Prognostic Value of the Six-Second Spirometry in Patients with Chronic Obstructive Pulmonary Disease: A Cohort Study

BACKGROUND: The six-second spirometry has been proposed as an alternative to diagnose airflow limitation, although its prognostic value in patients with chronic obstructive pulmonary disease (COPD) remains unknown. The purpose of this study was to determine the prognostic value of the postbronchodilator forced expiratory volume in 1 second (FEV(1))/forced expiratory volume in 6 seconds (FEV(6)) ratio and FEV(6) in COPD patients. METHODS AND FINDINGS: The study population consisted of 2,614 consecutive stable patients with COPD. The patients were monitored for an average period of 4.3 years regarding mortality, hospitalizations by COPD exacerbations, diagnosis of lung cancer, and annual lung function decline. The overall rate of death was 10.7 (95%CI: 8.7–12.7) per 1000 person-years. In addition to male gender, age and comorbidity, FEV(6) (hazard ratio [HR]: 0.981, 95%CI: 0.968–0.003) and FEV(1)/FEV(6) quartiles (lowest quartile (<74% pred.): HR 3.558, 95%CI: 1.752–7.224; and second quartile (74–84% pred.): HR 2.599, 95%CI: 1.215–5.561; versus best quartile (>0.89% pred.)) were independently associated with mortality, whereas FEV(1) was not retained in the model. 809 patients (30.9%) had at least one hospital admission due to COPD exacerbation. In addition to sex, age, smoking and comorbidity, FEV(1) and FEV(1)/FEV(6) quartiles were independent risk factors of hospitalization. FEV(6) was the only spirometric parameter independently related with lung function annual decline, while the FEV(6) and FEV(1)/FEV(6) quartiles were independent risk factors for lung cancer. CONCLUSIONS: In a general COPD outpatient population, airflow obstruction assessed by the FEV(1)/FEV(6) is an independent risk factor for both death and hospitalization.