Physiological impact of controlled emergency swimming ascents training in professional divers: evidence of subclinical lung stress.

Controlled emergency swimming ascent (CESA) training is a standard safety procedure in diving, which is designed to simulate ascent in the event of gas supply failure. However, the potential pulmonary risks associated with this exercise remain poorly documented. This study aimed to evaluate whether CESA training induces subclinical pulmonary alterations and assess the effectiveness of expiratory control during ascent. In Step 1, seven experienced military divers each performed two dives to 10 meters of seawater (msw): one control dive with normal breathing through a regulator and one CESA dive involving continuous expiration without a mouthpiece during ascent. Lung ultrasound was conducted before and after immersion to quantify extravascular lung water (EVLW) using ultrasound lung comets (ULCs). In Step 2, four divers performed CESA from 5 and 10 msw, although ventilatory kinetics were recorded using a custom underwater pneumotachograph. All divers remained asymptomatic throughout. However, ULCs increased significantly after CESA dives (0 vs. 7.3 ± 4.6, P < 0.01), but not after control dives [0 vs. 0.7 ± 0.7, not significant (NS)], suggesting subclinical pulmonary stress. Ventilatory analysis revealed marked interindividual variability: preascent expirations ranged from 15% to 45% of slow vital capacity (SVC), and residual volumes at the surface were between 5% and 12% of SVC. These findings indicate that even trained divers do not consistently match expiratory effort to gas expansion, potentially increasing mechanical stress on the lungs. CESA training may, therefore, expose healthy individuals to silent alveolar stress, highlighting the need for improved monitoring tools and individualized ventilatory assessment during ascent training.NEW & NOTEWORTHY This is the first study to objectively quantify pulmonary stress and expiratory dynamics during controlled emergency swimming ascent (CESA) in healthy and trained divers. Using lung ultrasound and underwater spirometry, we demonstrate that CESA induces subclinical alveolar alterations and reveals wide variability in expiratory strategies. These findings challenge current assumptions about the safety and reproducibility of CESA training and suggest the need for individualized ventilatory monitoring in diving instruction.