AltitudeOmics: the effect of high altitude ascent and acclimatisation on cerebral blood flow regulation (885.1)

Abstract

Adequate oxygen supply to the brain is critical to maintain brain function. Hypoxia presents a unique challenge in maintaining sufficient cerebral oxygen delivery (DO2). We assessed by ultrasound cerebral blood flow (CBF: internal carotid, vertebral arteries and middle cerebral artery velocity [MCAv]) and arterial blood pressure (index of cerebral autoregulation; CA) during rest and hypercapnic breathing (MCAv‐CO2 slope; index of cerebrovascular function) in 21 healthy subjects at sea‐level (SL) and upon arrival at 5260m (ALT1) and after 16 days of acclimatisation (ALT16). Cerebral DO2 was calculated as the product of arterial oxygen content (CaO2) and flow in each respective artery and summed to estimate global CBF. Global CBF increased ~70% upon arrival at ALT1 (P<0.05) and returned to SL values at ALT16 as a result of changes in cerebral vascular resistance. A reciprocal pattern in CaO2 maintained global cerebral DO2 across acclimatisation. MCAv‐CO2 slope was elevated by ~79% upon arrival at ALT1 and further increased by ~89% at ALT16 (P<0.05). Indexes of CA were reduced upon arrival at ALT1 (P<0.05), but did not change with acclimatisation at ALT16 (P>0.10). Cerebral DO2 was well maintained upon acute exposure and acclimatisation to hypoxia. Cerebrovascular function was enhanced with acclimatisation to high altitude, but these changes did not mitigate the reduction in CA associated with hypoxic exposure.Grant Funding Source: Supported by U.S. Department of Defense