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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a digital watch having an infrared
plethysmograph and, in prticular, to a remote pulse sensor cable for use
with a pulse sensing digital watch.
2. Description of the Prior Art
Pulse sensing digital watches are relatively new to the field of heart rate
monitoring but, nonetheless, their principles of operation are well known
and understood. One of the first pulse sensing watches on the market
utilizes an infrared pulse sensor mounted on a watch face and connected to
special electronics within the watch. The wearer activates the
plethysmograph electronics merely by pushing a button switch on the edge
of the watch case, then placing his fingertip over the infrared sensor,
and reading his pulse rate directly from the digital display.
Pulse rate sensing is dependent upon certain physiological changes which
occur during each cardiac cycle, i.e., the diastole and the systole. In
the diastole phase the cavities of the heart expand and fill with blood.
The diastolic pressure is the lowest arterial blood pressure of a cardiac
cycle occurring during the diastole of the heart. In the systole phase,
the heart contracts, forcing the blood onward thus keeping the circulation
up. The systolic pressure is the highest arterial pressure of a cardiac
cycle. The fresh blood supply from the heart is conducted by arteries, and
thence by capillaries. Veins return the blood supply to the heart. Blood
in the arteries and capillaries is under pressure and flows in waves due
to the beats of the heart. In response to the systole of the heart, the
pressure in the arterial/capillary system increases to its maximum value
and the system fills with the blood being pumped out of the heart. During
diastole, the heart fills with blood from the veins as the pressure drops
in the arterial/capillary system and the amount of blood in this system
decreases.
One's finger tips contain a great number of these tiny capillaries which
fill with a fresh blood supply during the systolic phase and empty during
the diastolic phase. Heart-rate measurement relies on the slight increase
in infrared light absorption by the blood in the capillaries of the
fingertip during the systolic pressure wave.
An infrared plethysmograph within a digital watch may include a light
emitting photodiode which emits either a continuous or a pulsed infrared
signal which is directed at the capillaries in the fingertip. The IR
reflected from the capillaries is detected by an infrared detector such as
a photodiode or phototransistor. The IR detector is coupled to a
microcomputer within the watch case. As explained above, the capillaries
are more reflective of IR energy during the diastole than the systole. The
microcomputer measures the differences in the signals reflected by the
capillaries, counts the intervals between them, amplifies the data,
averages the calculated heartbeat and displays it periodically after a
predetermined number of heartbeats.
The reasons for wearing such a pulse sensing watch may be as varied as the
number of individuals wearing them. But generally, persons are interested
in knowing their pulse while at rest, to indicate their degree of
relaxation, or during some activity, to determine, at least indirectly,
the stress they place on their hearts. Sampling one's own pulse rate at
rest is a simple procedure. The wearer merely turns the sensing
electronics on, places his finger over the infrared sensor gently, and
reads his pulse directly from the display. It is necessary to apply a
constant and light finger pressure against the infrared sensor, otherwise
false readings may occur. If too much pressure is applied, circulation
through those capillaries may be severely curtailed and low pulse readings
would result. If insufficient finger pressure is applied, the wearer's
finger may move relative to the sensor thereby giving false readings.
In order for one to have a more accurate reading of one's pulse during an
activity, the pulse should be read during that activity. Although a high
heart-beat rate during a strenuous activity is not immediately reduced
upon cessation of that activity, the heart does tend to slow down rapidly
when the activity is terminated. Therefore, it is most desirable to sample
one's pulse during the most strenuous phases for an accurate determination
of the stress one places on one's heart.
Monitoring one's pulse in the course of some activities may be difficult
because of the pressure requirements explained above. For example, a
runner while running places a finger of his right hand on the wristwatch
sensor worn on the left arm and hopes that he is applying the proper
pressure. This is a rather clumsy and awkward attitude. More than likely
the readings obtained would be inaccurate due to the pressure
requirements. In order to obtain precise readings, that person would have
to stop and take his pulse. However, when he stops, his heart has started
its slowing process and the readings he obtains are not representative of
his previously higher heartbeat.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simple
and reliable heartbeat monitoring system.
It is another object of the present invention to provide a pulse monitor
having remote sensing.
It is yet another object of the present invention to provide a
quick-release pulse sensor, cable and display operable with one hand.
It is still another object of the present invention to provide a pulse
sensor and display for monitoring heartbeat during activities which
require that both hands be free.
It is yet another object of the present invention to provide a remote pulse
sensing device for applying a constant pressure for accurate pulse
sensing.
It is another object of the present invention to provide a remote pulse
sensing cable not requiring a detachable pulse sensor unit.
It is still another object of the present invention to provide a device for
shielding a remote pulse sensor from ambient infrared signals.
In accordance with the foregoing objects, a quick release remote pulse
sensing device includes a local pulse sensor unit connectable to infrared
plethysmograph electronics. The local pulse sensor has a connector
receptacle for receiving a remote pulse sensor cable which simultaneously
disengages the local pulse sensor unit. The remote pulse sensor cable
connector has a retainer at the connector end for maintaining the
connector in place. A cuff applies the remote sensor unit to a wearer's
finger for pulse monitoring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of an infrared plethsymograph.
FIG. 2 is a perspective view illustrating a pulse sensing watch and a
remote sensor being worn.
FIG. 3 is a side view of a finger shield.
FIG. 4 is a plan view illustrating a remote pulse sensing cable according
to the present invention.
FIG. 5 is a plan view of the face of a pulse sensing digital watch.
FIG. 6 is a side view of the pulse sensor unit.
FIG. 7 is a cross-sectional view of the pulse sensor unit.
FIG. 8 is a plan view of the substrate to which the pulse sensing diodes
are connected.
FIG. 9 is a perspective view illustrating a leaf spring contact finger.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an infrared (IR) plethysmograph system as might be found
in a digital watch 10 as depicted in FIGS. 2 and 5. A sensor 12 includes a
light emitting photodiode 13 which transmits either a continuous wave IR
signal or a pulsed IR signal. Another photodiode 14, which is situated
next to the transmitting diode 13, receives the reflected IR energy. The
transmitter 13 is powered by a transistor 16 which is controlled by a
pulse generator 18. The transmitter 13 emits a pulsed infrared signal
which is directed to the finger's capillaries beneath the skin. Depending
on the phase of the pressure wave, either diastolic or systolic, the
transmitter signal will be more or less reflected to the receiver 14. A
signal conditioning section 20, directly coupled to the receiver 14,
cancels asynchronous ambient light.
The signal conditioning section 20 is coupled directly to an amplifier and
bandpass filter 22. The amplifier/filter 22 amplifies and filters the
systolic pressure wave pulses which typically occur 60 to 80 per minute
but which could easily double during periods of strenuous exercise,
sometimes exceeding 200 pulses per minute. The amplifier/filter 22 in
combination with the signal conditioning section 20 provides the pulse
counting function for the system.
The output signal of the amplifier/filter 22 is provided to the positive
input terminal of a voltage level discriminator 24. The discriminator 24
compares the input signal, at its positive input terminal, with a
reference voltage VR.sub.5, at its negative input terminal, which sets the
detection level for the systolic pulses. A train of pulses representative
of the heartbeat rate is transmitted to the digital watch timing and pulse
rate computation section 26 which detects the time between the pulse edges
such as the positive-going leading edges, of the systolic pulses in the
train. It then computes the pulse rate. The type of computations provided
by the section 26 is well known in the digital art and need not be
explained in further detail. The pulse rate is then displayed as a decimal
number by the digital watch's displays section 30.
A timing generator 28 responds to a crystal oscillator 29 and provides the
timing .phi..sub.1, .phi..sub.2 and .phi..sub.4 as well as a 32 KHZ clock
signal and a 1024 HZ signal to the computation section 26. The timing
signals .phi..sub.1 and .phi..sub.2 are applied to signal conditioning
section 20 for providing carrier cancellation during the sampling pulse
periods. The clock pulse signals .phi..sub.4 are used to drive the
transmitter 13 at a constant rate such as 73 HZ.
Depressing the push button switch 27 once, causes the timing and pulse rate
computation section 26 to generate an analog power control signal
.phi..sub.A which, in turn, causes the timing generator 28 to produce the
timing and control signals which control the plethysmograph. Pressing the
push button 27 a second time, causes the analog signal .phi..sub.A to be
turned off, thus turning the pulse monitoring function off.
A more detailed discussion of an infrared plethysmograph may be found in
copending applications Ser. Nos. 006,983 (now U.S. Pat. No. 4,260,951
issued Apr. 7, 1981) and965,816 (now U.S. Pat. No. 4,258,719 issued Mar.
31, 1981) respectively entitles "Measurement System Having Pole Zero
Cancellation" and "Heart Rate Measurement System" by Lanny L. Lewyn and
assigned to the assignee of the present application.
Referring now more specifically to the invention, FIG. 2 illustrates an
infrared plethysmograph digital watch 10 being worn by an individual. In
the usual operation mode, i.e., without remote pulse sensing, the the
wearer depresses the push button switch 27 to activate the plethysmograph
electronics. He then places his finger over the pulse sensor unit 12 and
the display 30 shows his pulse rate. The wearer may then depress the push
button switch 27 a second time to turn the pulse sensing electronics off.
This procedure would be followed in the case of the wearer being at rest
or when his activity is such that he can occupy both hands for taking his
pulse. However, when the wearer's activity is such that he must have one
or both hands free, the remote pulse sensing cable arrangement 40 is used.
The remote pulse sensing cable arrangement 40 is connected into the
connector receptacle (see FIGS. 6 and 7) on the side of the local pulse
sensor unit 12. The pulse sensor unit 12 has a slotted opening 15 (See
FIG. 6), parallel to the surface of the watch face, through which a
spade-like connector 42 end (See FIGS. 4 and 7) of a printed circuit cable
arrangement 40, is inserted. A loop 44, around the connector 42, is then
slipped down over the pulse sensor unit 12 to hold the spade-like
connector 42 in place. Inserting the connector 42 into the slot in the
local pulse sensor unit 12 disengages the latter from the infrared
electronics within and engages the remote sensor unit 48 (See FIG. 4) at
the other end of the cable arrangement 40. The remote sensor unit 48 is
held in place against the wearer's finger by a finger cuff 50. To operate
the remote pulse sensing cable arrangement 40, the wearer merely depresses
the push button switch 27 to activate the sensing electronics. The remote
pulse sensor 48 transmits the infrared signals into the tissue and blood
vessels of the wearer's finger which reflect variable amounts of the
infrared energy. The electronics within the watch compute the pulse rate
from the reflected signals as explained above.
The wearer may wish to shield the remote pulse sensor 48 from extraneous
infrared signals and thus he would use a finger boot or shield 49 which is
further described below in the next figure.
Using the remote pulse sensing cable arrangement 40 permits the wearer to
sample his pulse during an activity which requires the freedom of both
hands. Once the remote sensing cable 40 is plugged into the local pulse
sensor unit 12 and worn on the finger, the wearer need only activate the
plethysmograph system by pushing the button 27 once. A jogger, for
instance, may sample his pulse while engaged in the activity, without
being in the awkward position of jogging with his right hand locked onto
the wrist of his left hand.
Briefly, FIG. 3 illustrates the optional finger boot or shield 49 which may
be utilized to shield the pulse sensor unit 48 from an ambient infrared
interference light source. The boot 49 may be made of any suitable
material which is opaque to infrared such as plastic or rubber, and has a
circular opening 49a through which the sensor 48 is inserted. The
necessity of additional shielding is determined by the particular sensors
and electronics used. For example, the circuit of FIG. 1, provides for
automatic cancellation of spurious signals and additional shielding may
not be required.
The remote pulse sensing cable arrangement 40 according to FIG. 4 includes
a flexible flat printed cable 46 having at least three flat wires. Each of
the wires is 0.020 inch wide and each is separated by 0.020 inch from the
other. A fourth wire may be used to provide electrical interference
shielding around the signal wire from the receiver photodiode 14. The
flexible cable 46 may be of the well-known type having a plurality of thin
flat wires made of 1 oz. copper encased within a flat insulating material
such as polyimide sold under the trade name Kapton..RTM. It is preferable,
for safety purposes, to cover the flat cable 46 with two thin layers of
Teflon.RTM. fused together outside the width of the cable 46. Generally,
most flexible cables tend to be somewhat stiff and have sharp edges. In
order to prevent injury to the wearer from the sharp edges, the soft
Teflon covering is added. The end of the cable forms the spade-like
connector 42 which is insertable into the slotted receptacle on the side
of the local pulse sensor 12. The connector 42 is made by removing the
insulating material on one side of the cable from the area identified as
43. The loop 44 about the connector 42 is part of the cable 46. The inside
diameter of the loop 44 is determined by the diameter of the pulse sensor
unit 12. It is preferable to use the flexible flat printed cable because
the end of the cable can function as the connector. A safety feature of
flexible cable is that the loop 44 can break away if the cable should
become entangled so as to prevent injury to the wearer. For example, if
the cable 46 on a jogger's hand accidentally become entangled on a
stationary object while jogging, the loop 44 would break, thus preventing
injury. The cable 40 could still function without the loop 44, although it
would not be as securely fastened to the local pulse sensor 12 as before.
The other end of the cable 46 has a remote pulse sensor unit 48,
essentially identical to the local pulse sensor unit 12 except that it has
no receptacle. The remote sensor 48 has transmitter and receiver
photodiodes, 52 and 54, respectively, which are the same as the
photodiodes 13 and 14 in the local pulse sensor unit 12. The remote pulse
sensor unit 48 is situated in the middle of the finger cuff 50, which is
used to apply the sensor 48 to the wearer's finger. The finger cuff 50,
made of Velcro material, a trade name of Velcro U.S.A., Inc. is
permanently fastened to the cable 46 and remote sensor unit 48 by a
suitable adhesive. The Velcro cuff 50 permits easy one-hand application
and removal of the remote sensor cable 40.
Referring now to FIG. 5, the digital watch 10 has a pulse sensor unit 12
situated on the watch face just below the display 30. The pulse sensor 12
includes the transmitter diode 13 and the receiver diode 14 both directed
outwardly in a perpendicular direction to the plane of the watch face.
Depressing the pulse sensor switch 27 activates the infrared detection
electronics, causing the transmitter 13 to send an IR signal. The wearer
places his finger over the sensor 12, and the receiver diode 14 receives
the reflected IR from the capillaries in the wearer's finger. The return
signal is processed by the electronics within the watch 10 and the pulse
rate is periodically displayed on the display 30. For remote pulse
sensing, the cable assembly 40 is plugged into the right side of the local
sensor unit 12.
FIG. 6 is a side view of the local pulse sensor unit 12, and illustrates
the slotted opening 15 through which the cable connector 42 is inserted.
The contact fingers 32a-32d are visible through the slotted opening.
FIG. 7 is a cross-sectional view of the local pulse sensor unit 12. The
barrel or housing 34 extends from inside the watch 10 to a distance
approximately 0.120 inch above the watch's face. The transmitter and
receiver diodes, 13 and 14 respectively, extend through a spacer 35 at the
top of the housing 34. The photodiodes 13 and 14 are wired to one side of
a printed circuit substrate 36. The substrate has plated through holes
which connect with a series of four plated strips on the bottom side of
the substrate 36. Four leaf spring contacts 32a-32d are mounted to a
dielectric contact support member 37 and the top of the contacts are
touching the printed strips on the substrate 36. Each of the leaf spring
contacts is individually wired to its respective contact point within the
plethysmograph electronics. As the cable connector 42 is inserted through
the slot 15, the leaf spring contacts are pushed away from the contacts on
the substrate 36. The connector wires then make contact with the
leaf-spring contacts 32a-32d and the remote sensor unit 48 is ready for
activation. The dashed outline of the leaf spring contact illustrates the
folded down position of the contacts 32a-32d when the connector cable 42
is inserted through the slot 15.
Referring briefly to FIG. 8, the contact side of the substrate 36 is
illustrated in this cross-sectional view. The contacts 36a-36d are
conductive copper strips, each being electrically connected to the
opposite side of the substrate by plated through holes. The strips are
sufficiently wide and spaced so that they make electrical connection with
the leaf spring contact 32a-32d for conveying the signals between the
sensor unit 12 and the plethysmograph electronics.
A typical leaf spring contact 32 is illustrated in FIG. 9. The leaf spring
contact 32 has a short straight arm 38 used to mount the contact 32 by
inserting it through the support member 37. The long curved portion 39 of
the contact 32 makes contact with the plated contacts on the substrate 36
or the cable connector 42.
In summary, what has been provided by the present invention is a
quick-release, remote, pulse-sensing cable arrangement which utilizes a
flexible flat printed cable having a remote pulse sensor unit at one end.
The second end of the cable serves as a connector for inserting into a
receptacle on the side of a local pulse sensor unit mounted on a digital
watch. The local pulse sensor unit is simultaneously disengaged by the
insertion of the connector as the remote sensor is engaged.
Although the present invention has been shown and described with reference
to a particular embodiment, nevertheless, various changes and
modifications obvious to one skilled in the art to which the invention
pertains are deemed to be within the purview of the invention.
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