Please assess the completion status of the following clinical trial:

Trial Title: Treatment of Patients With the Obstructive Sleep Apnea Syndrome at Altitude

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: CROSSOVER
- Observational Model: None
- Primary Purpose: TREATMENT
- Time Perspective: None
- Masking: QUADRUPLE
- Phase: PHASE4
- Number of Arms: None

Eligibility Criteria:
Inclusion Criteria:~* Obstructive sleep apnea syndrome, successfully on CPAP therapy~* Residence at low altitude (\<800m)~* Obstructive apnea/hypopnea index \>20/h and a complaint of excessive daytime sleepiness before introduction of CPAP therapy.~* \>15 oxygen desaturations/h (\>3% dips) during an ambulatory nocturnal pulse oximetry performed at the end of a 4-night period without CPAP~Exclusion Criteria:~* Sleep disorders other than OSA.~* More than mild cardiovascular disease, unstable or recently diagnosed (within the last 6 months) cardiovascular disease such as arterial hypertension, coronary artery or cerebrovascular disease.~* Any lung disease, pulmonary hypertension.~* Chronic rhinitis.~* Treatment with drugs that affect respiratory center drive (benzodiazepines or other sedatives or sleep inducing drugs, morphine or codeine derivates), stimulants (modafinil, methylphenidate, theophylline)~* Internal, neurologic or psychiatric disease that interfere with sleep quality.~* Previous intolerance to moderate or low altitude (\<2600m).~* Exposure to altitudes \>1500m for \>1 day within the last 4 weeks before the study

- Gender: ALL
- Minimum Age: 20 Years
- Maximum Age: 70 Years
- Healthy Volunteers: f

Based on this trial design, predict the completion outcome and termination type (if applicable).