Synchronization of Respiratory Rhythm with Mechanical Ventilation by Respiratory CO2 Oscillations in Vagotomized Dogs

Abstract

The medullary respiratory rhythm generator of animals on a fixed rate mechanical ventilation tends to synchronize to the rate of mechanical ventilation. Since vagotomy abolishes this synchronization, phasic vagal afferent discharges arising from pulmonary stretch receptors are believed to carry the information of phasic lung movements (caused by mechanical ventilation), 1 Another source of phasic afferent input to the respiratory center is the respiratory oscillations of arterial Pco2 (CO2 oscillations), which can be sensed by the peripheral chemoreceptor. Therefore, it may be natural to postulate that, in the absence of vagal afferent input, the central respiratory rhythm could entrain to the phasic chemical afferent input arising from respiratory CO 2 oscillations. However, the effect of CO2 oscillations seems to depend upon their magnitude.2 In the present study, we determined a level of CO2 oscillations which is large enough to induce the synchronization in anesthetized, paralyzed and vagotomized dogs. The possible role of the entrainment by CO2 oscillations in the respiratory control is also discussed.