Non-nutritive swallowing and respiration coordination among states of alertness in adult sheep.

Swallowing is a powerful inhibitor of respiration. Its coordination with respiration is therefore crucial to avoid aspiration and apnea. The aim of this study was to determine the coordination between non-nutritive swallowing (NNS) and phases of the respiratory cycle, including the assessment of the effect of states of alertness in adult sheep. Six animals were surgically instrumented under general anesthesia to record electroencephalography, electro-oculography (state of alertness), diaphragmatic electromyography (EMG), nasal flow (respiration), esophageal EMG, and the thyroarytenoid muscle (NNS). Our results revealed that (1) the highest NNS frequency is observed in rapid eye movement (REM) sleep, especially for bursts of NNS; (2) while NNS begins mainly during inspiration in all states of alertness, REM sleep, however, is responsible for an increase in the proportion of NNS beginning in expiration; (3) the link between inspiration and NNS is not affected by rumination. In conclusion, the link between NNS and inspiration in adult sheep is similar to that of lambs but contrary to previous reports on NNS induced by water in humans. Whether these differences are related to interspecies differences or the experimental techniques clearly needs further studies on spontaneous NNS in humans.