Selection of reproducible forced expirograms: Percentage or fixed-volume criterion

The aim of this study was to evaluate whether the intrasession reproducibil ity of forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV 1) depends on height and lung volume. FVC tracings of 740 subjects (350 mal es) from a general population sample living in North Italy were analyzed. S ubjects filled out a standardized questionnaire and performed three accepta ble FVC maneuvers following the American Thoracic Society recommendations. The differences between the largest and the second largest FVC and FEV1 wer e computed as absolute (Delta FVC, Delta FEV1) and as percentage values (De lta FVC%, Delta FEV1%). The higher the tertiles of the largest FVC and FEV1 were, the higher were Delta FVC and Delta FEV1. Regarding FVC, borderline differences in both sexes for Delta FVC and in males significant difference s for Delta FVC% were found among the tertiles. Regarding FEV1, in both sex es Delta FEV1 significantly differed among the tertiles. Delta FVC and Delt a FEV1 correlated with height and lung volume in both sexes, except for Del ta FVC versus the largest. FVC in females. When Delta FVC and Delta FEV1 we re analyzed with respect to respiratory symptoms/diseases and smoking habit , no significant differences were observed in both sexes, except for Delta FEV1 between ever- and never-smoking males. It may be concluded that the in trasession within-subject variability of FVC and FEV1 is proportional to lu ng volume and height, regardless of the sex, presence of symptoms and smoki ng habit. Thus, our results confirm the usefulness of a reproducibility cri terion based on a percentage rather than on a fixed volume.