Phase averaged characterization of respiratory sinus arrhythmia pattern

A method for the accurate time domain characterization of respiratory sinus arrhythmia (RSA), is presented. Primary heart rate (HR) changes along the respiratory phase are evaluated iteratively far selective integration of multiple respiratory cycles. A complete modulating function (RSA pattern) is evaluated accurately, with free respiration and even in cases of severe arrhythmia. RSA magnitude, phase lag, and expirium/inspirium time ratio are also derived. In a group of 10 healthy subjects, a phase lag difference of 11.4+/-8.5% was observed between supine and standing postures, possibly ascribed to breathing mechanics. A second group of 15 healthy subjects in supine rest had a consistent RSA pattern in each subject, in repeated sessions (several weeks apart), suggesting a non-scalar individual index for cardio-respiratory coupling. The method may open new insight into the effects of vagal activity and changes in clinical conditions.