Thinking about breathing: Effects on respiratory sinus arrhythmia.

Respiratory sinus arrhythmia (RSA), the increase and decrease in instantaneous heart rate (HR) with inspiration and expiration, is commonly evaluated as function of breathing frequency f. However, to the extent that RSA plays a role in the efficiency of gas exchange, it may be expected to correlate better with HR/f ('breathing specific heart rate') than with f, because the former is a better reflection of the cardio-respiratory coupling. We measured RSA breath-by-breath in 209 young men and women during spontaneous breathing and during volitional breathing under auditory cues at vastly different f. In either case, and for both genders, RSA correlated better with HR/f than with f. As HR/f increased so did RSA, in a linear manner. When compared on the basis of HR/f, RSA did not differ significantly between spontaneous and volitional breathing. It is proposed that RSA is a central mechanism that ameliorates the matching between the quasi-continuous pulmonary blood flow and the intermittent airflow, irrespective of the type of ventilatory drive (cortical or autonomic).