Figure 1. Example of an obstructive apnea from polysomnography.

Tracings are from top to bottom: Chin EMG = electromyogram, EEGs = electroencephalograms, EKG = electrocardiogram, Thermocouple = measured airflow, etCO₂ = carbon dioxide, RC = rib cage and ABD = abdominal excursions, O₂ Sat = oxygen saturation measured by figure pulse oximetry, Pesoph = esophageal pressure. Airflow is absent in the face of effort observed on rib cage, abdominal and esophageal pressure tracings. Breathing resumes with the onset of arousal (increase in chin EMG and EEG α waves) and opening of upper airway. Please note the nadir of saturation is at the end of apnea just before resumption of breathing, followed by quick reoxygenation associated with arousal-terminating apnea. Contrast with Figure 2. (Modified from Javaheri et al. Sleep apnea types, mechanisms, and clinical cardiovascular consequences. J Am Coll Cardiol. 2017;69:841–858.)