A Meta-Analysis of Exhaled Nitric Oxide in Acute Normobaric Hypoxia.

BACKGROUND: The effect of hypoxia on the exhaled nitric oxide (NO) of humans is unresolved. Many studies have measured the fraction of exhaled NO (FENO) or the partial pressure of exhaled NO (PENO) in normobaric and hypobaric hypoxia, with differing results.

METHODS: To better understand NO physiology and altitude acclimatization, we employed a random effects meta-analysis to determine the effect of acute normobaric hypoxia on the PENO of humans. A total of 93 subjects from 7 published studies (with 9 groups) were included. The median duration of exposure was 30 min and the mean hypoxic PIo2 was 95 (SD=10) mmHg.

RESULTS: The weighted standardized mean difference (SMD) in PENO measured at baseline and during an acute exposure to normobaric hypoxia was not significantly different from zero (SMD=0.09; 95% CI=-0.17, 0.34; z=0.65).

CONCLUSION: Based on this meta-analysis, acute normobaric hypoxia does not affect the PENO measured from the mouths of humans. This result should be considered for interpretations of high-altitude (and hypobaric) measurements of exhaled NO. As the PENO is a potential biomarker for altitude-illness susceptibility, recognizing that normobaric hypoxia does not affect the PENO will be important for understanding previous associations between low exhaled NO and poor acclimatization to hypoxia.