Comparative Incidence of Decompression Sickness and Microparticles Release in Heliox vs. Nitrox Simulated Dives in Rats

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Introduction / Background: Decompression sickness (DCS) is driven by gas bubble formation and a subsequent thromboinflammatory response. Extracellular vesicles (EV) and especially microparticles (MP) have emerged as potential mediators of this inflammatory cascade. While the physical properties of inert gases are well-documented, the biological impact of helium versus nitrogen on MP release and content remains poorly understood. This study aims to evaluate DCS outcomes and characterize MP subtypes in a rat model using identical heliox and nitrox profiles. Hypothesis: The choice of diluent gas significantly influences the biological threshold for DCS. Materials and Methods: Male Sprague Dawley rats (n=12 per group) were subjected to simulated dives in a 40-liter hyperbaric chamber. Animals were compressed at 200 kPa/min to a pressure of 700 kPa for a bottom time of 90 minutes. Decompression was conducted at 50 kPa/min to atmospheric pressure. Two gas mixtures were compared: Nitrox 21% (79% N 2 , 21% O 2 ) and Heliox 21% (79% He, 21% O 2 ). Following decompression, rats were observed for 60 minutes for clinical signs of DCS and blood was collected for the isolation of MPs. These rats were compared with controls rats exposed to the same gas at atmospheric pressure (n=6 per group). Characterization included flow cytometry for thrombo-inflammatory markers, including P-selectin, CD142, phalloidin, and thrombospondin. Results Experimental runs demonstrated a significant difference in DCS incidence between the two gas mixtures despite identical pressure-time profiles. Nitrox 21% dives resulted in a severe DCS rate of 83%, whereas Heliox 21% dives resulted in a substantia ly lower rate of 33%. Preliminary flow cytometry results showed a significant decrease in MPs concentration in helium diving rats without DCS compared with helium controls (p = 0.0317). This was associated with reduced proportions of CD142 (p = 0.02214) and phalloidin positive MPs (p = 0.01502). Following nitrogen exposure, DCS rats showed a trend toward increased MP concentration (p = 0.0992), also nitrogen-exposed DCS rats exhibited a reduced proportion of thrombospondin-positive MPs (p = 0.01931). Although preliminary results have already provided insights into MPs, further analyses, including their OMICS content (proteins, mRNA, miRNA), are ongoing to complete these findings. Conclusion In this rat model, helium-based decompression resulted in a lower incidence of DCS associated with a decrease in pro-inflammatory/coagulant MPs. Ongoing analysis of MP subtypes should further elucidate whether helium mitigates the thrombo-inflammatory response typically triggered by nitrogen-based bubbles. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

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