Abstract
Water transport and local (airway) hydration are critical for the normal functioning of lungs and airways. Currently, there is uncertainty regarding the effects of systemic dehydration on pulmonary function. Our aims were 1) to clarify the impact of exercise- or fluid restriction-induced dehydration on pulmonary function in healthy adults; and 2) to establish whether systemic or local rehydration can reverse dehydration-induced alterations in pulmonary function. Ten healthy participants performed four experimental trials in a randomized order (2 h exercise in the heat twice and 28 h fluid restriction twice). Pulmonary function was assessed using spirometry and whole body plethysmography in the euhydrated, dehydrated, and rehydrated states. Oral fluid consumption was used for systemic rehydration and nebulized isotonic saline inhalation for local rehydration. Both exercise and fluid restriction induced mild dehydration (2.7 ± 0.7% and 2.5 ± 0.4% body mass loss, respectively; P < 0.001) and elevated plasma osmolality (P < 0.001). Dehydration across all four trials was accompanied by a reduction in forced vital capacity (152 ± 143 mL, P < 0.01) and concomitant increases in residual volume (216 ± 177 mL, P < 0.01) and functional residual capacity (130 ± 144 mL, P < 0.01), with no statistical differences between modes of dehydration. These changes were normalized by fluid consumption but not nebulization. Our results suggest that, in healthy adults: 1) mild systemic dehydration induced by exercise or fluid restriction leads to pulmonary function impairment, primarily localized to small airways; and 2) systemic, but not local, rehydration reverses these potentially deleterious alterations.NEW & NOTEWORTHY This study demonstrates that, in healthy adults, mild systemic dehydration induced by exercise in the heat or a prolonged period of fluid restriction leads to negative alterations in pulmonary function, primarily localized to small airways. Oral rehydration, but not nebulized isotonic saline, is able to restore pulmonary function in dehydrated individuals. Our findings highlight the importance of maintaining an adequate systemic fluid balance to preserve pulmonary function.
Highlights
Systemic dehydration, defined as a deficit of total body water [1], commonly occurs in individuals who perform sustained physical activity in hot environments [2], as well as in patients and older adults [3]
NEW & NOTEWORTHY This study demonstrates that, in healthy adults, mild systemic dehydration induced by exercise in the heat or a prolonged period of fluid restriction leads to negative alterations in pulmonary function, primarily localized to small airways
Pulmonary function was checked for normality via spirometry, with forced expiratory volume in 1 s (FEV1) >80% predicted and FEV1/FVC >70% used as inclusion criteria and Global Lung Function Initiative 2012 equations used as reference [14]
Summary
Systemic dehydration, defined as a deficit of total body water [1], commonly occurs in individuals who perform sustained physical activity in hot environments [2], as well as in patients and older adults [3]. Even at mild levels [i.e., $2–3% body mass loss [1]], systemic dehydration can have unfavorable effects on multiple organ systems, including the cardiovascular, renal, and nervous systems [4] and can compromise physical and cognitive performance [1]. Two previous studies showed deleterious alterations in expiratory flow or lung volumes in healthy adults [5] and in athletes with mild asthma [6] following mild systemic dehydration (up to 2.5% body mass loss). A third study [7] showed improvements in selected measures of pulmonary function [including increases in forced expiratory volume in 1 s (FEV1) and in the FEV1 to forced vital capacity ratio (FEV1/FVC)] in healthy adults following moderate dehydration (4.5% body mass loss). The different population groups and severities of dehydration, as well as the various modes of dehydration [i.e., fluid restriction [5] vs. exercise [6] vs. diuretic drug [7]], have generated uncertainty regarding the impact of systemic dehydration on pulmonary function
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