Responses of the Vasomotor Center to Hypoxia After Denervation of Carotid and Aortic Bodies

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Abstract
The expts. show the reactions of the chemoceptively deafferented vasomotor center to hypoxia as indicated by changes of blood flow in a limb (dog). separately perfused under controlled hemodynamic conditions and connected to the body only by its nerves. The reactions are assumed to indicate the direct action of hypoxia upon the center. Though markedly attenuated as compared with those of intact animals, the reactions of the chemoceptively deafferented vasomotor center to hypoxia included both excitation and depression. Excitation appeared most frequently, being present in 75 of 97 hypoxic episodes in 10 of 11 animals. Depression dominated in 13 of 97 reactions. In 29, excitation dominated at some phase and depression at others. It is suggested that oxygen deficiency simultaneously exerts 2 separate and opposite influences upon vasomotor neurons, one excitatory and the other depressant, the activity of the center at any stage of hypoxia reflecting their algebraic sum, and varying patterns of response reflecting varying balance between them resulting from their different rates of development and different relative intensities with different degrees of hypoxia. The expts. also demonstrate powerful hypoxic hypotensogenic factors acting independently of the vasomotor center which the excitatory action of hypoxia upon the center is unable to counteract in the absence of carotid-aortic chemoreflex support.

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