Is airway damage during physical exercise related to airway dehydration? Inputs from a computational model.

In healthy subjects, at low minute ventilation (V̇E) during physical exercise, the water content and the temperature of the airways are well regulated. However, with the increase in V̇E, the bronchial mucosa becomes dehydrated and epithelial damage occurs. Our goal was to demonstrate the correspondence between the ventilatory threshold inducing epithelial damage, measured experimentally, and the dehydration threshold, estimated numerically. In 16 healthy adults, we assessed epithelial damage before and following a 30-min continuous cycling exercise at 70% of maximal work rate, by measuring the variation pre- to post-exercise of serum club cell protein (cc16/cr). Blood samples were collected at rest, just at the end of the standardized 10-min warm-up, and immediately, 30 min and 60 min post-exercise. V̇E was measured continuously during exercise. Airway water and heat losses were estimated using a computational model adapted to the experimental conditions and were compared to a literature-based threshold of dehydration. Eleven participants exceeded the threshold for bronchial dehydration during exercise (group A) and 5 did not (group B). Compared to post warm-up, the increase in cc16/cr post-exercise was significant (mean increase ± SEM: 0.48 ± 0.08 ng.l-1, i.e. 101 ± 32%, p < 0.001) only in group A but not in group B (mean difference ± SEM: 0.10 ± 0.04 ng.l-1, i.e. 13 ± 7 %, p = 0.79). Our findings suggest that the use of a computational model may be helpful to estimate an individual dehydration threshold of the airways that is associated with epithelial damage during physical exercise.