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BACKGROUND OF THE INVENTION
This invention relates to an apparatus for analyzing the propagation of
arterial pulse waves through vascular vessels in order to diagnose
circulatory diseases by analyzing the nature of arterial pulse wave
propagation through the circulatory system, i.e. from the heart to the
peripheral portions of the circulatory system and the like.
Methods of analyzing the speed of wave propagation as a pulse wave
propagates through an artery, is generally known. In such prior art
methods, waveforms of a phonocardiogram (PKG) or an electrocardiogram
(EKG) and selected forms of pulse waves are simultaneously drawn on the
same recording paper. Each wave form is analyzed, and the distance between
specific positions along the circulatory system is measured by using a
scale. The obtained results are converted into the time taken for the
pulse wave to propagate from the center (i.e. heart) to the periphery of
the circulatory system, and the speed of the propagating arterial pulse
wave is measured using the above-described propagation-length compensation
procedure.
Japanese Patent Publication No. 6930/1982 discloses another type of
apparatus for measuring the speed of an arterial pulse wave. In order to
save labor and time necessary to compute the speed of an arterial pulse
wave for each occurrence of arterial pulse wave propagation, the steps of
the method are automated.
However, although the state of arteriosclerosis can be, to a certain
degree, diagnosed with the above-described speed measurement, there has
been no apparatus clinically applied for a circulatory system which
efficiently analyzes the nature of arterial pulse wave propagation for the
purpose of diagnosing a variety of vascular diseases or tension states of
vascular walls.
SUMMARY OF THE INVENTION
Accordingly, a primary object of the present invention is to provide a
method of and apparatus for automatically and non-invasively analyzing the
fluctuation and distribution of the propagation time of arterial pulse
waves. Such method and apparatus are based upon a fact that the degree of
fluctuation in the propagation time of the arterial pulse wave from the
center of the circulatory system (i.e. heart) to the periphery thereof,
can serve as a diagnostic index of vascular wall tensions or an indication
of diseases through a statistical analysis of such propagation times.
Another object of the present invention is to provide a method and
apparatus for automatically and non-invasively analyzing the degree or
rate of defectively-propagated contraction in addition to analyzing the
fluctuation and distribution of the propagation time of the arterial pulse
wave. Such method and apparatus are based upon a fact that the rate of
generation of so-called "defectively-propagated contractions" (i.e. can be
obtained on the basis of ascertained propagation time of an arterial pulse
wave). Notably, such defectively-propagated contractions are determined
where an effective pulse wave is not propagated to the periphery of the
circulatory system notwithstanding the occurrence of cardiac muscle
contraction, or where arterial pulse waves cannot distinctly propagate
over a certain range or portion of the circulatory system.
In the present invention, in order to achieve the above-described objects,
an "R-wave" contained in a detected electrocardiographic signal and the
peak value (i.e. top or bottom peak) of an arterial plethysmographic
signal sensed at a peripheral blood vessel portion, are detected for each
pulse. From such detections, an R-wave signal and peak arterial pulse wave
signal are generated, respectively. The time interval between the detected
R-wave signal and detected peak pulse wave signal, .DELTA.t.sub.R-P' is
successively counted and is designated as the arterial pulse wave
propagation time. On the basis of the computed arterial pulse wave
propagation times, a statistical analysis is then performed with respect
to the distribution of the arterial propagation times of an arterial pulse
wave, and also with respect to the degree of defectively-propagated
contractions, e.g. where peak arterial pulse signal is not detected
between consecutively detected R-wave signals.
According to the present invention, circulatory diseases such as
arteriosclerosis can be diagnosed by detecting the arterial pulse wave
propagation time from the center of the circulatory system to the
periphery thereof. Also, using the thus-obtained data regarding the
variations in propagation time of arterial pulse waves for a predetermined
time period, a more precise diagnosis of circulatory diseases can be
conducted by the combination of arterial pulse wave propagation time
variation data with data analysis of ECG or R-R interval fluctuation data.
Furthermore, on the basis of the degree or rate of defectively-propagated
contractions, circulatory diseases indicated by varying degrees of
arrhythmia, can be diagnosed.
Furthermore, it is expected that the present invention will contribute to
the future development in application of the "arterial pulse wave
propagation parameters" to clinical practice.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block functional diagram illustrating the organizational
structure of apparatus for analyzing the propagation of arterial pulse
waves in accordance with the principles of the present invention;
FIG. 2 is a block diagram illustrating the structure of the apparatus for
analyzing the propagation of arterial pulse waves according to an
embodiment of the present invention;
FIG. 3 is a graphical representation illustrating each operating waveform
utilized in the method and apparatus of the present invention;
FIG. 4 is a graphical representation illustrating the state displayed on a
cathode ray tube monitor according to the embodiment;
FIG. 5 is a graphical representation illustrating the state displayed on a
cathode ray tube monitor according to another embodiment;
FIG. 6 is a schematic diagram illustrating a modified example of a circuit
according to the embodiment shown in FIG. 2; and
FIG. 7 is a schematic diagram illustrating another modified example of a
circuit according to the embodiment shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a functional-block diagram illustrating the basic structure of
apparatus for analyzing the propagation of arterial pulse waves according
to the present invention. In general, the apparatus comprises a variety of
components organized and cooperating with each other for "arterial pulse
wave propagation time" determination and analysis.
In particular, means 1 is provided for detecting, amplifying and outputting
electrocardiographic signals which have been introduced through electrodes
attached to the breast or extremities of a patient. Means 2 is provided
for detecting the R-wave component contained in the detected
electrocardiographic signal, and outputting an R wave timing signal at the
occurrence of this detection. Notably, the R-wave component of the QRS
complex signal of an electrocardiographic signal, is an electrical signal
representative of the contraction of the heart muscle of the left
ventricle. An arterial pulse wave detecting means 3, such as
plethysmograph or pulse oximeter, is provided and is attached to a
peripheral blood vessel portion for the purpose of detecting an arterial
pulse wave, i.e. arterial plethysmographic signal, which is representative
of the flow of blood through the vessels, caused by variation in size
thereof in response to the engorgement and displacement of blood. A means
4 is provided for detecting either the top or the bottom "peak" of the
detected arterial plethysmographic signal (i.e. peak arterial pulse wave
signal), and for outputting a pulse wave peak timing signal at the time of
this detection. Means 5 is provided for measuring pulse wave propagation
time, that is, successively measuring the time interval from after the
time that R-wave timing signal has been generated, to the time of
generation of the pulse wave peak timing signal. A pulse wave propagation
time analyzing means 6 is provided for calculating the distribution of
pulse wave propagation times. Also, a defectively-propagated contraction
analyzing means 7 is provided, which detects the defectively-propagated
contraction and analyzes the degree or rate of the same. Such
defectively-propagated contractions are detected, for example, when a peak
arterial pulse wave timing signal is not generated between the occurrence
of consecutive R-wave signals. In addition, an outputting means 8 is
provided for displaying or recording the result of the analysis performed
by the two above-described analyzing means.
The R-wave detection means 2 successively detects R-wave signal components
contained in an electrocardiographic signal and outputs an R-wave timing
signal indicating the precise time at which each such detection occurs.
Primarily, this device serves to determine when the origination of an
arterial pulse wave (i.e. from the heart) occurs. On the other hand, the
arterial pulse wave "peak" detecting means 4 detects the peak (i.e. either
the extreme top or bottom) of the arterial plethysmographic signal, which
is generated after and in response to the generation of the
electrocardiographic signal. The arterial pulse wave peak detecting means
4 outputs the peak timing signal indicating the time of the "peak"
detection. As a result of this procedure, the pulse wave propagation time
(i.e. .DELTA.t.sub.R-P) between the R-wave timing signal and the arterial
pulse wave peak timing signal (also referred to as the R-P interval) is
measured for every reoccurrence of the R-wave component in the QRS complex
of the electrocardiographic signal generated.
The pulse wave propagation time analyzing means 6 thereafter analyzes over
a predetermined time period, the distribution of each arterial pulse wave
propagation time so as to provide a trend indication and histogram
indication of the arterial pulse wave propagation time data, and also a
calculated measure of the standard deviation of such data. The outputting
means 8 then displays and/or records the results of the above-described
analysis.
The defectively-propagated contraction analyzing means 7 detects a
defectively-propagated contraction on the basis of a determination that no
arterial pulse wave "peak" timing signal has been detected between
detected R-wave timing signals. The defectively-propagated contraction
analyzing means 7 also analyzes the degree of defectively-propagated
contractions in terms of (i) the rate between the number of
defectively-propagated contractions with respect to a predetermined time
period, (ii) the rate between the detected number of arterial pulse waves,
and/or (iii) the number of defectively-propagated contractions with
respect to the heart rate. The analyzing means 7 enables the outputting
means 8 to display or record the result of the analysis.
The arterial pulse wave generally takes anywhere in the range of 100-350
milliseconds to propagate through a length of 1 meter, whereas the usual
time interval of the R-wave timing signals are in the range of 600-1000
milliseconds. Therefore, even when taking into consideration the time
period required for the arterial pulse wave to appear in the origin of the
ascending aorta in response to the generation of the R-wave signal, the
arterial plethysmographic signal does not interfere with the
electrocardiographic signal at the periphery, that is, before the
generation of the next R wave signal, and is thereby assuredly
distinguishable from the electrocardiographic signal.
Referring to FIG. 2, there is shown in greater detail the structure of a
circuit for use in the apparatus for analyzing the propagation of an
arterial pulse wave in accordance with the principles of the present
invention. Therein, reference numeral 10, in particular, represents an
amplifier for amplifying the electrocardiographic signal which has been
introduced into electrodes 10a attached to the breast. Reference numeral
11 represents an R wave detection circuit for detecting the R wave
contained in the electrocardiographic signal (a) and for outputting an R
wave timing signal (b) at the time of this detection. Reference numeral 12
represents an R wave interval counting circuit for counting clock pulses,
CK, which have the interval of, for example, 100 .mu.s, and which are
supplied between the R wave timing signals (b) by a timing signal
generating circuit 29. Reference numeral 13 represents a latch circuit for
holding the counted value immediately before being reset every input of
the R wave timing signals (b).
Reference numeral 15 represents a digital pulse wave detector for detecting
the arterial plethysmographic signal sensed by a pickup 15a attached, for
example, to the tip of a patient's finger. Reference numeral 16 represents
a "bottom" (i.e. minimum level) peak detecting circuit for detecting the
"bottom peak" of arterial pulse wave (c) shown in FIG. 3 in a
differentiating manner, and for outputting a "bottom peak" arterial pulse
timing signal (d) at the time of this detection. Reference numeral 17
represents a pulse wave interval counting circuit for counting the clock
pulses, CK, which are produced between the "bottom peak" arterial pulse
timing signals (d). Reference numeral 18 represents a latch circuit for
holding the count immediately before resetting every input of the "bottom
peak" arterial pulse timing signals (d).
Reference numeral 20 represents a counter for counting the number of the
R-wave timing signals (b) (supplied by a timing signal generating circuit
29) until a reset signal RS is supplied, having, for example, an interval
of two minutes. Reference numeral 20a represents a counter for counting a
bottom timing signal (d) in the similar manner. Reference numeral 21
represents a circuit for calculating the rate of defectively-propagated
contraction. Such a rate of "contraction propagation defects" is computed
by performing division of a quotient (i.e. numerator/denominator) in such
a manner that the count obtained by the counter 20 functions as a
denominator while the count obtained by the counter 20a functions as a
numerator. Reference numeral 22 represents a numeral-indicator for
indicating, in the form of numerals, the rate of defects in contraction
propagation.
As an alternative to the above-described embodiment, the
defectively-propagated contraction rate calculating circuit 21 may have
the output signal from the defectively-propagated contraction detecting
circuit 26 counted by the counter 20a so as to make this count function as
a numerator.
Reference numeral 23 represents a pulse wave propagation time counting
circuit which counts the number of the clock pulses, CK, provided by
circuit 29 as input during a time period measured from the time of input
of the R-wave timing signal (b), to the time of input of the "bottom peak"
arterial pulse timing signal (d). By the above-described operation of the
"pulse wave propagation time counting circuit" 23, the time taken for the
arterial pulse wave to propagate from heart to a finger, is accurately
counted. Reference numeral 24 represents a latch circuit for latching (or
holding) the count immediately before the input of the next R-wave timing
signal (b).
Accordingly, by making the patient's fingertip a periphery, the present
invention is effective in diagnosing the nature of the artery walls, from
the aorta to the peripheral artery. Thus, the present invention can be
used effectively to diagnose the arteriosclerosis.
Reference numeral 26 represents a defectively propagated contraction
detecting circuit for outputting a pulse-formed signal representing the
defectively-propagated contraction if any "bottom peak" pulse timing
signal (d) is not input during the time period between consecutive R-wave
timing signals (b). Reference numeral 27 represents an emitter (e.g. a
visible or audible alarm) for indicating a defectively-propagated
contraction in response to the presence of an input signal thereto,
thereby providing detection of a defectively-propagated contraction.
Reference numeral 28 represents a cathode ray tube monitor which displays
electrocardiographic waveform (a) and arterial pulse wave signal (c).
Monitor 28 also displays a bar graph by converting the digital signal
taken from the latch circuits 13, 18 and 24, into a graphical plot wherein
an analog amplitude extends in the direction of the ordinate axis and time
lapse of, for example, two minutes, is represented along the abscissa
axis. The above-described components 22, 27 and 28 provide means for
outputting the result of the analysis according to the present invention.
Operation of the above-described apparatus for analyzing the propagation of
arterial pulse waves, will now be described with reference to FIGS. 3 and
4.
At the beginning of counting, when a signal representing start of operation
is input to the timing signal generating circuit 29, the reset signal RS
is output to reset each of the components 20, 20a and 21, and thereby
generation of the clock pulses, CK, commences. The R-wave detecting
circuit 11 detects the R-wave contained in the electrocardiographic signal
(b), and provides as output, the R-wave timing signal (b) in a manner
known in the art. The R-wave interval counting circuit 12 counts the
number of the clock pulses CK during this interval, and causes the latch
circuit 13 to hold as interval data between the R-waves (R-R), the count
held by counter 12 at the time of the input of the next R-wave timing
signal (b). Thereafter, counter 12 once again starts counting upon
receiving the next R-wave timing signal (b) as input to counter
The "bottom peak" pulse wave detecting circuit 16 detects the "bottom peak"
of the input arterial plethysmographic signal (c), and provides as output
the "bottom peak" pulse wave timing signal (d). The pulse wave interval
counter 17 counts the number of the clock pulses CK during this interval,
and causes the latch circuit 18 to hold as interval data between
consecutive pulse waves, the count held by counter 17 at the time of the
input of the next "bottom peak" timing signal (d). Thereafter, counter 17
once again starts counting upon receiving the next "bottom peak" timing
signal (d) as input to counter 17.
The pulse wave propagation time counting circuit 23 counts the number of
the clock pulses CK received upon the input of the R-wave timing signal
(b) to counter 23, and causes the latch circuit 24 to hold as data
representative of the pulse wave propagation time, the count held by
counter 23 at the time of input of the bottom timing signal (d) to counter
23. Thereafter, counter 23 once again starts counting upon receiving the
next R-wave timing signal as input to counter 23.
In the preferred embodiment, throughout the above-described operation, the
cathode ray tube monitor 28 displays at a proper sweeping speed, the
electrocardiographic signal (a), and the arterial pulse wave signal (c),
as shown in FIG. 4. It also displays data regarding the R-wave interval,
the arterial pulse wave interval, and the arterial pulse wave propagation
time held by the latch circuits 13, 18 and 24. Such display is carrie out
by successively converting the data into analog pulse wave forms in the
direction of the ordinate axis corresponding to the respective data
levels. As a result, they are successively displayed by shifting
downwardly at a relatively lower speed.
The circuit 26 for detecting the defectively-propagated contraction causes
the emitter 27 to instantaneously emit light upon the detection of every
defectively-propagated contraction. Two minutes after the operation start,
the reset signal RS is generated, and the defectively-propagated
contraction rate calculating circuit 21 conducts the division, holds its
result until the input of the next reset signal RS, and the numeral
indicator 22 displays this result. On the other hand, as can be seen on
the cathode ray tube monitor 28, over the two-minute interval the
fluctuation of "biophysical parameters", e.g. (i) the R-wave interval,
(ii) the pulse wave interval, and (iii) the pulse wave propagation time,
are easily recognizable from the amplitude changes in the corresponding
envelopes. In this regard, reference is made to FIG. 3, wherein the number
of the analog pulse waveforms in the direction of the ordinate axis is
reduced with respect to the actual number thereof.
As indicated in FIG. 5, data held in the latch circuits 13, 18 and 24 can
be provided to a CPU for statistical analysis. For example, in such an
embodiment, data corresponding to each of the above-described parameters
determined over a predetermined time interval is processed using
statistical analysis so as to produce histogram data thereof. Thereafter,
such histogram data is displayed on the cathode ray tube monitor 28.
Accordingly, a histogram "on the R-wave timing intervals", and a histogram
"on the peak timing intervals of plethysmographic signals" are computed,
and the results provided thereby can be used by doctors, medical
technicians and the like for the above-described medical diagnostic
purposes. Furthermore, the average and the standard deviation with respect
to such detected parameters, may be calculated and output in numerical
form.
As shown in FIG. 6, the provision of a gate generating circuit 38 and AND
gate 39 can be used to remove noise signals, such as the arterial pulse
waves and the like, which do not depend upon the same heart beat. This
circuit functions by allowing the pulse wave "peak" detecting means 16 to
generate a pulse wave peak timing signal (d) only in response to a pulse
wave "peak" which has been generated within a predetermined "gated" time
period. Notably, over such a gated time period both the peak timing signal
(d) and the R-wave timing signal (b) originated from the same heart beat,
and thus are naturally correlated.
In connection with such a desired signal gating function, circuit 38 is
provided for generating a gate which establishes a predetermined time
period during which an arterial plethysmographic signal (c) is "triggered"
by the R-wave timing signal (b) after a predetermined time delay, in order
to ensure that the arterial plethysmographic signal (c) depends upon the
same heart beat which has generated the triggering R-wave timing signal.
The AND gate 39 is connected to the bottom detecting circuit 16, and the
bottom peak pulse wave timing signal (b) is connected to one of the inputs
to the AND gate 39 while pulse wave timing signal (d) is provided thereto
as the other input. As a result of this configuration, the gate generating
circuit of the present invention, in effect, disenables operation of the
bottom detecting circuit 16 at times other than during this "gated" time
period, since at all other times, the circuit 38 generates a reversed
polarity signal with respect to the other input to the AND gate 39 of FIG.
6.
Notably, the electrodes 10a can be attached to the portions of a patient's
body other than the breast. In a case where the electrodes 10a are
attached to the breast as described above, they can be arranged to provide
a known "impedance plethysmogram", i.e. by applying a high-frequency
current of small amplitude to two of the electrodes 10a attached to the
breast. However, as illustrated in FIG. 7, a circuit can be added to the
circuit shown in FIG. 2. This would result in apparatus which is capable
of confirming the correlation between the pulse wave propagation time
(i.e. R-P time interval) and expiratory and inspiratory phases of a
patient's respiratory cycle, and thereby provide a tool for diagnosing,
for example, the elasticity of vascular walls.
In particular, such modification would involve the addition of the
following circuits and devices: a respiratory wave pattern detecting
circuit 31; an expiratory and inspiratory phase detecting circuit 32; an
R-wave input timing determining circuit 33; arithmetic circuits 34 and
34a; a selection circuit 75; and numeral indicators 36 and 36a.
In such an embodiment shown in FIG. 7, the respiratory wave pattern
detecting circuit 31 receives as input, a voltage signal detected by the
electrodes 10a, and is fully capable of detecting respiratory wave pattern
depending upon the thus-detected voltage change. The expiratory and
inspiratory phase detecting circuit 32 is capable of detecting expiratory
phase and inspiratory phase from the detected voltage signal. As shown in
FIG. 2, the R-wave input timing determining circuit 33 receives as input,
the R-wave timing signal (b), and is capable of determining whether or not
both these two successive signals have been input to the expiratory phase
or the inspiratory phase detecting circuit 32. The arithmetic circuits 34
and 34a calculate e.g. over a time period of three minutes, (i) the
average of the maximum R-wave intervals (i.e. R-R interval) of the
expiratory phase, (ii) the standard deviation of this average, (iii) the
average of the maximum R-wave intervals (i.e. R-R interval) of the
inspiratory phase, and (iv) the standard deviation of this average. The
selection circuit 35 supplies the retained value in the latch circuit 13
shown in FIG. 2, to either the arithmetic circuit 34 or 34a. The selection
circuit 35 carries out this supply function in response to the
determination signal output from the R wave input timing determining
circuit 33, or does not supply the same to both the arithmetic circuits 34
and 34a when the two successive R wave timing signals (b) are not present
in expiratory phase and inspiratory phase. Finally, numeral-indicators 36
and 36a indicate to the operator, the above-described average and standard
deviations of the expiratory phase and inspiratory phase, respectively, of
the monitored respiratory cycle of the patient.
Usually, the R-R wave timing intervals in the expiratory phase and those in
the inspiratory phase, are different from each other. However, according
to another aspect of the present invention, it is now possible to diagnose
the fluctuation of elasticity of vascular walls, and in turn, the tone of
autonomic nerves such as vagal nerves governing the elasticity of vascular
walls. This diagnosis method is carried out by first monitoring the R-R
wave time intervals of both inspiratory and expiratory phase of the
respiratory cycle of a patient. Notably, the R-R wave intervals associated
with the expiratory and inspiratory phases, respectively, can be confirmed
using numeral indicators 36 and 36a. Then, the respective R-R wave
intervals are correlated to the pulse wave propagation time (i.e. the R-P
interval), so as to correlate data from which the elasticity or tone of
vascular walls can be diagnosed.
While the particular embodiments shown and described above have been proven
to be useful in many applications involving the biophysiological
instrumentation arts, further modifications of the present invention
herein disclosed will occur to those skilled in the art to which the
present invention pertains and all such modifications are deemed to be
within the scope and spirit of the present invention defined by the
following claims.
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