Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops

Area of Science:

• Diving physiology
• Hyperbaric medicine

Background:

• The French Navy employs Marine Nationale 90 (MN90) decompression tables for air dives up to 60 meters.
• The current incidence of decompression sickness (DCS) for deep dives (45-60 msw) using MN90 tables is approximately 1 in 3000 dives.

Purpose of the Study:

• To evaluate the safety and efficacy of experimental ascent profiles (EAPs) compared to standard MN90 tables for deep air dives.
• To assess the impact of different deep stop strategies on bubble formation and DCS risk.

Main Methods:

• Three EAPs were tested in a hyperbaric chamber with eight subjects performing dives to 50 or 60 msw.
• Subjects ascended using either the standard MN90 tables or an EAP, with precordial bubbles monitored via Doppler ultrasound post-dive.
• Protocols varied in depth, duration, surface interval, and deep stop placement (e.g., Protocol I: 60 msw, deep stops from 27 msw; Protocol II: 50 msw repetitive dive, deep stop from 18 msw; Protocol III: 60 msw, single deep stop at 25 msw).

Main Results:

• Protocol I EAP resulted in significant bubble formation (Spencer grade 2-3) persisting for 120 minutes post-dive, with one DCS case, showing no improvement over MN90.
• Protocol II EAP led to severe bubbling in all eight subjects, prompting the discontinuation of EAPs with longer deep stops.
• Protocol III EAP demonstrated no significant difference in bubbling compared to the standard MN90 profile.

Conclusions:

• The implementation of deep stops in experimental ascent profiles requires cautious evaluation.
• Two tested EAPs offered no discernible benefit over standard decompression tables, and one protocol increased bubble formation, suggesting potential risks associated with modified ascent profiles.