Short-term recovery of heart rate variability and its relationship with blood pressure after different intensity treadmill exercise

Background : Heart rate variability (HRV) provides an opportunity to capture the tiny but early signs that may predict the future cardiovascular risk in healthy individuals and further, helps understand how well the cardiovascular autonomic system works. Aims of this study were to elucidate short-term recovery of HRV and its relationship with blood pressure recovery after different intensity treadmill exercise. Methods : Fifteen healthy participants performed four different conditions (REST; speed 6km/h; speed 8km/h; speed 10km/h), systolic and diastolic blood pressure per 30s (SBP, DBP) and 5-mins consecutive heart beats intervals were measured after each trial. Autonomic nervous regulation was evaluated using HRV time-frequency domain indices and heart rate asymmetry (HRA) indices. Each index was calculated using 5 mins electrocardiogram (ECG) series and consecutive 30-s windows in 5 mins. Results : the vagally related indices (RMSSD, pNN50 and HF) decreased and the indices representing overall variability (SDNN, LF) had different trends as intensity increasing. The sympathetic-vagal balance parameter LF/HF increased, too. HRV indices had strong correlations with DBP but weak with SBP. Meanwhile, heart rate asymmetry vanished after each trial. Conclusions : The findings suggested a vagal withdrawal as soon as the end of treadmill exercise. It could be concluded that sympathetic modulation was stronger as intensity increasing. During recovery period, DBP was mediated by vagal activation and sympathetic withdrawal. The diminished asymmetry in Poincaré plot was the result of sympathetic acceleration and vagal reduction.