Exercise-induced plasma volume expansion and post-exercise parasympathetic reactivation

The purpose of this study was to investigate the effect of exercise-induced plasma volume expansion on post-exercise parasympathetic reactivation. Before (D0) and 2 days after (D+2) a supramaximal exercise session, 11 men (21.4 ± 2.6 years and BMI = 23.0 ± 1.4) performed 6-min of submaximal running where heart rate (HR) recovery (HRR) and HR variability (HRV) indices were calculated during the first 10 min of recovery. Relative plasma volume changes (∆PV) were calculated using changes in hematocrit and hemoglobin measured over consecutive mornings from D0 to D+2. Parasympathetic reactivation was evaluated through HRR and vagal-related indexes calculated during a stationary period of recovery. Compared with D0, ∆PV (+4.8%, P < 0.01) and all vagal-related HRV indices were significantly higher at D+2 (all P < 0.05). HRR was not different between trials. Changes in HRV indices, but not HRR, were related to ∆PV (all P < 0.01). HRR and HRV indices characterize distinct independent aspects of cardiac parasympathetic function, with HRV indices being more sensitive to changes in plasma volume than HRR.