Alterations of Ventilation to Perfusion Ratios Distribution Associated with Successive Clinical Stages of Pulmonary Emphysema*

Abstract

A comparative study of the several factors related to respiratory gas exchange was made in 22 patients suffering from chronic pulmonary emphysema at varying stages of this disease. Expired gas concentrations of CO2 and N2 were continuously monitored at mouth level while subjects breathed 1st a gas mixture containing 90% O2 and 10% N2 for 11 to 15 min., and then a mixture the equivalent of room air in O2 and N2 concentration for a like period of time. Samples of arterial blood and expired gas were collected prior to and on completion of the washout with the 90% O2 gas, and following wash in with the room air mixture. These samples of blood and gas were tested for O2 and CO2 with gas electrodes, and N2 concentration of the blood samples was determined by gas chromatograph, while N2 concentration of expired gas samples was calculated as the difference between 100% and the sum of O2 and CO2 concentrations. The factors determined by measurement and calculation from this data included alveolar ventilation, lung volume, blood flow, and the relationships of these to each other in a 3 compartment system; alveolar-arterial differences of each of the 3 respiratory gases; and distribution of ventilation to per-fusion ratios (VA/Q) throughout the lung. Findings indicate changes in distribution of VA/Q to be the main cause of progressive impairment of gas exchange with worsening of the disease process. The lowering of over-all VA/Q accompanying advancing clinical symptoms is probably not as significant as changes in distribution of different VA/Q units. As the clinical disease advances there is a decrease in number of normal VA/Q units as more and more units move away from this category in both directions; most of these become low VA/Q units, but some become units with higher ratios. Also, the rate of blood flow, or percentage of total blood flow, going to low VA/Q units is as important to the production of hypoxia and hypercarbia as the actual level of low VA/Q ratio value.