Cardiac baroreflex sensitivity during repeated handgrip exercise: Comparisons with sit-stand maneuvers and spontaneous rest.

The cardiac baroreflex regulates arterial pressure via autonomic heart rate control. While sit-stand maneuvers (SSM) have been used to assess baroreflex sensitivity (BRS), they may be impractical for physically immobile individuals. This study examined cardiac BRS during repeated handgrip exercise (RHE) compared to SSM and spontaneous rest. Twenty participants (10 females) performed 5-min RHE and SSM at 0.10 and 0.05 Hz in random order after spontaneous rest. Cardiac BRS was calculated using transfer function analysis (BRS_TFA) and the sequence method (BRS_SM) in low (LF: 0.05-0.15 Hz) and very low (VLF: 0.02-0.07 Hz) frequencies. Power spectral density (PSD) quantified systolic blood pressure (SBP) and R-R interval (RRI) oscillations. Compared to rest, 0.10 and 0.05 Hz RHE significantly increased SBP and RRI PSDs, with the highest values observed during SSM in both frequencies. RHE significantly increased LF and VLF BRS_TFA coherence by 132% and 142%, while SSM increased them by 144% and 209%. Regardless of analytical methods, BRS remained unchanged during RHE compared to rest, but it significantly decreased during 0.10 Hz SSM, which correlated with increased heart rate. These findings suggest that RHE improves BRS_TFA estimation via increased coherence, whereas reduced BRS during SSM suggests baroreflex resetting.