Association between Years of Diving Service and Pulmonary Function in Military Divers

Background: Military underwater operations personnel are repeatedly exposed to hyperbaric environments and increased respiratory workload, which may influence pulmonary function over time. However, the association between years of diving service and detailed pulmonary function parameters remains unclear in military diving populations. Aim: To investigate the association between years of diving service and pulmonary function among military underwater operations personnel. Methods: This cross-sectional study enrolled personnel of the Underwater Operations Unit who underwent comprehensive pulmonary function testing, including spirometry and body plethysmography. Participants were categorized as either shorter-service (<10 years of diving service) or longer-service (≥10 years of diving service) divers. Pulmonary function parameters included static lung volumes and flow–volume loop-derived indices. Between-group comparisons were performed using the Mann–Whitney U test, and correlations between years of diving service and pulmonary function parameters were assessed using Spearman’s rank correlation analysis. Results: Most of the lung volumes and conventional spirometric indices did not differ significantly between shorter-service and longer-service divers. However, longer-service divers exhibited significantly lower functional residual capacity and reduced residual volume/total lung capacity expressed as a percentage of measured/predicted values. The forced expiratory volume in 1s/forced vital capacity ratio was also significantly lower in longer-service divers. Conclusion: Among military underwater operations personnel, longer diving service duration is associated with specific alterations in lung volume distribution and expiratory flow ratios, whereas overall ventilatory capacity remains preserved. These findings are consistent with functional respiratory adaptations rather than pulmonary impairment.