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Claims  |
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What is claimed is:
1. A system for automatically detecting an adventitious sound from a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for sequentially comparing the individual sound waves of at least a
portion of the sound signal with a first predetermined time interval to
identify an initial deflection wave having a duration falling within said
first predetermined time interval; and
means, responsive to said means for comparing, for identifying an
adventitious sound occurring within said sound signal when each of from
2-16 consecutive sound waves following said initial deflection wave has a
duration falling within a second predetermined time interval.
2. A system for automatically detecting an adventitious sound in a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for establishing at least one of a predetermined time interval and a
threshold signal value based on an average signal value of at least a
portion of said sound signal;
means, responsive to said means for establishing, for sequentially
comparing said sound waves to at least one of said threshold signal value
and said predetermined time interval to identify a first wave having at
least one of an amplitude at least as large as said threshold signal value
and a duration falling within said predetermined time interval;
means, responsive to said means for sequentially comparing, for identifying
an adventitious sound when at least one consecutive wave following said
first wave has at least one of an amplitude at least as large as said
threshold signal value and a duration falling within said predetermined
time interval; and
means for conditioning said sound signal to attenuate normal sounds,
including a filter for attenuating sound signals having frequency lower
then approximately 80 hertz and greater than approximately 2000 hertz.
3. The system of claim 2 in which said means for conditioning includes
means for digitizing said sound signal.
4. The system of claim 2 in which said means for conditioning includes
means for amplifying said sound signal.
5. The system of claim 2 in which said means for conditioning includes
means for storing a sample sound signal.
6. The system of claim 5 in which said sample sound signal includes an
analog sound signal sample.
7. A system for automatically detecting an adventitious sound in a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for establishing at least one of a predetermined time interval and a
threshold signal value based on an average signal value of at least a
portion of said sound signal;
means, responsive to said means for establishing, for sequentially
comparing said sound waves to at least one of said threshold signal value
and said predetermined time interval to identify a first wave having at
least one of an amplitude at least as large as said threshold signal value
and a duration falling within said predetermined time interval;
means, responsive to said means for sequentially comparing, for identifying
an adventitious sound when at least one consecutive wave following said
first wave has at least one of an amplitude at least as large as said
threshold signal value and a duration falling within said predetermined
time interval; and
means, responsive to said means for identifying, for determining the type
of adventitious sound occurring in said sound signal.
8. The system of claim 7 in which said means for determining includes means
for establishing the duration of the adventitious sound.
9. The system of claim 8 in which said means for determining further
includes means, responsive to said means for establishing, for identifying
a squeak or squawk if said adventitious sound duration is between 25 and
250 milliseconds.
10. The system of claim 8 in which said means for determining further
includes means, responsive to said means for establishing, for identifying
a wheeze or rhonchus if said adventitious sound duration is greater than
250 milliseconds.
11. The system of claim 8 in which said means for determining further
includes means, responsive to said means for establishing, for identifying
a crackle if said adventitious sound duration is less than 25
milliseconds.
12. A system for automatically detecting an adventitious sound from a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for determining an average signal value of at least a portion of said
sound signal;
means for generating a threshold value based on said average signal value;
means for sequentially comparing the sound waves of at least a portion of
the sound signal with a predetermined time interval to identify an initial
deflection wave having a duration falling within said time interval;
means, responsive to said means for sequentially comparing, for
sequentially comparing the amplitude of individual sound waves following
said initial deflection wave to said threshold value;
means, responsive to said means for sequentially comparing sound waves
amplitude for identifying an adventitious sound occurring within the sound
signal when each of a plurality of consecutive sound waves following said
initial deflection wave has an amplitude at least as large as said
threshold value; and
means for determining the initial slope of the wave following said initial
deflection wave.
13. The system of claim 12 further including means, responsive to said
means for determining the initial slope, for comparing the initial slope
with a predetermined slope range to identify a wave following said initial
deflection wave having an initial slope falling within the slope range.
14. The system of claim 13 in which said means for identifying is further
responsive to said means for comparing the initial slope for identifying
an adventitious sound only when the initial slope of the wave following
said initial deflection wave is within said slope range.
15. A system for automatically detecting an adventitious sound signal
formed of a plurality of successive sound waves required from a patient,
comprising:
means for establishing and a threshold signal value based on an average
signal value of at least a portion of said sound signal;
means, responsive to said means for establishing, for sequentially
comparing said sound waves to at least one of said threshold signal value
and said predetermined time interval to identify a first wave having at
least one of an amplitude at least as large as said threshold signal value
and a duration falling within said predetermined timer interval;
means, responsive to said means for sequentially comparing, for identifying
an adventitious sound when at least one consecutive wave following said
first wave has at least one of an amplitude at least as large as said
threshold signal value and a duration falling within said predetermined
timer interval; and
means, responsive to said means for identifying, for determining the number
of lung sounds in said sound signal.
16. A system for automatically detecting an adventitious sound signal
formed of a plurality of successive sound waves received from a patient,
comprising:
means for establishing at least one of a time interval consisting of a
series of predetermined time intervals which progressively increase in
duration and a threshold signal value based on an average signal value of
at least a portion of said sound signal;
means, responsive to said means for establishing, for sequentially
comparing said sound waves to at least one of said threshold signal value
and said predetermined time interval to identify a first wave having at
least one of an amplitude at least as large as said threshold signal value
and a duration falling within said predetermined time interval; and
means, responsive to said means for sequentially comparing, for identifying
an adventitious sound when at least one consecutive wave following said
first wave has at least one of an amplitude at least as large as said
threshold signal value and a duration falling within said predetermined
time interval.
17. A system for automatically detecting an adventitious sound from a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for determining an average signal value of at least a portion of said
sound signal;
means for generating a threshold value based on said average signal value;
means for sequentially comparing the sound waves of at least a portion of
the sound signal with a predetermined time interval to identify an initial
deflection wave having a duration falling within said time interval;
means, responsive to said means for sequentially comparing, for
sequentially comparing the amplitude of individual sound waves following
said initial deflection wave to said threshold value;
means for comparing the total sum of waves including the initial deflection
wave and the number of consecutive sound waves after said initial
deflection wave having an amplitude at least at large as said threshold
value to a predetermined wave count range between three to sixteen waves;
and
means, responsive to said means for sequentially comparing sound wave
amplitudes and responsive to said means for comparing, for identifying an
adventitious sound occurring within the sound signal when each of a
plurality of consecutive sound waves following said initial deflection
wave has an amplitude at least as large as said threshold value and for
identifying an adventitious sound only when said sum total of waves is
within said predetermined wave count range.
18. A system for automatically detecting an adventitious wound from a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for determining an average signal value of at least a portion of said
sound signal;
means for generating a threshold value based on said average signal value;
means for sequentially comparing the sound waves of at least a portion of
the sound signal with a predetermined time interval to identify an initial
deflection wave having a duration falling within said time interval;
means, responsive to said means for sequentially comparing, for
sequentially comparing the amplitude of individual sound waves following
said initial deflection wave to said threshold value;
comparator means for sequentially comparing at least a portion of the sound
waves following said initial deflection wave with said predetermined time
interval;
counter means, responsive to said comparator means, for resolving the
number of consecutive sound waves following said initial deflection wave
having a duration falling within said predetermining time interval;
means for comparing the duration of said consecutive sound waves having a
duration falling within said predetermined time interval to the duration
of the previously occurring sound wave; and
means, responsive to said means for sequentially comparing the sound waves,
responsive to said means for sequentially comparing sound waves amplitudes
and responsive to said means for comparing the duration of said
consecutive sound waves, for identifying an adventitious sound occurring
within the sound signal when each of a plurality of consecutive sound
waves following said initial deflection wave has an amplitude at least as
large as said threshold value and for identifying an adventitious sound
only when a plurality of successive sound waves following said initial
deflection wave have progressively increasing durations.
19. A system for automatically detecting an adventitious sound from a sound
signal formed of a plurality of successive sound waves received from a
patient, comprising:
means for determining an average signal value of at least a portion of said
sound signal;
means for generating a threshold value based on said average signal value;
means for sequentially comparing the sound waves of at least a portion of
the sound signal with a predetermined time interval from between
approximately 0.125 to approximately 3.0 milliseconds to identify an
initial deflection wave having a duration falling within said time
interval;
means, responsive to said means for sequentially comparing, for
sequentially comparing the amplitude of individual sound waves following
said initial deflection wave to said threshold value; and
means, responsive to said means for sequentially comparing the sound waves
and sound wave amplitudes, for identifying an adventitious sound occurring
within the sound signal when each of a plurality of consecutive sound
waves following said initial deflection wave has an amplitude at least as
large as said threshold value. |
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Claims |
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Description |
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FIELD OF INVENTION
This invention relates to a diagnostic method and apparatus for detecting
breathing abnormalities in humans to diagnose lung disorders and more
particularly to such an apparatus and method which automatically detects
adventitious lung sounds.
BACKGROUND OF INVENTION
Listening to various adventitious or abnormal breathing sounds has proven
to be an important diagnostic tool for detecting and monitoring certain
types of lung diseases. Abnormal pulmonary sounds are generally detected
by placing a stethoscope over selective areas of a patient's chest and
listening for the sounds directly. The type of abnormal sound, its
location, and its frequency of occurrence are used to make determinations
of the type of disease and its severity.
The detected sounds are typically classified into normal lung sounds or
adventitious (abnormal) sounds, usually divided into continuous or
discontinuous sounds depending on their duration. Continuous sounds are
further divided into wheezes, which are high-pitched, hissing sounds and
rhonchi, which are low-pitched, snoring sounds. Discontinuous sounds are
similarly divided into coarse crackles, which are short intermittent
explosive sounds having a low pitch, or fine crackles, which are
distinguished from coarse crackles in that they are less loud, shorter in
duration, and higher in pitch. Other adventitious sounds include pleural
friction rub and bronchial breathing.
Generally, it is a difficult task for an observer to detect accurately
various lung sound abnormalities, since they are frequently of short
duration, sometimes of relatively low amplitude, and generally mixed in
with normal breathing sounds, which sometimes obscure the abnormal sounds.
Furthermore, the task of classifying, quantifying and documenting lung
sounds is difficult to accomplish with a stethoscope. Observers vary
greatly in their abilities in this regard, making diagnosis less reliable.
An apparatus which forms visual waveforms representing the breathing sounds
of a patient using a time-expanded scale has been disclosed by the present
inventor in U.S. Pat. No. 3,990,435. This apparatus permits a trained
observer to visually delineate the abnormal sounds from normal sounds.
This has greatly improved diagnostic accuracy and helped clarify the
previously confused lung sound nomenclature. Diagnosis, however, depends
on the observer to properly sort and distinguish the different abnormal
lung sounds from the normal lung sounds detected at various locations. The
manual sorting of lung sounds visually or acoustically is a tedious task
whose accuracy depends on the experience and alertness of the observer.
Another method of adventitious sound detection employs one or more bandpass
filters to selectively detect sounds in preselected frequency ranges.
Abnormal sound identification is based on the percentage of the total
sample made up of sounds in the selected ranges. This technique is very
unreliable; many of the adventitious sounds have components in the same or
overlapping frequency ranges. As a result, the technique often cannot
distinguish the different types of sounds, especially when more than one
type is present.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide a system for
automatically identifying adventitious (abnormal) sounds from a patient.
It is a further object of this invention to provide a system for
automatically identifying crackles, wheezes, rhonchi, squeaks and squawks.
It is a further object of this invention to provide a system for
automatically counting such adventitious sounds.
This invention results from the realization that a simple, noninvasive and
harmless way of analyzing illnesses associated with lung disease can be
achieved by automatically identifying adventitious lung sounds in a
patient by sequentially comparing each half cycle sound wave in a lung
sound signal with predetermined wave duration and/or amplitude criteria to
identify sounds based on a comparison of these results to expert analyses
of typical sound signals of the different types of adventitious lung
sounds.
This invention features a system and method for automatically detecting an
adventitious sound from a sound signal formed of a plurality of successive
sound waves received from a patient. The system features means for
establishing at least one of a predetermined time interval and a threshold
signal value based on an average signal value of at least a portion of the
sound signal, and means, responsive to the means for establishing, for
sequentially comparing the sound waves to at least one of the threshold
signal value and the predetermined time interval to identify a first wave
having at least one of an amplitude at least as large as the threshold
value and a duration falling within the predetermined time interval.
Further included are means, responsive to the means for sequentially
comparing, for identifying an adventitious sound when at least one
consecutive wave following the first wave has at least one of an amplitude
at least as large as the threshold signal value and a duration falling
within the predetermined time interval.
Preferably, the system includes means for receiving the sound signal from a
patient, which may be accomplished with an electronic stethoscope. Also
included may be means for conditioning the sound signal to attenuate
normal sounds. That may be accomplished with a filter for attenuating
sound signals having frequencies lower than approximately 80 hertz and
greater than approximately 2000 hertz. The system may further include
means for storing a sample sound signal, which may include an analog sound
signal sample. The means for conditioning the sound signal may also
include means for digitizing that signal. Also included may be means for
amplifying the sound signal.
Preferably, the system includes means for determining an average signal
value of at least a portion of the sound signal, and means for generating
a threshold value based on that average value. In that embodiment, there
may further be included means for sequentially comparing the sound waves
with the predetermined time interval to identify an initial deflection
wave having a duration falling within the time interval. Further included
may be means, responsive to the means for sequentially comparing the sound
waves, for sequentially comparing the sound waves following the initial
deflection wave to the threshold value, and means for identifying an
adventitious sound occurring within the sound signal only when a plurality
of consecutive sound waves including the initial deflection wave have an
amplitude at least as large as the threshold value.
The system preferably also includes means for comparing the total sum of
waves including the initial deflection wave and the number of consecutive
sound waves thereafter having an amplitude at least as large as the
threshold value to a predetermined wave count range. In that case, the
means for identifying is preferably responsive to the means for comparing
the total sum of waves for identifying an adventitious sound only when the
total sum of waves is within the predetermined wave count range. That wave
count range is preferably from two to sixteen waves.
The system may further include means for determining the initial slope of
the wave following the initial deflection wave, and means, responsive to
the means for determining the initial slope, for comparing the initial
slope with the predetermined slope range to identify a wave following the
initial deflection wave having an initial slope falling within that slope
range. In that case, the means for identifying is preferably further
responsive to the means for comparing the initial slope for identifying an
adventitious sound only when the initial slope of the wave following the
initial deflection wave is within the slope range.
The system may also include comparator means for comparing the individual
durations of at least a portion of the sound waves following the initial
deflection wave with the predetermined time interval. In that case, a
counter is preferably included, responsive to the comparator, for
resolving the number of consecutive sound waves including the initial wave
having a duration falling within the predetermined time interval. The
means for identifying may then be responsive to the counter means for
identifying an adventitious sound only when a plurality of consecutive
sound waves have a duration falling within the predetermined time
interval.
In an alternative embodiment, the system may further include means for
comparing the individual durations of the consecutive sound waves having a
duration falling within the predetermined time interval to the duration of
the previously occurring sound wave. In that case, the means for
identifying may be further responsive to the means for comparing the
duration of the consecutive sound waves for identifying an adventitious
sound only when a plurality of successive sound waves following the
initial deflection wave have progressively increasing durations. The
predetermined time interval may be from approximately 0.125 to
approximately 3.0 milliseconds. The system may identify the sound based on
overall duration; a crackle lasting less than 25 milliseconds; a squeak or
squawk lasting from 25 to 250 milliseconds; and a wheeze or rhonchus
lasting more than 250 milliseconds. The other identification criteria may
also be employed to further differentiate the type of adventitious sound.
DISCLOSURE OF PREFERRED EMBODIMENT
Other objects, features and advantages will occur to one skilled in the art
from the following description of a preferred embodiment and the
accompanying drawings, in which:
FIG. 1 is a waveform illustrating an abnormal lung sound illustrative of an
adventitious sound detected by the system of this invention;
FIGS. 2A, 2B, 2C, 3A, 3B, 3C, 4A and 4B are flowcharts illustrating the
operation of the system according to this invention;
FIG. 5 is a simplified schematic diagram illustrating a system according to
this invention for automatically identifying an adventitious lung sound in
a patient;
FIG. 6 is a more detailed schematic diagram of the system of FIG. 5
featuring the signal conditioner;
FIG. 7 is a more detailed schematic diagram of the system of FIG. 5
detailing the detection module; and
FIGS. 8A, B and C are plots of the relative wave amplitude distributions in
a normal lung sound, crackle and rhonchus, respectively, illustrating the
amplitude detection method of adventitious lung sound identification
according to this invention.
A lung sound detection system according to this invention automatically
detects an adventitious sound from a sound signal received from a patient
consisting of a number of sequential sound waves. An adventitious sound is
identified from information derived from the durations of the individual
sound waves or their amplitudes, or both. In one embodiment, when a
preselected number of consecutive waves in the sound signal meet the
established duration and/or amplitude parameters, the group of waves is
identified as an adventitious sound. Preferably, an entire sound signal
consisting of at least one inspiration and expiration cycle is checked in
this manner, and the number and type of adventitious sounds occurring in
the sound signal is determined.
There are many types of adventitious sounds which may be identified by the
system and method according to this invention. Adventitious sound
identification has always been an important diagnostic tool. However,
until recently, uniform standards for identifying adventitious sounds did
not exist. In U.S. Pat. No. 3,990,435, incorporated herein by reference,
some of those different types of adventitious sounds were shown and
described. The sounds called rales in that patent are now known as
crackles. The different types of adventitious sounds have historically
been identified by the physician using a stethoscope. In the referenced
U.S. patent, a breath sound diagnostic apparatus was disclosed which
visually displayed on a time-expanded scale a representation of lung
sounds. That apparatus provided practitioners the ability to visually
identify adventitious sounds.
The commonly occurring adventitious sounds may be briefly described as
follows. Crackles are typically artifacts having a duration of less than
twenty-five milliseconds. A crackle typically includes from two to sixteen
consecutive half cycle sound waves each having a duration of from
approximately 0.125 to approximately 3.0 milliseconds. Coarse crackles are
relatively loud and low-pitched; fine crackles are softer, shorter,
higher-pitched sounds. The durations of the half cycle waves in a crackle
typically increase as the event progresses.
A wheeze is typically a continuous, high pitched polyphonic musical sound
lasting at least 250 milliseconds. The sound may have two predominant
frequencies, one centered between 350 and 500 Hz, and the other below
that. The half cycle sound waves are typically relatively uniform
throughout the artifact. A rhonchus is typically a continuous low pitched,
snoring sound which is visually similar to a wheeze, with a duration of at
least 250 milliseconds. The primary difference between the wheeze and
rhonchus is the frequency; the rhonchus typically is monophonic, with a
predominant frequency below 350 Hz. Squeaks and squawks are short high
pitched chirping sounds with typical durations between twenty-five and 250
milliseconds. Visually, the wave form is relatively uniform. Thus, the
system and method of this invention also contemplates identification based
on sequential comparison of individual sound wave durations to establishd
duration criteria based on the dominant frequencies or overall sound
duration.
A further identification factor may be based on an analysis of the
distribution of the half cycle sound wave amplitudes occurring in the
sound signal. Normal lung sounds have a relatively random amplitude
distribution. The wave amplitude distribution in a crackle has been found
to be relatively narrow; the majority of the waves have similar
amplitudes. On the other hand, the amplitude distribution in a typical
rhonchus is wide; there are relatively even numbers of waves having
several different amplitudes. Adventitious sound identification based on
the amplitude distribution criteria may be used alone or in conjunction
with one or more of the other criteria.
This invention thus provides for automatic identification of adventitious
sounds based on the amplitude and/or duration of the half cycle sound
waves forming the sound, as well as the overall duration of the artifact
itself. The system and method of this invention provides the flexibility
for identification based on these factors in accordance with established
definitions of adventitious sounds.
In a preferred embodiment, a crackle is identified as follows: an average
value of the sound signal is determined and a threshold value is generated
from that average value. The individual sound waves of the sound signal
are then compared to a predetermined time interval to detect an initial
deflection wave having a duration falling within that interval. Once an
initial deflection wave is identified, the lung sound detection system
sequentially analyzes the sound waves immediately following the initial
deflection wave to identify the adventitious sound.
In this preferred embodiment, the initial slope of the wave immediately
following the initial deflection wave is preferably determined. The
initial slope is defined as a slope of the wave immediately after the
first zero crossing. If the slope is within a predetermined range of
slopes, the system continues the analysis. If the slope does not fall
within the selected range, the system returns to the duration analysis,
looking for the next initial deflection wave.
When the slope is within the preselected range, the system determines the
number of sequential waves following the initial deflection wave meeting
established duration and amplitude criteria. A wave is identified as
potentially part of an adventitious sound when it has an amplitude at
least as large as the preestablished threshold value and a duration
falling within the preselected range. The duration of each wave is also
compared to the duration of the immediately preceding wave; a wave is
identified as being potentially part of an adventitious sound only when
its duration is greater than that of the preceding wave, as long as its
duration stays within the preselected duration range.
The sound is then identified as a crackle by comparing the number of
sequential waves having the established criteria to a preselected wave
count. For example, the system may be enabled to identify a portion of the
sound signal as a crackle when the number of consecutive waves including
the initial deflection wave meeting the established criteria is between
two and sixteen. If the number is less than two or greater than sixteen,
the system does not identify the group of waves as a crackle and the
operation returns to wave analysis for identification of the next initial
deflection wave. Alternatively, the sequential wave count may continue for
identification of continuous sounds. For example, the sound may be a
wheeze or rhonchus if there are at least seventeen consecutive waves
meeting the criteria. For continuous sounds, increasing duration is
typically not used as a criterion. The system may then distinguish the
specific type of continuous sound based on other criteria.
Adventitious sounds may be identified in other manners as is more fully
described below. The above description of a preferred embodiment is simply
one example of a rigorous sound signal analysis for adventitious sound
identification.
There is shown in FIG. 1 an example of a portion 39 of a sound signal
received from a patient. The portion includes successive half-cycle sound
waves 40, 41, 46 and 47. Portion 39 illustrates a crackle; waves 40, 41,
46 and 47 are sequential waves which meet the criteria established for
identification of such an adventitious sound. Wave 40 is an initial
deflection wave, which is identified as a wave having a duration falling
within a predetermined time interval. The duration of the wave is defined
as the time between zero crossings, established by line 45.
After the identification of initial deflection wave 40, the system
preferably determines initial slope 44 of next wave 41. The system
identifies wave 41 as potentially belonging to an adventitious sound when
its duration, or time between zero crossings, T.sub.2 -T.sub.1, falls
within the predetermined range of durations. Alternatively, wave 41 may be
identified when its amplitude is at least as large as previously
established threshold value 42. For waves in the opposite direction,
threshold value 43 having the same absolute value as threshold value 42 is
established.
The duration and/or amplitude of successive waves is then compared to the
preestablished criteria for determination of the number of consecutive
waves having those criteria. Additionally, the system may compare the
durations of the successive waves and identify a wave only when its
duration is greater than the previous wave in the group identified as a
potential adventitious sound. When the number of consecutive waves
identified is at least two and no more than sixteen, the system identifies
the wave group as a crackle. The analysis then continues with the next
wave after the adventitious sound to look for the next initial deflection
wave. Preferably, the system scans the entire sound signal in this manner
and determines the number and type of adventitious sounds for use by the
physician in diagnosis.
Flow charts for embodiments of the system and method according to this
invention are shown in FIGS. 2 through 4. In one embodiment, FIG. 2A,
adventitious sounds such as crackles are identified by first selecting a
sample of a predetermined duration from the sound signal, step 100. The
sample duration may be a portion of or an entire inspiration and
expiration cycle, or more than one such cycle. The sample average is
determined, step 102, preferably as the root mean square of the signal
value. The root means square is preferably the square root of the average
square of the instantaneous magnitude of the voltages. This average value
is then used to establish threshold values, step 104. As an example,
threshold value that are plus and minus three times the average value have
been found to be useful for identifying crackles. The threshold value may
be established based on the operator experience, and previous patient
history.
The system then compares sequentially the half cycle sound waves of the
sample to the threshold values, step 105. If the wave amplitude is as
large as a threshold, the system moves on to step 110, in which wave
counter N is incremented. If N is greater than 16, N is reset, step 115.
If N is not greater than 16, operation proceeds to an amplitude review of
the next wave, steps 106 and 105. If the amplitude is not as large as the
threshold, operation proceeds to step 112.
The total number N of consecutive waves including the first wave satisfying
the identification criterion forms in this example the basis for
identification. As a non-limiting example, to identify a crackle, N may be
chosen as between 2 and 16. The number employed is based on expert
evaluation of visual representations of an adventitious sound identified
as a crackle. If N is greater than 16, the group of waves is not a crackle
and operation returns to step 106 through step 115. If N is less than 16,
and greater than 2, the crackle counter is incremented, step 114, the wave
counter is reset, step 115, and operation returns to step 106 for analysis
of the remainder of the sample.
Two additional steps which may be added to the flow chart of FIG. 2A are
shown in FIG. 2B. After a first wave having at least the threshold
amplitude is identified, step 105, operation may continue to step 115 for
a determination of the initial slope of the next wave. If slope S is
between 375 and 400, as is more fully described below in conjunction with
FIG. 7, the operation continues to step 110. Preferably, only the initial
slope of the wave immediately following the first wave identified in step
105 is checked. Thus, steps 115 and 116 would be passed through only
once--immediately after initial wave identification. After that, the
system checks only the wave amplitude as described above in conjunction
with FIG. 2A.
Another set of steps which may be added to the flow chart of FIG. 2A is
shown in FIG. 2C. After the number N of waves satisfying the amplitude
criterion are counted, step 112, operation may continue to step 200 for
amplitude comparison range setting. Step 200 may comprise reading
comparison ranges from a lookup table or allowing the operator to set the
ranges as desired. The amplitude ranges may be established by plotting the
number of waves having given amplitudes as is more fully described below
in conjunction with FIGS. 8A through 8C. The result is similar to an
expert system in that the system and method according to this invention
may compare the wave amplitude distribution to that known to exist for the
different types of adventitious sounds to identify the occurrence of that
type of sound. Operation proceeds to step 202 in which the system
determines the wave amplitudes and step 204 in which the determined
amplitudes are compared to the established comparison ranges. The result
is similar in effect to plotting the amplitude ranges as shown below.
In identification of crackles, step 206 is included for comparison of the
wave distribution to that of a typical crackle. It should be understood
that for identification of other types of adventitious sounds, the
comparison may be made to known amplitude distributions for each of the
types of adventitious sounds. The artifact may then be identified by
comparison of the amplitude distributions to those established amplitude
distributions. At step 206, if the distribution is more similar to crackle
distribution, operation proceeds to step 114. If not, operation proceeds
to step 115. For a system in which something other than a crackle, or more
than just a crackle, is being monitored, rather than proceeding to step
115, the operation could proceed to additional steps similar to step 206
for a comparison of the wave distribution range to distributions for other
types of adventitious sounds, for example, wheezes, rhonchi, squeaks and
squawks.
A flow chart for an alternative embodiment of the adventitious sound
identification system is shown in FIGS. 3A, 3B and 3C. System 119
sequentially compares wave durations to a selected time interval and
determines the number of sequential waves having a duration falling within
that interval to identify an adventitious sound. After selection of a time
interval for comparison to wave durations, step 120, operation proceeds to
step 122, in which the wave durations are sequentially compared to the
selected time interval. When a first wave having a duration within that
range is found, operation continues to step 126, in which counter N is
incremented. If N is not greater than 16, step 124, the monitoring loop
continues through step 123. Steps 122, 126, 124 and 123 thus provide
sequential wave duration monitoring. If the number of successive waves
having a duration within the predetermined range of durations is greater
than sixteen, step 124, the group is not a crackle and operation returns
to step 123 through step 129 to begin looking for the next initial
deflection wave.
After the sequential identification of a number N of waves having the
established duration, operation continues to step 128. If N is greater
than or equal to two or less than or equal to sixteen, the crackle counter
is incremented, step 130, counter N is reset, step 129, and operation
continues, step 123, for identification of the remainder of the crackles
in the sound sample. If N does not fall within this range, the group of
waves is not identified as a crackle and the operation continues by
resetting the counter, step 129, moving to the next wave, step 123, and
looking for the next initial deflection wave, step 122.
FIG. 3B illustrates an additional two steps which may be added to the
embodiment of FIG. 3A for identifying waves only if their durations
progressively increase. Steps 125 and 127 may be added after step 122 for
incrementing wave counter N after identification of the first or initial
deflection wave only if the duration of the wave is greater than the
previous wave duration. This provides the further limitation that the
waves of the adventitious sound must progressively increase in duration.
FIG. 3C illustrates steps which may be added to the embodiment of FIG. 3A
for identifying an adventitious sound (in this case a crackle) only if the
artifact duration is within set duration parameters. After identification
of N waves potentially comprising a crackle, step 128, operation would
proceed to step 131, in which the duration parameters for the different
types of adventitious sounds would be set by the operator or retrieved
from a preestablished memory location. Duration ranges for some of the
types of adventitious sounds have been detailed above.
In step 132, the artifact duration is determined, and compared to the
established artifact duration parameters, step 134. In this example, only
crackles are being monitored. However, typically the system and method of
this invention contemplate monitoring for numerous types of advantitious
sounds; in that case, steps similar to step 134 would be added for
comparison of the established artifact duration to the duration parameters
for the other types of adventitious sounds. Operation then proceeds to
step 129 if the duration is not in the desired range, or step 130 if it
is.
The dominant frequency may also be used as a means of identification,
preferably together with the overall sound duration. The frequency is
determined using the half-cycle duration criteria by, for example, setting
a minimum and maximum individual wave duration window for sequential wave
comparison. For example, to count waves having a frequency of less than
350 hertz, the duration parameters are set as greater than approximatly
1.4 milliseconds per half cycle. For 350-500 hertz, the duration must be
between approximately 1.0 and 1.4 milliseconds. Using the frequency
criterion, one may distinguish between squeaks and squawks as a first,
high-pitched group, and wheeezes and rhonchi as a second, low-pitched
group. Wheezes and rhonchi may be individually distinguished based on the
existence of two dominant frequencies in a wheeze; while both have a
dominant frequency between 0-350 hertz, the wheeze has a second sound or
note between approximately 350-500 hertz. These measurements, together
with the overall duration based on number of consecutive waves, provide a
further means of identifying the several types of adventitious sounds.
FIGS. 4A and 4B illustrate a flow chart of an embodiment of the present
invention in which adventitious sounds are identified by comparison of the
individual sound waves of the sound signal to several of the parameters
which form a part of this invention. The operator selects a wave count
range for identification of an adventitious sound, step 149, time interval
for comparison to the wave duration, step 150, and a slope range for the
initial slope of the wave following the initial deflection wave, step 151.
The operator also selects the sample size, step 160. After a determination
of an average value of the sample, step 162, the threshold values are set,
step 164, in response to a selection of the threshold parameter, step 163.
The individual waves of the sound signal | | |
