Mechanisms Underlying Exercise-Induced Improvements in Respiratory Function in Cystic Fibrosis: A Review

Abstract

Regular exercise and physical activity are recommended as a part of cystic fibrosis (CF) physiotherapy. Exercise has been shown to increase airway surface liquid hydration (ASL) and cilia beat frequency (CBF), enhance mucus clearance (MCC), and prolong the development of lung disease in CF patients; however, the mechanisms responsible for these improvements are unclear. Purpose: This review describes the possible mechanisms by which exercise may improve respiratory function in CF patients in order to demonstrate to experts in the exercise physiology and medical fields the value of exercise to improve quality of life in CF patients. Methods: A review of the English language medical literature was performed to elucidate the relationship between exercise and CF respiratory function. Results/Discussion: The exact mechanisms whereby exercise improves respiratory function in CF are not yet fully understood; however, several mechanisms may play a collective role. First, arginine-vasopressin and atrial natriuretic factor have been shown to increase ASL and CBF in airway epithelia in vitro. The interaction between these systemic blood volume regulators and the CF epithelia will be described, and then comparisons will be made between the concentrations reached during various exercise protocols and those used in the in vitro studies. Second, mechanical perturbations have been shown to stimulate the release of nucleotides by the respiratory epithelia resulting in increased ASL, CBF, and MCC via purinergic receptor activation in vitro. The relationship between mechanical stressors, nucleotide release, and epithelial physiology in the CF airway will be described. Finally, the level of shear and transmural stress, as well as the oscillations in mechanical stress due to exercise-induced hyperpnoea will be described and compared with the levels of stress imposed during the in vitro studies. Conclusion: Elevated concentrations in systemic blood volume regulators and/or local nucleotide release due to mechanical stress during exercise increases airway hydration and mucus clearance, thereby delaying the pathogenesis of CF lung disease. Regular participation by CF patients in exercise programs may improve respiratory function and quality of life, and therefore is an important aspect of CF healthcare.