Cannulation and continuous cross-sectional area measurement of small blood vessels

Techniques have been developed for the study of isolated small arteries. To pressurize and perfuse segments of these vessels, a cannula with a low resistance to flow was developed. This cannula consisted of two concentric micropipettes. The end of a vessel segment was sucked into the inner pipette and clamped by applying subatmospheric pressure on the outer pipette. Subsequently, the vessel was pressurized via the inner pipette. To enable perfusion, the segment was cannulated at both ends. Mean cross-sectional area (CSA) of the cannulated segments was continuously measured using a fluorescence technique. The emission of light by fluorescein isothiocyanate (FITC) labeled dextran in the vessel lumen was measured using a photomultiplier tube (PMT). PMT current was linearly related to the vessel CSA. Twenty-nine rat mesenteric vessels with inside diameters ranging from 110 to 350 microns (mean 226 microns) when maximally dilated at 80 mm Hg were cannulated. CSA was monitored during variations in perfusion pressure and addition of vasoactive agents.