Exhaled breath temperature as a tool for monitoring asthma control after an attack in children

BACKGROUND: Exhaled breath temperature (EBT) has been suggested as a non-invasive marker of airway inflammation in asthma. There have been no studies examining longitudinal changes in EBT following asthma attacks. OBJECTIVE: To investigate changes in EBT during and after an asthma attack and to relate these changes to changes in respiratory physiological measurements. METHODS: We evaluated 38 hospitalized children aged 5-18 years diagnosed with an asthma attack. Spirometry was performed upon hospitalization. During hospitalization, EBT, peak expiratory flow rate (PEFR), and asthma score were measured daily. These tests were repeated 1 week and 1 month after discharge. The overall PEFR change, temporal changes in plateau values at the end of expiration, and time-dynamic associations were evaluated using linear mixed models. RESULTS: FEV1 was lower at admission than at discharge (63.3 ± 24 vs 99.5 ± 14 percent of predicted, P < 0.001). The EBT was higher at admission than at 1 week after discharge (34.1°C [range: 33.9-34.8°C] vs 33.6°C [range: 33.0-34.2°C], P = 0.007); overall, EBTs decreased over time (P = 0.007). Among individual subjects, decreased EBT was correlated with increased PEFR over time. Furthermore, plateau values at the end of expiration had a time-dependent, dynamic association with the PEFR during hospitalization (P = 0.005) and between asthma attack onset and asthma status stabilization (P = 0.032). CONCLUSIONS: The EBT was elevated during asthma attacks and gradually decreased until asthma was well controlled. The EBT may be a useful, non-invasive tool for monitoring asthma control in children.