Proposed Thalmann Algorithm Air Diving Decompression Table for the Swedish Armed Forces Based on Logistic Probabilistic Modeling of No-Stop Air Diving Data

Abstract

The Swedish Armed Forces (SwAF) air dive tables are under revision. Currently, the air dive table from US Navy (USN) Diving manual (DM) Rev.6 is used with a msw to fsw conversion. Since 2017, USN has been diving according to USN DM rev. 7, which incorporates updated air dive tables derived from the exponential linear decompression algorithm (EL-DCM) Thalmann with VVAL79 parameters. The SwAF decided to replicate and analyze the USN table development methodology before revising their current tables. The ambition was to potentially find a table that correlates with the desired risk of decompression sickness. New compartmental parameters for the EL-DCM algorithm, called SWEN21B, were developed by applying maximum likelihood methods on 2953 scientifically controlled direct ascent air dives with known outcomes of decompression sickness (DCS). The targeted probability of DCS for direct ascent air dives was ≤1% overall and ≤1‰ for neurological DCS (CNS-DCS). 154 wet validation dives were performed with air between 18-57 msw. Both direct ascent and decompression stop dives were conducted, resulting in two joint pain DCS (18msw/59min), one leg numbness CNS-DCS (51msw/10min with deco-stop), and nine marginal DCS, such as rashes and itching. A total of three DCS, including one CNS-DCS, yield a predicted risk level (95% confidence interval) of 0.4-5.6% for DCS and 0.0-3.6% for CNS-DCS. Two out of three divers with DCS had patent foramen ovale, PFO. The SWEN21 table is recommended for the SwAF for air diving as it, after results from validation dives, suggests being within the desired risk levels for DCS and CNS-DCS.