in order to include the event in the report.) "arousals" are sudden shifts in brain wave activity. they may be caused by 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. mr. j----, age 41, 5'8" tall, 265 lbs., came to the sleep lab to rule out obstructive sleep apnea. he complains of some snoring and daytime sleepiness. his score on the epworth sleepiness scale is elevated at 15 (out of possible 24 points), affirming excessive daytime sleepiness (normal is <10/24). this single-night diagnostic sleep study shows evidence for obstructive sleep apnea (osa). for the full night his apnea+hypopnea index was elevated at 18.1 events/hr. (normal <5 events/hr; this is "moderate" osa). while sleeping supine, his ahi was twice that, at 37.1 events/hr. he also had some oxygen desaturation; for 11% of sleep time his sao2 was between 80% and 90%. results of this study indicate mr. j---- would benefit from cpap. to this end, i recommend that he return to the lab for a cpap titration study. 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" to whoever is paying for the study. the split-night study has these disadvantages: there is less time to make a diagnosis of osa (medicare in the us requires a minimum of 2 hours of diagnosis time before the mask can be applied); and there is less time to assure an adequate cpap titration. if the titration begins with only a few hours of sleep left, the remaining time may not assure a proper cpap titration, and the patient may still have to return to the lab. because of costs, more and more studies for "sleep apnea" are attempted as split-night studies when there is early evidence for osa. (note that both types of study, with and without a cpap mask, are still polysomnograms.) when the cpap mask is worn, however, the flow-measurement lead in the patient's nose is removed. instead, the cpap machine relays all flow-measurement data to the computer. the below report is an example report which might be produced from a split night study: mr. b____, age 38, 6 ft. tall, 348 lbs., came to the hospital sleep lab to diagnose or rule out obstructive sleep apnea. this polysomnogram consisted of overnight recording of left and right eog, submental emg, left and right anterior emg, central and occipital eeg, ekg, airflow measurement, respiratory effort and pulse oximetry. the test was done without supplemental oxygen. his latency to sleep onset was slightly prolonged at 28.5 minutes. sleep efficiency was normal at 89.3% (413.5 minutes sleep time out of 463 minutes in bed). during the first 71 minutes of sleep mr. b____ manifested 83 obstructive apneas, 3 central apneas, 1 mixed apnea and 28 hypopneas, for an elevated apnea+hypopnea index (ahi) of 97 events/hr (*"severe" osa). his lowest sao2 during the pre-cpap period was 72%. cpap was then applied at 5 cm h2o, and sequentially titrated to a final pressure of 17 cm h2o. at this pressure his ahi was 4 events/hr. and the low sao2 had increased to 89%. this final titration level occurred while he was in rem sleep. mask used was a respironics classic nasal (medium-size). in summary, this split night study shows severe osa in the pre-cpap period, with definite improvement on high levels of cpap. at 17 cm h2o his ahi was normal at 4 events/hr. and low sao2 was 89%. based on this split night study i recommend he start on nasal cpap 17 cm h2o along with heated humidity.