Methods of quantifying respiratory modulation in human PR electrocardiographic intervals

Respiratory sinus arrhythmia (RSA) is a clinically useful measure of heart rate variability which can be estimated by analyzing RR intervals. Respiratory related variation in atrioventricular nodal conduction (which we term RCV) may also be physiologically and clinically significant. RCV can be calculated through its influence on PR intervals. Two methods of estimating RCV in spontaneous and paced breathing are presented; these are cross spectral coherence and cosinor fitting measures. It was found that both techniques show statistically significant respiratory modulation of RR and PR interval duration, although the magnitude of RSA was found to be greater than RCV as expected. Changing posture from supine to standing caused a statistically significant drop in RSA for spontaneous breathing, but not paced breathing. The postural change also reduced RCV for both spontaneous and paced breathing, but this change was not statistically significant.