In vivo quantitation of epithelial lining fluid in dog lung.

We used an original saturation bronchoalveolar lavage (SBAL) technique (Eur. Respir. J. 1995;8[Suppl. 19]398S) to quantitate lung epithelial lining fluid volume (VELF) in dogs in two separate experiments: control and after oleic-acid-induced injury. We confirmed the hypothesis that 99mTc-DTPA, infused at constant plasma activity, reaches equilibrium with epithelial lining fluid after 90 min. We performed eight sequential lavages 215 min after beginning the infusion of 99mTc-DTPA. 99mTc-DTPA activity (Qn) in the lavage fluid increased linearly with time, suggesting transport from the plasma into the alveoli during lavage. We extrapolated Qn to time zero (Q0), when 99mTc-DTPA was not affected by lavage. VELF was calculated from: VELF = Q0/Cp, (Cp: 99mTc-DTPA mean plasma activity). 125I-albumin was used as a nondiffusible alveolar indicator to measure the fluid volume present in the lavaged segment (Vt,n). Vt,n plateaud for n >= 4. VELF/Vt,n(n = 5,8) was 1.7 +/- 0.4 and 25.0 +/- 4.4% (p < 0.05) in control and injury experiments, respectively. SBAL allowed reliable measurements of VELF and detection of alveolar edema fluid in the injured lung.