To assess the rate of decline of FEVI over time in patients with GOLD stage 3- 4 COPD and compare the rate of decline in non smokers and smokers.
The primary outcome was the rate of decline of FEV1 /year in current smokers versus non smokers; secondary outcomes included the rate of decline in FEV1 at different stages of airflow obstruction.
In a retrospective case series, we included patients with a primary diagnosis of COPD, GOLD stage 3- 4 under regular review with 3 years spirometry data performed in the respiratory clinic using standard methods. The sample was divided into non- smokers, persistent smokers, and intermittent quitters.
Data was available for 95 patients range 3-23 years.
The rate of decline in smokers was significantly higher than non-smokers. The mean (SD) decline in FEV1 (ml/yr) was faster in earlier stages in GOLD2 53.2 (16.7); GOLD3 32.0 (29.7) and GOLD4 5.9 (7.2). In the overall sample the line of best fit of FEV1 over time was exponential.

Rate if decline in FEV1 in ml/year
intermittent quitters2561.147.2
Non- smokers4537.845.7

The rates of decline (mean (SD)) in non-smokers GOLD3 was 33.9 (35.3) and GOLD4 17.3 (51.3) and for smokers GOLD3 = 42.7 (34.5) and GOLD4 = 25.3 (N/A).
Even in late stages the decline in FEV1 is faster in smokers than intermittent quitters who declined faster than non smokers. Unlike the Fletcher Peto diagram we found that the decline in FEV1 was faster in earlier than later stages. The benefits of quitting diminish as the disease progresses. To minimise lung damage it is essential identify people in early stages and for them to stop smoking immediately.