Fractional exhaled breath temperature in patients with asthma, chronic obstructive pulmonary disease, or systemic sclerosis compared to healthy controls.

Exhaled breath temperature has been suggested to reflect airway inflammation, and it would be plausible to measure the peripheral airway temperature as a correlate to peripheral airway inflammation. This study aims to explore the relative peripheral airway temperature in patients with asthma, chronic obstructive pulmonary disease (COPD) or systemic sclerosis (SSc) compared to healthy controls, and relate to lung function and exhaled nitric oxide. Sixty-five subjects (16 asthmatics, 18 COPD patients, 17 SSc patients and 14 healthy subjects) performed fractional exhaled breath temperature measurements using a novel device, fractional exhaled NO measurements, spirometry, impulse oscillometry, body plethysmography and CO-diffusion capacity test. A significant overall difference among all the patient groups was seen in both the Tmax (= peak values of the entire exhalation) and T3max (= peak value of the last fraction of the exhaled volume). A significant difference in T3/T1 ratio (= the ratio of peripheral versus central air temperature) was found between asthmatic subjects and those with COPD or SSc. In addition, T1max (= temperature in the central), T3max (= peripheral airways) and the T3/T1ratio related to several volumetric measurements (both in absolute values and as percent predicted), such as vital capacity, total lung capacity, forced expiratory volume in 1 s, and diffusion capacity. The temperature ratio of the peripheral versus central airways was lower in patients with COPD or SSc compared to asthmatics, who in turn presented similar levels as the controls. There was also a large overlap between the groups. Overall, the airway temperatures were related to absolute lung volumes, and specifically, the peripheral temperature was related to the gas diffusion capacity (% predicted), suggesting a link to the vascular component.