Failure of body plethysmography to reflect functional deterioration seen in chronic obstructive pulmonary disease.

Measurements of lung volumes, airway conductance (Ca) and expiratory flow rates were compared in 40 patients with chronic obstructive pulmonary d i i (COPD) who were observed for an average of 3.3 years. The first and find study of each patient were compared and the average changes for the group were analyzed statistically. Although a diminution in expiratory flow rate was an almost invariable finding, changes in Ca, specific conductance, residual volume, residual volume/total lung capacity, functional residual volume and expiratory reserve volume did not show any consistent change. Patients who were more severely impaired in terms of expiratory flow tended to show more consistent deterioration in Ca and C~/VTO. However, the initial level of Ca and Ca/VT,; did not indicate in which direction these functions would change with time. It is concluded that at least for the short term follow-up of COPD body plethysmography does not reflect the clear deterioration manifested by the reduction in expiratory flow rate seen in this disease.