Relative latency of responses of chemoreceptor afferents from aortic and carotid bodies

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Abstract
Discharges from aortic and carotid body chemoreceptor afferents were simultaneously recorded in 18 anesthetized cats to test the hypothesis that aortic chemoreceptors, because of their proximity to the heart, respond to changes in arterial blood gases before carotid chemoreceptors. Carotid chemoreceptor responses to the onset of hypoxia and hypercapnia, and to the i.v. administered excitatory drugs (cyanide, nicotine, and doxapram), preceded those of aortic chemoreceptors. This unexpected result may be due to differences in microcirculation and mass transport. The relative speed of responses to changes in arterial blood pressure were also studied. The aortic chemoreceptors responded to decreases in arterial blood pressure before the carotid chemoreceptors, supporting the idea that the aortic body has microcirculatory impediments not generally present in the carotid body. Carotid bodies appear to be more suited for monitoring blood gas changes due to respiration, whereas aortic bodies are for monitoring circulation.