Sleeping and Breathing: Sleep Removes Wakeful Motor Compensations (Part 1)

An obvious example of an anatomic abnormality causing sleep disordered breathing is obstructive sleep apnea caused by micrognathia. When the patient is awake, the pharyngeal airway is patent, but with sleep onset it occludes. We can infer, therefore, that wakefulness provides enhanced motor activation of upper airway muscles, which compensates for the tendency of a short mandible to close the pharyngeal airway. This motor compensation involves the neurons of the upper airway premotor network and undoubtedly involves higher neural “centers.” The salient fact is that this nonvoluntary activation of pharyngeal muscles by the higher nervous system is eliminated when vigilance shifts from wakefulness to non-REM sleep. A similar sequence is postulated for most patients with obstructive sleep apnea. An even more common example of the action of wakefulness to promote a patent pharyngeal airway can be inferred from observations at the bedside of a sleeping normal human. Comparison of supraglottic resistance measured while awake and during non-REM sleep reveals a large (approximately 2-fold) increase during sleep. This shift reveals that, in awake normal man, contraction of the pharyngeal dilator muscles contributes to patency of the collapsible pharyngeal airway. buy asthma inhaler

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