Characteristics of biosignals

Introduction
A biosignal can be defined as a physiological phenomenom, a body variable that can be measured and monitored. Since the number of physiological mechanisms is nearly unlimited, the diversity of biosignals is huge. This can also be justified by the fact that there are many ways to classify the biosignals:


 * Existence
 * Dynamic
 * Origin

As referred the variety of biosignals is nearly unlimited, this makes a unique classification of biosignals impossible. Their classification is based on their characteristics.

Existence
This first method takes the existence of biosignals as a way to classify them, dividing the biosignals into:

This kind of Biosignals exist without any excitation from outside body and are always present in the Human Body because is source is already inside the body. One example is the electrocardiographic signal (ECG) induce by electrical heart muscle excitation with the peaks Q-P-R-T-S.
 * Permanent Biosignals

This group of biosignals includes biosignals that are artificially induced. In contrast with the permanent biosignals this ones exist only during the excitation. It means that, when the artificial induction is over the induced biosignal decays with a time constant determined by the body properties. One example is the electric plethsysmography, here an artificial current is induced in the tissue. The voltage is then registered as an induced biosignal.
 * Induced Biosignals

Dynamic
The second method takes in consideration the dynamic nature of the biosignal according to: Static biosignals carry information during their steady-state lever wich may show slow changes over the time. For example the body temperature, which shows slightly changes during the day, that's why we can consider it a static biosignal. Dynamic biosignals show big changes during time, for example the heart rate. The course of the heart rate represents a highly dynamic biosignal.
 * Static Biosignal
 * Dynamic Biosignal

Origin
The last method is origin of the biosignal as a basis for their classification, here are some examples:
 * Electric Biosignals
 * Magnetic Biosignals
 * Mechanic Biosignals
 * Optic Biosignals
 * Acoustic Biosignals
 * Chemical Biosignals
 * Thermal Biosignal