Lung scan abnormalities in asthma and their correlation with lung function

We have used asthma as a model of airways disease to test how well an automated, quantitative method of analysis of lung scans correlates with physiological measurements of disturbed lung function and gas exchange. We studies 25 asthmatics (age 16-73) of widely differing severity (forced expiratory volume in 1-s (FEV1) 22%-123% of predicted value), who had airways tests, arterial blood gas analysis, and krypton-technetium lung scans within a short time of each other. In all patients with airways obstruction and in some with normal function during remission, scans showed the typical appearances of multiple defects of ventilation and perfusion. The severity of ventilation defects was computed from the posterior view of the krypton scan compared to an age- and sex-matched normal range to yield an underventilation score. This correlated closely with the severity of airways obstruction as measured by forced expiratory manoeuvres. Ventilation and perfusion defects were usually imperfectly matched; the severity of this was computed using a subtraction method applied to the counts on the posterior krypton and technetium scans. The degree of mismatch was inversely related to the arterial partial pressure of oxygen (r = -0.86). The results suggest that computer scan analysis can provide useful functional information about the lung in airways disease.