A simple and non-invasive method to determine the ventilation-perfusion ratio of the lung and the effective lung...

A method is presented to obtain the ventilation-perfusion ratio non-invasively. To describe the properties of gasexchange over the lung we used the law of mass conservation. The use of sinusoidal changes in the concentration of a tracergas in the inspired mixture results in a simple formulation of the variation in the concentration in the expired mixture over the variation in the inspired mixture. A careful selection of tracergas and cycleperiod of the sinus enables us to neglect the influence of venous return leaving the ventilation-perfusion ratio as sole physiological variable in the formulation. The lungperfusion can be obtained by measuring the total ventilation and correcting this value for deadspace ventilation. The method can be used to evaluate the influences of techniques like positive end-expired pressure and increased carbon dioxyde levels on shunting. It is also suited for monitoring purposes.