Role of arterial O2 flow in peripheral chemoreceptor excitation

Assurance of adequate oxygen flow is a fundamental issue for all oxygen-consuming organisms. In higher organisms, aortic and carotid body chemoreceptors are known to sense arterial hypoxia, but the factors that allow aortic and carotid body chemoreceptors to sense the level of O2 circulation deserve further clarification. Experiments in the cat are presented in which the activity of chemoreceptor afferents from aortic and carotid bodies was monitored while arterial O2 flow was manipulated by i) lowering PaO2, ii) carboxyhemoglobinemia, iii) anemia, and iv) lowering systemic blood pressure. All of the above alterations stimulated aortic body chemoreceptors, indicating that hemoglobin-bound O2 participated in the maintenance of the receptor PO2 level. In contrast, most carotid body chemoreceptors were not stimulated by moderate carboxyhemoglobinemia, anemia and/or hypotension, indicating that hemoglobin-bound O2 normally did not influence the receptor tissue PO2. However, hypotension at a low O2 capacity did stimulate the receptors. In aortic body circulation, O2 flow was already critical, and therefore the chemoreceptors were sensitive to O2 transport capacity whereas carotid body chemoreceptors were not, presumably because of a large blood flow. Accordingly, aortic body chemoreceptors are more suited for monitoring circulatory O2 flow and carotid chemoreceptors for respiratory O2 flow.