Latency in onset of decompression sickness on direct ascent from air saturation.

Twenty-four human subjects were exposed to compressed air at simulated depths ranging from 45 ft seawater gauge (fsw) (2.36 ATA) to 75 fsw (3.27 ATA) for periods of time sufficient to allow saturation of most tissues with inert gas. From each of four depths (45, 55, 65 and 75 fsw), subjects ascended directly to 1 ATA, where they remained for 30, 17, 13, and 10 min, respectively. During this time the onset of Doppler detected venous gas emboli (VGE), pruritus, and any other symptomatology was monitored and recorded. In the ascending excursion from 45 fsw (n = 18), the mean appearance times of pruritus and VGE were 19.3 +/- 7.5 (mean +/- SD) and 21.9 +/- 7.4 min, respectively, with one case of pain-only decompression sickness (DCS). The excursion from 55 fsw (n = 17) shortened these times to 9.2 +/- 3.3 and 14.4 +/- 3.2 min, respectively, with two cases of DCS, one each of pain-only and serious types. In the excursion from 65 fsw (n = 23), mean pruritus and VGE appearance times were 6.3 +/- 1.4 and 10.8 +/- 1.9 min, respectively, with no cases of DCS. The excursion from 75 fsw (n = 6) resulted in appearance times of 4.8 +/- 0.8 and 8.2 +/- 1.2, respectively, with one case of pain-only DCS. Sufficient cases of DCS did not occur in any of the excursions to allow determination of mean appearance times. The relationship between pressure reduction and appearance times of pruritus and VGE, and the threshold time of DCS, can be described mathematically. We conclude that latency in the development of DCS on direct ascent from air saturation exists and is of sufficient magnitude to permit practical application in emergency decompressions or unpressurized transfers between compressed air or N2-O2 environments.