Deep versus shallow decompression stops: illustration of different decompression strategies used in technical diving

Despite evolution in decompression algorithms, decompression illness is still an issue. Reducing vascular gas emboli (VGE) production by varying decompression procedures is very common among divers. Several methods have been tried, either mechanical, cardiovascular, desaturation-aimed or biochemical, with encouraging results. In this study, we tested two different decompression methods: one called DEEP, where the decompression starts deeper, the other one SHALLOW, where shallower stops were planned, for the same dive and decompression time.

In total, 18 healthy, non-smoking divers participated [1 female, 17 males; mean age 44.94 ± 5.74 years; body mass index (BMI) 27.3 ± 5.9 kg/m2]. Each diver performed two standardized Open Circuit trimix (21/35) dives, decompression mix EAN50. The deep profile used stops at 21, 18, 15, 12, 9, 6, and 3 meters. The shallow profile used stops at 9, 6, 3, with the same total bottom and decompression times for both groups. All dives were done in a pool (Y-40, Montegrotto, Italy) at a depth of 40 m for 40 min of bottom time and 80 minutes of total runtime. VGE counts were recorded every 15 min from 0 (0-5 min) to 90 min by echocardiography.

Vascular gas emboli were significantly reduced after the deep stops decompression procedure (DEEP: 6.7 ± 7.2 VGE per heartbeat vs. shallow: 10.7 ± 11.6 VGE per heartbeat, p = 0.0006). Three DCS cases were recorded after the "shallow" stop procedure (p = 0.24 Fisher's exact test).

There are significant differences between the two tested decompression procedures. The DEEP procedure resulted in a lower production of bubbles compared to the SHALLOW procedure.