Range of Sympathetic Discharge and Reflex Vascular Adjustments in Skeletal Muscle during Hemorrhagic Hypotension

Abstract

Abstract Lundgren, O., J Hemorrhage is associated with an increase in the sympathetic vasoconstrictor fiber discharge to skeletal muscle, ranging from values below 1 imp/sec up to about 7 implsec, the rate of discharge being related to the extent of bleeding. The reflex increase in sympathetic activity is, as a rule, fairly well maintained during prolonged hemorrhage. Normally, this elicits a reflex constriction of resistance and capacitance vessels and an increase in the pre‐/post‐capillary resistance ratio leading to decreased capillary pressure and absorption of extravascular fluid. The constriction of the capacitance vessels and the fluid absorption both tend to compensate for the reduction of intravascular fluid volume in the early phase of hemorrhage. However, there is a gradual decline in the reflex vascular response, despite maintained vasoconstrictor fiber discharge, evidently due to competitive action of locally produced dilator factors. This decline is more pronounced the more severe the reduction in muscle blood Row accompanying hemorrhage. The decline is more pronounced in the precapillary vessels than in postcapillary vessels. Therefore, in the later stages of hemorrhage the pre‐/postcapillary resistance ratio may decrease to such an extent that fluid escapes from the circulation by filtration, leading to further derangement of cardiovascular function.