Respiratory sinus arrhythmia during a mental attention task: the role of breathing-specific heart rate.

It is known that a mental attention task (MAT) can modify the magnitude of the increase in instantaneous heart rate (HR) with inspiration, or Respiratory Sinus Arrhythmia (RSA). Here, we asked whether the RSA changes were mediated by the changes in HR, breathing frequency (f) or HR/f ('breathing specific heart rate'). This latter reflects the degree of coupling between pulmonary blood and air flows, the optimization of which may be the function of RSA. RSA (computed as the difference between peak and trough instantaneous HR of each breath, in percent of mean HR) was measured breath-by-breath in 119 young men and women (19.6 ± 0.1 year old) during spontaneous breathing and during a MAT, which consisted in finger tapping at acoustic cues delivered in various patterns. During MAT, breathing became more rapid (+2.2 breaths/min, P < 0.001) and shallow (78% of rest, P < 0.001) and HR decreased slightly (-1 beats/min, P < 0.05). RSA dropped from 13.4 ± 0.7 to 11.6 ± 0.7% (P < 0.0001), because of the drop in the inspiratory peak of instantaneous HR, and so did HR/f, from 5.8 ± 0.2 to 4.9 ± 0.2 beats/breath (P < 0.0001).The results were very similar between genders. The magnitude of the changes in HR/f correlated linearly with those of RSA, so that those subjects who decreased HR/f the most also had the largest decrease in RSA and the few who increased HR/f during MAT also increased RSA. We conclude that this type of mental task changed RSA by a magnitude that depended on its effect on HR/f. The results support the concept that RSA is a central cardio-respiratory mechanism to ameliorate the matching between pulmonary blood and air flows, whether the ventilatory drive originates spontaneously or is under cortical influences.