A method for time-domain analysis of respiratory sinus arrhythmia

Respiration-related heart rate variability - respiratory sinus arrhythmia (RSA) - is clearly related to vagal activity. Usually it is analysed in frequency domain. An improved method for the assessment of the RSA in timedomain is proposed and evaluated on a control group of 12 healthy volunteers (9 male, 3 female; age 31-70). The method is based on a measurement of respiration rate, combined with a reliable beat-to-beat heart rate determination. RR intervals of each respiration cycle are superimposed to obtain average RSA. The study of RSA in the time-domain can provide more information about the adaptation process and possible parasympathetic response of the heart, e.g. after heart surgery, because the shape of a typical RSA curve and its phase (relative to the measured breathing) are obtained. The time domain analysis of RSA is simple and does not need forced timing of respiration. We confirmed that the proposed methodology could be used in ambulatory and remote monitoring environments to follow the long-term changes in the RSA.