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 in human skeletal muscle. The interaction between these systems where one system can override or modify the other makes blood flow regulation complicated. Determinations of muscle blood flow can thus be challenging especially when considering the shortcomings and limitations of the available measurement methods. This thesis focuses on two different topics of which both are dependent on sympathetic tone.

First, the common use of venous occlusion plethysmography (VOP) with only one strain gauge attached per limb is a method with obvious pitfalls. The inherent problems with this simplification of the original VOP method are highlighted in Study I-II where small variations in sympathetic tone and venous pressure proved to have a considerable influence on the results. The basic circumstance to this variability is the curvo-linear pressure/volume relationship in the veins and the fact that redistribution of blood can occur between individual limb segments. The results clearly demonstrate that events taking place under one 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 local blood flow response to adrenaline. Two studies were conducted to test if an acute small muscle injury (Study III) and chronic muscle damage (Study IV) influences the normal blood flow effect of adrenaline. In support of the hypothesis we found that the microdialysis catheter-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 no significant change in blood flow was seen with adrenaline-infusion in the absence of the catheter (conventional 133Xe administration). The adverse adrenaline effect is likely to be related to the degree of invasiveness. Hence, it would be expected that any type of invasive measuring device causing a muscle injury could possibly provoke a similar reaction. This finding has a general physiological implication, but has also implications for the use of invasive techniques to study blood flow regulation in skeletal muscle.

Previous studies of tennis elbow (TE) have reported signs of diffuse muscle damage and decreased blood flow in the affected extensor carpi radialis brevis (ECRB) muscle. We conducted a case-control study (IV) to test the hypothesis that the muscle damage in the ECRB in TE alters the blood flow response to adrenaline in a vasoconstrictory direction. Muscle blood flow was determined with local clearance of 99mTechnetium during an i.v. infusion of adrenaline. In support of the hypothesis, the blood flow reaction to adrenaline was markedly different in the two study groups. Whereas the infusion did not significantly influence 99mTechnetium-clearance in the ECRB of controls there was a significantly decreased clearance in the patients. The altered adrenaline effect indicates a vascular dysregulation in TE, which is likely to be of clinical significance by contributing to the development and maintenance of the chronic muscle pain in this large patient group. Whether the vasoregulatory alteration, which would be expected to involve recurring relative muscle ischemia, represents the primary aetiology 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 adrenaline on skeletal muscle blood flow in a vasoconstrictory direction.