Fixed airflow obstruction due to asthma or chronic obstructive pulmonary disease: 5-year follow-up

Background: Both smokers and patients with asthma can experience fixed airflow obstruction, which is associated with distinctive patterns of airway pathology. The influence of fixed airflow obstruction on the prognosis of these patients is unknown.

Objective: We sought to investigate lung function decline and exacerbations in a 5-year prospective study of subjects with fixed airflow obstruction due to asthma or chronic obstructive pulmonary disease (COPD). We also sought to explore correlations between functional, pathological, and clinical features.

Methods: Patients with fixed airflow obstruction due to asthma (n = 16) or COPD (n = 21) and a control group of asthmatic patients with fully reversible airflow obstruction (n = 15) were followed for 5 years.

Results: The rates of decline in FEV(1) were similar in patients with fixed airflow obstruction caused by asthma (-49.7 +/- 10.6 mL/y) or COPD (-51.4 +/- 9.8 mL/y) and were higher than in asthmatic patients with reversible airflow obstruction (-18.1 +/- 10.1 mL/y, P < .01). Exacerbation rates were also higher in patients with fixed airflow obstruction caused by asthma (1.41 +/- 0.26 per patient-year) or COPD (1.98 +/- 0.3 per patient-year) compared with those seen in asthmatic patients with reversible airflow obstruction (0.53 +/- 0.11 per patient-year, P < .01). Baseline exhaled nitric oxide levels and sputum eosinophil counts correlated with the FEV(1) decline in asthmatic patients with fixed airflow obstruction. By contrast, baseline sputum neutrophil counts, emphysema scores, comorbidities, and exacerbation frequency correlated directly and pulmonary diffusion capacity correlated inversely with the FEV(1) decline in patients with COPD.

Conclusion: In both patients with asthma and those with COPD, fixed airflow obstruction is associated with increased lung function decline and frequency of exacerbations. Nevertheless, the decline in lung function entails the specific pathological and clinical features of the underlying diseases.