Assessment of the cerebral pressure-flow relationship using psychological stress to manipulate blood pressure

Recent evidence indicates that cerebral autoregulation (CA) might be more pressure passive than previously thought. That is, cerebral blood flow, traditionally thought to be regulated independently of prevailing mean arterial pressure (MAP), might fluctuate, to some extent, as a function of MAP. However, due to limitations associated with experimental usage of pharmaceuticals to manipulate MAP and inconsistent control of arterial carbon dioxide, questions remain regarding the MAP-cerebral blood flow relationship, especially during typical daily activities that alter MAP. Therefore, the current study aimed to assess CA using a nonpharmacological acute psychological stress task to augment MAP, while at the same time controlling for end-tidal carbon dioxide (P_ET CO₂ ). Twenty-five healthy young adults completed a stressful task while continuous measures of MAP, middle cerebral artery blood flow velocity (MCAv), and P_ET CO₂ were recorded. Slope values obtained from hierarchical linear regression were used to assess the strength of the MAP-MCAv relationship and control for P_ET CO₂ . The stress task significantly increased MAP (p < 0.001) and MCAv (p < 0.001), and decreased P_ET CO₂ (p = 0.05). For every 10 mmHg task-induced increase in MAP, MCAv increased by ≈3.5%; task-induced changes in P_ET CO₂ did not appreciably change the MAP-MCAv relationship. Greater task-induced MAP responses were significantly related to decreased MAP-MCAv slope values, consistent with CA. These data support the hypothesis that CA is more pressure passive than previously thought and provide initial evidence indicating that a pressure-passive MAP-MCAv relationship may play a role in the observed associations between MAP stress responses, stroke, and cerebrovascular disease.