LUNG FUNCTION STUDIES. VIII. ANALYSIS OF ALVEOLAR VENTILATION BY PULMONARY N2 CLEARANCE CURVES 12

Abstract

A comprehensive analysis of pulmonary fuinction must include measurements of pulmonary ventilation, diffusion, and circulation. An accurate measurement of alveolar ventilation, independent of diffusion and circulation, is desirable. To date, no method has been wholly satisfactory (3). One approach has been by study of the time course of equilibration of alveolar gas with a foreign inspired gas, such as H2 (4), He (5-7) or pure 02 (8-15). A principal difficulty has been to differentiate between the effects of an enlarged respiratory dead space and of uneven alveolar ventilation, both of which can retard the completion of equilibration. The development by Lilly and Hervey of the N2 meter, for continuous analysis of N2 concentration of respired gas, permits an automatic breath-by-breath analysis of gas expired during and after the change from breathing air to uninterrupted breathing of 02. The ensuring progressive elimination of pulmonary N2 represents the process of equilibration with a N2-free gas, and may be analyzed in terms of alveolar ventilation. This paper presents the pulmonary N2 clearance curves obtained from healthy persons and patients with cardiorespiratory disease, and a method for analysis of these curves which yields a comprehensive picture of the volume and time characteristics of alveolar ventilation. The