The Different Respiratory Effects of Inspiratory and Expiratory Stimulations of the Carotid Sinus Nerve and Carotid Body

Abstract

In the half-century since the discovery of the chemoreceptor function of the carotid bodies, a great deal has been learned about their function and effects on respiration. However, the organization of their afferent input to the central nervous system is still not well defined. In the past it had been assumed that if carotid body afferent impulses reached the brain they would always have the expected excitatory effect, i.e., i f they arrived during expiration they would somehow be stored and remembered until the next breath where their effect would b e manifested. Over the past few years, however, it has become apparent that afferent input does not act on the central neural respiratory controller in such a simple manner. In the case of peripheral chemoreceptors the respiratory response appears to depend not only on the characteristics of the source but also on the time in the respiratory cycle that the stimulus occurs^1–6, ⁸, ⁹. This finding has several important implications: (l) it suggests that carotid body signals are not well “stored and remembered” in the central control system and thus has implications for the understanding of its organization; (2) since the chemical signal at the carotid body is varying in an oscillating manner, the timing of the peak of that oscillation with relation to the respiratory cycle could be an important variable affecting respiratory output.