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".