Exhaled breath temperature in asthmatic and healthy children

Background Asthma is a chronic inflammatory condition of the airways and the most common chronic disorder in childhood. Approximately 10-12% of the children in Italy today suffer from asthma. Asthma is commonly monitored on the basis of symptoms, exacerbations/use of rescue medication and spirometry. Several non-invasive markers for the evaluation of airway inflammation have been studied. These markers can easily be implemented in a routine asthma control visit and are easily measured in children. In the last 10 years research has especially been focused on the exhaled breath temperature (EBT) as a novel marker for airway inflammation in asthmatic patients. Objective The aim of this study was to investigate EBT in asthmatic patients and healthy children. This study was primarily focused on reproducibility of EBT measurements and the ability to distinguish healthy controls from asthmatic patients by means of EBT. Methods One hundred twenty four children, 63 healthy children (mean age 11.3 years, 28 male) and 61 asthmatic children (mean age 11.1 years, 45 male), have been evaluated. They underwent skin prick testing, EBT measurements, FENO measurements and spirometry. Questionnaires were obtained and body temperature, environmental temperature and humidity were recorded. EBT was measured with the tidal breathing technique, also know as the Popov method. Results EBT measurements were highly reproducible. The within-session reproducibility for duplicate measurements had an ICC of 0.95°C and a CR of 2.05°C. The second measurement tended to be higher than the first measurement, consistent with a learning effect. Between-session within-day reproducibility of EBT was still high and slightly decreased as sessions elapsed one month apart (ICC of 0.86°C and CR of 3.06°C). EBT increased with age (r = 0.47, p = 0.000). Similar EBT was measured in healthy controls and asthmatic patients [median (IQR); 33.0 (1.6°C) vs 32.6 (3.3°C), p = 0.080], even when subjects were matched according to gender and age. Normalized EBT (nEBT), obtained by subtracting environmental temperature from EBT, was significantly lower in patients treated with corticosteroids as compared with untreated patients and healthy controls (8.5 (3.9°C) vs 10.8 (3.9°C) vs 11.3 (4.2°C), p = 0.004). Conclusion Measurements of EBT are highly reproducible. While no different EBT was found between healthy and asthmatic children, a corrected EBT by environmental temperature (nEBT, as described in a previous study) evidenced low nEBT values in asthmatic children treated with corticosteroids suggesting downregulated airway inflammation. EBT measurements could be suitable for monitoring inflammatory changes (and perhaps asthma control) in the individual subject.