Uneven ventilation in smokers.

A body plethysmographic technique designed to detect small degrees of uneven ventilation in the lungs is presented. The technique is based on the same theoretical model as the frequency dependence of compliance. It has the advantage of requiring little time, no cooperation by the subject and no computation. Signs of uneven ventilation were found in 3 of the 42 normal controls, in 6 of 51 light smokers and in 66 of 103 heavy smokers. The data are compared with measurements of closing volume, of the slope of phase III of the single breath nitrogen washout and of maximal mid-expiratory flow rate.