[Cardiac vagal withdrawal during stressful tasks estimated by the baroreflex sensitivity and respiratory sinus...

The primary purpose of this study was to compare the changes in baroreflex sensitivity (BRS) with those in respiratory sinus arrhythmia (RSA) during mental arithmetic (MA) and reaction time (RT) tasks. BRS was assessed by the sequence scanning method (Bertinieri et al., 1988) combined with the vascular unloading technique that enables beat-by-beat measurement in systolic blood pressure. Twenty-eight male college students were given both MA and RT tasks with the order counterbalanced. Results indicated significant differences in BRS and RSA reactivity that seems to be evidence for a stronger vagal withdrawal in MA. Reactivity in RSA was correlated more closely with respiratory variables (respiration rate, tidal volume, and end-tidal CO2) than in BRS. These findings suggest that BRS is more suitable for estimating cardiac parasympathetic control because of its greater independence from respiratory activity. The results were discussed concerning the patterning of cardiorespiratory stress responses.