Mechanics of a thin walled collapsible microtube.
The purpose of this study is to measure the transmural pressure-cross sectional area relation of micro tubes (240 microns diameter) and to compare the measured perfusion pressure-flow relation with the pressure-flow relation calculated from the experimental pressure-cross sectional area relation. The microtubes are made by dipping a glass mould in a latex solution and glueing their outside ends to the inside of glass pipettes. The pressure-cross sectional area relation is determined both with a microplethysmograph (pressure-volume relation) and the microscope (pressure-diameter relations). Heparinized blood is used to include the rheological properties of blood as a perfusion medium. Static pressure-flow relations are obtained with a constant velocity piston pump for two values of external pressure (0 and 10 kPa) and with two downstream resistor settings (0 and 380 kPa cm-3 sec). The calculated pressure-flow relations using length and the experimental pressure-cross sectional area relation, Poiseuille's law, and accounting for the diameter- and shear-dependent viscosity compared well with the relations obtained from the experiments. It is also found that the pressure-flow relation shows an apparent zero flow pressure axis intercept (the extrapolation of the pressure-flow relation to the pressure axis), which can therefore be explained on the basis of the shape of the pressure-area relations.
Sipkema
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Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
Westerhof
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D006439:Hemodynamics; D008432:Mathematical Computing; D008833:Microcirculation / Q000502:physiology*; D008955:Models, Cardiovascular; D008961:Models, Structural; D012039:Regional Blood Flow; D012212:Rheology