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Biomedical Engineering Program, University of Texas at Arlington, Arlington 76019; and Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235
Received 22 March 1996; accepted in final form 14 February 1997.
Frank, Andreas O., C. J. Charles Chuong, and Robert L. Johnson. A finite-element model of oxygen diffusion in the
pulmonary capillaries. J. Appl.
Physiol. 82(6): 2036-2044, 1997.
We determined the overall pulmonary diffusing capacity
(DL) and the diffusing capacities of the alveolar membrane (Dm) and the red blood cell (RBC)
segments (De) of the diffusional pathway for
O2 by using a two-dimensional
finite-element model developed to represent the sheet-flow
characteristics of pulmonary capillaries. An axisymmetric model was
also considered to assess the effect of geometric configuration. Results showed the membrane segment contributing the major resistance, with the RBC segment resistance increasing as
O2 saturation
(SO2) rises during the RBC transit:
RBC contributed 7% of the total resistance at the capillary inlet
(SO2 = 75%) and 30% toward the
capillary end (SO2 = 95%) for a 45%
hematocrit (Hct). Both Dm and DL
increased as the Hct increased but began approaching a plateau near an
Hct of 35%, due to competition between RBCs for
O2 influx. Both Dm and
DL were found to be relatively insensitive (2~4%) to changes in plasma protein concentration (28~45%). Axisymmetric results showed similar trends for all Hct and
protein concentrations but consistently overestimated the diffusing
capacities (~2.2 times), primarily because of an exaggerated air-tissue barrier surface area. The two-dimensional model correlated reasonably well with experimental data and can better represent the
O2 uptake of the pulmonary
capillary bed.
finite-element method modeling; hematocrit; plasma protein concentration
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