Density and frequency dependence of resistance in early airway obstruction.

The forced oscillation technique is a noninvasive and effort-independent test used to characterize the mechanical impedance of the respiratory system. The aim of this study was to assess the sensitivity of this method in detecting early airway abnormalities caused by smoking or occupational hazards. Respiratory mechanical parameters by the forced oscillation technique and maximal expiratory flow volume (MEFV) curves were obtained in a group of 82 workers from a gas manufacturing plant. In addition, the variations in the frequency dependence of total respiratory resistance between air breathing and a mixture of helium-oxygen (He-O2) were measured. All parameters were normalized for age, height, and weight. In order to compare the 2 types of testing, multiple linear regressions were performed with smoking or exposure as independent variables on one hand and parameters of the 2 types of testing on the other hand. This statistical procedure showed that 2 parameters of the forced oscillation technique constantly reached higher levels of significance than those of the MEFV parameters in the regression equations describing smoking history and occupational exposure: these were the frequency dependence of resistance and the change in frequency dependence between air and He-O2 breathing. When nonsmokers, ex-smokers, and smokers were considered separately, the degree of frequency dependence of resistance and the change in frequency dependence between air and He-O2 breathing were the only parameters that were significantly different between these 3 groups (one-way analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)