The detrended fluctuation analysis of heartbeat intervals in time series during stress tests

The Detrended Fluctuation Analysis (DFA) is a method of nonlinear dynamics usually used to the characterization of non-stationary signals. Particularly, this technique provides information about correlations of heartbeat intervals time series. The objective of this work is to analyze with DFA cardiovascular alterations that are not present at rest in order to determine the cardiac stress. The RR series of healthy subjects with an average age of 20 years old and subjects with an average age of 40 years old, both with sedentary lifestyle, under stress tests on a treadmill at different speeds were obtained from a Holter monitor. These series are recorded both at rest and at stress test. Information about cardiac stress is acquired from the stress test series. In principle, it is possible to know the health status and physical condition from the subject. The main purpose is to find correlations between the DFA exponent and the stress test parameters. It was verified that RR time series of young people have long-range correlations and these correlations decrease for RR time series of middle-aged adults. In addition, it was able to determine, at least qualitatively, the cardiac stress during the different stress tests which is an important parameter to assess the heart condition.