The present study aims to document and assess changes in single parameters of pulse wave analysis (ASI single parameters) as well as to evaluate ASI cardiovascular risk assessment before initiation of CPAP therapy and after 6 months of CPAP therapy in patients with obstructive sleep apnea.

Obstructive sleep apnea (OSA) is characterized by repeated occurrence of apneas or reduced inspiratory air flow due to obstructions of the upper airways (hypopneas). These recurring events are accompanied by intermittent hypoxemia and sympathetic activation, leading to hemodynamic oscillations including relevant variations of pulse wave and blood pressure. Thus, OSA is associated with cardiovascular diseases and was identified as an independent risk factor for hypertension.

Direct effects of obstructive respiratory events (obstructive apneas and hypopneas) include changes of the peripheral pulse wave. The latter can easily be measured by finger plethysmography, e.g. by using established pulse oximeters. Certain pulse wave characteristics and their reaction towards obstructive respiratory events may provide information on cardiovascular function and thereby help in individual cardiovascular risk assessment.

Recently, Grote et al. published a concept for cardiovascular risk assessment based on pulse oximetry and pulse wave analysis ("ASI" - Grote et al. 2011, CHEST). The algorithm described herein is able to differentiate between high and low risk patients according to ESH/ESC risk classification (high risk = 4 and 5, low risk 1-3). To that end, oxygen saturation as measured by pulse oximetry, reductions in pulse wave amplitude, pulse rate accelerations, pulse propagation time and cardiorespiratory coupling are taken into account to calculate a quantitative total risk.

A successful OSA therapy applying positive airway pressure (e.g. CPAP) normalizes sleep-related breathing disturbances and thus counterbalances hemodynamic oscillations. This presumably results in reduced cardiovascular risk and should be detectable by measurable changes in pulse wave. This study aims to evaluate these effects by analyzing the single pulse wave parameters, which are part of the ASI algorithm. At the same time, established risk factors as well as the objective therapy outcome will be documented from the established sleep medicine viewpoint.

Inclusion Criteria:

• Sleep-related breathing disorders with an apnea-hypopnea index ≥15/h and <30% central respiratory events (OSA patients)
• Stable optimal medication according to European Society of Cardiology guidelines (if applicable)

Exclusion Criteria:

• Prior exposure to positive airway pressure treatment
• Atrial fibrillation
• Facial anomalies or injuries inhibiting proper mask fit
• Pregnancy and/or lactation
• Acute life-threatening illness (e.g. instable angina pectoris, acute bronchial asthma, heart failure New York Heart Association stage IV, myocardial infarction, exacerbated Chronic obstructive pulmonary disease, malignant tumor requiring treatment)
• Drug or alcohol abuse
• Intake of hypnotics/sedatives
• Any medical, psychological or other condition impairing the patient's ability to provide informed consent