Do respiratory sinus arrhythmia and respiratory phase durations impact heart rate variability asymmetry in healthy subjects?

Asymmetry is a peculiar aspect of the heart period (HP) variability. Although robustly detected in healthy subjects and reduced with aging, the origin of the HP variability asymmetry (HPVA) is still partially unknown. In this work, we tested the hypothesis that the asymmetry of the respiratory pattern with a ratio (E/I) of expiratory (EXP) to inspiratory (INSP) phase larger than 1 and the presence of respiratory sinus arrhythmia (RSA) could play some role in the generation of the HPVA. We studied 19 young healthy subjects during spontaneous breathing (SB) and controlled breathing at 10 breaths/minute (CB10). We found that during CB10 HPVA, RSA, INSP and EXP durations increased, while the E/I did not vary. HPVA indexes were correlated with RSA and EXP duration, but they were uncorrelated with E/I. We conclude that the RSA and the length of the respiratory phases are factors influencing the HPV A in young healthy subject, even though the relation is weak.