COPD is a condition of airflow limitation causing dyspnea, which steadily progress together at a generally predictable rate, eventually causing debilitation and death. Right?
Not usually, say a growing chorus of COPD experts after reviewing a growing portfolio of observational data.
Casanova et al followed 751 patients with COPD (almost all men) for a median of 5 years, some up to 10. All had had 3 or more spirometry measurements over the study period. Their lung function (FEV1) and symptoms (BODE index) were remarkably stable throughout the study period.
In fact, only 18% of patients had a rate of FEV1 decline deemed statistically significant. (In this rapid-decline group, the yearly loss in FEV1 was -86 mL). In the large majority (82%) of patients, FEV1 declined a non-statistically significant amount, with a mean of 28 mL per year. About half of the patients clustered between +20 mL per year, and -40 mL per year, according to their histogram. (Many had several “up-and-down” FEV1 measurements, which won’t surprise anyone who’s tried to interpret spirometry in patients longitudinally.)
In COPD, it may be that the more lung function you have, the faster you lose it: those with the highest FEV1s at baseline/study entry had the highest rates of FEV1 decline. Low body mass index (BMI) was also independently associated with decline in FEV1.
The BODE index, which more broadly measures respiratory limitation and severity of COPD, and more accurately predicts mortality than FEV1 or other measures alone, was also stable over time in the large majority (86%) of patients. Only 14% had a stat.significant worsening of +0.55 points per year. Those with the worst lung function tended to also have the most rapid functional deterioration.
This all jibes well with another dogma-challenging study we reviewed last month from the New England Journal, which suggested that in half or more people with COPD, FEV1 falls at only ~30 mL per year or so — hardly different than never-smoking age matched controls without COPD. Only 38% had FEV1 declines of > 40 mL … and 8% had FEV1 increases of 20 mL or more. Those with higher FEV1s at baseline also had more rapid declines, in that observational study.
Casanova C et al. The Progression of Chronic Obstructive Pulmonary Disease Is Heterogeneous. The Experience of the BODE Cohort. Am J Respir Crit Care Med 2011;184:1015-1021.