Pressure measurements in the mammalian microvasculature

The servo nulling system for measuring pressures in the microvasculature system described by Wiederhielm was redesigned and utilized to measure pressures in the mammalian mesentric circulation, the hamster cheek pouch, and the rat cremaster muscle. A systems analysis of the components shows that direct-pressure measurements of suitable fidelity can be made with conventional transducers through microcannulas down to 10–15 μ diameter, and that for smaller diameters active systems are required. The system developed operates with a 25-Hz frequency response in the presence of routine electrical noise. Results obtained show that pressures in arterioles and venules in the mammalian mesenteric circulation are greater than the plasma colloidal osmotic pressure, while in corresponding vessels in muscle, venular pressures are lower than the colloidal osmotic pressure.