What are the key features of sleep deprivation versus sleep apnea?
In sleep deprivation, the person does not sleep but breathes normally. In sleep apnea, the person sleeps but does not breathe well during sleep. One can objectively measure excessive daytime sleepiness (EDS) with a standardized tool, such as the Epworth Sleepiness Scale (ESS). One must appreciate that this screening tool is specific but not sensitive. An ESS score > 9 to 10 is consistent with EDS, but not necessarily OSA. The greatest clinical use for this scale is serial tracking of patients in response to therapy. It is important to remember that the ESS does not correlate with (1) objective testing for sleepiness; (2) likelihood of OSA on overnight PSG; and (3) the patient’s perception of sleep-related problems. Patients with acute or chronic shortening of sleep resist the drive to sleep with no impairment of gas exchange. In OSA, there is a repetitive collapse of the upper airway, which induces apneic and hypopneic episodes despite persistent thoracic and abdominal respiratory effort. This leads to mechanical loading on the upper airway, chest wall, and diaphragm. What follows are hypoxia, hypercarbia, and a marked increase in SNS tone. OSA often leads to disruption or fragmentation of the usual sleep–wake cycle and endocrine responsiveness. Both can contribute to fatigue and daytime sleepiness. In contrast, if EDS is secondary to sleep deprivation, the patient’s sleep continuity is normal and is often associated with an increase in SWS.