Cardiovascular reflex adjustments to static muscular contractions in the canine hindlimb.

FISHER, MICHAEL L., AND DONALD 0. NUTTER. Cardiovascular reJlex adjustments to static muscular contractions in the canine hindlimb. Am. J. Physiol. 226(3) : 648-655. 1974.-The cardiovascular response to 30-s tetanic muscular contractions was studied in the anesthetized dog. A significant systemic pressor reflex occurred during handlimb contractions evoked by both spinal ventral nerve root (Ls L7) stimulation and tibia1 nerve stimulation. The pressor reflex was associated with a small increase in heart rate and significant increases in stroke volume, cardiac output, and left ventricular contractility. A small net decline was calculated for systemic resistance. In contrast, the baroreceptor pressor reflex evoked by carotid arterial occlusion involved a significant increase in systemic resistance and small, variable changes in stroke volume and cardiac output. Static contractions increased local venous potassium concentration, osmolality, and Pcog while Pop and pH fell. Limb venous potassium and osmolality levels in excess of those resulting from static contractions were produced by the close intra-arterial infusion of potassium and hyperosmolar solutions, and with the exception of glucose infusions resulting in a venous osmolality elevation disproportionate to that observed during static exercise, did not evoke a systemic pressor response. A multifactorial trigger mechanism for the static exercise reflex is suggested by these data.