stage 0: OHS-risk (OSA / no hypercapnia)

stage I: obesity associated hypoventilation (intermittent hypercapnia during sleep, arterial carbon dioxide partial pressure (PaCO2) or transcutaneous carbon dioxide partial pressure (PtcCO2) morning ~ evening), bicarbonate < 27 mmol/L awake)

stage II: obesity associated hypoventilation (intermittent hypercapnia during sleep, PaCO2 or PtcCO2 morning > evening, bicarbonate ≥ 27 mmol/L awake)

stage III: OHS (hypercapnia, carbon dioxide partial pressure (PCO2) > 45 mmHg awake)

stage IV: OHS with end organ damage (hypercapnia , PCO2 > 45 mmHg awake, cardiometabolic comorbidities)

diagnostic tests: magnetic phrenic nerve stimulation, diaphragmatic ultrasound

cervical and cortical stimulation of N. Vagus

minute volumen (L/min)

difference between intraesophageal and intragastral pressure after posterior magnetic stimulation of the phrenic nerves

electroneurography after posterior magnetic stimulation of the phrenic nerves

excursion of the diaphragm

thickness of the diaphragm

mouth occlusion pressure (kPa)

maximal inspiratory mouth pressure (kPa)

Correlation between PImax and transdiaphragmatic pressure