Total respiratory resistance by forced oscillation in normal subjects.

Total respiratory resistance (Rrs) was studied by the forced oscillation technique at a frequency of 3 cps in 76 normal subjects (36 men, 40 women), ages 21 to 64 years. Slopes (equivalent to specific conductance) assuming a linear relationship with zero intercept between 1/Rrs and thoracic gas volume (TGV) were computed. In women, expiratory slopes were significantly less than inspiratory slopes; moreover, slopes decreased significantly with height and were significantly less in current smokers. For men, there were no consistently significant relationships between slopes and phase, age, height, weight, or smoking habits. Predicted resistance and estimates of the 5th and 95th percentiles of inspiratory, expiratory, and average resistance are presented for all men combined and for currently nonsmoking women. The fact that, in contrast to men, asymptomatic, current women smokers showed an elevation in Rrs when compared to nonsmoking women merits further study.