The effects of a 5 second bend over maneuver on cerebral perfusion and autoregulation upon standing from squat

PURPOSE To investigate the effects of maintaining a bent over posture (BOP) for 5 s upon rising from squat on cerebral autoregulation. METHODS 8 healthy subjects (24.4 ± 1.9 years) completed 1 min of quiet standing, followed by 1 min of squat, followed by rising from squat over a 1–2 s period and then no maneuver (CON) or a BOP maneuver for 5 s before standing upright. Middle cerebral artery blood velocity (MCABV (cm/s); Transcranial Doppler) and mean arterial blood pressure at heart level (MAP (mmHg); finger photoplethysmography) were continuously measured. Cerebral vascular conductance (CVC) was calculated from MCA blood pressure (MCABP) and MCABV. MCABP was estimated by accounting for the hydrostatic column between the heart and the MCA. RESULTS Data are mean Δ from bsl ± SD. BOP attenuated the decrease in MCABV during the first 5 s upon rising from squat compared to CON (−6.5 ± 2.5 vs. −12.1 ± 3.1, P<0.05). MAP hypotension during the same time period was abolished in BOP (+3.8 ± 10.0 vs. −12.9 ± 4.5, P<0.05). Upon restoring upright posture in BOP, the MAP nadir ~10 s after rising was virtually identical but the drop in MCABV was attenuated in BOP, indicating CVC was functionally increased (+0.41 ± 0.3 vs. +0.2 ± 0.1, P=0.1). CONCLUSIONS The BOP maneuver blunts disturbances to cerebral perfusion following rising from squat during the 5 s that it is maintained and enhances cerebral vasodilation at the MAP nadir after rising. NSERC.