Cardiac output distribution during induced static muscular contractions in the dog.

Previous experiments in the dog have shown that static contractions of the muscles of one limb elicit a reflex increase of resistance in the vessels of the opposite limb, along with an increase of systemic blood pressure. The aim of the present experiments was to examine whether this reflex can cause a redistribution of cardiac output from the resting areas, in favor of the working parts. In 17 anesthetized and ventilated dogs, static contraction of the muscles of the right thigh was elicited with electrodes inserted into these muscles. The carotid sinuses were kept at constant pressure and the vagi cut. During static contractions systemic blood pressure and cardiac output increased by 17.7 +/- 3.1 and 24.2 +/- 5.5%, respectively. The blood flow measured with an electromagnetic flowmeter decreased by 21.9 +/- 5.3% in the femoral artery of the resting limb and increased by 101 +/- 21% in the femoral artery of the "active limb". Data obtained in six dogs with injection of radioactive microspheres during stimulations show that blood flow decreased not only in the muscles of the rising limb (34 +/- 10%), but also in several other resting areas, such as skin (38 +/- 8%), kidney (24 +/- 8%), gut (38 +/- 6%), and tongue (23 +/- 3%). The results show that the reflex under study causes a redistribution of the cardiac output during static muscular contractions.