Changes in pattern of breathing following baroreceptor stimulation in cats.

The effects of baroreceptor stimulation produced by a sudden rise in arterial pressure on respiratory pattern were studied at various levels of PaCO2 and PaO2 in 8 anesthetized cats. A sudden rise in arterial pressure decreased both tidal volume and respiratory frequency. For a given increase in arterial pressure, the decrease in tidal volume was constant at all levels of PaCO2 and PaO2 examined, whereas the decrease in respiratory frequency became progressively lower as the level of chemical drive increased, regardless of the type of chemical stimuli. Analysis of respiratory duration revealed that the decrease in respiratory frequency during baroreceptor stimulation was solely due to prolongation of expiration. These observations were obtained in the intact as well as in the vagotomized animals but were not seen after bilateral sinus nerve section. They suggest that the central respiratory mechanisms controlling respiratory frequency are directly involved in the reduction in respiratory frequency during baroreceptor stimulation.