Clearance of ^99mTc-Labeled Albumin from Lungs in Anesthetized Guinea Pigs

Abstract

Gamma imaging was used to measure the rate of clearance of aerosolized ^99mTc-human serum albumin (HSA) from the lungs of control guinea pigs and guinea pigs that received increased lung inflation or lung injury. Anesthetized guinea pigs were ventilated for 6 min with an aerosol of HSA and the radioactivity in the chest was monitored for 2 h with a gamma camera to determine whether the clearance rate would be a reliable assessment of lung epithelial permeability. Increased lung volumes were effected by application of 5 or 7 cm H₂O positive end-expired pressure (5-PEEP and 7-PEEP, respectively). Lung injury was induced either by intravenous oleic acid (OA, 27–73 μl/kg) or inhalation of nitrogen dioxide (NO₂, 80–100 ppm) for 2 h. Postmortem extravascular lung water volume (EVLW) provided an assessment of the degree of lung injury. Tracer clearance rates in animals receiving 5 or 7 cm H₂O PEEP were not significantly different from controls (K = 0.15 ± 0.05 and 0.24 ± 0.10 vs 0.12 ± 0.03%/min, respectively, p < .05). Animals exposed to NO₂ had faster tracer clearance rates (K = 0.33 ± 0.21%/min, p < .05) and higher EVLW (5.8 ± 3.0 vs 3.7 ± 0.2 mL/g dry lung, p <.05) than controls. Clearance rates of HSA from the lungs of NO₂-exposed guinea pigs correlated well with injury as assessed by EVLW(r = .93, p <.01). Clearance rates of HSA and EVLW in animals receiving oleic acid were significantly higher than controls and the group receiving 5 cm H₂O PEEP (K = 0.58 ± 0.41%/min, EVLW = 8.1 ± 0.8 mL/g dry lung tissue, p < .05), but there was no correlation between these parameters in this injury model. It is concluded that imaging of the disappearance of radiolabeled HSA in the guinea pig can be a useful index of lung epithelial permeability, but this technique is limited to certain models of lung injury.