WATER-LOSS WITHOUT HEAT-FLUX IN EXERCISE-INDUCED BRONCHOSPASM

We identified inspired gas conditions that result in no net respirator y heat loss, an isenthalpic condition, but induce a mucosal loss of wa ter. Inspired gas at 37-degrees-C with 47 mm Hg water vapor pressure, 56-degrees-C with 38 mm Hg; and 78-degrees-C with 27 mm Hg has the sam e heat content as fully saturated air at body temperature. In four nor mal subjects hyperventilating at a minute ventilation of 30 times thei r FEV1 for 6 min, expired temperatures at the mouth averaged 39-degree s, 43-degrees, and 43-degrees-C for the three conditions. Retrotrachea l esophageal temperatures did not fall in any subject, thereby demonst rating the absence of significant airway cooling. Nine subjects with e xercise-induced bronchospasm were tested under the same conditions. Ba seline functions showed an FEV1 of 85 +/- 10% of predicted (mean +/- S D), FVC, 98 +/- 13% of predicted, and FEV1/FVC, 79 +/- 4% of predicted . The asthmatic subjects demonstrated postchallenge mean falls in FEV1 of 3.4%, 6.2%, and 10.1% for the three conditions, with bronchospasm increasing as the temperature of the inspired air increased (p = 0.001 ). The amount of respiratory water lost from the respiratory mucosa si gnificantly correlated with the resultant bronchospastic response as m easured by the fall in FEV1 (p = 0.017), but the net respiratory heat lost did not significantly correlate (p = 0.113). This study demonstra tes that bronchospasm can be induced without significant respiratory h eat loss or airway cooling and suggests that it is proportional to the amount of water lost from mucosal surfaces.