Failure of Body Plethysmography to Reflect Functional Deterioration Seen in Chronic Obstructive Pulmonary Disease

¹ Director, Cardiopulmonary Laboratory, Grasslands Hospital; Professor of Medicine, New York Medical College
² Associate Director, Cardiopulmonary Laboratory, Grasslands Hospitals

Measurements of lung volumes, airway conductance (Ca) and expiratory flow rates were compared in 40 patients with chronic obstructive pulmonary disease (COPD) who were observed for an average of 3.3 years. The first and final 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 Ca/V_TG. However, the initial level of Ca and Ca/V_TG 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 deteroration manifested by the reduction in expiratory flow rate seen in this disease.