Diffusion-dependent contribution to the slope of the alveolar plateau

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Abstract

Two healthy subjects performed single breath tests, the inspired gas containing 90% O2, 5% He and 5% SF6. The slope of the alveolar plateau was computed for N2, He and SF6. The following experimental conditions were considered variable: (1) preinspiratory lung volume (PILV) with inspired volume (VT) equal to 1 L, (2) VT with PILV equal to functional residual capacity (FRC) with and without 10 sec of breath-hold (BH) time, (3) VT with PILV = FRC + 1 L, (4) flow with VT = 1L and PILV = FRC with and without 10 sec end inspiration BH and (5) BH time with VT = 1 L and PILV = FRC. The slope dependence on the different variables was compared with simulations performed with two multibrach point models of the human acinus with different asymmetries. The model simulations give a coherent picture of all the experiment observations. The present work gives support to previous analyses which suggest that inter dependence of transport by convection and diffusion in the periphery of the lung is a major component of the slope of the alveolar plateau.

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