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BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates generally to the medical diagnostic field and
more particularly to a method and apparatus for detecting heart sounds and
for generating accurately timed reference signals coincident with the
first and second heart sounds of a cardiac cycle. The present invention
further relates to the control of medical diagnostic imaging apparatus
based on first and/or second heart sound reference signals.
B. Description of the Prior Art
Various medical diagnostic methods and apparatus of the prior art have
attempted to detect heart sounds and to distinguish between the first and
second heart sounds by amplitude or by gating with the R wave of the ECG.
Further, the prior art arrangements utilize the timing relationships
between successive heart sounds and the first and second heart sounds for
analysis purposes. Other prior art arrangements have attempted to
synchronize, gate or trigger cardiac imaging apparatus on the basis of
heart sound amplitudes, patient cardiac pulse signals, or
electrocardiogram signals and delay techniques.
For example, U.S. Pat. No. 4,094,308 to Cormier detects heart sounds to
develop an electrical phonocardiogram via an inverse filter network
denoted as a deconvolution function. A phonocardiogram transducer is
placed in contact with the chest of a patient whereupon acoustical energy
of the heart sounds is converted into electrical energy. The resultant
signal waveform after the deconvolution filter provides impulse functions
for each heart sound with the basic purpose of the apparatus to determine
the systolic time intervals such as: (1) the pre-ejection phase or period
denoted as the elapsed time from the Q-wave onset (in the
electrocardiogram waveform) to the opening of the aortic valve; or (2) the
left ventricular ejection time equal to the length of time the aortic
valve remains open as determined by the time difference between the two
impulse signals. The apparatus distinguishes the impulses derived from the
heart sounds on the basis of amplitude to establish timing markers for the
measurement of the systolic time intervals and the accompanying heart
rate. The larger amplitude signal is stated to occur during the closing of
the aortic valve. Pulse height detection of the rectified signals
resulting from the process is achieved with hysteretic comparators and
with digital level converters regulating extracted voltages and current
pulses to trigger digital logic networks and microcomputer circuits which
selectively activate electronic counters, timers and dividers to measure
the pre-ejection phase, the left ventricular ejection time, the ratio of
these two quantities, and the heart rate.
U.S. Pat. No. 3,318,303 to Hammacher measures heart sounds by use of a
contact microphone and provides outputs distinguishing the first and
second heart sounds of each heart cycle by generating impulses coincident
with each heart sound. While the first and second heart sounds are
distinguished and separately analyzed, the first and second heart sounds
are not differentiated by the timing relationships between the heart
sounds in the overall heart cycle but merely by the state of a flip-flop
which changes state upon the detection of each heart sound to thereby
output two series of pulses, one for each heart sound in each heart cycle.
The purpose of the Hammacher method and apparatus is to accurately
determine heart beat frequency by comparing the periodic rates of each of
the pulse trains corresponding to the first and second heart sounds and
comparing the heartbeat frequency rate between the two pulse trains.
Hammacher also mentions the detection of the first heartbeat by
combination with the R-wave of the ECG.
U.S. Pat. No. 3,581,735 to Gentner, et al. is directed to
phonocardiographic apparatus for measuring fetal heart frequency and
utilizes the relationships of detected heart sounds in accordance with the
overall period of the heart rate to detect missed heartbeats to provide
accurate indications of the heart frequency. Specifically, the analysis
utilizes physiological criteria to determine if heart sounds have been
missed by comparing the time between successive detected heart sounds and
the overall heart cycle to determine if an accurate heart frequency has
been detected. For example, if the second heart sound is not detected and
missed, a low heart rate frequency results and the ratio between
successive heart sounds and the overall period is analyzed and if this
ratio is approximately equal, it is determined that a heart sound has been
missed; since at low heart rate frequencies such a ratio is
physiologically impossible as the time between the first and second heart
sounds is much less than the time between the second heart sound of the
first cycle and the first heart sound of the next cycle for low frequency
heart rates. However, if a high heart rate frequency is detected and the
ratio is approximately equal, it is determined than an accurate heart rate
freqeuncy has been detected. There is no distinguishing between the first
and second heart sounds as the systolic and diastolic events to
differentiate the heart sounds.
U.S. Pat. No. 3,498,292 to Jorgensen, et al. is directed to a heart sound
sequence indicator to detect and indicate the first and second heart
sounds and their respective intervals on respective systolic and diastolic
indicators. The determination and distinguishing of the heart sounds is
achieved by derivation from the electrocardiogram waveform and appropriate
timing circuitry and the arrangement does not directly detect or
discriminate heart sounds.
U.S. Pat. Nos. 3,171,892, 3,954,098 3,921,623, Re. 27,042, 3,878,832 and
3,132,208 are directed to various prior art techniques that analyze heart
sounds for various purposes. For example, U.S. Pat. No. 3,171,892 utilizes
an acoustic pickup device for detection of the fetal heart rate within
another organism and utilizes pulse duration discriminator means to
distinguish the fetal heart rate pulse waves from that of the mother by
the pulse width of the heartbeat rate signals. U.S. Pat. No. 3,954,098 to
Dick et al is directed to heart display apparatus and triggering of the
display from a delayed ECG signal. U.S. Pat. No. 3,921,623 is directed to
an acoustical heartbeat measuring circuit for analyzing specific
frequencies occurring in the heartbeat and includes a filter having a
predetermined frequency response to output an indication of a number of
output signals. U.S. Pat. No. Re. 27,042 is directed to an examination of
the characteristics of heart sounds as detected by a microphone pickup. An
electrocardiogram sequencing network controls the systolic and diastolic
interrogation intervals and thus the heart sounds are detected under
control of the electrocardiogram sequencing. U.S. Pat. No. 3,878,832 is
directed to a system for analyzing heart defects as detected by random
noise from a composite signal that includes a periodic portion and a
random noise portion. U.S. Pat. No. 3,132,208 is directed to a variable
conductivity gate circuit for amplifier selectivity in an electronic
stethoscope.
Considering various prior art techniques for utilizing heart sounds and/or
ECG signals to control diagnostic display, U.S. Pat. No. 3,220,404 to
DelLucchese is directed to a combined X-ray and phonocardiographic camera
wherein the horizontal sweep of a display device is gated when heart
sounds detected by a microphone exceed a predetermined level.
U.S. Pat. No. 2,190,389 to Strauss, et al. is directed to the control of
X-ray apparatus by means of a heart movement or pulse beat pickup and
providing an adjustable time delay to activate the X-ray tube of the
apparatus. A pulse pickup is affected by means of a compression cuff or
bag applied to the wrist with pressure variations being transmitted to act
upon a piezoelectric crystal.
U.S. Pat. No. 3,825,751 to Geratsdorfer is directed to a method of
activating X-ray apparatus by means of electrocardiogram signals and
providing a predetermined delay to activate the apparatus for
approximating the appropriate time of activation based on the
electrocardiogram waveform.
U.S. Pat. No. 3,626,932 to Becker is directed to a method and apparatus for
producing a double exposure, X-ray photograph of a heart at two different
points during the cardiac cycle by causing an X-ray machine to produce an
X-ray burst at a first given point in a cycle and then another burst at a
second different point during the cycle. The method and apparatus utilizes
a synchronizer for detecting the R-wave peak from electrocardiogram
waveform and includes various adjustable pulse delay means for proper
synchronization.
U.S. Pat. No. 3,557,371 to Becker is similarly directed to a method and
apparatus for calibrating a cardiac X-ray synchronizer to cause an X-ray
machine to produce an X-ray burst at a given adjustable point in the
cardiac cycle of a patient disposed in the burst path. The R-wave peak in
the electrocardiogram waveform is detected to produce a signal actuating
the machine at a given adjustable time after the R-wave peak.
U.S. Pat. No. 2,152,045 to Gulland is directed to a body operated switch
apparatus for synchronizing X-ray exposures utilizing a mercury switch
mechanically operated by pulse, respiratory or other movements of the body
and includes delayed action for timing exposures of X-rays or other
photographs of the heart, lungs, etc.
U.S. Pat. No. 3,344,275 to Marchal, et al. is directed to radiology
apparatus for effecting a simultaneous recording of a relatively slow
variation of density such as of the lungs during respiration and also of
the small variations of density due to the circulation of the blood.
Activation of the two channels of information is controlled by an
electrocardiogram input.
U.S. Pat. No. 4,240,440 to Groch et al. is directed to method and apparatus
for obtaining a nuclear kymogram of regional heart wall motion in
synchronism with a display of the ECG signal; the dispaly being triggered
under the control of the ECG signal.
Various other display arrangements controlled by the ECG signals are
described in the following publications:
"Clinical Assessment of Left Ventricular Regional Contraction Pattern and
Ejection Fraction by Height Resolution Gated Scintography", Berman et al.,
Journal of Nuclear Medicine, Volume 16, Number 10, pp. 865-874;
"Thallium-201 Myocardial Imaging: Characterization of the ECG-Synchronized
Imager", Hamilton et al., Journal of Nuclear Medicine, Volume 19, Number
10, pp. 1103-1110;
"Left Ventricular Function in Acute Myocardial Infarction Evaluated by
Gated Scintiphotograph", Rigo et al., Circulation, Volume 50, pp. 678-684,
1974;
"A Real-Time System for Multi-Image Gated Cardiac Studies", Bacharach et
al., Journal of Nuclear Medicine, Volume 18, Number 1, pp. 79-84, 1977;
and
"Comparison of Defect Detection or Ungated vs. Gated Thallium-201 Cardiac
Imager", McKusick et al., Journal of Nuclear Medicine, Volume 19, Number
6, p. 725.
U.S. Pat. No. 3,993,995 to Kaplan, et al. is directed to a respiration
monitor and utilizes arrangements for the automatic triggering of an X-ray
machine at the instance of respiration extremes.
Thus, while the arrangements of the prior art have attempted to detect and
distinguish between heart sounds, these prior art arrangements are not
entirely suitable for accurately distinguishing between the first and
second heart sounds and for providing accurately timed reference signals
synchronized with the first and/or second heart sounds. Further, the prior
art arrangements do not provide accurate and efficient diagnostic analysis
to synchronize analysis data and/or images by accurately timed first
and/or second heart sounds.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provide a
method and apparatus for detecting heart sounds and for generating
accurately timed reference signals coincident with the first and second
heart sounds of a cardiac cycle based on the time relationship of the
detected heart sounds.
It is another object of the present invention to provide a method of
controlling diagnostic apparatus to provide accurately synchronized data
analysis and/or images of cardiac function under the control of accurate
first and/or second heart sound signals.
It is a further object of the present invention to provide a method and
apparatus for providing first and second heart sound signals wherein the
heart sound signals are distinguished and provided only when the two
sequenced signals satisfy a time relationship such that both signals occur
within a window of time, the appropriate window of time being selected in
accordance with the cardiac cycle of the patient being monitored and
predetermined characteristics of the cardiac cycle.
It is yet another object of the present invention to provide a method of
controlling cardiac diagnostic apparatus wherein an accurately determined
second heart sound signal is utilized to correct the gating of analysis
data or to accurately initiate analysis throughout the diastolic interval
starting at systole.
It is a further object of the present invention to provide a method of
controlling the accumulation of cardiac data through the use of accurate
first and/or second heart sound signals for patients with pacemakers,
serious arrhythmias and other cardiac characteristics that cause
distortion of the electrical impulse denoted as ECG or functional
relationships that cause spurious heart sounds that could be erroneously
detected as the first or second heart sound.
Briefly, these and other objects of the present invention are efficienctly
achieved by providing a method and apparatus for detecting heart sounds
and for generating accurately timed reference signals coincident with the
first and second heart sounds of a cardiac cycle. The detection and
generation of the first and second heart sound signals are based on the
time relationship of the detected heart sounds. Further, there is provided
a method of utilizing the generated first and second heart sound reference
signals for synchronization or gating of medical diagnostic imaging
apparatus. Thus the medical diagnostic imaging apparatus is controlled to
accept data or an image as determined by the first and/or second heart
sound reference points for improved diagnostic purposes. For example, the
diagnostic apparatus may be controlled to provide improved diagnostic
information for phase analysis of gated blood pool studies. The heart
sound detecting apparatus further provides for detection based on either
the timing relationship between the heart sounds or by the R-wave of the
ECG signal. The heart sound detecting apparatus includes a display to
selectively provide a read-out of the time interval or rate of various
heart cycle parameters including first to second heart sound time
interval, first heart sound to first heart sound rate or time interval,
heart rate, heart cycle period, R-wave to R-wave rate or interval, R-wave
to first heart sound time interval, R-wave to sound heart sound time
interval, and R-wave to R-delay signal as selected on the apparatus. The
heart sound detecting apparatus includes arrangements for the simultaneous
recording and playback of heart sounds and the ECG waveform signals on a
common channel or track.
The invention both as to its organization and method of operation together
with further objects and advantages thereof will best be understood by
reference to the following specifications taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram representation of heart sound detection and
gating apparatus to generate first and second heart sound signals in
accordance with the present invention;
FIG. 2 is a block diagram representation of ECG gating apparatus and
recording apparatus of the present invention for use with the heart sound
detection and triggering apparatus of FIG. 1;
FIG. 3 is a graphic representation versus time of the operation of the
heart sound detection and triggering apparatus of FIGS. 1 and 2 in a timed
mode of operation and a typical heart cycle illustrating the first and
second heart sounds and the ECG waveform associated therewith;
FIGS. 4a through j when assembled as shown in FIG. 4k form a schematic,
logic and block diagram representation of a detailed specific embodiment
of the heart sound detection and triggering apparatus of FIG. 1.
FIG. 5 is a representation of various timing diagrams and signal
relationships in the specific embodiment of the heart sound detection and
triggering apparatus of FIG. 4 regarding a first to second heart sound
timing detection mode of operation;
FIG. 6 is a representation of various timing diagrams and signal
relationships in the specific embodiment of the heart sound detection and
triggering apparatus of FIG. 4 regarding an ECG R-wave detection mode of
operation;
FIG. 7 is a graphical representation useful in illustrating the operation
of the present invention of FIG. 4 and illustrating look-up table ranges
of operation for setting timing windows in connection with heart sound
detecting; and
FIG. 8 is a block diagram representation of diagnostic apparatus for use
with the present invention and illustrating the control of diagnostic
apparatus in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, the heart sound detection and triggering apparatus
10 of the present invention includes a heart sound signal selector switch
12 that selectively connects one of three heart sound audio signal inputs
14, 16 or 18 to a common output 20 of the selector switch 12.
The heart sound signal input 14 is derived at the output of a sound
transducing circuit 22 from either a single sound transducer input 24 or
form dual sound transducing inputs 26, 28. The second transducing inputs
24, 26, 28 are connected in various applications to sound transducing
apparatus or microphones placed on the chest of a patient under
investigation. The dual sound transducing inputs 26 and 28 are each
respectively connected to a sound transducer placed on a different chest
position. Accordingly, one sound transducer receives a higher amplitude
from the heart sounds of a patient through the chest cavity while the
second sound transducer receives a relatively lower amplitude heart signal
based on the positioning of the second sound transducer at a somewhat more
remote location from the heart position. Thus, the sound transducing
inputs at 26 and 28 receive essentially equal inputs of background sounds
and body sounds as modified by the patient's body for common mode
rejection of these unwanted background sounds such as respiration or room
noise. The sound transducing inputs 24, 26 and 28 are connected to a
preamplifier stage 30. The outputs 32 and 34 of the preamplifier stage 30
are connected to two inputs of a differential amplifier stage 36. In the
case of dual sound transducer inputs, differential amplifier 36 responds
only to the differential heart sound signals and essentially rejects all
common mode unwanted signals. In the case of a single sound transducer at
24, the output 34 is amplified by the differential amplifier stage 36. The
amplified output 38 of the differential amplifier stage 36 is processed by
a filter stage 40 to provide the heart sound signal input 14. The filter
stage 40 is arranged to eliminate any frequencies unrelated to first and
second heart sounds.
The heart sound signal input 16 is provided by an external amplifier/filter
arrangement referred to generally at 42 for use with external sound
transducing and amplifying apparatus. The heart sound signal input 18 is
provided at the output of a two Khz. cutoff low pass filter stage 44 from
a recorded heart sound input 46. The recorded heart sound input 46 is
provided at the output of a recorded heart sound ECG and buffer stage 48
(see FIG. 2). The input to the recorded heart sound ECG and buffer stage
48 is connected to a playback transducing output 50 of a recorder (FIG.
2). The recorded heart sounds and ECG waveforms of a patient are recorded
on a common channel or track by a recording arrangement for use with the
present invention for analysis at a time subsequent to actual recording of
the heart sounds and the ECG waveform of a patient under investigation for
future, further analysis.
The output 20 of the heart sound signal selector switch 12 is connected
through a filter stage 52. In a specific embodiment the filter stage 52 is
a low pass filter with a cut-off frequency below 500 Hz. which is arranged
to eliminate some of the audio signals associated with heart sound
transducing but which are unrelated to the actual first and second heart
sounds. The output 54 of the filter stage 52 is connected through an AGC
amplifier stage 56 to normalize signal levels for the subsequent detection
and gating stages of the arrangement 10.
A first output 58 of the AGC stage 56 is connected through a heart sound
display buffer stage 60 to provide a display output 62 of heart sounds for
analysis. A second output 64 of the AGC stage 56 is connected as a summing
output for recording along with ECG waveforms to a recording arrangement
as will be discussed in more detail in connection with the ECG gating
apparatus of FIG. 2.
The output 64 of the AGC stage 56 is also connected through a positive
enveloper and squaring stage 66 which essentially repositions all negative
portions of the heart sound waveform at 64 into the positive enveloped
signal domain and also squares the input to accentuate the heart sound
signals in the positive envelope. The output 68 of the positive enveloper
and squaring stage 66 is connected through a comparator or peak detector
stage 70 to provide at output 72 a digital trigger signal in response to
the heart sounds.
Referring now to FIG. 3, typical first and second heart sounds associated
with a typical cardiac cycle are illustrated in conjunction with the ECG
waveform with the heart sounds defining the systolic and diastolic
intervals of the overall cardiac cycle.
The digital heart sound trigger signals at 72 are connected to a digitally
variable digital filter stage 74. The digital filter stage 74 provides
pulse shaping and a heart sound signal pulse output at 76 in response to
each heart sound trigger signal at 72 in accordance with a digital
selection signal at 78. The digital filter stage 74 in accordance with the
digital selection signal 78 also provides a variable lock-out time window
such that the digital filter is inhibited from outputting additional heart
sound signals at 76 within the time interval of the lock-out time
immediately after a heart sound signal output at 76.
The digital selection signal 78 is provided by a digital integrator and
timing control stage 80 that determines appropriate digital selection
signals at 78 in accordance with the cardiac cycle and heart sound timing
of the apparatus 10. The digital integrator and timing control stage 80
receives data signals at 82 from a display and control file 84. A data
address input 86 is provided to the display and control file from a system
timing control stage 88.
The digital heart sound pulse signals at 76 are connected to a window
trigger selector stage 92 and a window mode control stage 100. The window
trigger selector stage 92 provides a digital trigger control signal at 94
to control operation of a digitally variable time window stage 90 in
accordance with either the digital heart sound pulse signal at 76 in a
timed mode (T-mode) of operation or an ECG R-wave signal 96 provided as an
input to the window trigger selector stage 92 from the ECG apparatus of
FIG. 2 in an ECG R-wave (E-mode) of operation.
The trigger selection of the window trigger selector stage 92 is
accomplished by a selection input from a selection switch arrangement at
97. In a first E-mode switch state of the arrangement 97, the window
trigger selector stage 92 provides a trigger control signal at 94 in
accordance with the ECG R-wave signal at 96. In a second T-mode switch
state of the switch arrangement 97, the window trigger selector stage 92
provides a trigger control signal at 94 in accordance with the heart sound
pulse signal at 76.
The digitally variable time window stage 90 also includes as an input the
digital selection signal 78. The digitally variable time window stage 90
sets one or more variable time windows in accordance with the data state
of the digital selection signal 78 and the mode of operation as set by
switch 97. In accordance with the variable time window or windows, the
digitally variable time window stage 90 provides appropriately timed heart
sound enable signals at 98 and at 104 to the window mode control stage
100.
The window mode control stage 100 in accordance with the inputs from the
heart sound enable signals 98 and 104, and the digital heart sound pulse
signals at 76 outputs a first heart sound trigger signal at 106 and a
second heart sound trigger signal at 108.
Thus, the digital filter stage 74, the window trigger selector 92, the
digitally variable time window stage 90, and the window mode control stage
100 function in combination as a digital time filter as variably set by
the digital selection signal 78 to detect the heart sound pulse signals at
76 and distinguish between the first and second heart sounds. The variable
time windows are automatically adjusted by the heart sound detection and
triggering apparatus 10 to accurately distinguish between the first and
second heart sounds for patients with heart rates in a specific
predetermined range; e.g., 15-250 beats (heart cycles) per minute in a
specific embodiment. The operation of the apparatus 10 to adjust the time
window and to detect the heart sounds will be discussed in more detail
hereinafter.
The first heart sound trigger signal 106 and the second heart sound trigger
signal 108 are provided as inputs to a system trigger select output stage
110 that functions as a selector switch to output a system trigger output
signal at 112 for the triggering and control of diagnostic equipment. The
trigger select stage 110 also includes the ECG R-wave trigger signal 96
and an ECG R-wave delayed trigger signal 116 as inputs. The signals 96 and
116 are provided from the ECG apparatus of FIG. 2. The system trigger
output 112 is also connected through a display trigger stage 118 to
provide a display study trigger signal 120 at the appropriate level.
The first and second heart sound trigger signals 106 and 108 respectively
and the ECG signals 96 and 116 are also connected as inputs to a display
input selection and pulse-to-pulse gate stage 122. The display selection
and pulse gate stage 122 includes a selection switch 123 for selecting one
of a predetermined number of parameters for display selection as rates
(beats per minute) or time intervals (in milliseconds), including, for
example, in a specific embodiment first to second heart sounds time
interval (F-S), first heart sound to first heart sound time interval (F-F)
or (F-F) rate, ECG R-wave to R-wave rate (R-R rate) or time interval
(R-R), ECG R-wave to first heart sound time interval (R-F), ECG R-wave to
second heart sound time interval (R-S), and ECG R-wave to R-wave delayed
time interval (R-RD) as set on a delay selector. A display 130 discussed
hereinafter is controlled to display each of the parameters. The display
selection and pulse gate stage 122 responds to the selected trigger
signals as set on the selection switch 123 and provides appropriate
corresponding timing signals, display signals and mode select signals to
provide accurate time interval or rate data for display purposes and also
for system control.
Specifically, the display selection and pulse gate stage 122 provides a
rate/time interval select output at 124 to appropriately control the
system timing control stage 88 in a binary mode corresponding to rate and
in a decimal mode corresponding to time interval. The rate/time interval
select output 124 is also connected as a selector input to a time interval
or rate selector stage 126.
The time interval or rate selector stage 126 outputs display data at 128 to
the display 130. The time interval or rate selector stage 126 includes
time interval data inputs at 86 from the system timing control stage 88.
Further, the time interval or rate selector stage includes rate data
inputs at 132. Thus, the time interval or rate selector stage 126 outputs
at 128 either the rate data from the rate data input 132 or the time
interval data from the time interval data input 86 in accordance with the
selector signal at 124. The system timing control stage 88 includes a
clock input at 134 from a system timing clock 136. The system timing clock
136 is enabled to output clock pulses at 134 when enabled by a clock
enable input 138 from the display selection and pulse gate stage 122. The
system timing control stage 88 also includes a preset input at 140 to
preset the stage 88 at the start of a time interval or rate determination
based on the first trigger signal received by the display input and pulse
gate stage 122 in accordance with the selected functions. Further, the
display selection and pulse gate stage 122 also stops the time interval or
rate determination by means of the enable signal 138 to the system timing
clock 136.
For example, if the display selection and pulse gate stage 122 is set to
the first to second heart sound display selection mode, the system timing
control stage 88 will be controlled to start timing interval count data
upon the occurrence of the first heart sound pulse signal at 106 and the
system timing control stage 88 will stop the count upon the occurrence of
the second heart signal. The accumulated count at output 86 then
corresponds to the time interval of first to second heart sound signals.
The time interval or rate select stage 126 in accordance with a time
interval select signal at 124 provides the time interval data at 128 for
display.
Considering a rate display, the display and control file 84 is addressed by
the data output 86 with the system timing control functioning to count in
the rate mode as set by the rate/time select signal 124. In response to
the address at 86, the display and control file 84 outputs at 132 the rate
data corresponding to the count data address input. With the select signal
124 in the rate mode, the time interval or rate select stage 126 outputs
the rate data 132 at the display output 128.
Referring now to FIG. 2 and considering the ECG gating apparatus 150, the
ECG input leads generally referred to at 152 include a conventional three
lead ECG input from electrocardiogram apparatus including a human ground
and the left shoulder and right side patient sensors. The ECG inputs 152
are connected to an ECG isolation amplifier stage 154 that provides a
signal at 156 to a DC restorer stage 158. The DC restorer stage 158 is
provided to stabilize the DC level of the ECG waveform which commonly
experiences disturbances of the DC level. The output 160 of the DC
restorer stage 158 is connected as a first selection input to an ECG
selector switch 162. The output 164 of the selector switch 162 is
connected to an AGC amplifier stage 166.
The ECG selector switch 162 also includes a second input 168 from an
external ECG input arrangement at 170. A third input 172 to the selector
switch 162 is provided from a recorded ECG signal path. The recorded ECG
signal at 172 is provided at the output of an ECG demodulator stage 174.
The ECG demodulator stage 174 receives an input at 46 from the recorded
heart sound ECG buffer stage 48 from the recorder input 50. The ECG
demodulator stage 174 demodulates the recorded ECG signal which is
modulated by a 7 Khz. signal (in a specific embodiment) for recording and
includes a high-pass filter having a band pass starting at approximately 5
Khz for a specific embodiment of 7 KHz. modulation frequency.
The AGC stage 166 normalizes the selected input at 164 from the selector
switch 162 to appropriate levels for the remaining gating circuitry of the
ECG apparatus 150. The output 176 of the AGC stage 166 is connected to an
ECG filter stage 178 which eliminates unwanted frequency signals
associated with the ECG waveform. The ECG filter stage 178 also provides
some degree of isolation for the R-wave of the ECG waveform.
The ECG filter 178 provides an output at 180 connected through an ECG
display buffer stage 182. The ECG display buffer stage 182 provides an
output at 184 for display apparatus to display the ECG waveform.
The output 180 of the filter 178 is also connected through an ECG modulator
stage 186 that modulates the ECG waveform at 180 with a 7 Khz. modulation
frequency to provide an ECG modulated waveform for recording at output
188. The output 188 is connected to an ECG modulated and heart sound
summing amplifier driver stage 190 along with the heart sound signal 64.
The summing amplifier and driver stage 190 provides an output at 192 to
recording apparatus to record the combined heart sound and ECG modulated
waveforms on a common channel or track on an appropriate recording medium
such as tape.
The ECG filter stage 178 also provides an output 194 to an ECG absolute
value amplifier stage 196. The ECG absolute value amplifier stage 196
transforms or folds the negative portion of the ECG waveform into the
positive half and provides processing isolation to account for the
possibility of misplaced leads causing false triggers from the ECG
waveform from portions of the ECG waveform other than the R-wave.
The output 198 of the ECG absolute value amplifier stage 196 is connected
through an ECG squaring circuit 200 to provide an output 202 to an ECG
peak detector stage 204. The ECG squaring circuit 200 accentuates the
R-wave of the ECG waveform. Thus the ECG peak detector stage 204 receives
a waveform to allow appropriate and accurate triggering on the R-wave.
The output 206 of the ECG peak detector 204 is provided to an ECG digital
filter stage 208. The ECG digital filter stage 208 provides a lock-out of
any non-R-wave triggering signals by providing a lock-out time period on a
digital basis for a predetermined period of time following the occurrence
of the R-wave. The output 210 of the ECG digital filter stage 208 is
connected through an ECG delayed trigger stage 212 to provide the ECG
R-wave delayed signal at 116 connected as an input to the display
selection stage 122. The output 210 of the ECG digital filter stage 208 is
also connected through an ECG trigger stage 214 to provide the ECG R-wave
trigger signal 96.
Considering the operation of the heart sound detection and triggering
apparatus 10 in more detail and referring again now to FIGS. 1 and 3, with
the trigger mode selection switch in the time or T-mode, the distinction
between the first and second heart sounds is accomplished based solely on
the timing relationships between the heart sound signals at 76. When using
the terms first and second heart | | |
