Baroreflex Sensitivity Assessment With Repeated Handgrip Exercise: A Comparison With Sit-stand Maneuvers

The baroreflex plays an important role in short-term blood pressure (BP) regulation via modulation of heart rate (HR). The baroreflex sensitivity (BRS) can be estimated by transfer function analysis (TFA), while its reliability depends on coherence between BP and HR. Postural change, such as sit-stand maneuvers (SSM), have been used to augment the BP and HR variability and increase their coherence, although SSM may be difficult to perform in individuals with limited physical ability. PURPOSE: To determine whether repeated handgrip exercise (RHE) can augment BP and HR variability and increase their coherence for the BRS estimation. METHODS: After a 5-minute spontaneous rest, 20 healthy participants (age = 31 ± 7 years, 10 women) underwent four experimental conditions in random order: RHE performed at 30% of the maximal voluntary contractions (0.05 Hz and 0.10 Hz) and repeated SSM (0.05 Hz and 0.10 Hz). During each condition, systolic BP (SBP) and R-R interval (RRI) were continuously measured. TFA coherence, gain (i.e., BRS), and phase as well as power spectral density (PSD) of SBP and RRI were calculated. Based on previous research, we defined 0.023-0.070 Hz as very low frequency (VLF) and 0.078-0.148 Hz as low frequency (LF). RESULTS: Compared to resting, RHE significantly increased PSD of SBP by 186% and 816% at VLF and LF, respectively (all p < 0.05). PSD of RRI significantly increased during RHE compared to resting by 1317% at LF (p < 0.05) without a significant difference in VLF. Coherence significantly increased during RHE compared to resting in both frequency bands (VLF: 0.64 ± 0.05 vs. 0.45 ± 0.03, LF: 0.87 ± 0.04 vs. 0.67 ± 0.04, all p < 0.05), while SSM showed the highest coherence values (VLF: 0.92 ± 0.02, LF: 0.95 ± 0.02, all p < 0.001 vs. rest and RHE). There were no significant differences in BRS between RHE and spontaneous rest in both frequency bands, while SSM showed the lowest BRS in LF (rest: 7.6 ± 2.5 ms/mmHg, RHE: 8.7 ± 3.7 ms/mmHg, SSM: 3.5 ± 0.5 ms/mmHg, p < 0.001). Phase decreased during RHE compared to resting in LF (-0.69 ± 0.07 vs. -0.33 ± 0.07 radians, p < 0.001) without a significant difference in VLF. CONCLUSION: RHE significantly augmented the BP and HR variability and increased their coherence which may improve BRS estimations using TFA.