Blood Flow in Human Skeletal Muscle The Effect of Adrenaline and the Influence of a Small Muscle Injury
Abstract: A variety of vasoregulatory systems are involved in the complex control of blood flow inhuman skeletal muscle. The interaction between these systems where one system canoverride or modify the other makes blood flow regulation complicated. Determinations ofmuscle blood flow can thus be challenging especially when considering the shortcomingsand limitations of the available measurement methods. This thesis focuses on two differenttopics of which both are dependent on sympathetic tone.First, the common use of venous occlusion plethysmography (VOP) with only one straingauge attached per limb is a method with obvious pitfalls. The inherent problems with thissimplification of the original VOP method are highlighted in Study I-II where small variationsin sympathetic tone and venous pressure proved to have a considerable influence on theresults. The basic circumstance to this variability is the curvo-linear pressure/volumerelationship in the veins and the fact that redistribution of blood can occur betweenindividual limb segments. The results clearly demonstrate that events taking place underone strain gauge cannot be strictly duplicated in adjacent portions of the limb.Secondly, recent reports have indicated that a minor muscle trauma might change the localblood flow response to adrenaline. Two studies were conducted to test if an acute smallmuscle injury (Study III) and chronic muscle damage (Study IV) influences the normal bloodflow effect of adrenaline. In support of the hypothesis we found that the microdialysiscatheter-induced muscle injury in Study III caused a significant vasoconstriction during an i.v.adrenaline infusion, as measured with 133Xenon clearance next to the catheter, whereas nosignificant change in blood flow was seen with adrenaline-infusion in the absence of thecatheter (conventional 133Xe administration). The adverse adrenaline effect is likely to berelated to the degree of invasiveness. Hence, it would be expected that any type of invasivemeasuring device causing a muscle injury could possibly provoke a similar reaction. Thisfinding has a general physiological implication, but has also implications for the use ofinvasive techniques to study blood flow regulation in skeletal muscle.Previous studies of tennis elbow (TE) have reported signs of diffuse muscle damage anddecreased blood flow in the affected extensor carpi radialis brevis (ECRB) muscle. Weconducted a case-control study (IV) to test the hypothesis that the muscle damage in the ECRBin TE alters the blood flow response to adrenaline in a vasoconstrictory direction. Muscleblood flow was determined with local clearance of 99mTechnetium during an i.v. infusion ofadrenaline. In support of the hypothesis, the blood flow reaction to adrenaline was markedlydifferent in the two study groups. Whereas the infusion did not significantly influence99mTechnetium-clearance in the ECRB of controls there was a significantly decreased clearancein the patients. The altered adrenaline effect indicates a vascular dysregulation in TE, which islikely to be of clinical significance by contributing to the development and maintenance of thechronic muscle pain in this large patient group. Whether the vasoregulatory alteration, whichwould be expected to involve recurring relative muscle ischemia, represents the primaryaetiology in TE or is a secondary effect of the muscle injury cannot be determined.In conclusion, a small muscle injury, acute or chronic, seems to alter the effect of adrenalineon skeletal muscle blood flow in a vasoconstrictory direction.
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