Heart Rate Variability in Spontaneous and Controlled Breathing: a HF power vs. Parasympathetic Activity Index study

Respiratory sinus arrhythmia (RSA) refers to the changes in heart rate (HR) that occur with respiratory activity. While HR oscillations in the high frequency (HF) band (0.14-0.4 Hz) primarily reflect variations in cardiac vagal activity, changes in respiratory rate (frequency) and amplitude within that HF band affect RSA and thus any vagal activity metric which relies on RSA, including HF spectral power of HR variability (HRV) series. In this study, HF power estimates were compared to the recently introduced Parasympathetic Activity Index (PAI) by analyzing HRV series gathered during spontaneous and controlled respiration. HF power showed significant changes at different respiratory rates, as previously found, while PAI quantified relatively stable vagal activity across different respiratory rates. Thus, HF power was affected by both vagal activity and respiratory rate, whereas PAI appears to be modulated primarily by cardiac vagal activity.