Single-passage extraction and permeability estimation of sodium in normal dogs lungs

Bolus injections of 24NaCl, 131I-albumin, and indocyanine green dye were made into the right atria of anesthetized, ventilated dogs. Blood was sampled from the femoral artery, and from the dilution curves, instantaneous extractions, E2(t), and area averaged extractions, E3(t), were calculated for sodium at various plasma flows (Fp). Flow reduction was produced by transient inferior vena cava obstruction. E2(t) and E3(t) within any dilution curve generally started off with a high value, then decreased with time. The E3 that occurred at the peak of the albumin-dilution curve were about 0.11 for plasma flow of 0.75 liter/min and tended to decrease as flow increased. Parallel study of the sodium extravascular space at equilibrium gave values of 0.3-0.4 g of plasma sodium per g of tissue, suggesting that this volume is not infinitely small. Since the E was low it is unlikely that the high initial E(t) and the decreasing E(t) were due to early back flux. Calculation of capillary permeability surface area product [PS = Fp loge (1 - E)] showed an increasing PS with plasma flows. The injection of 9-mum microspheres at low and high total blood flow gave evidence supporting a decrease of capillary surface area (S) with decreasing total blood flow. Regional pulmonary blood flow also showed marked heterogeneity. Because of the low average extraction of sodium in the lung, insensitivity of the method in normal lungs cannot be excluded.