Autonomic cardiac regulation to slow-paced respiration in seated and supine positions

PURPOSE: Respiratory modulation and positional control are the main two regulators of cardiac autonomic activity. Although both slow-paced breathing and supine position promote parasympathetic regulation, their interaction remains poorly documented. Here, the objective of this work is to study the interaction between these two autonomic controls. METHODS: Twenty healthy volunteers (12 males, 8 females), age of 25.9 ± 3.9 years were included in this study. They were randomly subjected to 6 different slow and controlled breathing at 4.5, 5, 5.5, 6, 6.5, and 7 min/cycles for 3 min in supine or seated position after a 3 min baseline recording in spontaneous breathing. ECG was continuously monitored and RR intervals (RRI), total power (Ptot), the standard deviation of normal R-R intervals (SDNN), high frequency power (HF), the root mean square of successive R-R interval differences (RMSSD), and low frequency power (LF) were calculated to study autonomic regulation. RESULTS: We observed (1) a similar increase in parasympathetic (RMSSD and LF) and overall autonomic (RRI, Ptot, and SDNN) activities in slow-paced breathing conditions, whatever the respiratory rate in comparison with control spontaneous breathing; (2) these autonomic parameters increased in sitting position, but in parasympathetic (RMSSD and LF) and overall autonomic (Ptot, and SDNN) activities interacted with respiratory control and were higher in seated slow-paced breathing. CONCLUSION: These results showed that (1) whatever the slow-paced breathing frequency, slow breathing favours parasympathetic control and slow heart rhythm; and (2) seated position favors autonomic cardiovascular interaction between respiratory modulation and positional control.