[Limitation of RI imaging in evaluating lung function test--development of new methods].

We developed two methods for determining the regional distribution of (1) RV/TLC and air trapping during forced expiration and (2) the ratio or pulmonary blood volume to blood flow. 1) The regional distributions of RV/TLC and air trapping ratio: A.T.R. (air trapping caused by forced expiration) were measured in respiratory disease cases and normal subjects using Xe-133 gas. In normal subjects, RV/TLC gradually decreased from the apex to the base of the lung. A.T.R. was very low in all lung fields. In chronic emphysema (CPE), both RV/TLC and A.T.R. were much higher than the value in normal subjects at the highly diseased areas. In contrast, in case of diffuse panbronchiolitis (DPB), RV/TLC remained within the normal range and A.T.R. was increased considerably in the diseased regions. These results suggest that airway obstruction occurs only during the forced expiration in DPB. 2) The regional distribution of the ratio of pulmonary blood volume to blood flow (tau p) were measured in a normal subject and a case of mitral regurgitation. In both subjects, the distribution of 1/tau p consisted of three zones: upper, middle and lower. The distribution of 1/tau p was constant in the middle zone, but, in the upper and lower zones, it decreased in proportion to the distance from the middle zone. In the case of mitral regurgitation, the middle zone shifted to the apex. Applying the results to the lung perfusion model proposed by West, it was suggested that these phenomena might reflect the increase of the pulmonary venous pressure and the perfusion disorder in the lower lung.