Gj. Argyros et al., WATER-LOSS WITHOUT HEAT-FLUX IN EXERCISE-INDUCED BRONCHOSPASM, The American review of respiratory disease, 147(6), 1993, pp. 1419-1424
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.