Changes in pulmonary function and airway mechanics with increased serum osmolality

Dehydration and associated increases in plasma osmolality have been shown to decrease pulmonary function. The suggested mechanism is a decline in small airway function and premature airway closure caused by increased osmolality, but this has not been directly tested. The purpose of this study was to measure pulmonary function, closing capacity, and maximal flow-static recoil curves pre- and postinfusion of isotonic and hypertonic saline in men (<i>n</i> = 7) and women (<i>n</i> = 7) with an exploratory comparison between sexes. We found that the hypertonic saline infusion significantly increased serum osmolality (287 ± 3 vs. 311 ± 17 mosmol/kgH₂O; <i>P</i> < 0.001) leading to decreases in forced vital capacity and forced expired volume in 1 s (4.6 ± 1.1 L and 3.9 ± 0.9 L, respectively) compared with preinfusion (4.8 ± 1.1 L and 4.1 ± 0.9 L, respectively; <i>P</i> = 0.002-0.02) with no effect of sex (<i>P</i> = 0.06-0.39). There was a significant main effect of time for residual volume, closing volume, and closing capacity such that following both isotonic and hypertonic saline, these values were increased compared with preinfusion (<i>P</i> = 0.001-0.033). In addition, maximal flow for a given lung recoil pressure was decreased following hypertonic saline infusion. Thus, pulmonary function decreased following increased serum osmolality, and this change may be caused by small airway dysfunction and premature airway compression and closure.<b>NEW & NOTEWORTHY</b> Increased serum osmolality through hypertonic saline infusion leads to a decrease in forced vital capacity and forced expiratory volume in 1 s. This decline in pulmonary function is likely resultant from changes in airway structure and function based on changes in closing capacity and maximal flow-static recoil curves following hypertonic saline infusion.