title: Effects of flow heterogeneity on the measurement of capillary exchange in the lung.
abstract: The effects of flow heterogeneity on the measurement of transcapillary escape of small molecules for perfused in situ sheep lungs were evaluated. Lungs were studied at five flows (1.5-5.0 l/min) ranging from zone 1 to zone 3 conditions. At each flow, multiple indicator-dilution curves were collected using 14C-labeled urea (U) or butanediol (B) as the diffusing tracer, and radiolabeled 15-microns microspheres were injected. The lungs were removed, dried, sectioned, weighed, and counted for microsphere radioactivity. Flow heterogeneity expressed as relative dispersion, decreased with increasing flow, from 0.838 +/- 0.179 (mean +/- SD, n = 8) to 0.447 +/- 0.119 (n = 6). We applied homogeneous flow models of capillary exchange to compute permeability-surface area product (PS) and a related parameter, D1/2S, for diffusing tracers. (D is effective diffusivity of capillary exchange.) PS and D1/2S increased to a maximum with increasing flow, but the ratio of D1/2SU to D1/2SB remained constant. A new model incorporating flow heterogeneity and recruitment (the variable recruitment model) was used. The variable recruitment model described the effects of flow on capillary recruitment, but incorporating heterogeneity into the computation did not alter D1/2S values from those computed assuming homogeneous flow.
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Caruthers
authors.forename: T R
authors.initials: TR
authors.lastname: Harris
authors.forename: K A
authors.initials: KA
authors.lastname: Overholser
authors.forename: N A
authors.initials: NA
authors.lastname: Pou
authors.forename: R E
authors.initials: RE
authors.lastname: Parker
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D002199:Capillary Permeability / Q000502:physiology*; D002250:Carbon Radioisotopes; D008168:Lung / Q000098:blood supply* / Q000502:physiology; D008863:Microspheres; D008955:Models, Cardiovascular; D011652:Pulmonary Circulation / Q000502:physiology*; D012756:Sheep
chemical_list: D002250:Carbon Radioisotopes