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Claims  |
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I claim:
1. In an electronic sphygmomanometer, the combination comprising:
means for providing detected korotkoff sounds and associated korotkoff
sound precursors as electrical signals, each of said korotkoff sound
precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
and
means for analyzing the waveforms of all said electrical signals to
determine selectively the presence of specified korotkoff sound precursors
and the conformity of such precursors with predetermined waveform
characteristics, whereby those electrical signals having waveforms
representative of true korotkoff sounds are separated from those
electrical signals which do not represent true korotkoff sounds.
2. A combination as set forth in claim 1, wherein said means for analyzing
said waveforms includes a diastolic channel, a systolic channel and an
amplitude channel, the electrical output from said amplitude channel being
selectively gated by either of said diastolic channel and said systolic
channel.
3. A combination as set forth in claim 2, wherein said diastolic channel
evaluates the amplitude of a waveform precursor to a korotkoff spike.
4. A combination as set forth in claim 2, wherein said diastolic channel
evaluates the area of a waveform precursor to a korotkoff spike.
5. A combination as set forth in claim 2, wherein said diastolic channel
evaluates the time duration of a waveform precursor to a korotkoff spike.
6. A combination as set forth in claim 2, wherein said diastolic channel
evaluates the amplitude, area and time duration of a waveform precursor to
a korotkoff spike.
7. A combination as set forth in claim 2, wherein said systolic channel
evaluates the slope of the leading edge of a korotkoff spike.
8. A combination as set forth in claim 2, wherein said systolic channel
evaluates the duration of the leading edge of a korotkoff spike.
9. A combination as set forth in claim 2, wherein said systolic channel
evaluates the slope and time duration of the leading edge of a korotkoff
spike.
10. The combination as set forth in claim 2, wherein said amplitude channel
measures the amplitude of a korotkoff spike.
11. The combination as set forth in claim 10, wherein said amplitude
channel measures said amplitude along the trailing edge of said korotkoff
spike.
12. A combination as set forth in claim 1, wherein said means for analyzing
said waveforms includes:
means for measuring the amplitude, area and time duration of a waveform
precursor to a korotkoff spike; and
means for measuring the slope and time duration of the leading edge of a
korotkoff spike.
13. In an electronic sphygmomanometer for analyzing korotkoff sounds
produced by an auscultation blood pressure measuring process, the
combination comprising:
first means for providing korotkoff sounds and associated korotkoff sound
precursors as input electrical signals, each of said korotkoff sound
precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
second means for analyzing the waveforms of all of said input electrical
signals to determine selectively the presence of specified korotkoff sound
precursors and their conformity with predetermined waveform
characteristics; and
third means responsive to said second means for selectively producing
output electrical signals in time correlation only with those input
electrical signals corresponding to true korotkoff sounds, whereby those
input electrical signals representing true korotkoff sounds are separated
from artifact and noise signals.
14. A combination as set forth in claim 13, wherein said third means
produces output electrical signals proportional in amplitude to those
input electrical signals representing true korotkoff sounds.
15. A combination as set forth in claim 13, wherein said second means
analyzes the amplitude of portions of said waveform.
16. A combination as set forth in claim 13, wherein said second means
analyzes the area of portions of said waveform.
17. A combination as set forth in claim 13, wherein said second means
analyzes the time duration of portions of said waveform.
18. An electronic sphygmomanometer as set forth in claim 17, and further
including:
first means for rectifying the waveforms of each of said input electrical
signals;
second means for integrating the area under the rectified waveform produced
by said first means.
19. Apparatus as set forth in claim 18, wherein said means for integrating
the area requires that a minimum amplitude threshold be exceeded to begin
integration.
20. Apparatus as set forth in claim 18, wherein said means for integrating
the area requires a minimum time period for the electrical output of the
integration to exceed a predetermined level.
21. Apparatus as set forth in claim 18, and further including:
discrimination means for measuring the magnitude of the electrical output
from said second means.
22. A combination as set forth in claim 13, wherein said second means
analyzes the slope of portions of said waveform.
23. An electronic sphygmomanometer, comprising:
input means for providing korotkoff sounds and associated korotkoff sound
precursors as input electrical signals, each of said korotkoff sound
precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
waveform analysis means for receiving and analyzing the waveforms of all of
said input electrical signals to determine selectively the presence of
specified korotkoff sound precursors and the conformity of each individual
input electrical signal with predetermined waveform characteristics and to
produce an electrical output indicative of the presence or absence of such
conformity, and thereby the presence or absence of said specified
precursors, for each such input electrical signal; and
output means responsive to said electrical output from said waveform
analysis means for producing output electrical signals indicative of only
those input electrical signals having waveforms representative of the
occurrence of true korotkoff sounds.
24. A sphygmomanometer as set forth in claim 23, wherein said waveform
analysis means measures the conformity of input electrical signals with
characteristics of a first class of generalized waveforms.
25. An electronic sphygmomanometer as set forth in claim 24, wherein said
waveform analysis means also measures the conformity of said input
electrical signals with the characteristics of a second class of
generalized waveforms.
26. An electronic sphygmomanometer as set forth in claim 23, wherein said
waveform analysis means measures the conformity of said input electrical
signals with characteristics of a plurality of classes of generalized
waveforms.
27. An electronic sphygmomanometer as set forth in claim 23, wherein said
waveform analysis means includes means for evaluating the amplitude, area
and time duration of a waveform precursor occurring immediately prior to a
korotkoff spike and of opposite polarity from said spike.
28. An electronic sphygmomanometer as set forth in claim 23, wherein said
waveform analysis means includes means for evaluating the time duration
and minimum slope of the leading edge of a korotkoff spike.
29. An electronic sphygmomanometer as set forth in claim 28, and further
including:
rectifier means for rectifying the waveforms of all of said input
electrical signals;
means for differentiating the electrical output of said rectifier means;
discriminator means for measuring the amplitude of electrical outputs from
said differentiator means; and
timing means for measuring the duration of electrical output from said
discriminator means.
30. An electronic sphygmomanometer as set forth in claim 23, wherein said
output means measures the amplitude of each korotkoff spike occurring in
an input electrical waveform and produces an output electrical signal
having an amplitude proportional to the base to peak amplitude of said
spike.
31. An electronic sphygmomanometer as set forth in claim 30, wherein said
amplitude is measured along the trailing edge of said korotkoff spike.
32. An electronic sphygmomanometer as set forth in claim 30, and further
including:
first rectifier means for rectifying the waveforms of all of said input
electrical signals;
differentiator means for differentiating the electrical output of said
first rectifier means;
second rectifier means for rectifying the electrical output of said
differentiator means; and
integration means for integrating the electrical output of said rectifier
means.
33. Apparatus as set forth in claim 32, wherein said second rectifier means
isolates the trailing edge of each korotkoff spike.
34. Apparatus as set forth in claim 32, wherein said integration means
produces output electrical pulses proportional in amplitude to the base to
peak amplitude of each korotkoff spike.
35. Apparatus as set forth in claim 34, wherein said amplitude is measured
along the trailing edge of each korotkoff spike.
36. An electronic sphgmomanometer as set forth in claim 32 and further
including:
gating means under the control of said waveform analysis means for
selectively passing electrical output as pulses from said second rectifier
means to said integration means.
37. Apparatus as set forth in claim 36, wherein said gating means enables
passage of electrical output from said rectifier means to said integration
means only when said waveform analysis means produces an electrical output
indicative of the presence of conformity between said input electrical
signals and said predetermined waveform characteristics.
38. Apparatus as set forth in claim 36, and further including:
control means for controlling the output of said gating means in response
to a variable amplitude threshold applied to said pulses.
39. Apparatus as set forth in claim 38, wherein said variable threshold
prevents passage of relatively small pulses for a period of time after
passage of relatively larger pulses.
40. Apparatus as set forth in claim 38, wherein said control means includes
a peak rectifier electrical circuit.
41. Apparatus as set forth in claim 40, wherein said control means includes
a discriminator latch and said gating means is enabled and disabled in
accordance with the electrical output state of said latch.
42. Apparatus as set forth in claim 41, wherein said peak rectifier
receives an electrical input from said output means.
43. Apparatus as set forth in claim 38, wherein said control means includes
a discriminator latch circuit.
44. Apparatus as set forth in claim 38, wherein said control means includes
both a peak rectifier and discriminator latch.
45. An electronic sphygmomanometer as set forth in claim 23, wherein said
waveform analysis means includes a first channel for evaluating the
amplitude, area and time duration of a waveform precursor to a korotkoff
spike and a second channel for evaluating the slope and time duration of
the leading edge of a korotkoff spike.
46. An electrical sphygmomanometer, comprising:
first means for providing electrical waveforms representing korotkoff
sounds and associated korotkoff sound precursors, each of said korotkoff
sound precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
second means for analyzing the amplitude selectively of portions of said
waveforms and producing an output pulse stream representative of the
amplitude and occurrence of those of said waveforms representing true
korotkoff events;
third means for determining selectively the presence of specified korotkoff
sound precursors by the correlation of said electrical waveforms with
prescribed waveform conditions;
fourth means for controlling the output of said first means in response to
waveform analysis by said second means; and
fifth means for analyzing the electrical output of said first means to
determine blood pressure.
47. An electronic sphygmomanometer as set forth in claim 46, wherein said
fifth means also determines heart rate.
48. Apparatus as set forth in claim 46, wherein said first means, said
second means, said third means and said fourth means are analog electrical
systems.
49. Apparatus as set forth in claim 46, wherein said fifth means is a
digital system.
50. Apparatus as set forth in claim 46, wherein said first means, said
second means, said third means, and said fourth means are analog systems
and said fifth means is a digital system.
51. In an electronic sphygmomanometer for analyzing korotkoff sounds
produced by an auscultation blood pressure measuring process, the
combination comprising:
first means for providing korotkoff sounds and associated korotkoff sound
precursors as input electrical signals, each of said korotkoff sound
precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
second means for prescreening selectively for the presence of specified
korotkoff sound precursors the waveforms of all of said input electrical
signals from said first means and producing output electrical signals in
time correlation only with those input electrical signals corresponding to
the occurrence of true korotkoff events; and
third means for analyzing the output electrical signals from said second
means to determine blood pressure.
52. Apparatus as set forth in claim 51, wherein said third means further
screens said output electrical signals to eliminate those electrical
signals representing events other than the occurrence of true korotkoff
events.
53. Apparatus as set forth in claim 51, wherein said second means is an
analog system.
54. Apparatus as set forth in claim 51, wherein said third means is a
digital system.
55. Apparatus as set forth in claim 54, wherein said second means includes
a diastolic channel, a systolic channel and an amplitude channel.
56. Apparatus as set forth in claim 55, wherein said diastolic channel
evaluates the amplitude, area and time duration of a waveform precursor to
a korotkoff spike.
57. Apparatus as set forth in claim 55, wherein said systolic channel
evaluates the slope and time duration of the leading edge of a korotkoff
spike.
58. Apparatus as set forth in claim 55, wherein said amplitude channel
measures the amplitude of a korotkoff spike.
59. Apparatus as set forth in claim 58, wherein said amplitude channel
measures said amplitude along the trailing edge of said korotkoff spike.
60. Apparatus as set forth in claim 51, wherein said third means also
determines heart rate.
61. Apparatus as set forth in claim 51, wherein said second means is an
analog system and said third means is a digital system.
62. An electronic sphygmomanometer, comprising:
first means for detecting electrical waveforms representing korotkoff
sounds and producing output pulses representing said korotkoff sounds;
second means for controlling the output of said first means in response to
a variable amplitude threshold applied to said pulses.
63. Apparatus as set forth in claim 62, wherein said variable threshold
prevents passage of relatively small pulses for a period of time after
passage of relatively larger pulses.
64. Apparatus as set forth in claim 63, wherein said peak rectifier
receives an electrical input from said first means.
65. Apparatus as set forth in claim 62, wherein said second means includes
a peak rectifier electrical circuit.
66. Apparatus as set forth in claim 62, wherein said second means includes
a discriminator latch circuit.
67. Apparatus as set forth in claim 62, wherein said first means includes a
control gate.
68. Apparatus as set forth in claim 67, wherein said second means includes
a discriminator latch and said control gate is enabled and disabled in
accordance with the electrical output state of said latch.
69. Apparatus as set forth in claim 63, wherein said second means includes
both a peak rectifier and discriminator latch.
70. Apparatus as set forth in claim 62, wherein said first means includes a
control gate, said second means includes a peak rectifier and
discriminator latch, and said control gate is opened and closed to
respectively pass and block the output pulses from said first means in
accordance with the electrical output state of said latch.
71. An electronic sphygmomanometer, comprising:
first means for providing electrical waveforms representing korotkoff
sounds and associated korotkoff sound precursors, each of said korotkoff
sound precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
second means for analyzing the amplitude selectively of portions of said
waveforms and producing an output pulse stream representing the amplitudes
and occurrences of those of said waveforms representing true korotkoff
events;
and third means for determining selectively the presence of specified
korotkoff sound precursors by the correlation of said electrical waveforms
with prescribed waveform characteristics and for controlling the output of
said second means in response to the waveform analysis of said third
means.
72. Apparatus as set forth in claim 71, and further including:
fourth means for frequency shaping the electrical input to said second
means.
73. Apparatus as set forth in claim 71, and further including:
fifth means for frequency shaping the electrical input to said third means.
74. Apparatus as set forth in claim 73, wherein said fifth means provides a
pass band substantially in the range from 1/2 Hz. to 20 Hz.
75. Apparatus as set forth in claim 72, wherein said fourth means provides
a first pass band substantially in the range from 15 Hz. to 150 Hz. and a
second pass band substantially in the range from 1/2 Hz. to 10 Hz., said
second pass band being attenuated relative to said first pass band.
76. In an electronic sphygmomanometer, the combination comprising:
first means for determining the amplitude selectively of the trailing edge
of a korotkoff signal spike and producing an output pulse proportional
thereto;
second means for correlating and measuring the amplitude, area and time
duration selectively of a precursor bulge preceding a korotkoff spike;
third means for correlating and measuring the slope and time duration
selectively of a leading edge of a korotkoff spike; and
fourth means responsive to an indication of successful correlation from
either of said second means and said third means for selectively enabling
said first means.
77. A combination as set forth in claim 76, wherein said second means is a
diastolic waveform analysis means.
78. A combination as set forth in claim 76, wherein said third means is a
systolic waveform analysis means.
79. A combination as set forth in claim 76, wherein said first means
includes a control gate for selectively passing or blocking the output
pulses from said first means.
80. A combination as set forth in claim 76, and further including;
fifth means for selecting enabling said first means in response to a
variable amplitude threshold applied to each output pulse from said first
means.
81. Apparatus as set forth in claim 80, wherein said variable amplitude
threshold prevents passage of relatively small output pulses from said
first means for a period of time after the passage of a relatively larger
output pulse from said first means.
82. A combination as set forth in claim 76, wherein said first means
provides electrical input to an integrator within said first means.
83. Apparatus as set forth in claim 82, and further including:
fifth means for selectively enabling said first means and simultaneously
controlling charging and discharging of said integrator.
84. Apparatus as set forth in claim 83 wherein said fifth means includes a
discriminator latch.
85. Apparatus as set forth in claim 83, wherein said fifth means includes a
peak rectifier and discriminator latch circuit and said peak rectifier
receives an electrical input from said first means.
86. Apparatus as set forth in claim 82, and further including:
fifth means for controlling the electrical output of said first means in
response to a variable amplitude threshold applied to electrical output
pulses from said first means and also controlling, charging and
discharging of said integrator.
87. A combination as set forth in claim 76, wherein the electrical input to
said first means is frequency shaped to provide a first pass band
substantially in the range of 15 Hz. to 150 Hz. and a second pass band
substantially in the range of 1/2 Hz. to 10 Hz., said second pass band
being attenuated relative to said first pass band.
88. A combination as set forth in claim 76, wherein the electrical input to
said second means and said third means is frequency shaped to provide a
pass band substantially in the range of 1/2 Hz. to 20 Hz.
89. In a method of blood pressure measurement, the steps of:
providing electrical input waveform signals representing korotkoff sounds
and associated korotkoff sound precursors, each of said korotkoff sound
precursors being included in the waveforms relating solely to the
individual korotkoff sound signal with which that precursor is associated;
and
analyzing the waveforms of all of said signals to determine selectively the
presence of specified korotkoff sound precursors and the conformity of
such precursors with predetermined waveform characteristics, whereby those
waveforms representative of true korotkoff sounds are separated from those
waveforms which do not represent true korotkoff sounds.
90. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the amplitude of a waveform precursor to a korotkoff spike.
91. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the area of a waveform precursor to a korotkoff spike.
92. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the time duration of a waveform precursor to a korotkoff spike.
93. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the slope of the leading edge of a korotkoff spike.
94. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the time duration of the leading edge a korotkoff spike.
95. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the amplitude of a korotkoff spike.
96. A method as set forth in claim 89, wherein said analyzing step
includes:
measuring the amplitude of a korotkoff spike along the trailing edge of the
korotkoff spike.
97. In an electronic sphygmomanometer, the combination comprising:
first means for determiming the amplitude selectively of the trailing edge
of a korotkoff signal spike and producing an output pulse proportional
thereto;
second means for correlating and measuring the amplitude, area and time
duration selectively of a precursor bulge preceding a korotkoff spike;
third means responsive to an indication of successful correlation from said
second means for selectively enabling said first means.
98. In an electronic sphygmomanometer, the combination comprising:
first means for determining the amplitude selectively of the trailing edge
of a korotkoff signal spike and producing an output pulse proportional
thereto;
second means for correlating and measuring the slope and time duration
selectively of a leading edge of a korotkoff spike; and
third means responsive to an indication of successful correlation from said
second means for selectively enabling said first means.
99. In an electronic sphygmomanometer, the combination comprising:
first means for correlating and measuring the amplitude, area and time
duration selectively of a precursor bulge preceding a korotkoff spike; and
second means for correlating and measuring the slope and time duration
selectively of a leading edge of a korotkoff spike. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates generally to improvements in methods and apparatus
for the measurement of blood pressure and heart rate and, more
particularly, to a new and improved electronic sphygmomanometer system
enabling very rapid, accurate, reliable and easily obtained blood pressure
and heart rate measurements.
It is common practice in the medical arts, as in hospitals and doctors'
offices, to employ an auscultation technique for measuring the blood
pressure of a patient by using the characteristics of the so-called
korotkoff sounds to determine the systolic and diastolic values of the
patient's blood pressure.
The korotkoff method typically makes use of an inflatable cuff surrounding
a portion of the patient's upper arm. Sufficient inflation of the cuff
closes off or completely occludes the brachial artery of the patient. As
air is released and the cuff is slowly deflated, a point is reached at
which the occluded artery begins to open for a very brief period during
each cardiac cycle. At this point, the cuff pressure, which is assumed in
using this process as being approximately equal to the blood pressure in
the brachial artery, will be that of the peak pressure obtained during the
cardiac cycle, this pressure being known in the medical arts as the
systolic blood pressure.
Detection of the point at which the artery first opens may be made by any
suitable listening device such as a stethoscope or microphone applied to
the arm over the artery, usually downstream of the inflated cuff. As the
artery opens, auscultatory sounds caused by the pulsating blood flow or
turbulence in the blood stream below the occlusion are sensed by the
listening device, and these sounds are referred to in the medical arts as
the well known korotkoff sounds. At the point of first detection, where
the decreasing cuff pressure is matched by the maximum blood pressure,
medical personnel skilled in the auscultation technique can detect the
pulsatile blood flow in the artery and the onset of korotkoff sounds, and
thereby determine the systolic blood pressure.
As the pressure in the cuff continues to drop, the korotkoff sounds
continue substantially in synchronization with the blood pressure pulses
produced during successive cardiac cycles. Eventually a point is reached
at which the artery remains open during the entire cardiac cycle and, at
this point, the korotkoff sounds cease entirely. The cuff pressure at this
point approximates the lowest blood pressure reached during the cardiac
cycle, with the heart essentially at rest, and this is known as the
diastolic blood pressure.
Hence, it will be apparent that, if values of the decreasing cuff pressure
are correlated with the korotkoff sound output of the stethoscope or
microphone, the cuff pressure at the time the first korotkoff sound occurs
is approximately equal to the systolic blood pressure, while the cuff
pressure at the time the last korotkoff sound occurs is approximately
equal to the diastolic blood pressure encountered during the measurement
process.
It will be apparent from the foregoing that conventional blood pressure
measurement procedures using an inflatable cuff and a suitable listening
device are prone to a number of significant deficiencies. In this regard,
medical personnel making such measurements are required to make rather
difficult determinations regarding the presence or absence of korotkoff
sounds which may be of relatively low and difficult to detect amplitudes
and are often intermixed and easily confused with ambiguous signals
generated by artifacts and both internal and external noise. In this
regard, noise and artifact signals generally appear to be produced more
frequently in sick patients than in healthy patients so that the process
is oftentimes more difficult to perform accurately in those instances
where the very requirement for a high degree of accuracy is greatest. In
addition, the determination of the end points for the onset and cessation
of the korotkoff sound pulse train is somewhat subjective and therefore
subject to further inaccuracy in the absence of considerable training and
much experience on the part of skilled medical personnel.
Since there are relatively few persons really capable of taking accurate
blood pressure measurements using conventional manual auscultation
techniques, various attempts have been made in the prior art to eliminate
the aforedescribed deficiencies by mechanizing the measurement process so
that the subjective factors introduced when an untrained person attempts
to measure blood pressures can be eliminated and, further, to provide some
discrimination against artifacts and noise. However, such automatic
systems for measuring blood pressure and, typically, associated heart
rate, have generally proven to be overly sensitive to spurious signals
generated by artifacts and noise and have proven, therefore, to be in many
instances less accurate than medical personnel using tried and true manual
procedures. As a consequence, automatic korotkoff sound monitoring systems
for determining blood pressure have experienced only limited acceptance by
the medical profession.
Hence, those concerned with the development and use of automatic
sphygmomanometers in the medical field have long recognized the need for
improved sphygmomanometer systems which enable more accurate and reliable
blood pressure and heart rate measurements to be made and which obviate
the need for a high degree of skill and subjective expertise on the part
of medical personnel making such measurements. The present invention
fulfills all of these needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides a new and
improved sphygmomanometer system embodying novel methods and apparatus for
accurately and reliably detecting, filtering, analyzing, verifying and
evaluating a korotkoff sound signal stream in determining systolic and
diastolic blood pressures and heart rate for a patient being monitored
during a measurement cycle.
Basically, the present invention is directed to an improved electronic
method and apparatus for verifying and certifying the genuineness of
korotkoff sound signals with a high degree of reliability and separating
such true korotkoff sound signals from a variety of artifact and noise
signals intermixed with the korotkoff sound signals in the incoming data
stream. This is accomplished by waveform analysis first performed upon all
of the incoming signal waveforms by means of an analog prescreening
subsystem. The analog analysis and filtering process is then continued and
further enhanced in a digital processing subsystem imposing additional
analysis constraints upon the data to further eliminate any contributions
due to noise and artifact signals remaining in the data stream as
potentially misleading quasi-korotkoff sound signals and to determine
heart rate. The digital processing subsystem then modifies and certifies
the resultant data as either reliable or unreliable and applies a
plurality of novel manipulations and tests upon the resultant data to
determine the most probable values for systolic and diastolic blood
pressure levels as indicated by the incoming signal stream detected during
the measurement cycle performed upon the patient.
In accordance with the invention, the auscultatory korotkoff sounds are
detected by a microphone and the electrical signal output from the
microphone is analyzed in a three channel analog prescreening subsystem
which filters the incoming data and provides as electrical output a pulse
train correctly correlating and marking the locations of korotkoff sound
signals in the time and blood pressure domains, with each output pulse
being proportional in amplitude to the amplitude of the corresponding
korotkoff sound signal represented. The analog prescreening subsystem
performs waveform analysis upon all of the incoming signal waveforms,
based upon the discovery of certain unique characteristics associated with
those waveforms correctly depicting true korotkoff sound signals, in
contrast with those waveforms representing a variety of artifact and noise
signals. In this connection, it has been discovered that waveform
characteristics of the incoming signals, as opposed to frequency
characteristics, provide the most reliable means for accurately separating
korotkoff sound signals from an electrical signal environment which also
includes artifact and noise signals falling within the typical frequency
domain associated with true korotkoff sound signals.
It has been discovered, in the development of the present invention, that
true korotkoff sound signals produced as incoming data from a microphone
transducer always assume one of two general classes of waveform
configurations, or hybrid waveforms in between these two classes of
waveform configurations which still possess certain key characteristics of
one or both general classes, all of which are subject to prescribed
analysis and recognition by the system of the present invention. These
characteristics include waveform shape, size and direction as measured by
polarity, amplitude, slope and timing.
In this regard, it has been determined that diastolic korotkoff sound
signals, i.e., those signal waveforms in the korotkoff sound signal stream
closer to the lower, diastolic blood pressure end of the korotkoff signal
spectrum, always have a precursor in the form of a slowly rising,
relatively low frequency region defining a bulge prior to the onset of the
oppositely directed korotkoff spike in the waveform. The resultant slowly
rising and oppositely directed precursor bulge leading the korotkoff spike
will, if the signal waveform depicts a true korotkoff sound, satisfy
certain constraints imposed upon the waveform by the analysis performed in
the analog prescreening subsystem regarding minimum ampl | | |
