EFFECT OF HYPOXIA ON LUNG FLUID BALANCE IN FERRETS

To determine how hypoxia may alter determinants of pulmonary transvasc ular fluid flux, adult male ferrets were exposed to either room air (C ) or hypoxia (H; Fl(O2) = 0.12) for 24 h. After anesthesia and ventila tion with C or H, the mean pulmonary artery pressures were 18.4 +/- 2. 2(SEM) and 27.3 +/- 2.9 mm Hg, respectively (p < 0.025). The right lun g was then removed for gravimetric analysis of lung water and the left lung was blood-perfused (similar to 142 ml/kg/min) and continuously w eighed for 15 min at left atrial pressures of 20, 25, and 30 mm Hg. Fi ltration coefficient (K-f) was estimated from the slopes of the relati onships of rate of weight gain versus change in vascular pressure over the last 5 min of each interval. Extravascular lung water/blood-free dry lung weight for C and H were 2.95 +/- 0.06 (SEM) and 3.53 +/- 0.09 ml/g, respectively (p < 0.01). K-f for C and H were 0.0645 +/- 0.0190 (SEM) and 0.0662 +/- 0.0085 ml/min/mm Hg/100 g, respectively (NS). In a second group of experiments, in which lungs were removed from ferre ts after 24 h exposures to C or H, protein reflection coefficients (si gma) were estimated by comparing the increases in perfusate hematocrit and protein concentrations during edema formation. Reflection coeffic ients for albumin were 0.64 +/- 0.03 (SEM) and 0.39 +/- 0.07 with C an d H, respectively (p < 0.01). The sigma values for IgG and IgM were no t affected. In a third group of experiments, isolated perfused ferret lungs were ventilated with Fl(O2) = 3.3% O-2 for 76 +/- 33 min (SD), f ollowed by 18% O-2 for 92 +/- 34 min or vice versa. With these brief e xposures to hypoxia, there was no effect on sigma for albumin, IgG, or IgM. We conclude that 24 h hypoxia may promote pulmonary edema format ion in ferret lungs by increasing the permeability of the vasculature to albumin, thereby decreasing the effectiveness of the plasma-interst itial oncotic pressure gradient. Hypoxic vasoconstriction-induced incr eases in vascular pressure may contribute further to edema formation.