Effects of Somatosensory Afferent on Cerebral Hemodynamics during Orthostatic Stimulation

Abstract

PURPOSE: The effect of somatosensory afferent on the cerebral circulatory control is not clear. This study aimed to reveal whether the somatosensory input from lower extremities can affect cerebral hemodynamic regulation during orthostatic stimulation. METHODS: Eleven young adults (4 women) underwent two consecutive 6-min lower body negative pressure (LBNP) stimulations (-30 mmHg and -50 mmHg) under following two conditions: hanging up the body by a harness (leg-free) and bracing feet on the wood board in the LBNP chamber with slight knee flexion (leg-resisted) against suction. These conditions were conducted in random order. Heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), end-tidal CO2 (EtCO2), and cerebral blood flow velocity (CBFv) from the middle cerebral artery were continuously recorded. Dynamic cerebral autoregulation (dCA) was evaluated by transfer function analysis. RESULTS: HR was significantly higher, and CO and EtCO2 were significantly lower during -50 mmHg of LBNP stimulation than each baseline value irrespective of leg conditions, whereas MAP and mean CBFv remained at similar levels throughout the LBNP stimulation under both leg conditions. Power spectral density of mean CBFv in the low-frequency range (0.07-0.2 Hz) significantly increased at -30 and -50 mmHg of LBNP stimulations in the leg-resisted condition (from 1.41 ±0.62 to 5.42±3.27 and 5.19±3.46) but not in the leg-free condition. Likewise, transfer function gain in the low-frequency range were significantly augmented at -30 and -50 mmHg of LBNP stimulations in the leg-resisted condition (from 1.22±0.34 to 1.58±0.39 and 1.56±0.43) but not in the leg-free condition. CONCLUSIONS: These results suggest that somatosensory afferent from lower extremities may modify cerebral hemodynamic regulation during orthostatic stimulation.