Starling Forces | Pathway Medicine
Capillary Fluid Exchange - YouTube
When the capillary was occluded near to the venous end, the red cells upstream of the probe could be seen to oscillate in time with the heart beatand slowly pack towards the probe. When the occlusion was at the arterial end,the cells downstream of the probe could frequently be seen to move out of thevessel and into the venule. These observations were interpreted as evidence tosupport Starling's hypothesis since when the venous end of the capillary wasoccluded, the whole capillary was exposed to arteriolar pressure and filtrationof plasma resulted. When the arterial end was occluded, the capillary wasexposed to venular pressure and net absorption of interstitial fluid generallyoccurred. Landis assumed that the red cells fitted tightly in the capillary withno leak of plasma around the cell margin and that the capillary cross sectionwas circular; then from measurement of the speed of movement of the red cellsalong the capillary he was able to make direct estimates of the filtration andabsorption rates per unit area of capillary wall. These he related to the meancapillary hydrostatic pressure obtained by micropuncture of side branches of thevessel under observation. Results from his studies are presented in Fig.13.40.The slope of the line through the data is the filtration coefficient JH (volumeflow-rate, per unit time, area and pressure drop, see Chapter 9, ); thiswas found to be approximately 5.6 x 10-5 (m3m-2 s-1 N-1 m2.
The Revised Starling Principle and Its Relevance ..
The observation that the filtration coefficient varies along the length of themicrovascular bed means that the simple form of Starling's hypothesis cannot beused to model the behaviour of the whole exchange bed. The balance point mayhowever be computed from Equation (13.3), for at that point