528 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



pathways does play a highly important role in the 

 control of cardiac output. This mechanism is in 

 addition to, but can hardly be held to be operating 

 to the exclusion of the fiber length-stroke work 

 relation. 



Lastly, it remains to consider the elements con- 

 cerned with the gathering of information on the basis 

 of which it is possible for the integrating network 

 appropriately to exploit the command system. In 

 this presentation, the carotid sinus has been put forth 

 as one important type of information gathering 

 element. It is hardly to be imagined that there are 

 not many others which are important and which 

 differ from each other not only qualitatively but also 

 in the relative dominance that each may acquire 

 under varying circumstances. Centrally placed chemo- 

 receptors must surely play an important role; the 

 powerful and diffuse reflex sympathetic effects 

 observed after stimulation of the central cut end of 

 the vagi can be thought likely to ha\'e some signifi- 

 cance other than that of simply conveying a noxious 

 stimulus even though a nerve carrying pain is, of 

 course, a significant information gathering element. 

 Peripherally placed receptors in muscles have also 

 been suggested (52). It would be difficult to imagine 

 that the senses of sight, hearing, smell, taste, and touch 

 do not also have access to the command system of the 

 circulation. The helpful work of Rushmer and his 

 colleagues (90, 91, iio) has done much to elucidate 

 the pathways over which supratentorial influences 

 can activate and exploit the command system of the 

 circulation in the ambient experimental organism, 

 a basic fact of importance apparent to any physician 

 who has measured the heart rate and blood pressure 

 of the so-called labile individual. The effects of 

 emotion, frustration, and conditioning on the circula- 

 tion, an expanding area of investigation, must yield 



increasingly profitable data not only in the under- 

 standing of normal physiology but in the understand- 

 ing of disease processes. It is to be expected that in- 

 formation gathering elements which reflexly produce 

 an anticipatory augmentation of the circulation will 

 be of special interest. When, as the result of visual, 

 olfactory, auditory, tactile, or painful stimulation, the 

 circulatory rate is increased in advance of the actual 

 need for an increased metabolic support of peripheral 

 tissues, such a reaction has obvious survival value 

 under situations of physical conflict or flight, and is 

 teleologically appropriate. Whether or not a circula- 

 tory architecture that has been evolved in relation to 

 an adaptation to varying physical challenges is also 

 as appropriate in an organism where the stresses are 

 predominantly of the emotional t)'pe will be one of the 

 interesting questions to be more precisely attacked 

 in the ensuing decades. The immediacy of a second 

 important question is, in some ways, even more 

 keenly felt. Namely, to what extent will a circulatory 

 architecture which, in its total evolutionary history, 

 has adapted to a i ^ environment function ade- 

 quately in the absence of gravity. 



In any case it has been our goal herein to systema- 

 tize certain of the criteria by means of which a more 

 effective and detailed examination of the command 

 system of the circulation can be made, and to exhibit 

 one example of the large effects to be obtained from 

 the stimulation of one important information gather- 

 ing element. It would be our hope that the effects of 

 such an attempted systematization might be to 

 facilitate a more critical and effective evaluation of 

 other information gathering elements both above and 

 below the tentorium. 



Grateful acknowledgment is made to Circulation Research 

 and American Journal of Cardwtoiiy for permission to reproduce 

 many of the figures used in this chapter. 



REFERENCES 



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4. Anrep, G. V. Regulation of the coronary circulation. 

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■955- 



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