Biomedical signals are those signals (phenomenon that conveys information) which are used primarily for extracting information on biological system under investigation. The purpose of extracting information could be as simple as feeling the pulse of a person on the wrist or as complex as analyzing the structure of internal soft tissues by ultrasound scanner.
Biomedical signals originate from a variety of sources such as:
These are unique to the biomedical systems. They are generated by nerve cells and muscle cells. Their basic source is the cell membrane potential which under certain conditions may be excited to generate an action potential. The electric field generated by the action of many cell constitutes the bio-electric signal. The most common examples of bioelectric signals are the ECG (electrocardiographic) and EEG (electroencephalographic) signals.
The measurement of acoustic signals created by many biomedical phenomena provides information about the underlying phenomena. The examples of such signals are; flow of blood in the heart, through the heart's valves and flow of air through the upper and lower airways and in the lungs which generate typical acoustic signal.
These signals originate from some mechanical function of the biological system. They include all types of motion and displacement signals, pressure and flow signals. The movement of the chest wall in accordance with the respiratory activity is an example of this type of signal.
The signals which are obtained as a result of chemical measurements from the living tissues or from samples analyzed in the laboratory. The examples are measurement of partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2) and concentration of various ions in the blood.
Extremely weak magnetic fields are produced by various organs such as the brain, heart and lungs. The measurement of these signals provides information which is not available in other types of biosignals such bioelectric signals. A typical example is that of magnetoencephalograph MEG signal from the brain.
These signals are generated as result of optical functions of the biological systems, occurring either naturally or induced by the measurement process. For example, blood oxygenation may be estimated by measuring the transmitted/back scattered light from a tissue at different wavelengths.
The impedance of the tissue is a source of important information concerning its composition, blood distribution and volume. The measurement of galvanic skin resistance GSR is a typical example of this type of signal. The bio-impedance signal is also obtained by injecting sinusoidal current in the tissue and measuring the voltage drop generated by the tissue impedance. The measurement of respiration rate based on bio-impedance technique is an example of this type of signals.[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]