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.
Introduction: Institute of Aerospace Medicine (IAM) Indian Air Force (IAF) conducts operational training in Aerospace Medicine for IAF fighter aircrew since 2009. This includes high-G training with qualifying criteria of demonstrating ability of the aircrew to sustain 9G for 5 s in closed-loop run (pilot-in-control) wearing anti-G suit while performing anti-G straining maneuver (AGSM). Incidences of inadvertent almost loss of consciousness (A-LOC)/G-induced loss of consciousness (G-LOC) are an unavoidable unintended consequence of such training. The aim of the paper is to study the incidence of G-LOC and A-LOC and its nature in the high-performance human centrifuge (HPHC) and compare it with our previous experiences. Material and Methods: A G-LOC/A-LOC proforma was designed at the Department of Acceleration Physiology and Spatial Orientation at IAM IAF to understand the nature and cause of the G-LOC/A-LOC. This was to be filled up by the aircrew on a voluntary basis. The data were analyzed using Microsoft Excel with a significance level set at 95% confidence interval and alpha ≤0.05. Results: Fifty-two aircrew (19.92%) experienced inadvertent G-LOC/A-LOC in 83 such episodes (54 G-LOC and 29 A-LOC) during the period January 2018–December 2018. Forty-seven aircrew experiencing G-LOC/ALOC agreed to be part of the study and filled up the proforma after the episodes. The incidence of G-LOC in the institute has reduced significantly over the past two decades, perhaps due to change in the HPHC used for training of aircrew. The incidence of G-LOC found in this study is comparable to the global incidence. Rise in heart rate was higher during A-LOC than G-LOC and was found to be statistically significant (t statistic = 2.33; P = 0.01). Relative incapacitation period was lesser than absolute incapacitation period during G-LOC and was found to be statistically significant (t statistic = 3.29, P = 0.001). G-level at which Type II G-LOC occurred was significantly higher than the Type I G-LOC. Conclusion: The incidence of A-LOC/G-LOC has reduced over the past two decades of high G training in IAF and is comparable to global incidence.
Introduction: Aircrew are repetitively exposed to positive Gz acceleration in fighter flying. Factors affecting +Gz tolerance vary among individuals and are determined by both modifiable and non-modifiable factors. Some of the non-modifiable factors influencing +Gz tolerance are age, gender, and height. The present study was undertaken to understand the relationship of these variables with relaxed +Gz tolerance. Material and Methods: The study involved a retrospective analysis of existing database of the high-performance human centrifuge at the Institute of Aerospace Medicine. Relevant data from 70 non-aircrew subjects were included for the study. Of these, 39 were male and 31 were female. The age and height varied from 27 to 38 years and 157 to 187 cm, respectively. The data were analyzed using Microsoft Office Excel® to find the correlation between age and height with relaxed +Gz tolerance. Relaxed +Gz tolerance of men and women was compared using unpaired t-test. Significance was set at P < 0.05. Results: The mean age, height, and relaxed +Gz tolerance of males were found to be 30.25 ± 4.3 years, 172.58 ± 6.5 cm, and 4.89 ± 0.67G, respectively, whereas those of females were 27.28 ± 3.36 years, 158.46 ± 6.78 cm, and 4.4 ± 0.85G, respectively. In both males and females, age and height showed no correlation with relaxed +Gz tolerance. However, the relaxed +Gz tolerance was found to be higher in males and this difference was statistically different (P = 0.008). Conclusion: Age and height showed no correlation with relaxed +Gz tolerance in both males and females nonaircrew subjects. Males exhibited a statistically significant, higher relaxed +Gz tolerance as compared to females.
Introduction: Motion sickness is a common problem faced during flying training. Aircrew with persistent motion sickness require motion sickness desensitization. Although many aircrew benefit from the motion sickness desensitization therapy (MSDT), a significant number of individuals fail to complete the desensitization program. Early prediction of desensitization program outcome would identify non-responders and help in increasing the efficiency of MSDT. Material and Methods: A retrospective survey of candidates who underwent MSDT at the Institute of Aerospace Medicine between 2009 and 2019 was done. Coriolis time interval (CTI) values of 28 candidates could be retrieved. Mean CTI values of the successful and unsuccessful candidates at 5 rotations per minute (RPM) were compared. Statistical analysis was done using independent t-test, binary logistic regression, and a receiver operator characteristics (ROC) analysis. Results: The unsuccessful group candidates (M = 14.3, SD = 8.7 s) had significantly higher mean CTI values at 5 RPM than the successful group candidates (M = 6, SD =2.3 s); t (15.09) = −3.43, P = 0.04. Logistic regression indicated that there was a significant association between the CTI values and MSDT outcome, Chi-square (1, n = 26) =12.73, P ≤ 0.001. ROC analysis revealed a statistically significant curve with a good predictive cutoff value for CTI to identify non-responders. Conclusion: Results indicated that CTI values are reliable indicators in predicting the outcome of MSDT. Inclusion of other parameters, both physiological and psychological, that have a good correlation with motion sickness may give us better predictive models. Such predictors will also help in better understanding of the pathophysiology of motion sickness and in formulating improved treatment modalities.
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