Return maps: a non-linear method for evaluation of respiratory sinus arrhythmia

A method of respiratory sinus arrhythmia (RSA) evaluation, the main component of short-term heart rate variability, based on non-linear dynamics, is described. The latter was approached with repeated construction of return maps (Ri vs Ri+lag) with an increasing lag from 1 to 25. The correlation coefficient for each map was calculated and then presented as a function of lag. Some quantitative measures were introduced and compared with time- and frequency-domain measures of RSA. The method was applied in 7 healthy subjects and in 6 patients with coronary heart disease. The effect of a different time of ECG registration, and of different study conditions (controlled breathing and autonomic blockade) were also studied.