Utilization of the repeated squat-stand model for studying the directional sensitivity of the cerebral pressure-flow relationship.

Hysteresis in the cerebral pressure-flow relationship describes the superior ability of the cerebrovasculature to buffer cerebral blood flow changes when mean arterial pressure (MAP) increases compared with when MAP decreases. This phenomenon can be evaluated by comparing the change in middle cerebral artery mean blood velocity (MCAv) per change in MAP during either acute increases or decreases in MAP induced by repeated squat-stands (RSS). However, no real baseline can be used for this particular protocol as there is no true stable reference point. Herein, we characterized a novel metric using the greatest MAP oscillations induced by RSS without using an independent baseline value and adjusted for time intervals (ΔMCAvT/ΔMAPT). We also examined whether this metric during each RSS transition was comparable between each other over a 5-min period. ΔMCAvT/ΔMAPT was calculated using the minimum to maximum MCAv and MAP for each RSS performed at 0.05 Hz and 0.10 Hz. We compared averaged ΔMCAvT/ΔMAPT during MAP increases and decreases in 74 healthy participants [9 women; 26 (20-74) yr]. ΔMCAvT/ΔMAPT was lower for MAP increases than MAP decreases at 0.10 Hz RSS only (0.91 ± 0.34 vs. 1.01 ± 0.44 cm·s-1/mmHg; P = 0.0013). For both frequency and MAP direction, time during RSS had no effect on ΔMCAvT/ΔMAPT. This novel analytical method supports the use of the RSS model to evaluate the directional sensitivity of the pressure-flow relationship. These results contribute to the importance of considering the direction of MAP changes, depending on the oscillations frequency when evaluating dynamic cerebral autoregulation.NEW & NOTEWORTHY Repeated squat-stand maneuvers are able to examine the directional sensitivity of the cerebral pressure-flow relationship. These maneuvers induce stable physiological cyclic changes where brain blood flow changes with blood pressure increases are buffered more than blood pressure decreases. These results highlight the importance of considering directional blood pressure changes within cerebral autoregulation.