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1 Introduction
The electrical, mechanical or chemical activity that occurs during spatial, temporal, or
spatiotemporal biological events such as heartbeats or muscle contractions produce biological
signals that can be measured and analyzed. These are known as biomedical signals or biosignals.
Consequently, biomedical signals contain information that can be used to explain the physiological
mechanisms underlying an event or a specific biological system. The processing of these signals
has special characteristics based on the complexity of the system under study, and in many cases
non-invasive methods and techniques for measurement are needed. Representing biomedical
signals in digital/electronic form facilitates processing and data analysis. The main objectives when
processing and analyzing these signals are the acquisition of information, diagnosis, monitoring,
therapy and monitoring and evaluation.
Phonocardiography is the recording of heart sounds, developed to improve the results
obtained with the traditional acoustic stethoscope. With the phonocardiogram (PCG), the sound
waves from heartbeats can be captured, recorded, measured and represented graphically using
appropriate instrumentation. The PCG can document the timing, relative intensity, frequency,
quality, tone, timbre and precise location of the different components of heart sound, in an
objective and repeatable manner [1].
The traditional method of auscultation of heart sounds is still a basic tool of initial analysis, and
is applied to evaluate the functional state of the heart. It can be an early indicator for referral to a
specialist. By auscultation, the doctor tries to identify and analyze the different sounds that make
up the heart sound, and then performs a synthesis of the extracted features towards some clinical
evaluation. The importance of cardiac auscultation has been maintained since the early 1950-80's.
During this period, the mechanisms of heart sounds and murmurs and precise correlations
between sound, pressure, motion and flow were elucidated. These were supported by studies
based on M-mode echocardiography and cardiac catheterization. At the time, a trained clinician
could arrive at a definitive bedside diagnosis, after a thorough examination and auscultation.
Fig. 1.
Visualization of a biomedical signal in a medical clinic.