Download computer-aided diagnosis of heart diseases based on

COMPUTER-AIDED DIAGNOSIS OF HEART DISEASES BASED ON
PHONOCARDIOGRAM INFORMATION
Eliézer Costa Bilange1, Mariléa de Cássia G. Vilela 2 and Francisco José Fraga da Silva 3
Abstract  Heart auscultation is a fundamental component
on cardiac diagnosis. Its importance is strongly related with
its non-invasive nature, low cost, and efficiency. It is,
however, a difficult skill to acquire since it demands good
teaching methods and a lot of training. In an attempt to
address these deficiencies, we have developed a computeaided heart sound analysis algorithm based on the
information carried by the instantaneous energy of the
phonocardiogram signal. This algorithm intends to
determine some heart sounds parameters prior to detecting
murmurs and splits that may be present, in order to evaluate
the patient heart’s condition. Many samples of normal and
abnormal heart sounds in Microsoft Wave format were
collected and their energy behaviors were used to develop
the algorithm. Preliminary results show that it is possible to
achieve a good precision in determining those parameters.
Figure 1 shows the Wiggers diagram, a correlation of the
heart sounds with electric and mechanical events of the
cardiac cycle.
Index Terms  algorithm, heart sounds, phonocardiogram,
auscultation.
INTRODUCTION
Heart auscultation is an essential tool in the diagnosis of
heart diseases. However, it can take several years for one to
learn and refine this skill. The lack of efficient teaching
methods and the high degree of subjectivity associated with
this technique are some of the reasons that make it so
difficult to teach and learn.
On the other hand, the low cost, the non-invasive
nature and the efficiency of heart auscultation keep it among
the most desirable ones in a physician. Also, the amount of
useful information that non-invasive methods such as
phonocardiograms can provide are of great importance for
diagnosing cardiovascular disorders.
The phonocardiogram is a recording of the sounds
produced by the heart, due to the opening or closure of any
of the heart valves, vibration of the tissue(provoked by the
blood movement), or even turbulence of the blood. The
phonocardiography is an approach that compares the
temporal relationships between the heart sounds (given by
the phonocardiogram) and the mechanical and electrical
events of the cardiac cycle, so that more information about
the functional integrity of the heart can become available.
1
FIGURE. 1
WIGGERS DIAGRAM.
The purpose of this project is to develop a system that
can analyze and automatically identify some fundamental
characteristics of the heart sounds such as frequency, systole
and diastole duration, as well as alterations like murmurs
and splits in order to help medical students in the tough
learning process of acquiring auscultation skills.
BACKGROUND – HEART SOUNDS
The heart’s pumping cycle is divided into two main
parts: systole and diastole. Systole is the period of
contraction of the heart muscles and diastole is their period
of relaxation.
There are four main sounds that can be produced by
cardiac activity, two of which can be clearly heard while
listening to a patient’s heart with a stethoscope. In normal
conditions the other two sounds cannot be heard, although
they can be registered in a phonocardiogram. There are two
Eliézer Costa Bilange, Instituto Nacional de Telecomunicações, Av. João de Camargo, 510, 37.540-000, Santa Rita do Sapucaí, MG, Brazil,
[email protected]
2
Mariléa de Cássia G. Vilela, Instituto Nacional de Telecomunicações, Av. João de Camargo, 510, 37.540-000, Santa Rita do Sapucaí, MG, Brazil,
[email protected]
3
Francisco José Fraga da Silva, Instituto Nacional de Telecomunicações, Av. João de Camargo, 510, 37.540-000, Santa Rita do Sapucaí, MG, Brazil,
[email protected]
important parameters of the heart sounds that must be
considered while listening to them: intensity and pitch. The
intensity is related to the amplitude of the sound heard, and
may be influenced by the distance between the stethoscope
and the origin of the sound. The pitch refers to the frequency
of the sound, measured in Hertz, but usually expressed in
terms high, medium or low. Figure 2 illustrates the four
sounds: S1, S2, S3 and S4.
Aortic
Area
Pulmonary
Area
Tricuspid
Area
Mitral
Area
FIGURE. 3
AUSCULTATORY AREAS ON THE CHEST.
Each of these areas is closer to one or another valve
according to their names. Thus, the sounds due to the
activity of specific valves are more intense in their
corresponding areas. For example, S1 can be better heard
either on the tricuspid or the mitral areas, since it represents
the sound of their closure.
FIGURE. 2
PHONOCARDIOGRAM – THE FOUR HEART SOUNDS
The first sound, called S1, is a low pitched and
relatively long sound, mainly due to the closure of the
atrioventricular valves (mitral and tricuspid valves), after the
blood has passed from the atria to the ventricles. The second
sound, called S2, is a high pitched and brief sound due to the
closure of the aortic and pulmonary valves.
The third sound, S3, occurs in the early rapid filling
phase of the ventricles and is due to the vibrations provoked
by the blood when it gets into the ventricles. It is low pitched
and generally audible only in children and in some adults.
The fourth sound, S4, occurs when the atria contract
and propel blood into the ventricles. It’s low pitched and it’s
not audible, but it can be recorded by the phonocardiogram.
Murmurs
As a result of high flows, or defects which influence
blood flow through the heart or great vessels, turbulence
may be produced in blood. These turbulences are shed and
sound results. These sounds are called murmurs (Figure 4).
Auscultation Sites
FIGURE. 4
There are four main areas of auscultation on a
patient’s chest (Figure 3) that are optimal sites for
auscultation, at which the intensity of the sound is the
highest because the sound is being transmitted through solid
tissues or through a minimal thickness of inflated lung. They
are the pulmonary area, the mitral area, the tricuspid area
and the aortic area.
PHONOCARDIOGRAM – EXAMPLE OF A HEART MURMUR.
The murmurs may be normal (innocent) or abnormal
(organic) and may encompass systole or part of it, diastole or
part of it or even may be present during both. Timing and
pitch of a murmur are of significant importance to determine
the heart’s condition.
Organic murmurs can be the symptoms of several
heart diseases, such as stenosis or insufficiency of any of the
four heart valves (mitral, tricuspid, pulmonary and aortic),
patent ductus arteriosus, ventricular septal defect and atrial
septal defect.
Splits
Splits of the heart sounds can also be normal or
abnormal, and can occur in the first heart sound, S1, in the
second heart sound, S2, or even in both. In the splitting, the
high pitched components of the sound are listened
separately. Splitting can be the symptom of one among
many cardiopaties, such as atrial septal defect, bundle
branch clocks and pulmonary stenosis. Figure 5 shows an
example of a split of the second heart sound, S2, in the time
domain and in the frequency domain.
FIGURE. 6
HEART SOUND IN MICROSOFT WAVE FORMAT AND ITS CORRESPONDING
INSTANTANEOUS ENERGY.
Then, the software analyses this array and through
these variations of energy with the time, the cardiac
frequency and the systole and diastole durations of each
heart sound are determined. These first determined features
are important in order to evaluate the heart’s condition, since
many heart diseases can cause alterations in the timing of the
events in the heart, resulting in alterations in the sounds’
timing.
RESULTS
FIGURE. 5
TIME AND FREQUENCY DOMAIN OF A SPLIT
So far, the normal heart sounds have had their
features determined with good precision. The algorithm for
the abnormal ones is still under study, considering that
murmurs and splits change the energy pattern of the sounds
and require a special algorithm, that can detect these
anomalies prior to determining the sounds’ characteristics.
Figure 7 shows an example of an Aortic Ejection Murmur
that elicits this great alteration in the sound’s pattern of the
abnormal heart sound in comparison with a normal one. The
phonocardiogram is shown in blue, while the behavior of the
instantaneous energy of the sound is in red.
METHOD
Several samples of normal and abnormal heart sounds
were collected, digitized and sampled at a rate of 4KHz and
a 16-bit resolution, in Microsoft WAVE format.
The digitized samples were then driven onto an
algorithm, implemented in Matlab, which divides the heart
sound’s signal into small slots of 5 miliseconds and outputs
an array containing the value of the instantaneous energy of
each slot. Thus, this array contains the behavior of the
signal’s energy with the time.
Figure 6 represents an example of a normal heart
sound being analyzed. The graph in blue is the
phonocardiogram and the graph in red shows the
instantaneous energy x time behavior.
FIGURE. 7
EXAMPLE OF A MURMUR.
Figure 8 shows an example of a split in the first
heart sound, S1, also emphasizing the significant alteration
in the sound’s energy pattern when analyzing a pathological
sound.
FIGURE. 8
EXAMPLE OF A SPLIT.
CONCLUSIONS AND DISCUSSION
It has been noticed that determining the energy of the
sounds is not enough to accomplish efficient murmur/split
detection. It is necessary to use it along with another
parameter. The signal’s instantaneous frequency or timefrequency relation are examples of possible parameters that
could be used as a second reference. Also, it is possible to
use electrocardiograms signals synchronized with the
phonocardiogram ones in order to settle a more solid
reference for the analysis.
ACKNOWLEDGMENT
The authors wish to thank INATEL for offering all the
necessary structure for the development of this work and
FINATEL for providing the research funding.
REFERENCES
[1]
Singi, G, "Fisiologia Dinâmica", 2001, pp 101-114.
[2]
Webster, J,G, "Medical Instrumentation", 1998, pp 308-312.