Studies of Total Pulmonary Capacity and Its Subdivisions Ix. Relationship to the Oxygen Saturation and Carbon Dioxide Content of the Arterial Blood 1

An index of the efficiency of the exchange of carbon dioxide and oxygen between the circulat- ing blood and the alveolar air may be derived from the analysis of the arterial blood. How- ever, it must be born in mind that changes in the gaseous content of the blood leaving the lungs may be brought about by a multiplicity of res- piratory and circulatory factors, so that the proper interpretation of the results presents considerable difficulties. Although numerous analyses of ar- terial blood have been made in various pulmonary conditions, a review of the literature reveals very few attempts to correlate these studies with simul- taneous studies of the external respiration. This is particularly true in the case of chronic pulmon- ary diseases, the fibroses and emphysema of the lungs. We have presented in previous communi- cations (1) (2), evidence showing that the changes observed in the total pulmonary capacity and its subdivisions in cases of pulmonary emphysema and fibrosis are closely related to the anatomical alterations and tend to be correlated with the degree of clinical respiratory disability. The purpose of this communication is to correlate the alterations in the gaseous content of the arterial blood with the pulmonary capacities in 37 cases of pulmonary fibrosis and in 24 cases of pulmonary emphysema.