Pulmonary function impairment in patients with combined pulmonary fibrosis and emphysema with and without airflow obstruction

Abstract

Background: The syndrome of combined pulmonary fibrosis and emphysema (CPFE) is a recently described entity associating upper-lobe emphysema and lower-lobe fibrosis. We sought to evaluate differences in pulmonary function between CPFE patients with and without airflow obstruction.

Subjects and methods: Thirty-one CPFE patients were divided into two groups according to the presence or absence of irreversible airflow obstruction based on spirometry (forced expiratory volume in 1 second/forced vital capacity <70% following inhalation of a β2-agonist) as follows: CPFE patients with airflow obstruction (CPFE OB(+) group, n=11), and CPFE patients without airflow obstruction (CPFE OB(-) group, n=20). Pulmonary function, including respiratory impedance evaluated using impulse oscillometry and dynamic hyperinflation following metronome-paced incremental hyperventilation, was retrospectively analyzed in comparison with that observed in 49 chronic obstructive pulmonary disease (COPD) patients (n=49).

Results: In imaging findings, low-attenuation-area scores on chest high-resolution computed tomography, representing the degree of emphysema, were significantly lower in the CPFE OB(-) group than in the CPFE OB(+) and COPD groups. In contrast, the severity of pulmonary fibrosis was greater in the CPFE OB(-) group than in the CPFE OB(+) group. In pulmonary function, lung hyperinflation was not apparent in the CPFE OB(-) group. Impairment of diffusion capacity was severe in both the CPFE OB(-) and CPFE OB(+) groups. Impulse oscillometry showed that respiratory resistance was not apparent in the CPFE OB(-) group compared with the COPD group, and that easy collapsibility of small airways during expiration of tidal breath was not apparent in the CPFE OB(+) group compared with the COPD group. Dynamic hyperinflation following metronome-paced incremental hyperventilation was significantly greater in the COPD group than in the CPFE OB(-) group, and also tended to be greater in the CPFE OB(+) group than in the CPFE OB(-) group.

Conclusion: The mechanisms underlying impairment of physiological function may differ among CPFE OB(+) patients, CPFE OB(-) patients, and COPD patients. CPFE is a heterogeneous disease, and may have distinct phenotypes physiologically and radiologically.

Keywords: COPD; CPFE; dynamic hyperinflation; respiratory impedance.

Figure 1

Respiratory impedance in the CPFE OB⁻, CPFE OB⁺, and COPD groups. Notes: *P<0.05, **P<0.01 versus COPD. Values are means ± standard error of the mean. Abbreviations: CPFE, combined pulmonary fibrosis and emphysema; OB-, without airflow obstruction; OB⁺, with airflow obstruction; COPD, chronic obstructive pulmonary disease; Rrs5, respiratory resistance at 5 Hz; Rrs20, respiratory resistance at 20 Hz; Xrs5, respiratory reactance at 5 Hz; △Xrs5, within-breath changes in Xrs5.

Figure 2

Inspiratory capacity as the respiratory rate was incrementally increased in the CPFE OB⁻, CPFE OB⁺, and COPD groups. Notes: Dynamic hyperinflation following metronome-paced incremental hyperventilation in the combined pulmonary fibrosis and emphysema (CPFE) without airflow obstruction (OB⁻), with airflow obstruction (CPFE OB⁺), and chronic obstructive pulmonary disease (COPD) groups. Inspiratory capacity (IC) from resting respiratory rate to rates of 20, 30, and 40 breaths per minute. **P<0.01 versus COPD; ^†P<0.05 versus CPFE OB⁺. Values are means ± standard error of the mean.

Figure 3

Decrease in inspiratory capacity from resting respiratory rates to the rate of 20, 30, and 40 breaths per minute, representing dynamic hyperinflation, in the CPFE OB⁻, CPFE OB⁺, and COPD groups. Notes: Dynamic hyperinflation following metronome-paced incremental hyperventilation in the combined pulmonary fibrosis and emphysema (CPFE) without airflow obstruction (OB⁻), with airflow obstruction (CPFE OB⁺), and chronic obstructive pulmonary disease (COPD) groups. Decrease in inspiratory capacity (IC) from resting respiratory rate to rates of 20, 30, and 40 breaths per minute. *P<0.05, **P<0.01 versus COPD. Values are means ± standard error of the mean.