The effect of hyperoxic environment on lung function and myopisation in an extended closed-circuit rebreather diving expedition

Introduction: Repetitive closed-circuit rebreather (CCR) dives subject the human body to a hyperoxic environment. Prolonged oxygen exposure can lead to lung abnormalities and myopic shift. The aim of this study was to analyse the effects of a 31-day period of repeated CCR dives on divers' lung function and visual acuity. Methods: The CCR divers recruited for the study were participating in a research project in Chuuk Lagoon, Micronesia. Weekly measurements included lung function using spirometry and visual acuity with a Snellen chart. Oxygen exposure was calculated using multiple models. The impact on spirometry was tested by comparing the values before and after the expedition and by running regression analysis against accumulated oxygen exposure. Results: The divers (n = 12) performed a total of 173 CCR dives with mean (SD) maximum depth of 38 (13.9) msw and dive time 101 (38.8) min. The daily oxygen exposure limits for unit pulmonary toxic dose and central nervous system toxicity were respected. One diver had a decrease in multiple lung function parameters. Another developed spirometric evidence of mild obstruction by the end of the expedition. However, there were no statistically significant changes in spirometry results. Visual acuity showed fluctuations throughout the expedition, but no overall trend. Conclusions: Diving expeditions can be executed safely when respecting the guidelines for oxygen exposure. Reasonable oxygen exposure does not seem to significantly affect lung function or visual acuity.