ABSTRACT

Plogmark O, Hjelte C, Olsson M, Ekström M, Frånberg O. Decompression at 1.3 versus 1.6 bar and Nitrogen Elimination and Venous Gas Emboli: A Randomized Controlled Trial. Undersea Hyperb Med. 2025 Fourth Quarter; 52(4):577-585.

Introduction: The optimal depth for decompression stops is unclear. We hypothesize that a decompression stop at 1.3 bar, compared with 1.6 bar, decreases post-dive whole-body nitrogen washout volumes and venous gas emboli (VGE).

Methods: In this randomized crossover trial, divers performed wet air dives of 40 minutes at 3.4 bar (340 kPa) with a seven-minute-long decompression stop at either 1.3 bar (Deco 1.3) or 1.6 bar (Deco 1.6) in randomized order. The primary outcome was the difference in post-dive whole body nitrogen washout volume, analyzed using multilevel linear regression. The secondary outcome was the difference in peak VGE detected by cardiac two-dimensional ultrasound, graded using the Eftedal-Brubakk scale, and analyzed with Wilcoxon matched-pairs signed-rank tests.

Results: Sixteen divers completed both Deco 1.3 and Deco 1.6. Post-dive whole body nitrogen washout volumes were measured in eight of the 16 participants and were lower with Deco 1.3 than Deco 1.6 (696 ml [95% confidence interval [CI], 601 to 790] versus 1068 ml [95% CI, 962 to 1174]), mean difference of 373 ml (95% CI, 243 to 502). Deco 1.3 had lower peak bubble grades than Deco 1.6 (interquartile range 2-3 versus 3-4; P=0.005), but the median grade was the same at 3.

Conclusions: Decompression stop at 1.3 bar instead of 1.6 bar decreased post-dive whole body nitrogen washout volume and VGE. These findings may inform the development of future decompression models.

Keywords: air diving; bubbles; decompression; nitrogen washout; physiology