Hypoxia signature: A useful tool for hypoxia recognition among aircrew

Introduction: Hypoxia, often referred to as “silent killer,” a common aeromedical stressor in aviation, may have catastrophic events in-flight unless recognized well in time. On exposure to hypoxia, an individual manifests a specific spectrum of symptoms referred to as “hypoxia signature.” The present study was conducted to assess the manifestation of “hypoxia signature” on repeated exposure to simulated hypobaric hypoxia for its potential usage as a tool for hypoxia recognition. Material and Methods: Twenty-two healthy adult volunteers were subjected to a simulated altitude of 22,000 feet for a duration of 5 min in the hypobaric altitude chamber. The symptoms experienced by the participants at the said altitude were recorded using a questionnaire. The heart rate (HR) and oxygen saturation (SpO2) were recorded during the exposure. The hypoxia exposure was repeated two more times with a minimum interval of 3 weeks between each. Paired t-test was used to compare the mean values of physiological parameters (HR and SpO2) between ground level and 22000 feet recorded in all the three exposures. The hypoxia symptoms and their severity reported during the exposures were compared with those of recalled symptoms (reported after 3 weeks of exposure) using McNemar test and Wilcoxon Signed Rank test, respectively. Results: Paired t-test revealed a statistically significant increase in HR and fall in SpO2 with rise in altitude from ground level to 22000 feet. The three most common symptoms consistently observed were lightheadedness, thinking slow, and warm feeling. The common hypoxic symptoms and their severity scores reported at 22,000 feet compared with recalled counterpart during subsequent exposures did not reveal any significant differences (P > 0.05). Conclusion: There was a high degree of similarity in the frequency and severity score of symptoms between acute exposure to hypobaric hypoxia and recall indicating evidence of repeatability of symptoms across the three sessions of hypoxia exposure within the individuals. This brings out the usefulness of “hypoxia signature” as a tool for hypoxia recognition and its application in hypoxia indoctrination and training for aircrew.