The relative safety of forward and reverse diving profiles

Area of Science:

• Diving Physiology
• Hyperbaric Medicine
• Risk Assessment

Background:

• Recent workshop recommendations suggested reversed dive profiles (RDP) do not increase decompression sickness (DCS) risk.
• This contradicts the conventional forward dive profile (FDP), where deeper dives are performed first.
• RDP allows deeper dives later in multi-level or repetitive diving, progressing from shallow to deep.

Purpose of the Study:

• To experimentally test the hypothesis that RDPs increase DCS risk compared to FDPs.
• To evaluate differences in DCS incidence between FDP and RDP in multi-level and repetitive dives.
• To provide data to re-examine workshop recommendations on dive profiles.

Main Methods:

• Two matched groups of 11 guinea pigs were exposed to multi-level diving profiles (FDP vs. RDP).
• Two groups of 11 guinea pigs each underwent repetitive dives, comparing FDP (deepest to shallowest) and RDP (shallowest to deepest).
• Diving profiles were adjusted in a second series of repetitive dives to increase DCS risk.

Main Results:

• In multi-level dives, 55% of RDP animals exhibited severe DCS and died, versus 0% in FDP animals (P=0.01).
• In repetitive dives, 33% of RDP exposures resulted in severe DCS, compared to 0% in FDP exposures (P=0.01).
• The incidence of severe DCS was significantly higher in the RDP group for both experimental setups.

Conclusions:

• Multi-level and repetitive dives performed using the conventional FDP are less hazardous than those using RDP.
• The study findings contradict recent workshop recommendations suggesting RDPs are safe.
• Further examination of RDP recommendations is warranted based on this experimental evidence.