Active oxygen transport in tissue by interstitial flow

Oxygen (O2) transport through diffusion from capillary to tissue has long been established by Krogh. However, the interstitial fluid in the interspace between tissue and capillary has a high Prandtl number around 103 and hence its convective mass transport is more efficient than its diffusive transport. The interstitial flow drained by the initial lymphatics contributes to the convective transport of O2 through tissue, which can be modeled as aligned blood capillaries in parallel and the initial lymphatics. It is found that both the O2 concentration distribution and the total O2 flux are sensitive to the flow rate of interstitial fluid. The convection contribution has been evaluated based on the Peclet number, feature flow rate, and convection-diffusion boundary. At the same interstitial flow rate, convection delivers more O2 to type I muscle fibers with a higher concentration of myoglobin than to type IIX muscle fibers. Even with a small external force, tissue with a higher specific hydraulic conductance (permeability) has a larger interstitial flow rate and a higher O2 transport rate than those in healthy tissue. Hence, the overall O2 transport from capillary to tissue includes two components, i.e., active convection transport by interstitial flow due to pressure gradient and passive diffusion transport due to concentration gradient. The active convective O2 transport is crucial for the recovery of damaged tissue where the contribution from passive diffusion transport is constrained by regulation of capillary opening. The convection facilitated O2 transport can be the basis for cell differentiation, morphogenesis, and therapeutic effects of massage and acupuncture. Key pointsO_LIInterstitial flow plays a key role in active O2 transport in tissue due to its high Prandtl number v/D~103; C_LIO_LIO2 transport in tissue is balanced by both active convection and passive diffusion transport. C_LIO_LIInterstitial flow in form of active convective transport can pump more than hundred times of O2 into tissue than those by passive diffusion transport due to the concentration gradient. C_LIO_LIActive convection transport can be triggered by external pressure, which is crucial for damage tissue recovery. C_LI