Pulmonary reflexes and breathing pattern during sleep in the opossum

Paradoxical sleep (PS) in the opossum (Didelphis virginiana) and other mammals is typically accompanied by irregular breathing, while even breathing is usually found during slow wave sleep (SWS). During PS certain brainstem reflexes are depressed, and it is possible that similar depression of pulmonary reflexes could contribute to the observed ventilatory uneveness. To test this possibility, we assessed pulmonary reflexes in the opossum during SWS and during PS when breathing was irregular. Prolongation of expiratory duration with airway occlusion at end inspiration and prolongation of inspiratory duration with airway occlusion at end expiration are both associated with pulmonary reflexes activated by lung inflation. These responses were obtained during PS, and the results suggested that the reflex effects, could be as prominent during PS as during SWS. Pulmonary deflation, producted by raising pressure around the thorax, increased breathing rate during both PS and SWS and generally increased the regularity of respiration during PS. Results of this study do not support the idea that irregular breathing during PS is associated wtih maintained depression of pulmonary reflexes.