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

In healthy subjects, at low minute ventilation (VE) during physical exercise, the water content and the temperature of the airways are well regulated. However, with the increase in VE, 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 young adults, we assessed epithelial damage before and following a 30-min continuous cycling exercise at 70% of maximal work rate, by measuring the variation of serum club cell protein (cc16/cr). VE was measured continuously during exercise. Airway water and heat loss were estimated using a computational model adapted to the experimental conditions and were compared to the theoretical threshold of dehydration. Eleven participants exceeded the theoretical threshold for bronchial dehydration during exercise (group A) and 5 did not (group B). The increase in cc16/cr was higher (p=0.007, d=1.40) in group A (0.50±0.25 ng.l-1) compared to group B (0.10±0.10 ng.l-1). This increase was significant in group A but not in group B (101± 100%, p < 0.001 and 13± 13 %, p = 0.28, respectively). 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.