numerous factors, including breathing abnormalities, leg movements, environmental noises, etc. An abnormal number of arousals indicates "interrupted sleep" and may explain a person's daytime symptoms of fatigue and/or sleepiness. Cardiac rhythm abnormalities. Leg movements. Body position during sleep. Oxygen saturation during sleep. Once scored, the test recording and the scoring data are sent to the sleep medicine physician for interpretation. Ideally, interpretation is done in conjunction with the medical history, a complete list of drugs the patient is taking, and any other relevant information that might impact the study such as napping done before the test. Once interpreted, the sleep physician writes a report that is sent to the referring provider, usually with specific recommendations based on the test results. Examples of summary reports The below example report describes a patient's situation, the results of some tests and mentions CPAP as a treatment for obstructive sleep apnea. CPAP is continuous positive airway pressure and is delivered via a mask to the patient's nose or the patient's nose and mouth. (Some masks cover one, some both). CPAP is typically prescribed after the diagnosis of OSA is made from a sleep study (i.e., after a PSG test). To determine the correct amount of pressure and the right mask type and size, and also to make sure the patient can tolerate this therapy, a "CPAP titration study" is recommended. This is the same as a "PSG" but with the addition of the mask applied so the technician can increase the airway pressure inside the mask as needed, until all, or most, of the patient's airway obstructions are eliminated. This report recommends that Mr. J---- return for a CPAP titration study, which means a return to the lab for a second all-night PSG (this one with the mask applied). Often, however, when a patient manifests OSA in the first 2 or 3 hours of the initial PSG, the technician will interrupt the study and apply the mask right then and there; the patient is awakened and fitted for a mask. The rest of the sleep study is then a "CPAP titration." When both the diagnostic PSG and a CPAP titration are done the same night, the entire study is called "split night". The split-night study has these advantages: The patient only has to come to the lab once, so it is less disruptive than is coming two different nights; It is "half as expensive"