Exhaled isoprene for monitoring recovery from acute hypoxic stress

Hypoxia-like incidents in-flight have increased over the past decade causing severe safety concerns across the aviation community. As a result, the need to monitor flight crews in real-time for the onset of hypoxic conditions is paramount for continued aeronautical safety. Here, hypoxic events were simulated in the laboratory via a reduced oxygen-breathing device to determine the effect of recovery gas oxygen concentration (21% and 100%) on exhaled breath volatile organic compound composition. Data from samples collected both serially (throughout the exposure), prior to, and following exposures yielded 326 statistically significant features, 203 of which were unique. Of those, 72 features were tentatively identified while 51 were verified with authentic standards. A comparison of samples collected serially between recovery and hypoxia time points shows a statistically significant reduction in exhaled breath isoprene (2-methyl-1,3-butadiene, log₂ FC -0.399, p = 0.005, FDR = 0.034, q = 0.033), however no significant difference in isoprene abundance was observed when comparing recovery gases (21% or 100% O₂, p = 0.152). Furthermore, examination of pre-/post-exposure 1 l bag breath samples illustrate an overall increase in exhaled isoprene abundance post-exposure (log₂ FC 0.393, p = 0.005, FDR = 0.094, q = 0.033) but again no significant difference between recovery gas (21% and 100%, p = 0.798) was observed. A statistically significant difference in trend was observed between isoprene abundance and recovery gases O₂ concentration when plotted against minimum oxygen saturation (p = 0.0419 100% O₂, p = 0.7034 21% O₂). Collectively, these results suggest exhaled isoprene is dynamic in the laboratory ROBD setup and additional experimentation will be required to fully understand the dynamics of isoprene in response to acute hypoxic stress.