Aortic body chemoreceptor responses to changes in PCO2 and PO2 in the cat

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Abstract
Responses of aortic chemoreceptor afferents to a range of arterial CO2 tension (PaCO2) changes at various levels of arterial O2 tension (PaO2) were investigated in 18 cats anesthetized with .alpha.-chloralose and maintained at 38.degree. C. Aortic chemoreceptor activity, end-tidal O2 pressure, end-tidal CO2 pressure, and arterial blood pressure were continuously monitored. Arterial blood gases were measured in steady states. Single or a few clearly identifiable afferents were studied during changes and steady states of PaO2 and PaCO2. All the aortic chemoreceptor afferent discharge rates increased with PaCO2 increases from hypocapnia (10-15 torr) to normocapnia and moderate hypercapnia (30-50 torr) and with PaO2 decreases from above 400 to 30 torr. Hypoxia augmented the response to PaCO2 most effectively in the range of 10-40 torr. At any PaO2, the discharge rate reached a plateau with sufficient intensity of hypercapnia. The PaCO2 stimulus threshold at a PaO2 of 440 torr was about 15 torr and at a PaO2 of 60 torr it was 10 torr. In the transition from hypocapnia to hypercapnia, responses increased gradually, usually without an overshoot. The steady-state responses to PaCO2 of the majority of aortic chemoreceptors resembled those of carotid chemoreceptors. The responses of both receptors can be attributed to the same basic type of mechanism.