Key result
Exposure to 25,000 ft is linked to ~33% decompression sickness risk versus none at 22,000 ft.
Why the study?
Severe decompression sickness occurrences in military parachutist dispatchers at 25,000 ft prompted this investigation into residual risks and the safety of repeat exposures during a single duty period.
Does repeated hypobaric chamber decompression to 25,000 ft and 22,000 ft cause decompression sickness in healthy men performing dispatcher activities?
Observational (n=15)
No
Does repeated hypobaric chamber decompression to 25,000 ft and 22,000 ft cause decompression sickness in healthy men performing dispatcher activities?
Repeated ascents to 25,000 ft carry a high risk of decompression sickness for parachutist dispatchers, whereas repeated ascents to 22,000 ft appear safe if ground intervals are brief.
Urges caution for repeated 25,000 ft exposures in dispatchers; leaves open optimal safe thresholds pending larger studies.
INTRODUCTION: Occurrences of severe decompression sickness (DCS) in military parachutist dispatchers at 25,000 ft (7620 m) prompted revision of exposure guidelines for high altitude parachuting. This study investigated residual risks to dispatchers and explored the potential for safely conducting repeat exposures in a single duty period. METHODS: In this study, 15 healthy men, ages 20–50 yr, undertook 2 profiles of repeated hypobaric chamber decompression conducting activities representative of dispatcher duties. Phase 1 comprised two ascents to 25,000 ft (7620 m) for 60 and then 90 min. Phase 2 included three ascents first to 25,000 ft for 60 min, followed by two ascents to 22,000 ft (6706 m) for 90 min. Denitrogenation was undertaken at 15,000 ft (4572 m) with successive ascents separated by 1-h air breaks at ground level. RESULTS: At 25,000 ft (7620 m), five cases of limb (knee) pain DCS developed, the earliest at 29 min. Additionally, multiple minor knee “niggles” occurred with activity but disappeared when seated at rest. No DCS and few niggles occurred at 22,000 ft (6706 m). Early, heavy, and sustained bubble loads were common at 25,000 ft, particularly in older subjects, but lighter and later loads followed repeat exposure, especially at 22,000 ft. DISCUSSION: Parachutist dispatchers are at high risk of DCS at 25,000 ft (7620 m) commensurate with their heavy level of exertion. However, the potential exists for repeated safe ascents to 22,000 ft (6706 m), in the same duty period, if turn-around times breathing air at ground level are brief. Older dispatchers (>40 yr) with functional right-to-left (intracardiac or pulmonary) vascular shunts will be at risk of arterialization of microbubbles. Connolly DM, D’Oyly TJ, Harridge SDR, Smith TG, Lee VM. Decompression sickness risk in parachutist dispatchers exposed repeatedly to high altitude . Aerosp Med Hum Perform. 2023; 94(9):666–677.
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Connolly et al. (2023) conducted an observational in Decompression sickness (n=15). Repeated hypobaric chamber decompression to 25,000 ft vs. Decompression to 22,000 ft was evaluated on Incidence of decompression sickness (DCS). Repeated hypobaric chamber exposure to 25,000 ft resulted in 5 cases of decompression sickness among 15 healthy male volunteers performing dispatcher activities, whereas no cases occurred at 22,000 ft.
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