Dynamics of exhaled breath temperature after smoking a cigarette and its association with lung function changes predictive of COPD risk in smokers: a cross-sectional study

Abstract

Exhaled breath temperature (EBT) is a biomarker of inflammation and vascularity of the airways already shown to predict incident COPD. This cross-sectional study was aimed to assess the potential of EBT in identifying “healthy” smokers susceptible to cigarette smoke toxicity of the airways and to the risk of developing COPD by analysing the dynamics of EBT after smoking a cigarette and its associations with their demographics (age, smoking burden) and lung function. The study included 55 current smokers of both sexes, 29–62 years of age, with median smoking exposure of 15 (10–71.8) pack-years. EBT was measured at baseline and 5, 15, 30, 45, and 60 min after smoking a single cigarette. Lung function was measured with spirometry followed by a bronchodilator test. To compare changes in EBT between repeated measurements we used the analysis of variance and the area under the curve (EBTAUC) as a dependent variable. Multivariate regression analysis was used to look for associations with patient characteristics and lung function in particular. The average (±SD) baseline EBT was 33.42±1.50 °C. The highest significant increase to 33.84 (1.25) °C was recorded 5 min after the cigarette was smoked (p=0.003), and it took one hour for it to return to the baseline. EBTAUC showed significant repeatability (ICC=0.85, p<0.001) and was significantly associated with age, body mass index, number of cigarettes smoked a day, baseline EBT, and baseline FEF75 (R2=0.39, p<0.001 for the model). Our results suggest that EBT after smoking a single cigarette could be used as early risk predictor of changes associated with chronic cigarette smoke exposure.

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“…A recent study showed that smokers have a full one degree C elevated breath temperature compared to non-smokers. 55 Furthermore, in the hour after a cigarette is smoked breath temperature is further increased by an average of .42 degrees C. Smokers are chronically experiencing a localized relative heating of the respiratory tract, believed to be principally related to increased blood flow associated with inflammation. 56 To the extent that temperature is implicated in a smoker's physiology, it is reasonable to consider that there are a host of much more benign ways to warm the respiratory tract than smoking.…”

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“…In line with this hypothesis, smoking can increase the temperature of the respiratory tract by an average of 1.25°C. This was determined by measuring the 5-minute post-smoking exhaled breath temperature [ 48 ], a variable with 98% specificity for predicting future development of COPD in smokers [ 4 ]. It is, however, unclear whether this rise of 1.25°C in temperature might be sufficient to induce promoter-specific H3K27me3 enrichment in certain genes, such as IL-6, in the epithelial cells of the respiratory tract.…”