Quantitative Assessment of Pulmonary Function

Abstract

In a search for more quantitative assessment of pulmonary function, the research concentrated on two major areas of investigation: Gross impairment of pulmonary gas exchange processes can often be attributed to regional deformation of normal ventilation-specific ventilation distributions. Hence, the first topic of investigation considers the recovery of such distributions in normal and diseased states, by a new method with which these distributions can be confidently recovered from inert gas elimination studies. The method is tested using theoretical nitrogen washout data and subsequently used to analyse experimental data from ten normal and two abnormal subjects. The recovered quasi-continuous distributions of ventilation to specific ventilation suggest that whereas young normal lungs behave as two principle respiratory zones of volume ratio 6.04, this ratio increases rapidly with age, and large deviations from the observed 'normal' pattern occur in diseased states. The second area of research considers the existence of pulmonary arteriovenous blood shunts which direct blood away from the ventilated regions of the lung, causing severe hypoxia. By means of a mathematical model of non-steady state inert gas exchange, a new method is described for rapid and accurate detection of shunt. The effects of regional inequalities of ventilation and perfusion, together with tracer solubility, are studied. The method is shown to merely require the continuous sampling of injectate and arterial blood tracer concentrations and the accuracy is independent of end-capillary gas concentrations and tracer solubility.