Respiratory reactance is related to future COPD exacerbations

Abstract

Forced oscillation technique (FOT) is a sensitive method for early diagnosis of obstructive disease, but its role in monitoring COPD is less established. The aim was to study the value of FOT in stable COPD disease in relation to future exacerbations. A total of 150 subjects with spirometry-verified COPD-diagnosis (mean age 67 +/− standard deviation (SD) 7 years, 61% females) performed FOT in the Uppsala centre of the Swedish, multicenter study Tools for Identifying Exacerbation (TIE) in COPD. Exacerbations over the coming year were assessed based on a questionnaire administered 1 year later in 113 subjects. Excerbation was defined as worsening of COPD leading to an unscheduled visit and/or prescription of antibiotics and/or course of oral corticosteroids. FOT values were expressed as z-scores (Oostveen et al. ERJ 2013). A significant difference was found for reactance at 5 Hz (X5) (mean ± SD) between subjects with future exacerbations (n=39) and those without future exacerbations (n=74): -4.3 ± 6.1 vs -1.0 ± 2.6, p<0.001. However no significant difference in resistance at 5 Hz was found between these two groups: 1.1 ± 1.3 vs 0.5 ± 1.4, p=0.06. Expiratory flow limitation, defined as difference between inspiratory and expiratory X5 >2.8 cm H2O/L/s, was found in 28 of the subjects. These subjects were characterized by higher prevalence of future exacerbations compared with subjects without EFL (74% vs 27%, p<0.001). This association was consistent even after adjusting for age, gender, current smoking, history of previous exacerbations (p=0.01). In conclusion, reactance at 5 Hz and especially the difference between inspiratory and expiratory reactance appear to be useful to predict future exacerbations in COPD.