Physiological Impact of Controlled Emergency Swimming Ascents (CESA) Training in Professional Divers: Evidence of Subclinical Lung Stress.

Abstract

Controlled Emergency Swimming Ascent (CESA) training is a standard safety procedure in diving, 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 to 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 while 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, NS), suggesting subclinical pulmonary stress. Ventilatory analysis revealed marked interindividual variability: pre-ascent 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.