[abstract] THE RELATIVE SAFETY OF FORWARD AND REVERSE DIVING PROFILES

Abstract

BACKGROUND: A recent workshop recommended that within certain restrictions, and from a decompression perspective, it is not substantially important whether one conducts dives from deep to shallow or shallow to deep. Thus, in multi-level dives, the deeper part of a dive may be performed later in the dive, while repetitive dives may progress from shallow to deep. These are referred to as reversed dive profiles (RDP). The consensus recommendations were made in the absence of experimental data. MATERIALS AND METHODS: We performed two experiments to test these recommendations. We first exposed two matched groups of 11 guinea pigs to a single multi-level diving profile [36msw for 30min, 24msw for 30min,12msw for 30min], one group in a forward progression (FDP), the other in reverse, and compared the incidence of severe DCS using the method of Albano1. Second, we compressed two groups each of 11 guinea pigs to three repetitive dives [30msw for 30min, 20msw for 30min, 10msw for 30 min, surface intervals 15 minutes]. Similarly, one group performed FDP and the other RDP. Again we compared the incidence of severe DCS. A second series of repetitive dives with increased depth and time was required to produce substantial risk of DCS [36msw for 40 min, 24msw for 40 min,12msw for 40 min]. RESULTS: Multi-level exposure: there was no evidence of DCS in any of the animals exposed to the FDP, while six (55percent) of the RDP group exhibited symptoms of severe DCS and ultimately died (P = 0.01). Repetitive exposures: there was no evidence of DCS in the FDP group versus seven (33percent) in the RDP (P=0.01). CONCLUSIONS: Our findings suggest that multi-level and repetitive dives performed in the established forward profile manner are less hazardous than those performed in the reverse profile mode. We believe the recommendations of the workshop should be re-examined. 1. Albano G. Principles and Observations on the Physiology of the Scuba Diver. ONR Dept of Navy. 1970. NOTE: Albano paper - http://archive.rubicon-foundation.org/3277