Heart rate response to arousal and lung inflation following upper airway obstruction in lambs

Abstract

Experiments were done to determine the influence of arousal from sleep and lung inflation on heart rate following upper airway obstruction in lambs. Ten lambs were anesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms, and measurements of systemic arterial blood pressure and arterial hemoglobin oxygen saturation (fiberoptic catheter oximeter). A tracheotomy was done and a fenestrated tracheostomy tube was placed in the trachea. A 5F balloon-tipped catheter was inserted into the tube so that the airway could be obstructed by inflating the balloon. No sooner than 3 days after surgery, measurements were made during a control period of normal tidal respiration, during upper airway obstruction immediately before arousal, during upper airway obstruction immediately after arousal, and following the first lung inflation. A total of 39 epochs of quiet sleep and 33 epochs of active sleep were obtained. Heart rate and oxygen saturation decreased (p < 0.05) during upper airway obstruction in quiet sleep and active sleep. Arousal from sleep did not significantly alter heart rate during continued upper airway obstruction. However, heart rate quickly returned toward control levels following the first lung inflation despite continued oxygen desaturation. These results provide evidence that the abrupt tachycardia following an apneic episode is related to lung inflation rather than to the arousal response per se.