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

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Abstract
The integrity of the alveolocapillary membrane in human cardiac (hydrostatic) (group 1) and noncardiac (permeability) (group 2) edema was examined by measuring the clearance of 2 i.v. radiotracers from the blood to suctioned bronchoalveolar secretions (BAS), representing pulmonary edema fluid. The clearances were compared to simultaneously measured pulmonary capillary wedge pressure (PCWP) and colloid osmotic pressure (COP), representing the intravascular Starling forces, Pmv and .pi.mv. 111In-labeled diethylenetriamine pentaacetic acid (DTPA), MW 504, a hydrophilic radiotracer that equilibrates with extracellular water, and 125I-labeled human serum albumin (HSA), MW 69,000, were injected i.v. Samples of blood and BAS were then collected hourly for 4-5 h and clearances were calculated. The clearance of both radiotracers was 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. 111In-DTPA clearance was linearly correlated with the PCWP-COP gradient in both groups (group 1, r2 = 0.726, P < 0.001; group 2, r2 = 0.879, P < 0.001) as was the clearance of 125I-HSA in group 2 (r2 = 0.35, P < 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. The greater permeability of the alveolocapillary membrane in noncardiac edema would prohibit any major resolution of edema by simple therapeutic alterations of this gradient.