Independent autonomic modulation of the sinoatrial and atrioventricular nodes assessed through RR and PR interval variation

The degree of coupling between autonomic nervous system influence on the sinoatrial (SA) and atrioventricular (AV) nodes is considered, using RR and PR intervals as indicators of ANS activity. Seventy minute recordings of electrocardiogram and respiratory measurements were made with data recorded in supine, standing, and sitting positions. Indices of respiratory sinus arrhythmia (RSA) for RR and PR intervals were calculated for 2-minute sections of deep breathing in both supine and standing positions. RSA indices for RR intervals were consistently higher in the supine position; no consistent pattern was seen for RSA in PR intervals. In addition, multiple regression analysis was carried out relating RR, PP, RP, and PR intervals in the three positions under the assumption of closely coupled ANS influence. The measured data was inconsistent with this assumption. We conclude that some independent ANS modulation occurs at the SA and AV nodes