The “Horse-Racing Effect” and Predicting Decline in Forced Expiratory Volume in One Second from Screening Spirometry1,2

Abstract

Longitudinal spirometric data on adults in a general population sample confirmed an overall relationship between rate of change in FEV₁ (ΔFEV₁) and mean FEV₁Ht³. This relationship between FEV, “slope” and “level” has been called a “horse-racing effect” and is the basis for the widely accepted concept that detecting a low FEV₁ will predict a rapid decline in FEV₁ and the development of clinically significant COPD. However, when both age and smoking habits were taken into account, the effect persisted only in male smokers. Even in them, it was dependent on the inclusion of part of the ΔFEV₁ in calculation of the mean FEV₁ value. While neither a low initial FEV₁/Ht³ nor percent predicted FEV₁ significantly predicted a subsequent rapid fall in FEV₁, presumably because of regression toward the mean, other initial spirometric variables proved better predictors, at least among male smokers. In them, a low FEV₁/FVC ratio on entry was almost uniformly associated with a high rate of decline in FEV₁. This was not seen in ex-smokers with similar initial spirometric findings. Also, ΔFEV₁ could not be predicted with any precision in women regardless of their smoking status. The findings strongly support the concept that detection of early airway disease by spirometric screening will identify those male smokers who are likely to develop clinically significant illness if they continue to smoke and that smoking cessation, even at this point, can markedly improve the prognosis. However, in view of the very rapid declines in FEV₁ seen in many subjects with early disease, in any person, there may be a relatively short age span during which the early stages of COPD can be reliably detected before the disease progresses to clinically significant impairment. These findings may have important implications in terms of the “early detection” Of COPD.