Impact of hydration on pulmonary function and ventilatory responses to exercise in healthy adults

Abstract

Water transport and airway hydration are vital for the normal physiological functioning of the lungs. Water supply to the airways stems primarily from the bronchial circulation, which arises from the systemic circulation. Little is currently known regarding the impact of systemic fluid loss upon pulmonary function. The over-arching aim of this thesis was to investigate the effects of systemic hydration on normal pulmonary function and the ventilatory response to exercise in healthy adults. The first experimental study (Chapter 4) aimed to assess the repeatability and reproducibility of pulmonary function testing (PFT) between and within days in healthy young adults. ‘Excellent’ repeatability and ‘very good’ reproducibility were shown for both spirometry and whole body plethysmography. In the second experiment (Chapter 5), these PFT were therefore used to evaluate the impact of mild systemic dehydration (2.5% body mass loss) and subsequent rehydration on pulmonary function in healthy young adults. Mild dehydration led to reductions in forced vital capacity and elevations in residual volume and functional residual capacity, indicative of impaired small airway function and potential gas trapping. Whilst systemic rehydration (fluid ingestion) restored pulmonary function, local rehydration (nebulised isotonic saline) had no effect, suggesting that increased plasma osmolality may contribute to small airway dysfunction during hypertonic-hypovolemia. In the third experimental chapter (Chapter 6), these findings were extended by demonstrating that i) a more severe state of dehydration negatively impacts small airway function of physically active young adults ii) ventilatory response to exercise is preserved and perceived breathing discomfort largely unaffected by moderate dehydration. Taken together, this thesis demonstrates the impact of systemic fluid loss upon the healthy human pulmonary system and provides insight into the potential mechanisms involved in dehydration-induced pulmonary alterations. In particular, these findings highlight a key role of hydration status upon small airway function, which could have particular relevance in older adults and those with pre-existing lung conditions.