Optical measurement of isolated canine lung filtration coefficients after alloxan infusion

In this study, lung filtration coefficient (K(fc)) was measured in eight isolated canine lung preparations by using three methods: standard gravimetric (Std), blood-corrected gravimetric (BC), and optical. The lungs were held in zone III conditions and were subjected to an average venous pressure increase of 8.79 ± 0.93 (mean ± SD) cmH₂O. The permeability of the lungs was increased with an infusion of alloxan (75 mg/kg). The resulting K(fc) values (in milliliters · min^-1 · cmH₂O^-1 · 100 g dry lung weight^-1) measured by using Std and BC gravimetric techniques before vs. after alloxan infusion were statistically different: Std, 0.527 ± 0.290 vs. 1.966 ± 0.283; BC, 0.313 ± 0.290 vs. 1.384 ± 0.290. However, the optical technique did not show any statistical difference between pre- and postinjury with alloxan, 0.280 ± 0.305 vs. 0.483 ± 0.297, respectively. The alloxan injury, quantified by using multiple-indicator techniques, showed an increase in permeability and a corresponding decrease in reflection coefficient for albumin (σ(f)). Because the optical method measures the product of K(fc) and σ(f), this study shows that albumin should not be used as an intravascular optical filtration marker when permeability is elevated. However, the optical technique, along with another means of measuring K(fc) (such as BC), can be used to calculate the σ(f) of a tracer (in this study, σ(f) of 0.894: at baseline and 0.348 after injury). Another important finding of this study was that the ratio of baseline-to-injury K(fc) values was not statistically different for Std and BC techniques, indicating that the percent contribution of slow blood-volume increases does not change because of injury.