Physiological incidents during 39 years of hypobaric chamber training in Japan

Hypobaric chamber training for military aircrew is very important for flight safety. Since we began hypobaric training in our laboratory in 1960, some trainees have suffered physiological incidents. This study will characterize the physiological incidents during hypobaric chamber training at the Japan Air Self-Defense Force (JASDF).

All available training records from 1960-1998 were reviewed and the frequency of physiological incidents counted and analyzed.

There were 29,677 trainees and 58,454 exposures. Overall frequency of physiological incidents was 6.3%. Physiological incidents included ear pain, paranasal sinus pain, abdominal pain, hypoxia, hyperventilation, joint pain, and toothache. Decompression sickness (DCS-I, simple joint pain only) was rare. In cases of DCS-I, joint pain was easily relieved with controlled descent. During the last three decades, overall prevalence of physiological incidents has gradually increased from 5.3 to approximately 6.1% before 1991, to 6.8-9.9% after 1991. However, prevalence rate showed no change through out the period when ear pain was factored out. The increase in prevalence was entirely due to an increased frequency of ear pain: 3.6 to approximately 4.6% before 1991, and 5.4 to approximately 7.2% after 1991.

DCS has not been a problem in the JASDF hypobaric chamber training experience. The majority of physiological incidents during hypobaric chamber training in JASDF have been ear pain, a minor but frequent obstacle to hypobaric training. The exact cause of the observed increase in frequency of Eustachian tube dysfunction currently remains unclear.