Exhaled nitric oxide is associated with acute mountain sickness susceptibility during exposure to normobaric hypoxia

Nitric oxide is a gaseous signaling molecule that participates in a large variety of physiological functions and may have a role in the pathology of altitude illnesses, such as acute mountain sickness (AMS). The effect of normobaric hypoxia on the fraction of exhaled NO ( [Formula: see text] ) is a controversial area of high altitude physiology, with the effect varying widely across studies. We exposed 19 male subjects to normobaric hypoxia for 6h and measured [Formula: see text] and AMS (via Lake Louise Score) each hour. For data analysis, subjects were divided into AMS-positive and AMS-negative groups based on their Lake Louise Scores during exposure. Eighteen subjects completed the study, and the incidence of AMS was 50%. Mean [Formula: see text] was unchanged at hour 1 but was significantly elevated above baseline for the remainder of the normobaric hypoxia exposure (p<0.001). Subjects who developed AMS had a significantly lower mean [Formula: see text] at baseline compared to resistant subjects (p=0.013). Further investigations are warranted to confirm our results and to understand the physiological basis of this association.