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This application is an improvement over the disclosure in Application Ser.
No. 755,018 filed Dec. 28, 1976, now abandoned.
This invention relates to body parameter display devices and particularly
to blood pressure and pulse rate indicating devices which are habitually
worn by the user in the form of a wrist watch.
There are a substantial number of people who are afflicted with cardiac or
cardiovascular difficulties which necessitate, or render desirable,
periodic monitoring of blood pressure and/or pulse rate. Although pulse
rate is capable of being read with a minimum of auxillary equipment, the
current commercially available technique for reading blood pressure is the
cuff device which not only requires a modicum of expertise to operate but
which is also bulky and not apt to be habitually carried. It will be
evident that it would be highly advantageous to provide a small blood
pressure monitor that can be habitually worn by an individual without the
least discomfort.
The provision of a wrist worn blood pressure and pulse rate indicator is
known in the prior art as shown in U.S. Pat. No. 3,535,067. It will be
apparent that this particular device is comprised of a multiplicity of
mechnaical parts which, by the nature thereof, are necessarily intricate,
expensive and prone to failure. Another wrist worn blood pressure and
pulse rate indicator is known in the prior art as shown in U.S. Pat. No.
2,756,741. This devices uses antiquated vacuum tube components and
contains a number of disadvantages, among which is that it is incapable of
being habitually worn.
Also known in the prior art are wrist worn electric pulse rate display
devices as shown in U.S. Pat. Nos. 3,742,937; 3,807,388; and 3,838,684. Of
similar import is the disclosure in U.S. Pat. No. 3,426,747. Other body
parameter display devices of more general interest are found in U.S. Pat.
Nos. 2,815,748; 3,714,939; and 3,871,362; and 3,996,926. Of more general
interest is the disclosure in U.S. Pat. No. 3,803,834.
One of the difficulties with habitually worn wrist carried electronic
devices is that the batteries used as a power supply have a moderate
expected life. When utilizing a habitually worn electronic device to
indicate such body parameters as blood pressure and pulse rate, it is
highly desirable that the expected battery life be extended as long as
possible.
The provision of piezoelectric devices that are mechanically distorted to
provide an electrical output used as a power source are known in the prior
art, such as shown in Biomedical Engineering Systems, pages 394-397 and
Transactions of the American Society for Artificial Internal Organs,
Volume 9, 1963, pages 174-177. Devices incorporating series connected
piezoelectric elements or delivering relatively high voltages are found in
U.S. Pat. Nos. 3,395,295; 3,397,328; and 3,590,287. Of more general
interest are the disclosures in U.S. Pat. No. 3,707,636 and Japan patent
46-30872.
The body parameter display device of this invention comprises a habitually
worn wrist watch having a casing incorporating a pressure sensor biased
against the wrist of the wearer. The pressure sensor delivers a first
electrical output which is electronically manipulated to deliver an
electrical signal of a value representative of the blood pressure of the
wearer. In addition, the first electrical output may be electronically
converted to deliver a signal representative of the pulse rate of the
user. The blood pressure and/or pulse signals are displayed on a digital
display array carried by the watch casing.
The pressure sensor delivers a second electrical output which is
manipulated to provide a power source for operating the electronic
components of the device and/or to charge a battery used to energize the
watch.
It is an object of this invention to provide a compact, inexpensive wrist
worn device having an extended battery life.
Another object of this invention is to provide a blood pressure display
device incorporating a pressure sensor which delivers an electrical output
that is manipulated to deliver a signal representative of a body parameter
and an electrical output which is used to energize the device and to
charge a battery thereof.
A further object of the invention is to provide a body worn blood pressure
display device incorporating a sensor for delivering sequential electrical
signals representative of sequential blood pressure pulses, a peak
detector for analyzing each signal for detecting the maximum peak in each
signal and delivering a value representative thereof and means for storing
the signal representative of the maximum peak and means for displaying the
maximum peak signal.
Other objects and a fuller understanding of the invention may be had by
referring to the following description and claims taken in conjunction
with the accompanying drawings.
IN THE DRAWINGS
FIG. 1 is an isometric view of a body parameter display device in
accordance with the principles of this invention;
FIG. 2 is a simplified block diagram of the circuitry in the device of FIG.
1;
FIG. 3 is a more complete block diagram of the circuitry of FIG. 2;
FIG. 4 is an isometric view of one form of sensor useable in the device of
this invention;
FIG. 5 is a graph representative of the pressure pulses occuring in a
single heartbeat;
FIG. 6 is a graph representative of the output of the circuitry of FIG. 3
over two successive operations thereof; and
FIG. 7 is a partial longitudinal cross-sectional view of the assembled
watch casing and band.
Referring to FIG. 1, there is illustrated a body parameter display device
10 embodied in a wrist watch comprising a casing 12 having a single
digital display array 14 visible through a conventional watch crystal 16
and providing a band 18 for mounting the watch casing on an individual's
wrist in a conventional manner.
Referring to FIGS. 2 and 3, there is housed inside the casing 12 a timing
circuit 20 having an output 22 connected to the display array 14 through a
lead 24, a conventional four bit latch 26 and a switch 28. The switch 28
may be of any suitable type, for example, comprising a switch element 30
and a switch actuator 32 extending out of the casing 12 arranged to
connect the timing circuit 20 to the display array 14 for indicating time
on the array 14 in a conventional manner. As will become more fully
apparent hereinafter, the purpose of the switch 28 is not necessarily to
isolate the display 14 from a power source or battery 34 to prolong the
life thereof but is instead to alternatively connect the single array 14
to a circuit 36 for displaying a value representative of a body parameter
on the array 14.
It is accordingly evident that the switch element 30 may be in a normally
open position as illustrated in FIG. 3 thereby requiring depression of the
switch actuator 32 to display time or may be in a normally closed position
to continuously display time on the array 14. In the embodiment of FIG. 3,
the user must push on the actuator 32 to indicate time and to display a
body parameter measurement. It will accordingly be evident that the
display 14 may include light emitting diodes, liquid crystals or any other
suitable indicating components.
The circuit 36 comprises a sensor 38 for converting pressure pulses applied
to a diaphragm or encapsulated feeler 40 into electrical signals on an
output 42 representative of the magnitude of the pressure pulses sensed by
the diaphragm 40. As shown best in FIG. 4, the sensor 38 is preferably a
stack of piezoelectric crystals or wafers 44, 46, 48 which are separated
by insulating layers and bonded together. The wafers 44, 46, 48 are
mounted, at one end thereof, by a bracket 50 to the watch casing 12.
Mounted on the other end of the wafers 44, 46, 48, offset from the axis
thereof, is a stem 52 of a pressure foot 54 having an enlarged head 56
extending through an opening (not shown) in the watch casing 12. the head
56 engages the diaphragm 40 which acts to seal the watch casing 12 against
the entry of moisture, dust and the like.
As best visualized by comparison of FIGS. 3 and 4, a lead 58 extends from
one of the piezoelectric wafers through a ground connection 60 and affords
a reference for the remaining leads 42, 62 of the pressure sensor 38. It
will be evident that distortion of the piezoelectric wafers 44, 46, 48 in
response to the pressure pulses of the wearer creates electrical signals
in the outputs 42, 62.
The output 42 of the sensor 38 is connected to an amplifier 64 and a
resistor 66 connected to a ground 68. The amplifier 64 also includes a
power input 70 and an output 72. The amplifier 64 desirably comprises a
four stage operational amplifier available from National Semiconductor as
a Model LM324. This type amplifier incorporates four independent
operational amplifiers in one component and is capable of operation from a
single voltage supply. Because only one amplifier is used as the amplifier
64, the other amplifiers are available for use in succeeding stages of the
circuit 36.
The output 72 of the amplifier 64 is connected to a low pass filter 74
which passes electrical signals of a frequency between direct current and
5 cycles per second and rejects electrical signals having a frequency
higher than 8 cycles per second by a minimum of thirty decibels per
octave. These requirement can be met with a conventional sixth order
active filter comprising the three unused operational amplifiers on the
four stage amplifier LM324 wired as illustrated in Active Filter Cookbook,
by Don Lancester, 1975, page 144. The signals appearing on an output 76 of
the filter 74 in the range of 6-7 cycles per second will be substantially
attenuated as will be apparent to those skilled in the art. A compact
amplifier/low pass filter is accordingly provided.
By using a very low frequency filter, only the very low frequencies
representative of pulse beats are allowed to pass into the output 76 of
the filter 74. Accordingly, all other frequencies are eliminated thereby
creating a rather clean signal on the output 76 from a somewhat noise
signal on the amplifier output 72.
One of the problems associated with the design of blood pressure display
devices using a sensor delivering an electrical output signal is that the
pressure input sensor is not a simple pressure spike. More typically, the
pressure sensed during a single heartbeat is as illustrated in FIG. 5
where the pressure peak 78 is caused directly by heart muscle contraction
whereas the secondary peak 80 or peaks are caused by contraction and
relaxation of arteries through which blood moves. The magnitude of the
secondary peaks 80 varies widely from individual-to-individual. Thus, the
secondary peaks 80 comprise noise or irrelevant data.
The filter output 76 is connected to a second amplifier 82 of any suitable
type having a power input 84 and an output 86 connected to a peak
detecting circuit 88. The peak detecting circuit 88 acts to detect only
the maximum peak 78 of the each pulse passed through the output 76, to
convert the peak 78 to a direct current voltage value representative of
the maximum value of each pulse peak 78 and to deliver the direct current
voltage to an output 90. The peak detecting circuit 88 may be of any
suitable type and conveniently comprises a capacitor 92 in series with a
diode 94, a second oppositely facing diode 96 connected at one end between
the capacitor 92 and the diode 94 and connected at the other end to a
ground connection 98, and a capacitor 100 connected at one end to the
output end of the diode 94 and connected at the other end to the ground
connection 98.
Connected to the output 90 is an amplifier 102 wired as a voltage follower
by having a lead 104 connecting the output 106 of the amplifier 102 to one
of its input terminals. The voltage following amplifier 102 acts to
maintain a voltage in a capacitor 108 that is identical with the highest
voltage appearing in the capacitor 100 during any series of pulses
delivered on the output 90 of the peak detecting circuit 88. The capacitor
108 is connected in parallel with a potentiometer 110 and both are
connected to a ground connection 112. The potentiometer 110 acts as a
calibrating device to display on the array 14 a value which corresponds
with the individual's blood pressure as measured by an alternative and
more direct mechanism, for example a cuff. Referring to FIG. 6, there are
shown a pair of response curves 114, 116 indicating the voltage appearing
in the output 118 of the potentiometer 110. The curves 114, 116 are
generated during successive depressions of the switch actuator 32 as
allowed by a lead 120, switch terminal 122 and switch element 124 on the
actuator 32 arranged to momentarily contact the terminal 122 during switch
actuation. When the actuator 32 is depressed to read out a blood pressure
value, the switch element 124 moves into contact with the terminal 122
thereby discharging the capacitor 100 to a ground 126 and then moves out
of contact with the terminal 122 thereby allowing the capacitor 100 to
hold a charge. When the switch actuator 32 is released, the switch element
124 momentarily moves into contact with the switch terminal 122 thereby
grounding the capacitor 100 and then moves out of contact therewith. The
momentary discharge of the capacitor 100 allows a fresh pressure sensing
to be read.
During generation of the curve 114, the voltage rises to a value 128
corresponding to the highest voltage value appearing in the capacitor 100
until a higher voltage value appears in the capacitor 100 which is
reflected in a voltage value 130 in the potentiometer output 118. When the
switch actuator 32 is disconnected from the potentiometer output 118, the
voltage leaks off of the capacitor 100 to the ground 112. Upon the next
depression of the switch actuator 32, the voltage curve 116 is generated
and exhibits a voltage value 132 corresponding to the voltage appearing in
the capacitor 100 until a higher value appears in the capacitor 100 which
is reflected as a voltage value 134.
Although a resistor of fixed value may be used in lieu of the potentiometer
110, the latter is preferred because it allows calibration or adjustment
of the circuit 36 in much the same manner as adjusting the gain of the
amplifiers 64, 82 would act to calibrate the circuit 36. As will be more
fully apparent hereinafter, the mechanical aspects of the display device
10 introduce a number of variables unrelated to blood pressure of the user
which can affect the values displayed on the array 14. By providing the
potentiometer 118, these mechanical variables can be adjusted out of the
system.
The potentiometer output 118 is connected to an analog-to-digital converter
136 where the analog voltage signal present on the output 118 is converted
to a digital signal on the lead 138. The converter 136 may be of any
suitable type such as is available from Motorola Semiconductor as MC14433.
All such converters operate to deliver a digital signal on the output 138
corresponding to the voltage level on the output 118. The converter 136
accordingly converts the signal on the output 118 into a signal which is
compatible with the display array 14.
The converter output 138 is connected to a terminal 140 adjacent a switch
element 142 on the actuator 32 which acts to connect the output 138 to a
lead 144 operatively connected to the four bit latch 26 and the array 14.
It will accordingly be seen that manipulation of the actuator 32 acts
selectively to display either a value representative of time or a value
representative of blood pressure on the array 14.
Referring to FIGS. 1 and 7, the watch band 18 is shown as comprising a pair
of wrist encircling straps 146, 148 respectively providing a buckle 150
and a plurality of openings 152. The strap 146 preferably provides an
elastic section 154 therein for purposes more fully explained hereinafter.
The straps 146, 148 provide a pair of spaced watch attaching devices 156,
158 of any suitable type which are illustrated as loops for securement to
a pin connection 160, 162 provided in a pair of ears 164, 166 comprising
part of the watch casing 12 as shown in FIG. 7.
Referring to FIG. 7, the diaphragm 40 of the sensor 38 projects below the
bottom of the watch casing 12 and is in pressure transmitting relation
with the enlarged pad 56 of the pressure foot 54. The diaphragm 40 need
extend only a very small distance below the watch casing 12, for example
one millimeter.
One of the difficulties of blood pressure display devices which are
designed to be habitually worn by the user is to provide consistent and
reliable readings on the array 14. There are a number of problems
including the establishment of consistent and reliable pressures between
the diaphragm 40 and the arm of the user, the establishment of consistent
and reliable pressures between the diaphragm 40 and the pressure foot 50
and calibration of the circuit 36. It will be evident that if the straps
146, 148 are bound very tightly to the user's wrist, the readings on the
array 14 may be significantly different than when the straps 146, 148 are
still snug but substantially looser. This variable is obviated to a
significant extent by the elastic portion 154 which acts to maintain a
more-or-less consistent hoop stress on the band 18. The attachment between
the watch casing 12 and the straps 146, 148 may, due to manufacturing
tolerances, constitute a variable which tends to change the readings on
the array 14 independently of the user's blood pressure. It is evident
that these problems are one-time or fitting problems to assure that the
device 10 is suited for use by a particular person.
In one respect, it is not essential that the array 14 display values which
are substantially accurate. This occurs when the user has been made aware
of what his blood pressure actually is, as measured by more conventional
equipment, concurrently with the readings on the array 14. By simple
comparison, the user will be aware that so long as the readings on the
array 14 remain the same, there is no substantial change in blood
pressure. This is, of course, somewhat less than desirable.
Although it is possible to correct these fitting problems mechanically, as
by adjusting the watch band 18 or by adjusting the mounting between the
casing 12 and the straps 146, 148, it is preferred to effect this
adjustment electrically in the circuit 36 by the adjustment of the
potentiometer 110 or by the provision of means for adjusting the gain in
the amplifiers 64, 82. Accordingly, when the device 10 is first fitted on
the wearer, a blood pressure reading is taken by a more conventional
device and the potentiometer 110 is adjusted until the readings displayed
on the array 14 correspond thereto. In addition to the elastic portion 154
and the calibration of the circuit 36, there may also be provided a switch
having a pressure foot extending out of the casing 12 and biased into
engagement with the user's wrist. This switch is in circuit with the
battery 34, for example, to prevent illumination of the array 14 until a
predetermined force depresses the foot and closes the switch. Thus, there
may be assurance that the straps 146, 148 are at least minimally snug on
the user's wrist.
Another problem in assuring consistent and reliable readings on the array
14 occurs because of slow changes in the user or in the device 10 which
are not related to pressure pulses applied to the sensor 38. If the user
gains or looses a substantial amount of weight or if the watch mounting
becomes loose in use, a change in the pressure contact between the user's
arm and the diaphragm 40 will occur thereby affecting the readings on the
array 14. These changes can be readily accomodated by periodic blood
pressure checks by the user's physician followed by recalibration of the
circuit 36 by manipulating the calibration means or potentiometer 110.
Referring back to FIG. 3, there is illustrated an alarm circuit 168 which
may be incorporated in the circuit 36 by a lead 170 connected to the
output 118 of the potentiometer 110. Connected to the lead 170 is a
comparator 172, such as an operational amplifier available from National
Semiconductor as Model LM339, having an input 174. The quantity of the
signal on the input 174 is adjustable by the provision of a potentiometer
or adjustable resistance 176 connected with the battery 34. When the
quantity of the signal on the input 174 equals the quantity of the signal
on the output 118, a circuit is completed through the comparator 172 and
its output 178 to energize an alarm transducer 180 thereby signalling the
user that his current blood pressure exceeds the limit value set into the
input 174. The alarm transducer 180 may be of any suitable type and may be
either of the audible or tactile variety. One suitable type alarm
transducer is found in a watch made by Citizens Quartz. It is evident that
the quantity of the signal on the input 174 is adjustable to accomodate a
wide range of high blood pressure readings which will trip the alarm 180.
In the alternative, the comparator 172 may be an operational amplifier
which is arranged to trigger the alarm 180 when the quantity of the signal
on the lead 170 falls below the quantity of the signal on the input 174.
In this circumstance, the alarm circuit 168 comprises a low blood pressure
monitor and does not trip until the blood pressure of the user falls below
a predetermined value. It will be further apparent that the comparator 172
may be configured to energize the alarm 180 in the event the signal on the
output 118 rises above a predetermined value and in the event it falls
below another predetermined value.
Also illustrated in FIG. 3 is a pulse readout circuit 182 for displaying
the pulse rate of the user on the array 14. The circuit 182 may be of any
suitable type but is illustrated as comprising a lead 184 connected to the
output 86 of the amplifier 82, a retriggerable one shot multivibrator 186,
a rate multiplier 188 and an output 190 connected to a switch terminal 192
adjacent a switch element 194 on the actuator 32. It will be apparent that
the signal on the output 86 carries a train of amplified pulses appearing
at a frequency of 0-5 cycles per second indicative of the pulses of the
user of the device 10. The multivibrator 186 conditions the signal to the
rate multiplier 188 and acts to deliver a single pulse for a short
predetermined duration in response to receiving a single pulse. Thus, the
multivibrator 186 is triggered by the signal from the peak 78 (FIG. 5) and
the delivered pulse from the multivibrator 186 masks the secondary pulses
80. Any suitable multivibrator such as a Model 74121 is operable. The rate
multiplier may also be of any suitable type, such as a Model 74167 from
Texas Instruments. The rate multiplier 188 basically acts to multiply the
number of pulses received from the multivibrator 186 by a constant to
produce a number of pulses per minute, corresponding to pulse rate, which
is displayed on the array 14 through the switch 28, a lead 196, and the
four bit latch 26.
As shown in FIG. 3, the circuit 36 may also comprise a temperature
subcircuit 198 for displaying a value representative of body temperature
on the array 14. The subcircuit 198 comprises a temperature sensor 200,
such as a thermistor, a silicon diode or an integrated circuit such as a
National Semiconductor Model 3911, for sensing temperature and delivering
a signal proportional thereto on an output 202. The sensor 200 may be
located in any convenient site on the underside of the watch casing 12.
The signal on the output 202 is amplified any any suitable amplifier 204
having an output 206 connected to a potentiometer 208. The potentiometer
208, of course, acts to calibrate the voltage appearing on its output 210
which is connected to one or a pair of switch terminals 212, 214. The
terminals 212, 214 comprise part of a switch 216 having a switch element
218 normally connecting the output 118 to the converter 136, a switch
element 220 normally spaced from the terminals 212, 214 and a switch
actuator 222 extending through the watch casing 12 as suggested in FIG. 1.
The terminal 214 is connected to the converter 136 by a lead 224. It is
accordingly apparent that depressing the switch actuator 222 causes the
output 118 to disengage from the converter 136 followed by coupling of the
temperature subcircuit 198 to the converter 136. The voltage signal on the
output 210 is then converted into a frequency, the magnitude of which is
counted by the watch display array 14 following depression of the switch
actuator 32.
It is well known that the temperature measured on an individual's body
depends to some extent on the location where the temperature is measured.
For example, it is well known that oral and rectal temperature readings
vary. It will accordingly be apparent that the potentiometer 208 may be
adjusted so that the readings visible on the array 14 correspond to a
temperature reading taken contemporaneously on the individual.
As shown in FIGS. 2 and 3, the pressure sensor 38 is connected by the lead
62 to a rectifier 226 and battery protection circuit 228 to the battery
34. The rectifier 226 may be of any convenient type and is shown as
including a capacitor 230 in series with a first diode 232. The rectifier
226 also comprises a second diode 234 connected at one end between the
capacitor 230 and the diode 232 and faces into the input end of the diode
232. The opposite end of the diode 234 is connected to ground 236. A
capacitor 238 is connected between the output end of the diode 232 and the
ground connection 236. As will be apparent to those skilled in the art,
the rectifier 236 comprises a voltage doubler or half wave rectifier and
acts to convert an alternating current input into a direct current output.
The protection circuit 228 comprises a diode 240 in series with and facing
in the same direction as the diode 232 and a zener diode 242 connected
between the output 244 of the diode 240 and a ground connection 246. The
diode 240 acts to isolate the battery 34 and prevents battery current from
leading off through the capacitor 238 and ground connection 236. The zener
diode 242 acts as a device to limit the voltage applied to the battery 34.
Consequently, the zener diode 242 is non-conductive until a voltage value
in excess of a predetermined level, for example two volts, appears in the
output 244 at which time the zener diode 242 conducts and provides a
conductive circuit between the output 244 and the ground connection 246 to
shunt the excess voltage.
The battery 34 is connected at one end to the ground connection 246 and is
connected at the opposite end to a lead 248 having a branch 250 connected
to the timing circuit 20 thereby providing power for the timing aspects of
the device 10. The lead 248 extends to a switch terminal 252 adjacent a
switch element 254 on the actuator 32. Upon depressing the switch actuator
32, the switch element 254 passes into contact with the switch terminal
252 and completes a circuit to a power lead 256 which is connected to the
various power inputs of the amplifiers and potentiometers.
It will accordingly be seen that the sensor 38 acts to deliver an
electrical signal which is manipulated to provide readouts of the pulse
rate of the wearer and/or the blood pressure of the wearer. In addition,
the sensor 38 provides an electrical output which is used to energize the
display array 14 and/or to charge the battery 34. Accordingly, the
expected life of the battery 34 will be substantially increased which is
of advantage in itself but which is also of importance in assuring the
user that the blood pressure and/or pulse readouts will operate for
substantial periods without fear of battery depletion.
Although the invention has been described in its preferred form with a
certain degree of particularity, it is understood that the present
disclosure of the preferred form is made only by way of example and that
numerous changes in the details of construction and the combination and
arrangement of parts may be resorted to without departing from the spirit
and scope of the invention as hereinafter claimed. It is intended that the
patent shall cover, by suitable expression in the appended claims,
whatever features of patentable novelty exist in the invention disclosed.
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