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PERSPECTIVES

Physiological determinants of the pulmonary filtration coefficient

Department of Physiology and Center for Lung Biology, College of Medicine, University of South Alabama, Mobile, Alabama

ABSTRACT

Current emphasis on translational application of genetic models of lung disease has renewed interest in the measurement of the gravimetric filtration coefficient (K_f) as a means to assess vascular permeability changes in isolated perfused lungs. The K_f is the product of the hydraulic conductivity and the filtration surface area, and is a sensitive measure of vascular fluid permeability when the pulmonary vessels are fully recruited and perfused. We have observed a remarkable consistency of the normalized baseline K_f values between species with widely varying body weights from mice to sheep. Uniformity of K_f values can be attributed to the thin alveolar capillary barrier required for gas exchange and the conserved matching of lung vascular surface area to the oxygen requirements of the body mass. An allometric correlation between the total lung filtration coefficient (K_f,t) and body weight in several species (r² = 1.00) had a slope that was similar to those reported for alveolar and pulmonary capillary surface areas and pulmonary diffusion coefficients determined by morphometric methods in these species. A consistent K_f is dependent on accurately separating the filtration and vascular volume components of lung weight gain, then K_f is a consistent and repeatable index of lung vascular permeability.

capillary permeability; vascular surface area; hydraulic conductivity