Increased exhaled breath temperature in subjects with uncontrolled asthma

Increased vascularity of the airway mucosa in asthma potentially increases heat loss in the airways.

To determine if the inflamed airways of subjects with uncontrolled asthma show increased exhaled breath temperature (EBT).

In 100 patients with persistent asthma and 50 healthy volunteers, we measured lung function by post-bronchodilator forced spirometry, the asthma control test (ACT) and EBT.

Patients with asthma, of whom 49 (49%) were female, with a mean (± standard error of the mean) age of 44 (±17) years and a predicted forced expiratory volume in one second of 71% (±16), had a significantly increased EBT, particularly those with uncontrolled asthma (n = 50, ACT ≤ 19, EBT 34.9 ± 0.8°C), compared to patients with controlled asthma (n = 50, ACT ≥ 20, EBT 33.7 ± 0.8°C) and healthy volunteers (n = 50, EBT 33.2 ± 0.2°C, P < 0.001).

We observed a higher temperature on exhaled breath in subjects with uncontrolled asthma than in subjects with controlled asthma and healthy controls. The increase in exhaled breath temperature may be a proxy for a raised airway inflammatory state in asthma patients.