Pressure-volume relations of lung and thoracic cage in pulmonary emphysema

¹ Department of Medicine, Cardiopulmonary Laboratory, State University of New York, Downstate Medical Center, Brooklyn, New York

In ten emphysematous and six normal subjects, the pressure-volume curve of the thoracic cage was obtained by arithmetic subtraction, since Pt (total pressure) = Pl (lung pressure) + Pc (thoracic cage pressure). A low compliance of the thoracic cage was found for five emphysematous patients whose total lung capacities (TLC) averaged 93 % of predicted values. In the remaining five patients whose TLC averaged 123% of predicted normal, the compliance values for all the components were nearly normal. In all ten of the patients a normal compliance for lung was found. The respective values of compliance, in liters per centimeter H₂O, for the patients with normal TLC were: total respiratory system, 0.039; lung, 0.132; and thoracic cage, 0.056; and for the patients with the larger TLC, were: total respiratory system, 0.075; lung, 0.141; and thoracic cage, 0.154 The major difference was the compliance of the thoracic wall which contributed to the reduction of the compliance of the total respiratory system. The data indicate that some emphysematous patients have a low compliance of the thoracic cage which contributes to the over-all increase in the elastic resistance of the total respiratory system.