Influence of Carotid Denervation on the Arousal and Cardiopulmonary Response to Rapidly Developing Hypoxemia in Lambs

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Abstract
Experiments were done on five lambs to determine if carotid denervation influences the arousal and cardiopulmonary responses to rapidly developing hypoxemia during sleep. Each lamb was anesthetized and instrumented for recordings of electrocorticogram, electrooculogram, nuchal and diaphragm electromyograms, and measurements of arterial blood pressure and arterial hemoglobin oxygen saturation. The carotid chemoreceptors and baroreceptors were denervated, a tracheostomy was done, and a fenestrated tracheostomy tube was placed in the trachea so that the inspired oxygen mixture could be changed quickly. No sooner than 3 d after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing 21% oxygen and during experimental periods of rapidly developing hypoxemia when the animal was breathing 5% oxygen. Rapidly developing hypoxemia was terminated during each epoch by changing the inspired gas mixture back to 21% oxygen once the animal aroused from sleep or once the arterial Hb oxygen saturation decreased to 30%. Arousal occurred during only 4 of 11 epochs in quiet sleep and during only 3 of 14 epochs in active sleep before the arterial Hb oxygen saturation decreased to 30%. These data provide evidence that the carotid chemoreceptors and/or carotid baroreceptors play a major role in causing arousal from sleep during rapidly developing hypoxemia in lambs.