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

Abstract

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) acutely increases compared to when MAP acutely 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 employed 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 ({Delta}MCAvT/{Delta}MAPT). We also examined whether this metric during each RSS transition were comparable between each other over a 5-min period. {Delta}MCAvT/{Delta}MAPT 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 {Delta}MCAvT/{Delta}MAPT during MAP increases and decreases in 74 healthy subjects [9 women; 32 {+/-} 13 years]. {Delta}MCAvT/{Delta}MAPT was lower for MAP increases than MAP decreases at 0.10 Hz RSS only (0.91 {+/-} 0.34 vs. 1.01 {+/-} 0.44 cm{middle dot}s-1/mmHg; p = 0.0013). For both frequency and MAP direction, time during RSS had no effect on {Delta}MCAvT/{Delta}MAPT. 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 when evaluating dynamic cerebral autoregulation. News & NoteworthyRepeated 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 decreases. These results highlight the importance of considering directional blood pressure changes within cerebral autoregulation.