Respiratory Muscle Strength in Patients With Obesity Hypoventilation Syndrome (OHS) or With a Precursor of the Disease

Inclusion Criteria: * patients with BMI \> 30 and obesity-associated hypoventilation stages I - IV * patients with BMI \> 30 and elevated OHS-risk (= obstructive sleep apnea without hypercapnia) * age:18-80 years * capacity to consent Exclusion Criteria: * any other disease, that causes ventilatory insufficiency * pacemaker, defibrillators or device for deep brain or vagus nerve stimulation * esophagitis, Barrett-esophagus, esophageal cancer * acute gastritis and ulcera ventriculi * epilepsy * any medical, psychological or other condition impairing the patient's ability to provide informed consent