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

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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 se...