Objective: To determine albumin exclusion from the pulmonary perivascular interstitium by using the continuous infusion methods coupled with direct samples of pulmonary interstitial fluid via the wick technique.
Methods: To evaluate extracellular albumin distribution volume, radioactive ((125)I) rabbit serum albumin (RSA) was delivered intravenously until reaching a steady-state tissue concentration. In anesthetized rabbits with ligated kidney pedicles, extracellular (V(x)) and intravascular (V(v)) fluid volumes were measured as the distribution volumes of (51)Cr-ethylenediaminetetraacetic a id and (131)I-RSA, respectively. Post mortem, lung samples and interstitial fluid collected via implanted wicks were assayed for isotope activity. The extravascular wick fluid equivalent albumin distribution volume (V(a,w)) was calculated assuming equal concentrations of (125)I-RSA in interstitial and wick fluid.
Results: The mean (+/-SE) V(x), V(v), and interstitial fluid volumes (V(i) = V(x) - V(v)) were 1896 +/- 61 (n = 8), 556.8 +/- 19, and 1329 +/- 73 microL/g of blood-free dry lung tissue weight, respectively. The mean albumin-excluded volume (V(e,a) = V(i) - V(a,w) and the excluded fraction (V(e,a)/V(i)) were 875.8 microL/g +/- 58 and 0.66 +/- 0.05, respectively.
Conclusions: At variance with previous indirect reports, the present data indicate that normal pulmonary parenchyma displays a tight fibrous structure that is highly restrictive with respect to plasma protein distribution.