Respiratory heat and moisture loss is associated with eosinophilic inflammation in asthma.

Increased mucosal vascularity is a hallmark of airway inflammation in asthma. It was hypothesised that this would lead to a detectable increase in respiratory heat and moisture loss (RHML), which would reflect the degree of airway inflammation present. A total of 23 subjects with asthma and 18 healthy controls had RHML measured in a cross-sectional study. The measurements were made using a device that combines temperature and humidity measurement during inspiration and expiration and allows precise control over inspirate conditions and ventilatory pattern. The subjects with asthma underwent parallel measurements of exhaled nitric oxide, sputum eosinophil percentage and exhaled breath condensate pH. Mean+/-SD RHML was elevated in patients with asthma (98.1+/-7.3 J.L(-1)) compared with control subjects (91.9+/-4.5 J.L(-1)). RHML measurement in asthma correlated with sputum eosinophil percentage. This novel correlation between thermal and cellular measurements in asthma suggests that both of these noninvasive indices are sensitive to the degree of underlying chronic airway inflammation.