>3 6 ° 



HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



found to be equal. Radial, median, and ulnar nerve 

 blocks were performed in one arm, above the elbow, 

 and the rate of the blood flow doubled in that limb. 

 Nerve blocks did not affect the rate of the blood flow 

 in the sympathectomized forearm. Therefore the 

 doubling of the flow in the normal forearm must 

 have been due to blocking sympathetic vasocon- 

 strictor fibers. Whereabouts were the vessels supplied 

 by these fibers? Nerve block doubled forearm blood 

 flow after the circulation in the skin had been arrested 

 by adrenaline electrophoresis. Therefore the release 

 of vasoconstrictor tone was deep to the skin, probably 

 in the skeletal muscles. Other authors have confirmed 

 this (166). It is interesting to note that brachial 

 plexus block is followed by an even greater increase 

 in forearm flow (23). Release of vasoconstrictor tone 

 in all muscles would increase the circulation through 

 the skeletal muscular system by 1.5 liter per min — the 

 increase in severe exercise is far greater, about 20 

 liter per min (21). Sympathetic vasoconstrictor tone 

 is also present in the resting muscle of the cat (13), 

 dog (10), and man (21), and probably in the muscle 

 vessels of all other mammals. 



EFFECT OF SYMPATHETIC VASOCONSTRICTORS UPON 

 RESISTANCE, BLOOD VOLUME, AND CAPILLARY FILTRA- 

 TION in skeletal muscle vessels. So far we have seen 

 that the vasoconstrictor fibers in muscle can increase 



the resistance to flow. They can also reduce capillary 

 filtration and increase venous constrictor tone. A 

 beautiful preparation shown in figure 7 has been 

 developed by Mellander (149) for simultaneous re- 

 cording of these effects. These studies will be briefly 

 described. They concern the effects of stimulation 

 of the abdominal sympathetic chain upon the cir- 

 culation in the hind parts of the cat — almost the whole 

 of the cat distal to the fifth lumbar vertebra. This 

 part of the cat consisted of skin, muscle, and bone in 

 the proportions of 1:4:1. The circulation through 

 bone could be neglected and the hind parts could be 

 regarded as a "combined skin-muscle region," a 

 few experiments with rather similar results were 

 made on skinned hind parts or "muscle regions." 

 Figure 8 shows a typical tracing. The arterial in- 

 flow pressure was maintained constant, by means 

 of a screw clip, at 120 mm Hg. Atropine was given 

 to exclude the action of the vasodilator fibers. The 

 abdominal sympathetic was stimulated for periods of 

 1 min, indicated by the signal marker, at the dif- 

 ferent frequencies shown on the tracing. The tracing 

 also shows the corresponding changes in the volume 

 of the hind parts, which were enclosed in a plethysmo- 

 graph communicating with a piston recorder. During 

 stimulation the hind parts shrank rapidly at first 

 and then more slowly. The initial rapid shrinking, 

 shown bv an almost vertical downstroke of the lever, 



KYMOGRAPH 



VOLUME PISTON RECORDER 



GADDUM RECORDER 



PLETHYSMOGRAPH 



SYMP. CHAINS 



TO INF. MESENT ART 



TO INF. CAVAL VEIN 

 FROM CAVAL VEIN 



HEATING PAD 



fig. 7. Preparation used by Mellander to investigate the effect of sympathetic vasoconstrictor nerve 

 stimulations upon vascular resistance, blood volume and capillary filtration rate in skeletal muscle 

 vessels. [After Mellander (149).] 



