The importance of spirometry was demonstrated in a study by van Schayck et al , who evaluated whether the progression of asthma or chronic bronchitis can be predicted by family physicians apart from lung function testing. They compared physical examination and peak flow results with FEV1 as indicators of decline. In chronic bronchitis, only 27% of the variance in FEV1 decline could be explained by the results of both the chest examination and the diurnal variation in peak flow rate. The authors concluded that it is difficult, if not impossible, to predict the rate of decline in obstructive airway disease through physical examination alone. While a strong association between an FEV 1 to FVC ratio of less than 70% and accelerated decline in FEV1 has been seen in male smokers, Burrows and colleagues observed no such clear relation in women. On the other hand, in the Lung.