Transcerebral Exchange Kinetics of Nitrite and Calcitonin Gene-Related Peptide in Acute Mountain Sickness

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Abstract
Background and Purpose— High-altitude headache is the primary symptom associated with acute mountain sickness, which may be caused by nitric oxide-mediated activation of the trigeminovascular system. Therefore, the present study examined the effects of inspiratory hypoxia on the transcerebral exchange kinetics of the vasoactive molecules, nitrite (NO 2 • ), and calcitonin gene-related peptide (CGRP). Methods— Ten males were examined in normoxia and after 9-hour exposure to hypoxia (12.9% O 2 ). Global cerebral blood flow was measured by the Kety-Schmidt technique with paired samples obtained from the radial artery and jugular venous bulb. Plasma CGRP and NO 2 • were analyzed via radioimmunoassay and ozone-based chemiluminescence. Net cerebral exchange was calculated by the Fick principle and acute mountain sickness/headache scores assessed via clinically validated questionnaires. Results— Hypoxia increased cerebral blood flow with a corresponding increase in acute mountain sickness and headache scores ( P 0.05). Conclusion— These findings argue against sustained trigeminovascular system activation as a significant event in acute mountain sickness.