Increased exhaled breath temperature in subjects with uncontrolled asthma

BACKGROUND: Increased vascularity of the airway mucosa in asthma potentially increases heat loss in the airways. OBJECTIVE: To determine if the inflamed airways of subjects with uncontrolled asthma show increased exhaled breath temperature (EBT). PATIENTS AND METHODS: 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. RESULTS: 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). CONCLUSION: 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.