Overnight Sleep Study The consenting participants were scheduled to undergo a hospital-based overnight sleep study using a US Food and Drug Administration-approved portable monitoring devices: the Watch-PAT (Itamar Medical, Caesarea, Israel). Watch-PAT is a four-channel unattended sleep monitoring device that measures peripheral arterial tone (PAT), pulse oximetry, heart rate, and actigraphy from a built-in actigraph. Respiratory events are identified by digital vasoconstriction mediated by α-adrenergic receptors that are sensitive to surges in sympathetic activity. Respiratory events are considered to be present when one of the following three criteria was met: a reduction in PAT amplitude with an acceleration of the pulse rate or an increase in wrist activity; a reduction in PAT amplitude with ≥3% oxyhemoglobin desaturation; and ≥4% oxyhemoglobin desaturation only. Although manual scoring and editing of the Watch-PAT signals are possible, we adopted results generated by the device algorithm alone with no intervention by the operator. The diagnosis of sleep apnea is confirmed if the AHI was greater than 15 events/h.