Similarity of Blood Flow in the Normal and the Sympathectomized Dog Hind Limb during Graded Exercise

Abstract

The possibility of sympathetic vasoconstrictor control of blood flow to active muscles was studied in dogs during graded exercise by comparing the blood flow in the normal with that in the Sympathectomized hind limb. Blood flow was measured by electromagnetic flow transducers around each external iliac artery, or inferred from the oxygen saturation of blood samples from the common iliac veins. The dogs either ran for successive periods of 3 minutes at 5.5 km/hr and grades of 0, 7, 14, 21, and 28% or ran each level of exercise separately. Unilateral lumbar sympathectomy (L-2 through L-7) was performed when the flow transducers were implanted or later by a snare technique. The latter allowed observations during exercise as early as 4 hours after sympathectomy. The magnitude of limb blood flow during exercise and the decline of exercise hyperemia were similar in the normal and the sympathectomized limb, as were the changes in the oxygen saturation of limb venous blood. However, electric stimulation of the lumbar sympathetic chain at the L-5 level in the conscious dog by a chronically implanted electrode reduced limb blood flow at all levels of exercise, the maximal flow of 1,000 ml/min was almost halved.