Clinical Note

Sleep apnea is a group of conditions characterized by pauses or reductions in breathing during sleep that last 10 sec or more. In most patients this leads to arterial hypoxemia and CO2 retention. When hypoxic or hypercapnic stimuli reach a sufficiently high level, breathing efforts increase and this arouses or awakens the individual. Apneas and arousals can occur repeatedly and cause sleep fragmentation and excessive daytime sleepiness. Cognitive and neurological effects may result from sleepiness or direct effects of intermittent hypoxia during recurrent apneas.

The two general classes of sleep apnea are central and obstructive. Central apneas occur when the efferent signal to the diaphragm is insufficient to trigger inspiration. Central apneas occur in all sleep stages but are more common in the early stages of NREM sleep (NREM stands for non-rapid eye movement). During NREM sleep (also called quiet sleep), a generalized decrease in neural and metabolic activity occurs. In NREM

sleep the threshold for the ventilatory response to CO2 increases. Coupled with a drop in metabolism, this pushes PaCO2 below the apneic threshold (see Ventilatory Response to CO2 section) and causes central apneas. PaCO2 increases during apnea and will eventually exceed the apneic threshold, so breathing resumes. Patients with central apnea also tend to have abnormally low ventilatory responses to CO2 during wakefulness. The most extreme example of a central sleep apnea is Ondine's curse, which is the complete cessation of breathing in a patient whenever he goes to sleep. Pure central sleep apnea is relatively rare, occurring in only 5% of patients suffering from sleep apnea.

Obstructive sleep apnea is more common and it occurs when the upper airways collapse during inspiratory efforts. Patients with obstructive sleep apnea are frequently sleepy during the day and almost always have a history of loud snoring. Obstructive sleep apnea occurs in almost 5% of

Sleep Apnea

Sleep Apnea

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