Arousal from Sleep during Rapidly Developing Hypoxemia in Lambs

Abstract

ABSTRACT. Arousal is an important protective response that may prevent severe hypoxemia and death during sleep. However, very little is known about arousal from sleep in response to respiratory stimuli in newborns. Experiments were therefore done to investigate the arousal response from sleep to rapidly developinghypoxemia in eight lambs. Each lamb was anesthetized and instrumented for record--ings of electrocorticogram, electrooculogram, nuchal and diaphragm electromyograms, and measurements of arterial hemoglobin oxygen saturation. A tracheotomy was done and a tracheostomy tube placed in the trachea so that the fraction of inspired oxygen could be changed quickly. No sooner than 3 days after surgery, measurements were made in quiet sleep and active sleep (AS) during 30-s control periods when the animals were breathing 21% oxygen and during experimental periods of hypoxemia when the animals were breathing either 10,5, or 0% oxygen in nitrogen. During quiet sleep, arousal occurred at similar arterial hemoglobin oxygen saturations (81 + 6% on 10% 0 2 , 80 + 5% on 5% O2 and 83 2 5% on 0% 0 2 ) suggesting that arousal was independent of the rate of change of arterial oxygen. However, during AS arousal occurred at different arterial hemoglobin oxygen saturations (76 + 6% on 10% 02, 55 2 11% on 5% 02, and 44 f 17% on 0% 02) suggesting that arousal was dependent on the rate of change of arterial oxygen. During some epochs of AS, electrocortical signs of cerebral hypoxia and primary apnea occurred before arousal. These data provide evidence that arousal from quiet sleep in response to hypoxemia occurs once an arousal threshold has been reached. However, during AS, arousal appears to follow an arousal latency once an arousal threshold has been reached. Furthermore, if the rate of change of oxygen is great enough during AS, signs of cerebral hypoxia and primary apnea may precede arousal. These data would allow one to speculate that if the rate of change of arterial oxygen is great enough during apnea in AS, arousal may fail to occur before hypoxic cerebral depression and ultimately death ensue. (Pediatr Res 22: [471][472][473][474][475][476][477]1987) Abbreviations ALTE, apparent life-threatening event Sa02, arterial hemoglobin oxygen saturation SIDS, sudden infant death syndrome

Influence of Carotid Denervation on the Arousal and Cardiopulmonary Responses to Upper Airway Obstruction in Lambs

“…1 SD) to 69 + 9% during upper airway obstruction (Table 1). In a previous study (13), we found that arousal occurred during only four of 1 1 epochs of quiet sleep before the arterial Hb oxygen saturation decreased to 30% during inhalation of 5% oxygen in carotid-denervated lambs; this is in marked contrast to what we have observed in carotid-intact lambs (10). In addition, we have also found that arousal occurred during only six of 12 epochs of quiet sleep within 2 min during inhalation of 10% carbon dioxide in carotid-denemated lambs (14); this again, is in marked contrast to what we have observed in carotid-intact lambs (1 2).…”

“…The electrophysiologic signals were high-pass filtered using the '/2-amplitude low-frequency response control on the A.C. preamplifiers (electrocorticogram 1.0 Hz, electrooculogram 0.3 Hz, and electromyograms 3 Hz). The amplified activity from the electrocorticogram was full-wave rectified and then integrated (model 7P 10 Polygraph Integrator, Grass Medical Instruments) to give a running record of the total accumulated area under the electrocortical waves (10). The tracing wrote out a ramp function, the slope of which was directly proportional to the ongoing input activity.…”

“…During quiet sleep, the point of arousal was determined by a change in the electrocorticogram from a high voltage-slow wave pattern to a low voltage-fast wave pattern with continued activity on the nuchal electromyogram (10). During active sleep, the point of arousal was determined by a return of tonic activity on the nuchal electromyogram with continued low voltage-fast wave activity on the electrocorticogram.…”

“…The following electrophysiologic criteria were used to define behavioral state once the animal was lying down (10). During quiet wakefulness, the electrocorticogram showed a fast wavelow voltage pattern; there were occasional eye movements and there was tonic activity on the nuchal electromyogram.…”

“…However, arousal from active sleep during upper airway obstruction occurs at a higher arterial Hb oxygen saturation than does arousal from active sleep during alveolar hypoxia alone (10) or during a combination of alveolar hypoxia and hypercarbia in young lambs (1 1).…”