The Renal Blood Flow 



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FIGURE 5 

 Figure J. The eflfective renal plasma flow, etc., during syncope induced by the sus- 

 tained upright posture in a hypertensive subject. Legend as in Figure 1. Note the slow- 

 ing of the heart rate (HR) which accompanies the fall in blood pressure. 



plays an important part. This experiment leaves us in no 

 doubt as to the possibility of nervous vasoconstriction in the 

 kidney, in spite of the primal autonomy of the renal circu- 

 lation. 



Again, I would like to comment in passing on a related 

 aspect of this experiment. It is frequently stated that ortho- 

 static syncope is caused by arteriolar dilatation following 

 vasomotor failure. But you will notice that the blood pres- 

 sure of the subject shown here gives no evidence of vasodila- 

 tation; rather he displays a picture of progressively decreasing 

 venous return with consequent decreasing cardiac output, 

 the arterioles seemingly remaining constricted to the end. 

 Though we cannot assert that it is invariably true, syncope in 

 this case was accompanied by a marked slowing of the heart, 



