The coexistence of emphysema and pulmonary fibrosis is known as combined pulmonary fibrosis and emphysema (CPFE). The aim of this study was to compare the lung mechanics measured by multi-frequency forced oscillation technique (FOT) among patients with CPFE, interstitial pneumonia (IP), and chronic obstructive pulmonary disease (COPD). FOT and pulmonary function tests were performed in 41 patients with CPFE, 47 with IP, and 86 with COPD. Whole-breath resistance at 20 Hz was significantly lower in patients with CPFE than in those with IP or COPD, irrespective of the severity of airflow limitation. Within-breath analyses of resistance revealed no difference among the 3 groups; however, the difference between inspiratory and expiratory phases of reactance at 5 Hz, which reflects expiratory flow limitation, in patients with CPFE was significantly higher than in those with IP and lower than in those with COPD. In conclusion, both emphysema and fibrosis affect lung mechanics in CPFE, leading to different findings from IP or COPD alone.
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