U.S. patent number 3,774,594 [Application Number 05/215,890] was granted by the patent office on 1973-11-27 for apparatus for telemetering of ekg signals from mobile stations.
This patent grant is currently assigned to Pioneer Medical Systems, Inc.. Invention is credited to Robert J. Huszar.
United States Patent |
3,774,594 |
Huszar |
November 27, 1973 |
APPARATUS FOR TELEMETERING OF EKG SIGNALS FROM MOBILE STATIONS
Abstract
A system for the radio transmission of EKG signals to a hospital
from an ambulance. After an initial limited transmission of EKG
waves, no further signals are transmitted unless the EKG (R--R)
rate departs significantly from the initial rate. The EKG signals
modulate a voltage controlled oscillator. A code is associated with
the transmission to identify patient, rescue vehicles and
hospital.
Inventors: |
Huszar; Robert J. (Hartford,
CT) |
Assignee: |
Pioneer Medical Systems, Inc.
(New Britain, CT)
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Family
ID: |
22804827 |
Appl.
No.: |
05/215,890 |
Filed: |
January 6, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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819226 |
Apr 25, 1969 |
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Current U.S.
Class: |
600/519;
128/903 |
Current CPC
Class: |
A61B
5/316 (20210101); A61B 5/0245 (20130101); G06K
9/00496 (20130101); A61B 5/0006 (20130101); G06K
2009/00939 (20130101); Y10S 128/903 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); A61B 5/04 (20060101); A61B
5/0245 (20060101); A61B 5/024 (20060101); A61B
5/117 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2.5P,2.5R,2.5T,2.6A,2.6F,2.6R,2.1A ;340/248A,248R,279 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,008,027 |
|
Oct 1965 |
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GB |
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1,264,680 |
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Mar 1968 |
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DT |
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Primary Examiner: Kamm; William E.
Parent Case Text
This is a continuation of application Ser. No. 819,226, filed Apr.
25, 1969, and now abandoned.
Claims
What is claimed is:
1. A telemetering system for transmission of physiological
parameters having normal periods, such as EKG signals having QRS
portions, including:
a. means for amplifying signals from a physiological parameter
having a period,
b. means for converting said signals into pulses of varying
width,
c. an fm radio transmitter,
d. the output of said converting means (b) modulating said
transmitter,
e. means for measuring the period of the parameter and switch means
for controlling the transmission by said radio of said signals,
f. means for actuating said transmitter switch when a subsequent
value of the periodicity of said parameter departs greater than a
predetermined amount from an initial periodicity of said
parameter,
g. a ramp generator,
h. a reference periodic voltage being generated by the ramp
generator,
i. means for diminishing to zero said ramp voltage with a period
initiating change in said parameter,
j. a first Zener diode in a path between said ramp generator and
switch means for conducting said ramp voltage to actuate said
switch means, when a subsequent periodicity of the parameter
increases beyond the reference periodicity,
k. means for supplying an operating potential apart from the ramp
generator to actuate said switch means,
l. means for shunting said operating potential to ground, said
means including a second Zener diode, having a lower breakdown
voltage than said first Zener, which is in a line defining a first
shunt to ground,
m. a second shunt means to ground, parallel with said first shunt
to ground, said second shunt being normally closed and opened only
upon a period initiating change in the parameter.
2. The system of claim 1 wherein,
a. said means (e) includes means for supplying a potential for
actuating said radio switch means, a first switch normally shunting
said potential to ground but which opens and fails to shunt upon a
period initiating change in the parameter, and a second switch
normally open but which shunts said potential to ground when said
reference voltage exceeds a predetermined value.
3. A telemetering system for transmission of physiological
parameters having periods, such as EKG signals having QRS portions,
including:
a. means for generating a periodic reference voltage corresponding
to an initial periodicity value of said parameter,
b. a radio transmitter having a radio transmission switch,
c. means for energizing the radio transmission switch by said
periodic reference voltage when it exceeds a first predetermined
value,
d. a second voltage source for energizing said radio transmission
switch,
e. means shunting to ground said second voltage source except upon
period initiating changes in said parameter,
f. means for shunting to ground said second voltage source when
said periodic reference voltage exceeds a second and lower
predetermined value,
g. whereby the radio transmission switch is energized and signals
corresponding to the physiological parameter are trans-mitted when
subsequent periodicity values of the parameters depart from initial
periodicity values by an amount greater than half of the difference
between the first and second predetermined values.
4. The system of claim 3 including,
a. means for visually presenting the periodic reference
voltage.
5. A telemetering system for transmission of physiological
parameters having normal periods, such as EKG signals having QRS
portions, including:
a. means for amplifying signals from a physiological parameter
having a period,
b. means for converting said signals into an audible frequency, of
variable pitch, in the range 600 to 2000 Hz,
c. an fm radio transmittter,
d. the output of said converting means (b) modulating said
transmitter,
e. means for measuring the period of the parameter and switch means
for controlling the transmission by said radio of said signals,
f. means for actuating said transmitter switch when a subsequent
value of the periodicity of said parameter departs greater than a
predetermined amount from an initial periodicity of said parameter,
said (f) means including a ramp generator, a reference periodic
voltage being generated by the ramp generator, means for
diminishing to zero said ramp voltage with a period initiating
change in said parameter,
g. a first Zener diode in a path between said ramp generator and
switch means for conducting said ramp voltage to actuate said
switch means, when a subsequent periodicity of the parameter
increases beyond the reference periodicity,
h. means for supplying an operating potential apart from the ramp
generator to actuate said switch means,
i. means for shunting said operating potential to ground, said
means including a second Zener diode, having a lower breakdown
voltage than said first Zener, which is in a line defining a first
shunt to ground,
j. a second shunt means to ground, parallel with said first shunt
to ground, said second shunt being normally closed and opened only
upon a period initiating change in the parameter.
6. The system of claim 5 wherein,
a. said means (e) includes means for supplying a potential for
actuating said radio switch means, a first switch normally shunting
said potential to ground but which opens and fails to shunt upon a
period initiating change in the parameter, and a second switch
normally open but which shunts said potential to ground when said
reference voltage exceeds a predetermined value.
Description
This invention relates to telemetering and more particularly to the
transmission from rescue vehicles of information correlated to a
physiological parameter. According to the invention, a system is
provided for the monitoring and transmitting of electrocardiogram
signals (EKG) from ambulances or other rescue vehicles while a
heart attack victim is en route to hospitals. The invention
comprehends the transmission of still other parameters, such as
respiration rate, blood pressure, and the like.
A great number (estimated at 400,000) of persons die in the United
States each year of heart attacks. Of this number, it is estimated
that approximately five-eighths of such deaths occur outside of a
hospital and after one hour of the initial attack. It is further
estimated that perhaps three-fourths of these deaths would be
preventable, provided proper diagnosis and medical attention could
be made available rapidly enough. Considering those instances where
medical attention is obtained, the victim must be brought from the
locale of the attack to a hospital for treatment. Such treatment
requires expert analysis of the particular heart condition before
proper ameliorative procedures can be administered. The more rapid
the analysis of the heart condition, the more rapidly treatment can
be provided. In the past, monitoring of the heart's EKG signals was
generally not possible until the victim arrived at a hospital. If
cardiac arrhythmias (heart standstill or fibrillation) occurred
during ambulance transit, they remained undetected until arrival.
By the practice of the present invention, EKG signals are radioed
for analysis by a physician at the hospital. In severe cases, the
doctor can then radio the ambulance and direct the attendants in
emergency external heart massage in order to keep blood flowing and
prevent brain damage or death due to oxygen starvation.
Accordingly, the main purpose of the present invention is to reduce
the time required for initial analysis of a heart condition. This
is achieved by initiating transmission of EKG data from an
ambulance to a hospital immediately upon placing the victim in the
ambulance, as opposed to the general practice of having to wait
until the patient is in the hospital before conducting EKG tests.
Because of the great demand for limited space in the wireless
spectrum, continuous transmission from a large number of rescue
vehicles is not practical. The present invention, accordingly,
permits the minimum time use of the airways for a single emergency.
This in turn enables a greater number of (ambulance) transmission
stations to use the same band for transmission.
IN THE DRAWINGS
FIG. 1 is a schematic view of the major portions of the
transmission system of the invention.
FIG. 2 is a detailed schematic view showing the automatic
transmission system of the invention, located in an ambulance.
FIG. 3 represents a normal potential v. time EKG.
FIG. 4 represents the potential v. time curve in a certain line in
the system of FIG. 2.
FIG. 5 represents a voltage generated by a portion of the system of
FIG. 2.
FIG. 5a represents the voltage applied to the base of transistor
Q.sub.6 in FIG. 2.
FIG. 6 shows the face of the meter M of FIG. 2.
FIG. 7 illustrates the receiving equipment located in a
hospital.
Referring now to FIG. 1 of the drawings, the illustration relates
to the taking of an electrocardiogram of a patient either
immediately before or immediately after he has been placed into an
ambulance or other rescue vehicle for transfer to a hospital. An
electrocardiogram may be defined as the amplification and
pictorialization of a naturally occurring .+-.3mv potential
generated in a tissue adjacent the heart. It is often taken by
coupling the left leg to the common terminal of a differential
amplifier and connecting the remaining two leads, respectively, to
the right and left arms. After being amplified by amplifier A, the
EKG information is fed to a radio transmitter whenever switch SW is
closed. As indicated in FIG. 1, the EKG signals modulate the output
(carrier) of a voltage controlled oscillator. The thus modulated
VCO oscillator signal passes to switch SW. The other portion of the
EKG is fed to a signal squaring circuit. The output from the square
wave generator actuates two relays, RL.sub.1 and RL.sub.2. The
former relay is coupled to a ramp generator and functions to ground
the potential generated by the ramp generator whenever the relay is
actuated, resetting it to zero. The latter relay RL.sub.2 maintains
its associated switch closed during the major portion of the EKG
signals, and becomes de-energized to thereby open the switch upon
the QRS portions of the EKG signals. When closed, a voltage +V is
shunted to ground by the RL.sub.2 switch. Relay RL.sub.3 controls a
normally open switch which shunts +V to ground whenever the voltage
generated by the ramp generator exceeds a predetermined amount,
here four volts. A fourth relay RL.sub.4 actuates radio
transmission with SW whenever either one of two conditions occur.
The first condition occurs when the voltage generated by the ramp
generator exceeds a predetermined amount, here 6 volts. In the
second condition neither of the switches associated with relays
RL.sub.2 or RL.sub.3 are closed to thereby shunt +V to ground and
+V then actuates RL.sub.4. By this arrangement, as will be apparent
from the more detailed discussion to follow, the EKG is only
transmitted (during the automatic transmission mode of operation of
the system) whenever the EKG heart rate departs from an initial
rate. The initial rate is whatever heart rate the victim had when
the EKG was first taken. The subsequent rate is any later rate the
victim displays while en route in the ambulance to the hospital. It
will be appreciated that this journey occurs during the initial and
often the most critical portion of the heart attack.
Referring now to FIG. 2 of the drawings, the patient is connected
to the system through three integrated circuit linear amplifiers
(A.sub.1, A.sub.2, A.sub.3) connected in a modified differential
amplifier, voltage follower configuration. The construction of such
amplifiers A.sub.1, A.sub.2, A.sub.3 is well known and forms no
part of the invention. The amplified EKG signals are applied over
wire 1 to a voltage controlled oscillator (VCO). The EKG modulates,
hcle by frequency modulation, the VCO output over a 1,400 Hertz
(Hz.) band between 600 and 2,000 Hz.
The VCO converts the EKG signal to an FM subcarrier compatible with
the transmission capabilities of the radio transmitter. The VCO is
a complimentary symmetry astable multivibrator which is driven
directly from the output of the EKG amplifier. The transistors Q16,
Q17 adjust the base bias voltage of the transistors Q14, Q18. This
adjustment alters the voltage at which the transistors switch,
hence the duration of their ON-OFF cycle, hence the multivibrator's
frequency. Two adjustments are provided: R.sub.43 for zero input or
center frequency, the other, R.sub.42, adjusts the slope of the VCO
transfer function, input voltage to output frequency. These
controls are not independent. The VCO square wave output is
filtered by a single pi section to remove high frequency
harmonics.
Amplified EKG signals are also applied over wire 2 to the base of
transistor Q.sub.1. The combination of Q.sub.1 and Q.sub.2 with
resistors R.sub.1 -R.sub.2 -R.sub.3 is proportioned such that
Q.sub.1 is completely cut off while Q.sub.2 conducts fully. The
drop across R.sub.3 provides the cut-off level of Q.sub.1.
The QRS portion of the EKG wave is quite large as compared to the
rest of the complex, note FIG. 3. This portion causes Q.sub.1 to
start to turn on which in turn lowers the base and emitter currents
of Q.sub.2. The regenerative action then switches Q.sub.1 into
strong conduction until the peak recedes; then Q.sub.1 switches off
and Q.sub.2 switches on providing a sharp square wave across
R.sub.2 and R.sub.3 for the period when the peak exceeds the value
of voltage across R.sub.3. This action produces square waves in the
lower conductor 2a, note FIG. 4.
Elements D.sub.3, R.sub.8, C.sub.3, Q.sub.5 and R.sub.9 provide an
integrator fed from source V, whose period is adjustable by
R.sub.8. The output of this integrator is linear. The integrator is
a ramp generator whose output is a potential which is employed as a
reference potential.
When the square wave voltage across R.sub.4 and R.sub.5 changes,
condenser C.sub.1 differentiates this voltage (FIG. 5a) to provide
a sharp positive pulse across R.sub.9 to fire Q.sub.6 which
discharges C.sub.3 to reset the ramp to zero.
Diode D.sub.1 conducts the ramp voltage over wire 3 to condenser
C.sub.5, which retains the last peak voltage obtained from the
ramp. Transistors Q.sub.7 and Q.sub.8 are Darlington connected to
provide an emitter follower to operate meter M which indicates the
last peak voltage of the integrator.
When the patient is first connected to the system, an operator
holds push button PB.sub.1, PB.sub.2 open to prevent the relay
RL.sub.4 from becoming energized. Radio transmission is thus
precluded. He then adjusts R.sub.8 so that the patient's heart rate
(R--R) causes the meter M (initial heart rate) to read 5 volts.
This should only require several EKG signals. PB.sub.1 and PB.sub.2
are released after which PB.sub.3 is depressed. This causes
monostable multivibrator MMV to start up, the action of which is to
throw normally open transistor Q.sub.11 into conduction for about 1
minute. Radio transmission takes place for this initial timed
period. During this time, the EKG is recorded at the hospital
receiving station. After this time, with no change in R--R rate,
the system is quiescent. PB.sub.3, Q.sub.9, Q.sub.10 and Q.sub.11
form a 1 minute initial transmit circuit. When the circuit has not
been operated for some time, Q.sub.10 is full ON due to bias
current through R.sub.19. The low collector voltage of Q.sub.10
prevents Q.sub.11 from receiving bias current so it is OFF. The
ratio of R.sub.15 and R.sub.16 is such that Q.sub.9 does not
receive bias current and it is OFF. Capacitor C.sub.6 is charged to
the supply voltage through R.sub.14. Depression of PB.sub.3
connects C.sub.6 to the base of Q.sub.9. C.sub.6 discharges
providing bias current for Q.sub.9 turning it ON. The collector
voltage of Q.sub.9 drops, C.sub.7 couples this drop to the base of
Q.sub.10 and it turns off. The collector voltage of Q.sub.10 rises
toward the supply voltage and Q.sub.11 turns on. Collector current
of Q.sub.11 flows through wire 8 connected to relay RL.sub.4. Relay
RL.sub.4 turns on operating the radio transmitter. Capacitor
C.sub.7 charges through R.sub.19. When the voltage on C.sub.7
reaches the emitter voltage of Q.sub.10, Q.sub.10 turns ON. The
collector voltage of Q.sub.10 drops turning off Q.sub.11. When
Q.sub.11 turns OFF, relay RL.sub.4 turns OFF and the transmitter
turns OFF. Q.sub.10 turning On also turns OFF Q.sub.9. The circuit
is ready for the next depression of PB.sub.4.
During quiescent operation the rise time of the first EKG pulse
fires Q.sub.1 and the square wave voltage in line 2a and across
R.sub.4 and R.sub.5 falls, producing a negative pulse on the base
of Q.sub.6 which is already cut off. When the EKG pulse falls,
Q.sub.1 cuts off, Q.sub.2 fires and a positive pulse is applied to
the base of Q.sub.6 to reset the ramp to zero by shunting its
voltage to ground.
If the R--R period between each succeeding EKG pulse remains
substantially constant (permissible deviation to be described
later) the ramp voltage will arrive at approximately 5 volts after
each integrating period.
Two actions should be observed: (1) should the heart rate increase
from the preset normal, the ramp voltage will reset to zero before
it reaches 5 volts; and (2) should the heart rate decrease, the
ramp voltage will build up and exceed 5 volts prior to the next R
peak.
The ramp voltage is applied over wire 4 to two Zener diodes,
Z.sub.1 and Z.sub.2, rated at 4 volts and 6 volts. This difference
defines a zone within which the R--R rate can fluctuate without
activating automatic transmission. Zener Z.sub.1 conducts the ramp
voltage to R.sub.10 when the ramp exceeds 4 volts (a heart rate of
120 per minute). Zener Z.sub.2 conducts the ramp to R.sub.11 when
the ramp exceeds 6 volts (a heart rate of 30 per minute).
The voltage across R.sub.4 and R.sub.5 during the peak of the QRS
wave is reduced to the point that Q.sub.3 cuts off. Current now
flows from +V.sub.1 through R.sub.6 over wire 5 to Q.sub.4.
However, since the voltage on the ramp (from the last QRS to QRS
period) exceeds 4 volts, Zener Z.sub.1 conducts current through
wire 7 to R.sub.10 and through R.sub.7 and C.sub.2 and the base of
Q.sub.4 holding it conducting. Condenser C.sub.2 provides a slight
delay before Q.sub.4 cuts off. When the EKG main pulse (QRS)
decays, Q.sub.3 conducts, pulling current on wire 6 below the
conduction point of D.sub.2. The rise of the square wave on R.sub.4
and R.sub.5 is differentiated by C.sub.1 to apply a positive pulse
to the base of Q.sub.6 which now resets the ramp to zero. Zener
Z.sub.1 opens and Q.sub.4 cuts off. Thus, during quiescent
operation, either Q.sub.3 or Q.sub.4 bleeds V.sub.1 to ground,
preventing it from triggering the gate of SCR.sub.1.
Should an EKG pulse (QRS) appear prior to the ramp attaining the 4
volt level (quickening of the heart rate) Q.sub.1 conducts on the
rise of the QRS complex causing Q.sub.2 to reduce the voltage
across R.sub.4 and R.sub.5, cutting off Q.sub.3. Zener Z.sub.1 has
not yet conducted and hence Q.sub.4 is cut off. Current now flows
from +V.sub.1 through R.sub.6, wire 6, through D.sub.2, through
R.sub.12, through PB.sub.2, to R.sub.13, and to the gate of
SCR.sub.1, which now fires and stays conducting. SCR.sub.1
conduction operates the transmitter relay RL.sub.4 to close switch
SW turning on the transmitter.
If the R--R period lengthens, due to a slowing or failure of the
heart to produce a normal QRS (cardiac standstill), the ramp will
continue to build up until Zener Z.sub.2 fires at 6 volts which
immediately places the ramp voltage through R.sub.12 to the gate of
SCR.sub.1, which fires and initiates radio transmission.
The meter M provides visual means for monitoring the heart rate and
also setting into the system the initial heart rate in accordance
with the patient's cardiac status. When the heart rate departs from
the preset value, it is extremely urgent that the hospital to which
the ambulance is proceeding be immediately alerted, advised of the
ambulance identity code and start receiving the EKG pattern. At
this crucial period, time does not permit coding transmission.
Therefore, this invention provides for simultaneous transmission of
the EKG signals and identity codes. SW provides the option for
continuous (C) or automatic (A) EKG transmission. Small bypass
capacitors C.sub.B of 2.3 mf placed, as indicated in FIG. 2, served
to improve operation by shunting radio frequency oscillations to
ground.
The audio spectrum may be divided into several bands, 300 Hertz to
600 Hertz, for identity coding, and the band from 600 to 2,000
Hertz for the EKG modulation. Q.sub.12 and Q.sub.13 operate a code
oscillator circuit. Code .music-sharp.1 in FIG. 2 designates a code
for, say, a particular rescue vehicle, while Codes .music-sharp.2
and .music-sharp.3 (of corresponding circuitry) designate the
hospital and the patient. Q.sub.12 and Q.sub.13 form a high gain
amplifier. Voltage fed from the collector of Q.sub.12 through
R.sub.28 is in phase with the signal at the base of Q.sub.13. The
tuned circuit formed by L.sub.1 and C.sub.15 provide the necessary
frequency selection to cause oscillation. R.sub.30 is a resistor
whose resistance changes with its power dissipation. This provides
ambient temperature compensation of the oscillator frequency,
D.sub.3, R.sub.32, R.sub.34 form bias adjustment circuit that
provides automatic output amplitude compensation.
A tone generator and a lamp connected in parallel and Q.sub.19
provides an audible and visual signal synchronous with each QRS
complex.
FIG. 6 illustrates one layout of the meter dial. Three zones are
provided to facilitate initial set in and rapid readout.
Referring now to FIG. 7 of the drawings, the receiver/demodulator
is shown. This device, which is usually located in the hospital,
consists of a demodulator which recovers the EKG signal from the
carrier and provides an output compatible with standard EKG
monitoring devices. The demodulator input is a two-stage (Q.sub.20,
Q.sub.21), high gain, saturating amplifier. The amplifier output is
a square wave at the input frequency. The square wave is
differentiated (C.sub.10, R.sub.56) and rectified (D.sub.11) to
produce a positive pulse train. These pulses trigger a monostable
multivibrator (Q.sub.22, Q.sub.23, Q.sub.23n) of 100 microsecond
duration.
The monostable multivibrator output is integrated by a 200 Hertz
low pass filter (F.sub.1). The filter output drives a differential
amplifier (Q.sub.24, Q.sub.25, Q.sub.26). The amplifier output is
attenuated 1,000 times to permit the use of standard EKG monitors.
The inverting input to the differential amplifier transistor
Q.sub.25 is used to adjust (R.sub.62) the output voltage to zero
when the subcarrier frequency is at the EKG zero input value
(center frequency).
Control of the monostable multivibrator pulse duration is also
provided (R.sub.59). This control adjusts the slope of the
demodulator transfer function, input frequency to output voltage.
These two controls are not independent.
A transmitter which has been found satisfactory is GE model "Royal
Professional", 30 w. solid state. Similarly, a suitable
commercially available receiver is GE model DM76KCU.
A tone actuated relay and tape recorder are coupled to the receiver
as illustrated at FIG. 7. A Bramco multichannel reed relay device
is satisfactory. The various reeds are resonant to several distinct
frequencies and are accordingly well suited to respond to the codes
sent with the EKG information. It will be recalled that the
filtered VCO (FIG. 2) output consists of square waves whose spacing
(frequency) is determined by the EKG signals, When received, these
waves contain the audio frequencies corresponding to the EKG
signals, the output at R.sub.70, R.sub.71 of the demodulator being
the fully reconstructed EKG, such as shown at FIG. 3.
* * * * *