Studies on regional differences in pre-inspiratory lung volume and pre-inspiratory alveolar N_2 concentration by a single breath method

Abstract

An essential function of the lung is to exchange gas between venous blood and air, so that gas distribution is important only in relation to blood distribution. Yet, no simple method of measuring regional differences in V_A/Q without employing radioactive gases has been introduced after West reported his method in 1957. Even though the measurement of uneven ventilation in the lung by a single breath O_2 method has come into routine use since Fowler's report and it can provide an acceptable index of the presence of regional differences, this method cannot give any index corresponding to a particular region. By the analysis of both Ar and N_2 measured after a single inspiration of Ar-O_2 mixture, we constructed a single compartment model in order to calculate pre-inspiratory lung volume (V_<Lφ>) and pre-inspiratory alveolar N_2 concentration (F_<AφN_2>), and we evaluated the changes in V_<Lφ> and F_<AφN_2> during the test expiration, as indices of regional differences in the ventilation and in the gas-exchange, respectively. Numerical values of V_<Lφ> and F_<AφN_2> could be also assigned to a series of functional units having regional differences.