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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



FIG. I. Walter Holbrook Gaskell, 1847-1914. 



crease in flow; then, following contraction; d) a 

 check in the rate of the stream while the veins re- 

 filled; e) a further large increase in flow; and finally 

 /) gradual restoration of the flow to the resting rate. 

 It is interesting to compare Gaskell's record with 

 that seen in figure 2 (bottom), which was made by 

 Kramer & Quensel (131) 50 years later. They deter- 

 mined the venous outflow of the dog's gastrocnemius 

 with a hot-wire anemometer. Kramer and his 

 colleagues recognized the following changes in out- 

 flow during maximal tetanic stimulation of the motor 

 nerve: a) an initial peak due to expression of blood; 



b) decrease in flow due to mechanical compression; 



c) increase in flow; then, after relaxation, d) transitory 

 decrease while the vessels refilled; e) hyperemia 

 reaching the maximum; /) restoration of the flow 

 to the resting rate. The agreement between Gaskell's 

 and Kramer's records is remarkable, the main dif- 

 ference being that the postexercise flow was greater 

 in Gaskell's experiment. Presumably in his experi- 

 ment the muscle had contracted more powerfully 

 during stimulation. 



So much for tetanic contraction. Figure 22 shows 

 the changes during rhythmic contraction. The record 

 is from another experiment of Kramer's (132). The 

 motor nerve to the gastrocnemius was stimulated for 

 1 sec every alternate sec for 5 min. Venous outflow- 

 increased rapidly during the first minute to reach a 

 steady level. Further increase in outflow occurred 

 immediately after the exercise because the stream 

 was no longer checked repetitively by mechanical 

 compression. Then after a few seconds it subsided to 

 the resting rate. 



In man the changes in flow in the forearm muscles 



during strong sustained contraction were determined 

 by Grant (113), who recorded the rate of the blood 

 flow by venous occlusion plethysmography. An ex- 

 cellent description of the method has been published 

 by Greenfield (114). Grant's subject gripped an iron 

 bar as hard as possible for 1 min. There was a small 

 increase in flow during the exercise and a large one 

 afterward. The vasodilatation during contraction was 

 not conspicuous because of compression of the vessels 

 I iv the contracted muscle. As soon as the muscle 

 relaxed, compression ceased and then blood flowed 

 rapidly into the veins. 



During strong contraction of the human gastroc- 

 nemius soleus the effect of mechanical compression 

 of the muscle vessels may stop the flow. For example, 

 when one is standing tiptoe on the ball of one foot, 

 supporting the whole weight of the body by contrac- 

 tion of the calf muscles, the blood flow in these 

 muscles is probably arrested. This was inferred from 

 records of the changes in temperature in these muscles 

 made while the subject was standing on tiptoe (28). 

 The length of time one can stand tiptoe on one leg 



MINUTES 



fig. a. Top: Changes in venous outflow from the extensor 

 group of muscles of the dog*s leg, during (R-R) and after 

 tetanic stimulation of the crural nerve. [From Gaskell (108).] 

 Bottom: Changes in the venous outflow from the gastrocnemius 

 muscle of the dog recorded during (R-R) and after tetanic 

 stimulation of the sciatic nerve. [From Kramer & Quensel 

 O3O.] 



