Over the past year, I have written several times about the effects of hypoxia, including a video, which showed not only how hypoxia may present itself, but how the hypoxic person may be oblivious to the effects. I also shared information regarding the use of the Reduced Oxygen Breathing Device (ROBD2), and how this system is used in military training to allow pilots to better prepare and understand the symptoms of hypoxia. You can read more here and here.
Today, I wanted to share an interesting study from the Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences in Bethesda, Maryland, and the Aviation Survival Training Center, Naval Survival Training Institute, Naval Operational Medicine Institute in Washington. The researchers were attempting to determine how effectively the ROBD (the earlier version of the ROBD2) reflected the reported symptoms of hypoxia when compared to in-flight occurrences.
The researchers began by surveying 566 aviators with a 20 question, anonymous survey about their flight experiences with hypoxia PRIOR to ROBD training. The survey included basic demographic questions followed by questions regarding in-flight hypoxia symptoms they may have experienced. For those who responded that they had experienced hypoxic symptoms in flight, additional questions were asked regarding which symptoms they had experienced.
A second group of 156 pilots were surveyed, also anonymously, following ROBD training at a simulated altitude of 25,000 ft (following the Navy's standard training protocols). Again, the survey included demographic questions as well as questions regarding any symptoms of hypoxia they may have experienced during the training.
Once the data was collected, the results were analyzed using a variety of means (including Chi-square analysis (alpha=0.05), Fischer’s exact test (alpha=0.05), and incident
risk ratios). I won't review all of the data and analysis, but some of the key findings are reviewed below.
For those surveyed regarding in-flight symptoms:
20% reported hypoxia symptoms at an average altitude of just over 25,000 ft
Of those who had experienced in-flight symptoms, over half (57%) were not wearing an oxygen mask when the symptoms started and only 21% reported the experience in naval aviation hazard reports (HAZREPs).
The most common symptoms reported were tingling, difficulty concentrating and dizziness.
When comparing the results of the two surveys, the researchers found:
5 of the 16 symptoms listed on the surveys had statistically significant differences in the reported levels (tingling, difficulty concentrating, air hunger, blurred vision, and lights dimming.
For the other 11 of the 16 symptoms, there was NO significant difference between the frequency reported during in-flight experiences and ROBD2 training experiences.