A study led by researchers at the Air Force Research Laboratory, 711th Human Performance Wing, Wright-Patterson AFB (OH, USA) has demonstrated a procedure, which may allow real-time, non-invasive detection of hypoxia under normobaric conditions.
Despite the training usually undertaken by pilots on appropriate recognition, and reaction to hypoxic symptoms, bursts of low oxygen or sudden loss of cabin pressure may prevent a pilot from observing the specific conditions prior to losing consciousness. This may pose an immediate threat to not just the pilot, but also the passengers, the aircraft and civilians on the ground.
The study published in the Journal of Breath Research establishes a potential experimental means for the monitoring and analysis of diagnostic biomarkers of hypoxia – volatile organic compounds (VOCs) – in non-invasive, in-flight conditions.
Changes in exhaled breath VOCs produced during periods of reduced oxygen (O2) levels were identified by exposing volunteers to simulated flight profiles, using a modified flight mask interfaced with a reduced O2 breathing device. Exhaled breath was analyzed by GC–MS, by collection of breath samples through two mechanisms – first, immediately prior to and following simulated hypoxia and recovery; and second, throughout the course of the simulation itself.
The authors identified seven VOCs that declined in response to hypoxic conditions, while isoprene was demonstrated to increase following the overall exposure profile. This set of VOCs, which display differential response to hypoxic exposure, could potentially be applied as a predictive biomarker in humans.
“We have several hypotheses regarding the underlying mechanisms resulting in the changes observed in the exhaled breath VOC profiles. However, due to obvious limitations in human subject testing, these hypotheses will be challenging to prove.” explained Sean Harshman, Research Scientist at the Air Force Research Laboratory, 711th Human Performance Wing.. “In spite of this fact, we are working to better understand hypoxic episodes mechanistically to validate our findings and to improve our non-invasive chemical sensing platforms. Our future and ongoing studies seek to confirm the data presented in this manuscript, develop a flight worthy chemical sensor, and begin further mechanistic studies of respiratory hypoxia. These data will allow us to gain a better understanding of hypoxic episodes and to better protect our flight crews.”
While attempts to achieve real-time monitoring of pilots for hypoxic risk appear to have taken off, further studies with experimental modifications that balance time resolution and GC–MS sensitivity, as well as those which seek to explain the underlying mechanisms for the observations will need to be undertaken, to validate these preliminary findings.
Sources: Scientists use exhaled breath to detect hypoxia; Harshman SW, Geier BA, Fan M et al. The identification of hypoxia biomarkers from exhaled breath under normobaric conditions. J. Breath Res. 9(4) (Doi:10.1088/1752-7155/9/4/047103) (2015).