Layers of interstitial fluid flow along a “slit-shaped” vascular adventitia

Abstract

Objective: Interstitial fluid flow through vascular adventitia has been disclosed recently. However, its kinetic pattern was unclear. Methods and Results:We used histological and topographical identifications to observe ISF flow along venous vessels in rabbits. By MRI in alive subjects, the inherent ISF flow pathways in legs, abdomen and thorax were enhanced by paramagnetic contrast from ankle dermis. By fluorescence stereomicroscopy and layer-by-layer dissection after the rabbits were sacrificed, the perivascular and adventitial connective tissues (PACT) along the saphenous veins and inferior vena cava were found to be stained by sodium fluorescein from ankle dermis, which coincided with the findings by MRI.By confocal microscopy and histological analysis, the stained PACT pathways were verified to be the fibrous connective tissues and consisted of longitudinally assembled fibers. By usages of nanoparticles and surfactants, a PACT pathway was found to be accessible for a nanoparticle under 100nm and contain two parts: a tunica channel part and an absorptive part. In real-time observations, the calculated velocity of a continuous ISF flow along fibers of a PACT pathway was 3.6-15.6 mm/sec. Conclusion:These data further revealed more kinetic features of a continuous ISF flow along vascular vessel. A multiscale, multilayer, and multiform "interstitial/interfacial fluid flow" throughout perivascular and adventitial connective tissues was suggested as one of kinetic and dynamic mechanisms for ISF flow, which might be another principal fluid dynamic pattern besides convective/vascular and diffusive transport in biological system.

An acupoint-originated human interstitial fluid circulatory network

“…ISF can circulate via the PACT pathways along the vascular vessels around the body: Using the in vivo imaging technique and histological identification, the ISF flow along vascular adventitia has been identified in several veins and arteries of systemic and pulmonary circulation. [ 23 , 24 ] In rabbits, the peripheral ISF in the ankle dermis was found to flow constantly along the veins in the lower extremity veins, inferior vena cava in the abdomen and thorax, and into the epicardium forming pericardial fluid. [ 23 ] The velocity of the constant adventitial ISF flow was estimated as 3.6 to 15.6 mm/s.…”

“…[ 23 ] The velocity of the constant adventitial ISF flow was estimated as 3.6 to 15.6 mm/s. [ 24 ] Meanwhile, the peripheral ISF was found to enter the capillaries or lymphatic vessels and merged into blood circulation. [ 23 , 24 ] A constant ISF flow along the veins and arteries of lower limbs was also observed in mice as well.…”

“…[ 24 ] Meanwhile, the peripheral ISF was found to enter the capillaries or lymphatic vessels and merged into blood circulation. [ 23 , 24 ] A constant ISF flow along the veins and arteries of lower limbs was also observed in mice as well. [ 25 ] In the rabbit pulmonary circulation, the ISF flow was found to flow along the pulmonary vein from the lung toward the heart.…”

“…[ 25 ] In the rabbit pulmonary circulation, the ISF flow was found to flow along the pulmonary vein from the lung toward the heart. [ 24 ]…”

“…Under a confocal laser microscope, the venous adventitia was found to comprise abundant fluorescently stained fibers and their surrounding gel-like matrix, which were the results of the fluorescent ISF flowing in the PACT pathways. [ 24 ] In the fibrous matrix, neither the fibers nor the fascia nor the gel can flow. We named the spaces in the PACT pathways for the constant ISF flow as an “interfacial zone or interspace” between a solid phase (a fiber or fascia) and a liquid phase (the gel/liquid substance).…”