Relationship between cerebral pulsatility index and vasodilatory responsiveness to a hypercapnic challenge

Introduction: Cerebral vascular function/health is critical for the precise matching of cerebral blood flow and thus oxygen/substrate delivery and the metabolic demands of the brain. Cerebral pulsatility index (PI) reflects cerebral vascular resistance and compliance, and therefore provides a measure of cerebral vascular stiffness. A higher PI indicates augmented stiffness and is associated with risk for/prevalence of advanced atherosclerosis and poor cerebral vascular autoregulation, both of which can predispose individuals to various detrimental conditions including stroke and reduced neurocognitive function. Cerebral vascular function/health is also often assessed by the vasodilatory response to a hypercapnic stimuli with higher responses being associated with better health while reduced responses are associated with poorer health outcomes including increased risk for the aforementioned cerebral vascular and neurocognitive diseases/conditions. However, to our knowledge the relationship between PI and the subsequent vasodilatory response to a hypercapnic stimuli remains unknown. Hypothesis: Accordingly, this study tested the hypothesis that there is a negative relationship between cerebral PI (i.e. cerebral vascular stiffness) and cerebral vasodilatory responsiveness such that elevated PI is associated with attenuated vasodilation during a hypercapnic challenge. Methods: Data is presented from69 healthy individuals (50 female. Age: 25±9 yrs; BMI: 25±5 kg/m 2 ). Continuous measures of heart rate, beat-to-beat blood pressure, end-tidal carbon dioxide concentration (PETCO 2 ), and middle cerebral artery blood velocity (MCAv) were assessed throughout the duration of data collection. Cerebral vascular function was indexed as PI ((MCAV systolic – MCAv diastolic)/MCAv mean) and cerebral vasodilatory responsiveness (% increase in cerebral vascular conductance (CVCi) slope) during 4-min of breathing a 6% carbon dioxide gas mixture (%CVCi/ΔPETCO 2 ). Results: PI during normocapnia was 0.78±0.16. During the hypercapnic stimuli PETCO 2 was increased by 11±2 mmHg and cerebral vasodilator responsiveness assessed as %CVCi slope was 2.9±1.2 %/mmHg. There was not a significant relationship between PI and %CVCi slope (R 2 =0.018, p= 0.13). Conclusion: These preliminary data indicate that cerebral vascular stiffness as indexed by PI does not have a primary effect on cerebral vasodilatory responsiveness to a hypercapnic stimuli. This project was supported by the University of Texas at Arlington College of Nursing and Health Innovation (RMB). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.