Dynamical analysis of biological signals with the 0-1 test

The 0-1 test distinguishes between regular and chaotic dynamics for a deterministic system using a time series. Here is presented how to use the test with biological signals. Between all the biological signals obtained as a times series, we present the results of applying the test and study with more details the photoplethysmogram (PPG) from different subjects; different biological signals of one subject are analyzed also with the test. PPG signal contains extensive physiological dynamics information; mainly used to heart rate monitoring and blood oxygen saturation. Based on its understandable statistics, several indices have been proposed and may apply to some clinical needs. However, continuous real-time monitoring, of the non-stationary biological signals, is frequently used on the modern intensive care unit. A deep understanding of the PPG signal will allow finding algorithms to evaluate other possible indices that give information about the dynamical system that constitutes the human body. We demonstrate that the PPG signal, as a time series, on a healthy individual, is a quasi-periodic signal. The parameters calculated for the analysis give some ideas of what the quasi-periodic properties mean. Results are on PPG signals from different healthy young people. The dynamical analysis of the PPG signal applying the 0-1 test allows distinguishing a regular dynamic, periodic o quasi-periodic, from a chaotic dynamics operating directly over the time series. The result obtained is compared with the results from well known time series that are random, chaotic, aperiodic, periodic, and quasi-periodic.