Pulmonary microvascular clearance of radiotracers in human cardiac and noncardiac pulmonary edema.

We examined the integrity of the alveolocapillary membrane in human cardiac (hydrostatic) (group 1) and noncardiac (permeability) (group 2) edema by measuring the clearance of two intravenously administered radiotracers from the blood to suctioned bronchoalveolar secretions (BAS), representing pulmonary edema fluid, and compared the clearances to simultaneously measured pulmonary capillary wedge pressure (PCWP) and colloid osmotic pressure (COP), representing the intravascular Starling forces, Pmv and pimv. 111In-labeled diethylenetriamine pentaacetic acid (DTPA), mol wt 504, a hydrophilic radiotracer that equilibrates with extracellular water, and 125I-labeled human serum albumin (HSA), mol we 69,000, were injected intravenously. Samples of blood and BAS were then collected hourly for 405 h, and clearances were calculated. We found the clearance of both radiotracers to be greater in group 2 than in group 1 patients, despite a low mean PCWP-COP gradient, indicating greater alveolocapillary membrane permeability membrane in noncardiac, than in cardiac edema. Furthermore, 111In-DTPA clearance was linearly correlated with the PCWP-COP gradient in both groups (group 1, R2 = 0.726, P less than 0.001; group 2, R2 = 0.879, p less than 0.001 as was the clearance of 125I-HSA in group 2 (R2 = 0.35, P less than 0.027). Clinically, the data suggest that in cardiac and noncardiac pulmonary edema the transmicrovascular flux of small and large solutes may be favorably influenced by therapeutic alterations aimed at widening the intravascular PCWP-COP gradient. However, the greater permeability of the alveolocapillary membrane in noncardiac edema would prohibit any major resolution of edema by simple therapeutic alterations of this gradient.