[Routine pulmonary function tests--contributing factors of various spirogram and flow-volume parameters and their value in the diagnosis of small airway disease].

Spirogram and flow-volume analysis seems to be the most reliable and sensitive measurement in the routine pulmonary function tests. However, there remain many problems in the interpretation of the obtained values. In the present study the contributing factors for the spirogram and flow-volume parameters were elucidated through the multiple variable analysis. The analyzed parameters were VC, FEV1, FEV1%, MMF, Vp, V75, V50, V25, V50/V25-ratio, MTC75-50, MTC50-25, MTC25-RV and MTC75-50/MTC25-RV-ratio of 219 nonsmoking normal subjects. The tested predictor variables were age, height, weight, body surface area and obesity index. An F value of more than 2.0 of the predictor variables was assumed significant. The value of the obtained regression equation in the diagnosis of the small airway disease was examined in each parameter of 215 smokers. Obtained regression equations are contained different sets of predictor variables as compared with the conventional equations. There remained not a few unknown factors other than the constitutional factors especially in flow-volume parameters. Despite the presence of these unknown factors V50, V25, MTC50-25, MTC25-RV and MTC75-40/MTC25-RV-ratio were shown to be valuable parameters in the evaluation of the small airway diseases. The difficulties in the measurement and the evaluation of spirometry and flow-volume analysis in the elderly subjects, as well as the use of different criteria for the aged are discussed.