Comparison of dynamic cerebral autoregulation and cardiac baroreceptor sensitivity between residents living at different altitudes

Permanent residence at high-altitude and chronic mountain sickness (CMS) may alter the cerebrovascular homeostasis and reactivity. 15/13/17 healthy participants living at sea-level (LL), 3800m (HL3800m) and 5100m (HL5100m), respectively, and 31 additional highlanders with CMS living at 5100m were recruited. Mean blood pressure (MAP), middle cerebral artery blood flow velocity (MCAv), cerebral oxygen delivery (CDO2), low/high frequency (LF/HF-heart rate variability) and baroreflex sensitivity (BRS) were assessed while sitting, during standing-up and while standing. Cerebral autoregulation index (ARI) was computed (ΔMCAv%baseline)/ΔMAP%baseline) in response to standing-up. Altitude and CMS were associated with hypoxemia and elevated hemoglobin concentration. While sitting, MAP increased, MCAv, and LFpower decreased with altitude but were unaffected by CMS; CDO2 was preserved. BRS was similar across all altitudes, but reduced with CMS. With standing-up, ARI was unaffected from altitude and CMS. Compared to sitting, standing was associated with elevated MAP but preserved MCAv, CDO2 and BRS across altitudes. LF/HF ratio increased in HL5100m compared to LL and HL3800m from sitting to standing. In CMS, similar effects as seen in HL5100m in MAP, MCAv and CDO2 were observed, but LF/HF ratio remained unaffected and BRS increased while standing. Altitude and CMS were associated with hypoxemia and excessive erythrocytosis; however, cerebral homeostasis while sitting, during standing-up and while standing were overall preserved due to altitude- and CMS-related adaptations in the cerebrovascular and autonomic nervous system, and blood pressure regulation.