 |
Claims  |
|
|
We claim:
1. Apparatus for measuring blood pressure, comprising:
transducer means for generating an electrical signal having an amplitude
corresponding to the magnitude of applied pressure;
means for pressing at least a portion of said transducer means adjacent an
area of a body where blood pressure pulses may be detected, the transducer
means generating electrical pressure pulses corresponding to the detected
blood pressure pulses, each of the electrical pressure pulses defining a
maximum voltage over a systolic interval and a minimum voltage over a
diastolic interval;
analog to digital converter means for sampling the voltage amplitude at a
plurality of points on each electrical pressure pulse and for generating a
coded data word for each sampled voltage, the data word defining the
pressure corresponding to the sampled voltage amplitude;
systolic comparator means for comparing said coded data words and storing
the data word defining the highest pressure;
diastolic comparator means for comparing said coded data words and storing
the data word defining the lowest pressure; and
pressure display means for displaying a representation of the stored data
word of the systolic comparator and of the diastolic comparator.
2. The apparatus of claim 1 wherein said transducer means includes a
piezoelectric crystal.
3. The apparatus of claim 1 wherein said systolic comparator means
includes:
shift register means for storing only one coded data word of said analog to
digital converter means at a particular instant of time;
means for storing in said shift register means the first coded data word
generated by said analog to digital converter means, and
means for comparing the coded data word stored in said shift register means
with a coded data word generated by said analog to digital converter means
and for storing the coded data word of said analog to digital converter
means in said shift register means if the coded word in said shift
register means is less than the coded data word of said analog to digital
converter means.
4. The apparatus of claim 1 wherein said diastolic comparator means
includes:
shift register means for storing only one coded data word of said analog to
digital converter means at a particular instant of time,
means for storing in said shift register means the first coded data word
generated by said analog to digital converter means, and
means for comparing the coded data word stored in said shift register means
with a coded data word generated by said analog to digital converter means
and for storing the coded data word of said analog to digital converter
means in said shift register means if the coded data word in said shift
register means is greater than the coded data word of said analog to
digital converter means.
5. The apparatus of claim 1 which is adapted for measuring heart rate, in
addition to blood pressure and comprising:
counter means for measuring the time interval between successive electrical
pressure pulses for generating coded addresses, each address
representative of the total magnitude of a fixed number of associated
measured time intervals, the fixed number being at least one;
memory means having a stored data table of heart rate codes, each heart
rate code being stored for access by an associated one of said coded
addresses and each heart rate code defining a value of heart rate that
will produce blood pressure pulses having the time interval represented by
the associated one of the coded addresses;
means for applying each coded address to access said memory means for at
least a time prior to the generation of a next successive coded address by
said counter means; and
heart rate display means for displaying a heart rate representation of the
accessed heart rate code in said memory means.
6. The apparatus of claim 5 wherein said counter means includes:
trigger means for generating an electrical trigger pulse in response to a
particular voltage level of each electrical pressure pulse,
timing means for registering a count state defining the time interval
between trigger pulses, the timing means responsive to a trigger pulse to
clear and begin counting at a particular frequency, and
bistable latch means responsive to a trigger pulse for storing the count
state of said timing means before the timing means is cleared, the stored
count state in the bistable latch means being applied as a coded address
to access said memory means.
7. The apparatus of claim 6 wherein said trigger means includes a peak
detector and a schmitt trigger.
8. The apparatus of claim 5 wherein said memory means is a read only
memory.
9. The apparatus of claim 5 wherein said means for pressing includes means
for pressing a pressure sensitive portion of said transducer means
adjacent the radial artery of a wrist.
10. The apparatus of claim 5 including means for registering the passage of
time and for displaying the time.
11. Apparatus for measuring heart rate and blood pressure, comprising:
transducer means for generating an electrical signal having an amplitude
corresponding to the magnitude of applied pressure;
means for pressing at least a portion of said transducer means adjacent an
area of a body where blood pressure pulses may be detected, the transducer
means generating electrical pressure pulses corresponding to the detected
blood pressure pulses, each of the electrical pressure pulses defining a
maximum voltage over a systolic interval and a minimum voltage over a
diastolic interval;
means for generating a coded representation of the pressure corresponding
to the maximum voltage generated by said transducer means in response to
said blood pressure pulses and for displaying the coded representation as
the systolic pressure;
means for generating a coded representation of the pressure corresponding
to the minimum voltage generated by said transducer means in response to
said blood pressure pulses and for displaying the coded representation as
the diastolic pressure;
counter means for measuring the time interval between successive electrical
pressure pulses and for generating coded addresses, each address
representative of the total magnitude of a fixed number of associated
measured time intervals, the fixed number being at least one;
memory means having a stored data table of heart rate codes, each heart
rate code being stored for access by an associated one of said coded
addresses and each heart rate code defining a value of heart rate that
will produce blood pressure pulses having the time interval represented by
the associated one of the coded addresses;
means for applying each coded address to access said memory means for at
least a time prior to the generation of a next successive coded address by
said counter means; and
rate display means for displaying a heart rate representation of the
accessed heart rate code in said memory means.
12. A wrist watch for registering the time and for measuring heart rate and
blood pressure from the blood pressure pulses of the radial artery of the
wrist, comprising:
transducer means for generating an electrical signal having an amplitude
corresponding to the magnitude of applied pressure;
means for pressing at least a portion of said transducer means adjacent to
the radial artery, the transducer means generating electrical pressure
pulses corresponding to the detected blood pressure pulses, each of the
electrical pressure pulses defining a maximum voltage over a systolic
interval and a minimum voltage over a diastolic interval;
analog to digital converter means for sampling the voltage amplitude at a
plurality of points on each electrical pressure pulse, and for generating
a coded data word for each sampled voltage, the data word defining the
pressure corresponding to the sampled voltage amplitude;
systolic comparator means for comparing said coded data words and storing
the data word defining the highest pressure;
diastolic comparator means for comparing said coded data words and storing
the data word defining the lowest pressure;
pressure display means for displaying a representation of the stored data
word of the systolic comparator and of the diastolic comparator;
counter means for measuring the time interval between successive electrical
pressure pulses and for generating coded addresses, each address
representative of the total magnitude of a fixed number of associated
measured time intervals, the fixed number being at least one;
memory means having a stored data table of heart rate codes, each heart
rate code being stored for access by an associated one of said coded
addresses and each heart rate code defining a value of heart rate that
will produce blood pressure pulses having the time interval represented by
the associated one of the coded addresses;
means for applying each coded address to access said memory means for at
least a time prior to the generation of a next successive coded address by
said counter means; and
rate display means for displaying a heart rate representation of the
accessed heart rate code in said memory means.
13. The wrist watch of claim 12 wherein said means for pressing includes an
adjustable wrist band.
14. The wrist watch of claim 12 wherein said means for pressing includes
switch means for applying power to the analog to digital converter means,
systolic and diastolic comparator means, pressure display means, counter
means, memory means, means for applying and rate display means when said
transducer is engaged adjacent the radial artery.
15. The apparatus of claim 12 wherein said systolic comparator means
includes:
shift register means for storing only one coded data word of said analog to
digital converter means at a particular instant of time;
means for storing in said shift register means a first coded data word
generated by said analog to digital converter means, and
means for comparing the coded data word stored in said shift register means
with a coded data word generated by said analog to digital converter means
and for storing the coded data word of said analog to digital converter
means in said shift register means if the coded word in said shift
register means is less than a coded data word of said analog to digital
converter means.
16. The apparatus of claim 12 wherein said diastolic comparator means
includes:
shift register means for storing only one coded data word of said analog to
digital converter means at a particular instant of time,
means for storing in said shift register means the first coded data word
generated by said analog to digital converter means, and
means for comparing the coded data word stored in said shift register means
with a coded data word generated by said analog to digital converter means
and for storing the coded data word of said analog to digital converter
means in said shift register means if the coded word in said shift
register means is greater than the coded data word of said analog to
digital converter means. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
DESCRIPTION
1. Technical Field
The invention relates to a wrist watch for measuring blood pressure and
heart rate and, more particularly, to such a watch including relatively
simple digital circuitry for measuring systolic and diastolic pressure and
for measuring heart rate quickly and accurately.
2. Background Art
Heart rate and blood pressure are important factors in determining the
state of a person's health and the physical condition of a person's body
in response to physical or emotional stress. A periodic monitoring of
these physical parameters is particularly important for individuals having
cardiac afflictions or high blood pressure. However, physically healthy
individuals may also desire to periodically monitor their heart rate and
blood pressure in stress situations, for example when engaging in
strenuous exercise.
Thus, there is a need for an apparatus that will conveniently and quickly
measure the heart rate and blood pressure of an individual and that will
not require an undue amount of training to operate. Also, it is important
that such an apparatus be compact and unobtrusive in use so that it may be
easily used in a variety of circumstances.
Accordingly, heart rate and blood pressure measuring apparatus, in
accordance with the invention, is mounted in a wrist unit that is also
used to tell time. Electronic circuitry in the unit is employed to measure
the rate and force of blood pressure pulses that pass through the radial
artery of the wrist. The unit then provides a digital display of the heart
rate in pulses per minute and the systolic and diastolic blood pressure in
millimeters of mercury.
Wrist-mounted heart rate monitors are known to the art and have been
disclosed, for example, in the U.S. patent to Orr et al, U.S. Pat. No.
3,807,388, wherein the duration of a heart beat is measured by counting
electrical pulses recurring at a known frequency. The duration of the
heart beat is then related to a particular average heart beat rate.
However, the measurement system of Orr et al does not directly measure the
heart rate and, therefore, is subject to inaccuracies of measurement due
to the instability of heart beat duration over brief intervals of time.
There is also disclosed in the patent to Prinz, U.S. Pat. No. 4,120,296 a
heart rate measuring wrist watch wherein electrical pulses having a
particular frequency are generated over the intervals between heart pulses
and are applied to a counter, the contents of the counter being stored for
display and the counter being cleared every 15 seconds to provide new
heart rate data. However, the apparatus of Prinz is fairly complicated and
is also subject to errors resulting from the operational drift of an
integrator and associated voltage sensitive oscillator that are employed
to generate the electrical timing pulses that are counted between the
heart rate pulses.
Accordingly, it is an object of the invention to provide a relatively
simple and accurate apparatus for noninvasively measuring the heart rate
of an individual.
Another object of the invention is to provide such a heart rate measuring
apparatus that may be mounted in a wrist watch and employed to provide a
digital display of heart rate in pulses per minute.
It has been suggested in the patent to M. J. Campanella, U.S. Pat. No.
2,756,741, that an indication of systolic blood pressure may be obtained
by employing a wrist-mounted apparatus to analyze the intensity of the
blood pressure pulses that pass through the radial artery of a wrist. A
piezoelectric transducer is applied adjacent to the radial artery of the
wrist to generate electrical signals corresponding to the blood pressure
pulses that pass through the artery. The electrical signals from the
transducer are applied to a vacuum tube circuit that includes a peak
detector that generates a voltage corresponding to the systolic pressure
occurring at the peak of each blood pressure pulse. The peak detected
signal is applied to a difference amplifier and an associated meter that
indicates the change of the detected systolic pressure with respect to a
normal, calibrated blood pressure.
The blood pressure measuring apparatus of Campanella is not employed to
measure diastolic blood pressure and, also, the vacuum tube signal
analyzing circuitry of Campanella is bulky and requires substantial power
to operate.
A blood pressure measuring apparatus is disclosed in the patent to Petzke
et al, U.S. Pat. No. 3,926,179, wherein a probe is applied adjacent the
radial artery of a wrist. A pressure-sensitive transducer on the probe
generates electrical signals corresponding to the blood pressure pulses of
the radial artery. The electrical pulses are applied to analog circuitry
that generates a systolic signal corresponding to the integrated voltage
at the peak of the electrical pulse signal and a diastolic signal
corresponding to the voltage at the low point of the pulse signal. The
analog apparatus of Petzke et al requires a substantial amount of power to
operate and, therefore, is not suitable for use in a watch that may be
worn on the wrist.
Accordingly, it is an object of the invention to provide a relatively
simple and low power electronic apparatus that may be mounted in a watch
to analyze measure blood pressure pulses at the radial artery of the wrist
and to thereby derive values for systolic and diastolic blood pressure.
These and other objects of this invention will become apparent from a
review of the detailed specification which follows and a consideration of
the accompanying drawings.
DISCLOSURE OF THE INVENTION
In order to achieve the objects of the invention and to overcome the
problems of the prior art, the blood pressure and heart rate measuring
watch, in accordance with the invention, includes a piezoelectric
transducer that is supported on a wrist band adjacent to the radial artery
of the wrist. The transducer generates electrical pressure pulses with
amplitudes that correspond to the magnitude of the blood pressure pulses
of the radial artery. The maximum voltage of the electrical pulses
corresponds to the systolic pressure within the artery and the minimum
voltage corresponds to the diastolic pressure.
An analog to digital convertor samples the voltage amplitude at a plurality
of points on each of the electrical pulses and generates corresponding
coded data words. A comparator means compares the coded data words and
stores the data word having the highest value and the data word having the
lowest value. The minimum and maximum data words are displayed to indicate
the diastolic and systolic pressure.
A counter is employed to register the time interval between successive
electrical pressure pulses as a count state that corresponds to the number
of clock pulses of a particular frequency that are generated over the
interval between the pressure pulses. The count state of the counter is
applied as an address to access a heart rate data word in a ROM memory.
The accessed data word defines a heart rate that will produce blood
pressure pulses having the time interval defined by the accessing count
state. The accessed heart rate data word of the ROM memory is then
displayed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a illustrates a side elevation view in partial section of the heart
rate and blood pressure measuring watch in accordance with the invention.
FIG. 1b illustrates the face of the watch of FIG. 1a.
FIG. 2 illustrates a side elevation view of the transducer support and
control switch for the watch of FIG. 1a.
FIG. 3 illustrates a side elevation view of a tension adjustment apparatus
for the band of the watch of FIG. 1a.
FIG. 4 illustrates a bottom elevation view of the tension adjustment
apparatus of FIG. 3.
FIG. 5 illustrates a block diagram of a circuit for operating the watch of
FIG. 1a.
BEST MODE FOR CARRYING OUT THE INVENTION
The remaining portion of this specification will describe preferred
embodiments of the invention when read in conjunction with the attached
drawings, in which like reference characters identify identical apparatus.
FIG. 1a illustrates a side elevation view in partial section of a blood
pressure and heart rate measuring watch, in accordance with the invention.
A watch case 1 contains electronic circuitry 3 that is employed to
register the time and also to generate electrical signals corresponding to
the blood pressure and heart rate of the wearer. The watch case 1 also
contains a power source, for example a battery 5, that powers the
electronic circuitry 3 and associated 7-segment type digital displays 4.
FIG. 1b illustrates the face of the digital display of the watch in
accordance with a preferred embodiment of the invention. The topmost
portion of the display shows the time in hours and minutes, a middle
portion shows the systolic and diastolic pressure separated by a slash
mark and the bottom portion of the display shows the heart rate in pulses
per minute. It should be appreciated that the display of FIG. 1b may be
comprised of either conventional 7-segment light emitting diode elements
or liquid crystal display elements. As shown in FIG. 1a, the digital
display and associated electronic circuitry and battery are enclosed by a
transparent crystal of a known type.
In normal operation, the time measuring circuitry of the watch of FIG. 1a
operates in a conventional manner to provide electrical signals
corresponding to the time. The watch casing 1 may include a button for
selectively activating the time display for a particular period of time,
in order to conserve the power of the battery 5. Of course, if the display
is a liquid crystal display, the time indication may be continuously shown
since very little power is required to operate the display.
As shown in FIG. 2, the blood pressure and pulse rate circuitry and
associated display elements of the watch are activated by pressing
inwardly on a hinged transducer support arm 9 having a pressure transducer
11 mounted on an inwardly extending portion of the arm. As the transducer
support arm 9 is pressed inwardly, the pressure transducer 11 is forced
into contact with the skin of the wrist adjacent to the radial artery 6 of
the wrist. The inward movement of the support arm activates a micro switch
10 that applies power to the blood pressure and pulse rate circuitry and
associated displays over power leads 19 that may be embedded or woven in
the material of a watch band 21. A sliding switch 13 is then engaged with
an outer notch 14 of the arm 9 so that the transducer 11 is held adjacent
to the radial artery. The sliding switch 13 is biased by a spring 17 so
that the switch will remain in engagement with the outer notch 14 and will
thereby maintain the support arm and transducer in an engaged, pressing
relation with the radial artery.
As shown in FIG. 1a, the micro switch 10 is deactivated and the blood
pressure and pulse rate measuring circuitry and associated displays are
thereby de-energized when the transducer 11 is disengaged from the radial
artery by moving the support arm 9 outwardly from the wrist and engaging
the switch 13 with an inner notch 15. It should be understood that
although the watch band 21 of FIG. 1a is shown as a chain-link band, other
types of bands may be employed without departing from the spirit of the
invention.
The pressure transducer 11 may suitably be comprised of a piezoelectric
crystal that generates an electrical signal having a voltage amplitude
that corresponds to the magnitude of applied pressure. Thus, when the
heart of the wearer of the watch contracts, a strong pulse of blood is
passed through the radial artery, thereby causing the artery to expand and
exert a pressure on the piezoelectric pressure transducer 11. The pressure
on the piezoelectric transducer will increase to a maximum point,
corresponding to the maximum contraction of the heart and, thereafter, the
pressure will decrease as the heart expands and the walls of the radial
artery contract.
It should be understood that the high internal pressure of the artery at
the point of maximum contraction of the heart is the systolic pressure and
the lower pressure within the artery at the point of maximum expansion of
the heart is the diastolic pressure. Accordingly, the piezoelectric
transducer 11 will register an electrical pulse corresponding to each
contraction and subsequent expansion of the heart and the voltage at the
peak of the electrical pulse will correspond to the systolic pressure,
while the low point of the pulse will correspond to the diastolic
pressure.
Although a piezoelectric crystal has been utilized as a pressure transducer
in a preferred embodiment of the invention, it should be appreciated that
other transducers known to the art may be employed without departing from
the spirit of the invention. However, the piezoelectric transducer is
desirable for this application since the transducer measures the direct
effect of the pressure exerted within the radial artery, while other
transducers, for example resistive strain gauges, measure secondary
effects such as the strain forces that are applied at the surface of the
skin due to the expansion of the radial artery.
Although there is only a fairly thin layer of tissue covering the radial
artery of the average wrist, the force exerted by the radial artery in
response to blood pressure pulses is sufficiently small to require that
the piezoelectric transducer 11 be held in contact with the wrist at a
fairly precise pressure so that the blood pressure pulse is properly
registered. In the U.S. patent to Petzke et al, U.S. Pat. No. 3,926,179,
it is indicated that blood pressure pulse signals may be maximized by
providing a pressure on the radial artery that is sufficient to flatten
the artery approximately half-way. In addition to maximizing the blood
pressure signals from the artery, the partial flattening of the artery
also causes the circumferential tension in the elastic wall of the artery
to act in a direction that is perpendicular to the radial pulses of the
blood pressure, so that the circumferential tension does not cause
inaccuracies in the magnitude of the pulse pressure.
Since individual wrists vary in size and since the skin thickness of wrists
also varies, it is necessary to provide a means for adjusting the critical
pressure of engagement of the piezoelectric transducer 11 and the radial
artery in accordance with the physical characteristics of the wrist of the
wearer of the watch. Thus, as shown in FIG. 1a, a tension adjustment
apparatus 23 is provided for the wrist band 21 of the watch in order to
adjust the size of the band and to thereby adjust the pressure at which
the transducer 11 is applied to the radial artery when the sliding switch
13 is engaged with the outer notch 14 of the support arm 9.
FIGS. 3 and 4 illustrate a tension adjustment apparatus that may be used to
adjust the size of the wrist band 21 in a preferred embodiment of the
invention. As shown in FIG. 3, the wrist band 21 may be comprised of links
and a connected adjustment housing 27. One end 29 of the adjustment
housing 27 is affixed to an end of a link 25 and the opposite end 31 of
the adjustment housing 27 is open to admit an associated end link 26 that
is affixed to a cam follower 33 that is slidably supported within the
adjustment housing. A tab end 35 of the cam follower 33 is engaged with a
spiral groove 34 formed in a cam 37 that is mounted for rotation about a
shaft 39 within the housing 27. A retainer clip 41 may be affixed at the
end of the shaft 39 to hold the cam 37 in a rotatably supported position
within the adjustment housing 27.
As shown in FIG. 4, the outward face of the cam 37 has a slot 43 that may
be engaged by a screwdriver, coin, or other thin object to rotate the cam
37. It should be understood that as the cam 37 rotates, the tab end 35 of
the cam follower 33 will follow the groove 38 in the cam 37 and will
thereby cause the cam follower 33 to be slidably moved either inwardly or
outwardly with respect to the adjustment housing 27, in accordance with
the direction of rotation of the cam 37. Thus, the pressure of engagement
of the piezoelectric transducer 11 and the radial artery of the wrist is
set by adjusting the tension of the wrist band 21.
It should be appreciated that the tension of the wrist band 21 must be
initially adjusted to correspond to the size of a particular person's
wrist and the circuitry of the invention must then be calibrated to
display proper pressure readings. Of course, a subsequent adjustment must
be made if the size of an individual's wrist changes, for example if the
individual loses or gains a substantial amount of weight.
FIG. 5 illustrates a block diagram of an electronic circuit that may be
employed to provide the time registration function and blood pressure and
heart rate measurement function in accordance with the invention. The time
registration circuitry corresponds to circuitry typically available in
commercial digital wrist watches. The time circuit includes a crystal
controlled oscillator 45 that generates, for example, a 16 KHz signal that
is applied to a corresponding divider 47 having a tap-off point at which a
pulse is generated each minute. The minute pulses are applied to a minute
counter 49 that defines a 59 count cycle and the overflow bit of the
minute counter is applied to an hour counter 51 that defines a 12 count
cycle. The binary outputs of the minute counter 49 and hour counter 51 are
applied to corresponding binary to BCD decoders 53 that connect with BCD
to seven-segment decoders 55 and seven-segment displays 57. It should be
appreciated that although particular circuit components have been
described with respect to the clock circuit of the invention, other known
components or circuits may be employed without departing from the spirit
of the invention.
In accordance with the invention, the heart rate of the wearer is measured
by applying the electrical input signal from the piezoelectric pressure
transducer 11 to an amplifier 59 having an adjustable gain. The gain of
the amplifier 59 is adjusted to generate a signal having a voltage swing
that is within the detection range of a corresponding peak detector
circuit 61.
The peak detector circuit 61 may operate in accordance with the description
provided in "Linear Integrated Circuits National", pgs. 3-20 (February,
1975). The peak detector circuit 61 generates a signal in response to a
particular value of input voltage. Thus, the peak detector circuit 61 will
generate a signal when the voltage at the output of the amplifier 59
reaches a particular predetermined level. The signal at the output of the
peak detector circuit 61 is applied to a schmitt trigger 63 that generates
a corresponding electrical counting pulse. Thus, it should be understood
that the schmitt trigger 63 generates an electrical counting pulse for
each blood pressure pulse that is registered by the transducer 11. The
peak detector circuit 61 ensures that the schmitt trigger 63 will not be
triggered by brief noise pulses that momentarily rise to a triggering
voltage level.
The triggering pulse of the schmitt trigger 63 is applied through a delay
64 to the clear input of a counter 65 and to the gate inputs of associated
bistable latches 69. The clock input of the counter 65 is connected to the
output of a counter clock 67 that may be derived from the divider 47 or
that may be generated by a separate adjustable oscillator.
When the piezoelectric transducer 11 is initially moved into contact with
the radial artery of a wrist, the micro switch 10 closes to apply power to
the blood pressure and heart rate circuit and the first heart pulse causes
the schmitt trigger to generate a trigger pulse that gates the contents of
the counter 65 into the bistable latches 69 and, thereafter, clears the
counter. The cleared counter then begins counting the pulses that are
generated by the counter clock 67 at a particular count frequency F. When
the second heart pulse causes a second trigger pulse to be generated by
the schmitt trigger 63, the number of pulses that were counted between the
first heart pulse and the second heart pulse are stored in the bistable
latches 69 and the counter is again cleared to begin counting pulses from
the clock 67. Thus, after each trigger pulse, the bistable latches have
stored the number of clock pulses that were counted between the current
and previous trigger pulse.
The count data stored in the bistable latches 69 is applied to the address
input of a programmed read only memory (ROM) 71. Thus, the memory is
accessed at an address location that corresponds to the time interval or
period T between successive heart pulses. Thus, for the time T in seconds
and, given a frequency F of the counter clock 67 in pulses per second, the
accessed address in the memory 71 is F.multidot.T.
The contents of the memory location F.multidot.T should correspond to a
heart rate, in pulses per minute that will produce heart pulses having a
period T. Therefore, the contents of the memory at the indicated address
should correspond to 60/T. It should be understood that the accuracy of
the heart rate measurement is dependent, in part, upon the available
storage capacity of the memory 71 and the associated frequency of the
counter clock 67.
As an example, if the possible range of heart rates is from 30 pulses per
minute to 120 pulses per minute, the corresponding measured period T
between heart beats ranges from 2 seconds to 0.5 seconds. If the desired
accuracy of time measurement is 0.01 seconds, the frequency of the counter
clock 67 should be adjusted to 100 pulses per second. Thus, for a heart
rate of 30 beats per minute, 200 pulses are counted in the counter 65
between heart beats and for a heart rate of 120 beats per minute, 50
counts are registered in the counter 65 between successive heart beats.
Accordingly, the expected range of pulse states of the counter 65 is from
50 to 200.
A coded representation corresponding to the heart rate of 30 beats per
minute is stored at the address 200 and a coded representation of a heart
rate of 6000/199 is stored at the next address 199. In general, at each
address x of the memory 71, a coded representation of a heart rate of
6000/x is stored. For a system having the count frequency F, a count state
x of the counter 65 will access a stored coded representation in the
memory 71 corresponding to a heart rate of (F/x).multidot.(60).
It should be understood that the heart rate circuit of FIG. 5 may be easily
modified to allow the counter 65 to accumulate a count for a plurality of
heart beat intervals. For example, an auxiliary counter may be employed to
operate the counter 65 so that count pulses from the clock 67 are
accumulated over a particular number of heart beats. Of course, the data
in the memory 71 must then be adjusted to take into account the increased
number of heart beats over which an accumulated count is taken.
If the data in the momory 71 is comprised of binary representations of the
indicated range of heart beat values, a binary to BCD decoder and BCD to
seven-segment decoder will be required to display the accessed heart rate
values on the seven-segment displays 77. The conversion steps may be
avoided if seven-segment representations of heart beat values are stored
in the momory 71. Thus, if seven-segment coding is utilized for the heart
beat values stored in the memory, the output of the memory may be applied
to the seven-segment displays through appropriate drivers. Alternatively,
the heart beat values may be programmed into the store as BCD values,
thereby avoiding the BCD decoding step and requiring only a BCD to
seven-segment decoder 75 to apply the heart rate data to the seven-segment
displays 77.
It should be appreciated that the programmed read only memory in the heart
rate computation circuit of FIG. 5 is employed to ensure that heart rate
amounts are generated quickly and accurately. Also, the memory is not
subject to errors caused by the expected operational drift of electronic
components over time.
It should be understood that the above-described circuit elements of the
heart rate measuring circuit of FIG. 5 are intended to be included as
functional components of an integrated circuit chip. Thus, the physical
size of the circuit elements of FIG. 5 may be reduced in a manner known to
the art to fit within the relatively small area contemplated for use in
the watch casing of FIG. 1a.
A portion of the circuit of FIG. 5 is directed to deriving a measurement of
the systolic and diastolic blood pressure from the electrical pulse signal
that is generated by the piezoelectric transducer 11. In operation, the
transducer 11 is pressed into contact with the radial artery, the sliding
switch 13 is engaged with the outer notch 14 and the micro switch 10 is
closed to energize the blood pressure and heart rate circuit.
The voltage pulses from the transducer 11 are then applied to an amplifier
73 having an adjustable gain and the amplifier passes amplified pulses to
an analog to digital converter 75. The voltage gain of the amplifier 73 is
adjusted to provide pulses with a voltage swing within the operational
range of the analog to digital converter 75. The converter 75 receives the
analog voltage pulse of the amplifier and a gating signal from a
millisecond clock 77 that may be taken from the divider 47 or generated by
an independent oscillator.
The gating clock 77 is adjusted to generate several thousand pulses per
second, and the pulses are applied by the converter to sample the voltage
at many points on each output pulse of the amplifier 73. Each of the
sampled voltages is then converted to a binary code that corresponds to
the pressure in millimeters of mercury that was applied to the transducer
11 to produce the sampled voltage at the output of the amplifier 73.
The binary code for the initial voltage sample of a pulse from the
amplifier 73 is applied to a first input of a comparator 79 and is stored
in a shift register 81 in response to a pulse from a gate control citrcuit
82 that is activated by the miro switch 10. The output of the shift
register 81 is applied to a second input of the comparator 79 and to
binary to BCD decoders 83. The outputs of the decoders 83 are applied to
corresponding BCD to seven-segment decoders 85 and the outputs of the
decoders 85 are then applied to corresponding seven-segment displays 87.
After the first sample from the converter 75 is applied to the comparator
79 and gated into the shift register 81, the binary code of the second
sample is applied to the input of the comparator 79 and, if the magnitude
of the binary code of the second sample is greater than the magnitude of
the binary code of the first sample, the comparator 79 operates to store
the larger binary code of the second sample in the shift register 81 by
overwriting the previously stored code.
Successive binary codes are applied to the comparator 79 and are compared
with the code stored in the shift register 81, and, if the code in the
shift register is smaller, the larger code is stored in the shift register
by overwriting the smaller stored code. Thus, the shift register 81 is
operated to store a maximum binary code that corresponds to the maximum
blood pressure that is measured by the transducer 11 and the maximum code
is displayed on the seven-segment display 87. It should be understood that
the maximum code stored in the shift register 81 corresponds to the
pressure in millimeters of mercury that is measured by the piezoelectric
transducer 11 at the peak or systolic point of the blood pressure pulses.
Thus, the seven-segment displays 87 show the measured systolic blood
pressure.
The diastolic blood pressure is measured in a fashion that is similar to
the measurement of the systolic blood pressure. In operation, the binary
coded signal for the initial sample is stored in a shift register 91 and
is applied to a comparator 89. Su | | |
