CIRCULATION IN SKELETAL MUSCLE 



1367 



LIGATURE 



fig. 13. Preparation used for investigating the effect of 

 hypothalamic stimulation in the skin and skeletal muscle of the 

 dog's hind limb. [After Eliasson el at. (78).] 



fibers exist and are activated during fainting and 

 emotional stress. During fainting, the vasovagal 

 syndrome, induced experimentally by hemorrhage, 

 the arterial blood pressure falls precipitously but 

 blood flow in the forearm increases. There must be 

 marked vasodilatation in the forearm (24). This 

 vasodilatation is absent in sympathectomized fore- 

 arms and is mediated by sympathetic fibers. It is 

 probably in the skeletal muscles, although this has 

 not yet been examined with the Hensel needle, or by- 

 observations of the changes in oxygen saturation 

 of the blood draining from the deep forearm veins, 

 or by inducing faints in subjects after arresting most 

 of the circulation in the forearm skin by adrenaline 

 electrophoresis. Is the vasodilatation due to inhibition 

 of sympathetic vasoconstrictor tone or to activation 

 of sympathetic vasodilator fibers? It is difficult to 

 devise a satisfactory experiment to decide which is 

 responsible. During the faint the average blood 

 flow in six nerve-blocked forearms was less than that 

 in six normally innervated forearms. Therefore it 

 seems likely that vasodilator fibers were activated 

 (22). However, in the cat simple inhibition of vaso- 



constrictor tone causes fall in arterial blood pressure 

 accompanied by increase in muscle blood flow (Fol- 

 kow, personal communication). 



It is worth noting that the vasodilatation in muscle 

 in fainting is probably large enough to be mainly 

 responsible for the fall in blood pressure and so for 

 loss of consciousness (24). 



Vasodilators to human muscle are probably acti- 

 vated in emotional stress. Wilkins and Eichna found 

 that calf blood flow increased when a subject was 

 given a mental arithmetic problem which took him 

 about 15 sec to solve. They thought that this vaso- 

 dilatation was mediated both by the sympathetic 

 nerves and by adrenaline secretion (179). Others 

 have studied the effect on forearm blood flow of 

 harassing subjects with mental arithmetic problems 

 for several minutes. They have shown with the Hen- 

 sel needle that the vasodilatation is in the forearm 

 muscles (44,83, 111), and that the response is re- 

 duced, though not abolished by atropine, so that 

 it is probably mediated to some extent by activity 

 in vasodilator fibers (16, 42). 



Blair et al. (37) frightened subjects by telling them 



BLOOD PRESSURE 



160 



mmHg 140 



I20 



MUSCULAR 

 BLOOD FLOW 



LEFT HIND LIMB 



SIGNAL 

 TIME 6OSEC 



CUTANEOUS 

 BLOOD FLOW 



RIGHT HIND LIMB 



SIGNAL 

 TIME 60 SEC 



fig. 14. Results obtained with the preparation shown in fig. 

 13. Stimulation of part of the hypothalamus caused vaso- 

 dilatation in the skeletal muscles and vasoconstriction in skin of 

 the hind limb. Section of the lumbar spinal cord did not abolish 

 these effects which were mediated by the sympathetic chains. 



