Abstract
Distribution of ventilation-perfusion ratio (VA/QC distribution) is one of the most important functional parameters of the lung. A new method for noninvasive measurement of VA/QC distribution is described. Based on a multiple compartment model which simulates the lung as an electric RC network, a concept of multiple compartment transfer function (MCTF) is proposed. A system of algebraic equations is derived from MCTF and the VAZQC distribution can be obtained by solving these equations according to the frequency response of the lung which is measured by continuous analysis of respiratory gas during the inspiration of the gas with sinusoidally varied halothane concentration.
Simultaneous and instantaneous analysis of physiological and inert gases is essential in this measurement. By employing an improved multicollector mass spectrometer, such measurement was accomplished with comparatively satisfactory sensitivity and stability. Another technical problem was to produce the air flow containing sinusoidally varied halothane concentration with a wider range of frequency components. It was achieved by using a commercially available flow controller combining with computer-controlled frequency modulation and synthesis technique.
Experimental results of normal subjects and patients with lung diseases gave physiologically reasonable results of VA/QC distributions. It is demonstrated that the method is useful in physiological studies and clinical diagnoses.
