop pumping cuff
2 because he has gone beyond the expected systolic pressure, and (2) to
set or initialize the up-down counter 16 and systolic and diastolic
displays, 17 and 18, shown in block diagram in FIG. 3. The bellows 7
spring rate and diameter is chosen to correspond to a predetermined blood
pressure, say 170 mm of Hg, when the electrical circuit described is
completed. Adjustable screw post 11 can be further used to calibrate the
apparatus initially to compensate for manufacturing tolerance variations
in the bellows spring rate. Calibration can be achieved by externally
setting the predetermined pressure in cavity 5 to say, 170 mm of Hg, and
adjusting the post 11 until electrical contact is made with disk 12.
A preferred form of linear encoder 19 comprises a linear scale 20 which is
attached to and moves with bellows 7, a reticle 21 which is fixed and
attached to the pneumatic sensor block 22, dual light emitting diodes
(LED) 23 which act as light sources, and dual photo-transistor cell
detectors 24 which measure the linear deflection or position of the
bellows 7 as it moves under the influence of the cuff pressure. Wires 25
are provided to power the LED light sources 23, and wires 26 are provided
to pick up the bellows 7 position signals from the linear encoder
photo-transistors 24. Thus, the encoder 19 is an optical/electronic
measuring system which provides linear incremental encoding of position.
Precision light weight Mylar or like plastic film strips constitute the
scale 20 and reticle 21 with high resolution lines and spaces,
photographically exposed, to produce encoder minimum count resolutions of
say 500 microinches. The encoder 19 is implemented in this invention so
that measurement of linear motion is accomplished by moving the linear
scale 20 with respect to the stationary reticle 21 to produce a light and
dark pattern as the collimated light from the light sources 23 passes
through the fine graduations on the linear scale 20 and the fixed
graduated reticle 21. This light and dark pattern is sensed by the pairs
of photo cells 24 which are placed back to back to minimize DC offset and
to enhance signal output.
As shown in FIG. 5, this compact encoder 19, equipped with cell 24 output,
converts the linear bellows 7 motion into low level sine/cosine waves 27
and 28. The zero crossings of the sine/cosine waves are converted into
digital signals for incremental counting. By assigning channel
designations to both sine and cosine waves, a phase relationship is
established for determining the direction of motion of the bellows 7. The
low level sine/cosine encoder 19 signals are amplified by amplifier 29 and
applied to an incremental logic circuit 30 which square off the waves and
provide pulses in conventional quadrature output as illustrated in FIG. 4.
The quadrature output is then processed logically, to provide up-down
pulses as well as encoder direction signals.
The encoder 19 may be designed such that every 0.0005" motion of the
bellows 7 corresponds to one digital encoder pulse; and the bellows 7 may
be chosen so that, 1 mm of Hg pressure, corresponds to 0.0005" of bellows
motion. Consequently, the sensitivity of apparatus 1 may be such that a
cuff pressure of 1 mm of Hg corresponds to 1 digital encoder pulse,
however, numerous other sensitivities are possible.
Once the set point pressure, of, say, 170 mm of Hg is achieved by the
action of the hand pump 3, the operator now slowly opens bleed valve 31
allowing the pressure in the cuff 2 and, consequently, in cavity 5 to
decrease. As the pressure decreases, bellows 7 starts deflecting downward
as a result of its natural spring constant restoring force. Electrical
contact is broken at the post 11 to metal disk 12 interface. This signal
is used to set the counter 16 and the systolic and diastolic displays 17
and 18 to 170, corresponding to: (a) the pressure to which apparatus 1 was
calibrated, and (b) the cuff 2 pressure at that instant of time. As the
pressure continues to decrease, as a result of the continuously bleeding
valve 31, a corresponding proportional bellows deflection and,
consequently, encoder pulse train is generated. This encoder pulse train
is fed to the up-down counter 16 illustrated in the logic block diagram,
FIG. 3. The up-down counter starts to count down from 170, 1 count for
every 1 mm of Hg pressure decrease. When the cuff pressure gets down to
the point where blood just begins to flow downstream of the cuff 2 into
the lower part of the arm, a slight pressure rise or pressure reversal is
noted, this being the pulse that a doctor picks up acoustically with a
stethoscope. This pressure rise is sensed by bellows 7 which suddenly and
momentarily reverses direction and is deflected upward. This reversal in
direction is logically detected by the incremental logic circuit 30 which
provides a change in encoder direction signal. This signal is fed to the
down-up count detector 32 which fires a single pulse signal to a latch 33.
Latch 33 then gates through by means of display 1 gate 34, the address in
counter 16, to a light emitting diode decoder driver 35. The decoder
driver 35 decodes the binary coded decimal signal to decimal and sets the
three digit display 17 with the systolic blood pressure. A similar action,
through single shot device 36, sets the systolic blood pressure on the
diastolic display 18 through display 2 gate 37 and decoder driver 38.
As the pressure continues to decrease the pressure reversals continue and
are picked up by the down-up detector 32. The down-up detector continues
to fire single pulses each and every time it senses a pressure reversal.
However, while latch 33 remains latched, conserving the systolic pressure
display 17 output, the diastolic display 18 continues to be updated as
each down-up count reversal detection causes the new counter address to be
dumped into the 3 digit diastolic display 18. Finally, when no more
pressure reversals occur corresponding to when a doctor observes that the
acoustic pulses cease to be heard with a stethoscope, the diastolic
pressure display 18 is set. The operator now just reads the systolic and
diastolic pressures from the displays 17 and 18.
In another embodiment, in lieu of utilizing the sudden changes of bellows
direction, which correspond to the acoustic pulses the doctor picks up, to
activate latch 33 and single shot 36 and, consequently, allowing the
address in counter 16 to gate through, the acoustic pulses may be detected
by means of an acoustic sensor or other similar device to act as the
gating trigger.
The apparatus 1 described herein is of lightweight compact form
approximately the same as a pocket size calculator with the two LED
displays 17 and 18 indicating diastolic and systolic pressures. The
apparatus 1 may be powered by batteries and/or alternating current.
Furthermore, by replacing the hand pump 3 with an automatic vacuum pump,
and the bleed valve 31 with a solenoid operated bleed valve, the digital
sphygmomanometer 1 may be made totally automatic. For example, a cuff 2
may be placed on a patient, and, on a regular interval of time, the
automatic pump may be activated by means of an external control system
(computer, stand-alone controller, etc.). When the pressure in the cuff 2
is sufficiently high, the bellows disk 12 contacts post 11, completing the
electrical circuit from post 11 to post 13. An electrical signal may then
be generated, which may be used to shut off the automatic pump and to open
the solenoid operated bleed valve. Once the solenoid operated bleed valve
is open the cuff pressure starts decreasing and the digital
sphygmomanometer 1 operates as previously described; except now totally
automatic.
Peripheral output devices, such as a printer or computer may also be
integrated to the systolic/diastolic calculator. The systolic/diastolic
pressures may be fed to these peripheral devices directly from the
calculator. When fed to the computer in Binary Coded Decimal, the data may
be further processed and computer diagnosed to alert a technician or nurse
of complications.
It is also conceivable that the blood pressure of numerous patients may be
automatically monitored simultaneously by placing a digital
sphygmomanometer 1 on each patient and feeding the data directly to a
control computer. This is shown diagrammatically in FIG. 6 wherein the
blood pressure data of each of numerous patients is fed to a remote
on-line computer 40 which automatically controls operation of pump 41 and
a bleed valve (not shown in FIG. 6). The computer 40 collects and stores
the blood pressure data from each patient in readable format and reports
problems directly on an output printer 42 and/or an output terminal 43
such as a cathode ray tube output terminal.
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