Between 2%-4% of adult population suffers from obstructive sleep apnea (OSAS)(1), which is characterized by obstructive snoring, repetitive apnea and hypopnea in sleep, repetitive cyclic oxygen saturation, as a result from sleep fragmentation related to the arousals in sleeping profile and clinical consequences like day drowsiness, neuropsychological deficits, raised danger of accidents and cardiovascular disease. (1-6). The therapy of choice is the application of nasal continuous positive airway pressure (CPAP) (7-9).

Increasing relevance obtain the combined sleep-related breathing disturbances, where the patient shows an obstructive sleep apnea syndrome and some central breathing disturbances in the polysomnography at night. Those patients frequently present with cardiovascular diseases. These combined night breathing disturbances are frequently insufficient to be mitigated exclusively with a CPAP therapy.

Some modifications of nCPAP therapy were developed in order to optimize the therapy-compliance and the effectiveness of the therapy. Bi-level-CPAP-devices produce two pressure levels: one for inspiration and another for expiration, so that the patients are able expire against a constant low pressure. An increase in the use of this application in comparison between the conventional or the automatic CPAP therapy could not be proved in early studies. (12, 13) The principle of the automatic nCPAP therapy is to recognize the patient's current need of pressure and to alter the pressure within a set range by applying different algorithms. Some studies have shown that this therapy increased compliance and comfort (14-16), while other studies could not confirm these results. (17, 18)

The result of the current study should prove if the treatment of a new algorithm therapy based on an automatic bi-level-system for patients with sleep-related respiratory disorders is as effectively and subjective more comfortable as the conventional CPAP therapy.

Patients with a particularly high need of pressure should experience a clear expiratory pressure relief and a higher comfort. Therefore a better compliance is to expect. In the same way patients with additional central respiratory disturbances should obtain a benefit from the bi-level modus. This new treatment would help particularly such "critical patients", who are not responding well to the CPAP therapy or find it uncomfortable.

Patients who meet all the above mentioned criteria and who were diagnosed as sleep-apnea syndrome patients in our hospital were asked to participate in the study. By a declaration of consent the patients were randomized in two different groups.

Group 1: started with CPAP at the first night and continued with Bi-level- APAP at the second night.

Group 2: began with Bi-level-APAP and ended with CPAP

Patients will be discharged with CPAP after the second night

Inclusion Criteria:

• Men and women > 18 years.
• Newly diagnosed of sleep-apnea-syndrome, AHI> 5 per hour associated with the usual manifestation of this syndrome.
• Declaration of consent.

Exclusion Criteria:

• Absence of declaration of consent.
• Other relevant sleep disorders like insomnia, restless legs, parasomnia
• Heart failure NYHA-CLASS III- IV.
• Myocardial infarction or unstable angina pectoris or cardiac surgery in within the last three months.
• Apnea-hypopnea-index < 5 per hour.
• Pregnancy.
• Malign diseases.
• Serious chronic oxygen-requiring pulmonary illness.
• Age under 18 years.