Cross circulation at the small blood vessel level in the dog paw

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Abstract
Small vessel responses to maximal sympathetic stimulation have been studied by establishing a cross circulation, at the small blood vessel level, between the two hind legs of the dog. This technique permitted the differentiation between vascular responses occurring upstream and downstream from the level of the cross circulation. Sciatic nerve stimulation stopped flow in both upstream and downstream arterial segments. Lumbar sympathetic trunk stimulation (which did not include all nerves supplying the digital vasculature) stopped flow in the upstream arteries, but allowed a restricted flow to continue in the downstream segments. Both lumber and sciatic nerve stimulation produced intense constriction of dorsal metatarsal and digital veins. Establishment of a cross circulation at either the dorsal metatarsal or dorsal digital vein level proved that in unstimulated vessels a retrograde flow from small vein to small artery was possible. During maximal sympathetic stimulation, constrictive closure of small veins prevented flow from occurring either upstream or downstream in metatarsal and digital veins until perfusion pressures were increased to approximately 100 mm Hg. Thus, constrictive closure of the venules protected the capillaries from the high small vein pressures developed during maximal sympathetic stimulation.

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