N₂ exchanges in hyperbaric environments: toward a model based on physiological gas transport (O₂ and CO₂)

Decompression sickness can occur in divers even when recommended decompression procedures are followed. Furthermore, the physiological state of individuals can significantly affect bubbling variability. These informations highlight the need for personalized input to improve decompression in SCUBA diving. The main objective of this study is to propose a fundamental framework for a new approach to inert gas exchanges. A physiological model of oxygen delivery to organs and tissues has been built and adapted to nitrogen. The validation of the model was made by transferring the N₂ to CO₂. Under normobaric conditions (air breathing, oxygen breathing, and static apnea) and hyperbaric conditions, the O₂ model replicates the reference physiological Po₂ (Spearman correlation tests P < 0.001). The inert gas models can simulate inert gas partial pressures under normobaric and hyperbaric conditions. However, the lack of reference values prevents direct validation of this new model. Therefore, the N₂ model has been transferred to CO₂. The resulting CO₂ model has been validated by comparing it with physiological reference values (Spearman correlation tests P < 0.01). The validity of the CO₂ model constructed from the N₂ model demonstrates the plausibility of this physiological model of inert gas exchanges. In the context of personalized decompression procedures, the proposed model is of significant interest as it enables the integration of physiological and morphological parameters (blood and respiratory flows, alveolo-capillary diffusion, respiratory and blood volumes, oxygen consumption rate, fat mass, etc.) into a model of nitrogen saturation/desaturation, in which oxygen and CO₂ partial pressures can also be incorporated.NEW & NOTEWORTHY This is the first model of inert gas transport based on the physiology of respiratory gas. It was built for O₂ delivery and validated against literature data; it was then transposed to N₂ exchanges. The transposition procedure was checked by transposing the N₂ model to CO₂ (and validated against literature data). This model opens the possibility to integrate physiological and morphological inputs in a personalized decompression procedure in SCUBA diving.