Alveolar epithelial surface area-volume relationship in isolated rat lungs

In vitro studies of the alveolar epithelial response to deformation require knowledge of the in situ mechanical environment of these cells. Because of the presence of tissue folding and crumpling, previous measurements of the alveolar surface area available for gas exchange are not equivalent to the epithelial surface area. To identify epithelial deformations in uniformly inflated lungs representative of the in vivo condition, we studied isolated Sprague-Dawley rat lungs (n = 31) fixed by perfusion with glutaraldehyde o n deflation after cycling three times at high lung volume (10-25 cmH(2)O). The epithelial basement membrane in 45 electron micrographs (x12,000)/rat w as traced, digitally scanned, and analyzed. Epithelial basement membrane su rface area (EBMSA) was computed from a morphometric relationship. EBMSA was found to increase 5, 16, 12, and 40% relative to EBMSA at 24% total lung c apacity at lung volumes of 42, 60, 82, and 100% total lung capacity, respec tively. The increases in EBMSA suggest that epithelial cells undergo signif icant deformations with large inflations and that alveolar basement membran e deformation may contribute to lung recoil at high lung pressures.