Single isotope evaluation of pulmonary capillary protein leak (ARDS model) using computerized gamma scintigraphy

Using a canine oleic acid model, a computerized gamma scintigraphic technique was evaluated to determine 1) ability to detect pulmonary capillary protein leak in a model temporally consistent with clinical adult respiratory distress syndrome (ARDS), 2) the possibility of providing a quantitative index of leak, and 3) the feasibility of closely spaced repeat evaluations. Study animals received oleic acid (controls, n = 10; 0.05 ml/kg, n = 10; 0.10 ml/kg, n = 12; 0.15 ml/kg, n = 6) 3 hours prior to a tracer dose of technetium-990m (99mTc) HSA. One animal in each dose group also received two repeat tracer injections spaced a minimum of 45 minutes apart. Digital images were obtained with a conventional gamma camera interfaced to a dedicated medical computer. Lung: heart ratio versus time curves were generated, and a slope index was calculated for each curve. Slope index values for all doses were significantly greater than control values (P(t) less than 0.0001). Each incremental dose increase was also significantly greater than the previous dose level. Oleic acid dose versus slope index fitted a linear regression model with r = 0.94. Repeat dosing produced index values with standard deviations less than the group sample standard deviations. We feel this technique may have application in the clinical study of pulmonary permeability edema.