An abrupt zero-preoxygenation altitude threshold for decompression sickness symptoms.

INTRODUCTION: The altitude threshold for decompression sickness (DCS) symptoms has been variously described as being 18,000 ft (5,487 m) to above 25,000 ft (7,620 m). Safety and efficiency of aerospace operations require more precise determination of the DCS threshold. METHODS: Subjects were 124 males who were exposed to simulated altitudes (11 at 11,500 ft; 10 at 15,000 ft; 8 at 16,500 ft; 10 at 18,100 ft; 10 at 19,800 ft; 20 at 21,200 ft; 20 at 22,500 ft; 10 at 23,800 ft, and 25 at 25,000 ft) for 4 to 8 h. All breathed 100% oxygen beginning with ascent. Subjects were monitored for precordial venous gas emboli (VGE) and DCS symptoms. Probit curves representing altitude vs. incidence of DCS symptoms and VGE allowed estimation of respective risk. RESULTS: VGE were first observed at 15,000 ft with increasing incidence at higher altitudes; over 50% at 21,200 ft and 70% or higher at 22,500 ft and above. The lowest altitude occurrence of DCS was a 5% incidence at 21,200 ft. At 22,500 ft, the DCS incidence abruptly climbed to 55%. CONCLUSION: A 5% threshold for DCS symptoms was concluded to be 20,500 ft under the conditions of this study. The abrupt increase in DCS symptoms, with zero-preoxygenation exposure above 21,200 ft implies a need for reconsideration of current USAF and FAA altitude exposure guidance.

Relationship between age and susceptibility to altitude decompression sickness.

BACKGROUND: Susceptibility to altitude decompression sickness (DCS) is influenced by a multitude of factors including, potentially, an individual's age. Previous attempts by authors to determine the effect of age on DCS susceptibility have produced conflicting results. The purpose of this study was to try to clarify that conflict and to quantify the impact of age on DCS risk. METHODS: We examined the Armstrong Laboratory DCS Hypobaric Research Database containing data on 1299 subject flight exposures conducted from 1983-94. Subjects were from 18-45 yr of age. Exposure altitudes ranged from 11,500 ft (3505 m) to 30,000 ft (9144 m). The duration of exposure varied from 3-8 h and preoxygenation time ranged from 0-2 h and 15 min. Data were compiled according to seven age groups. RESULTS: The results show a significant three-fold increase in susceptibility between the age group 18-21 and the group > 42 yr of age. The results also show a trend toward increased susceptibility between the 18-21 group and the groups between 26 and 41 yr of age. However, there was no significant change within the range of 26-41 yr. CONCLUSION: There is a trend toward increased DCS susceptibility with increasing age, with a particularly strong trend for individuals over 42 yr of age.