Sleep Related Breathing Disturbances and High Altitude Pulmonary Hypertension in Kyrgyz Highlanders

Inclusion Criteria: * high altitude pulmonary hypertension confirmed by clinical presentation and systolic pulmonary artery pressure \>50 mmHg measured by echocardiography at altitude of residence. * healthy subjects (high altitude controls) * Both genders * Age \>16 y * Kyrgyz ethnicity * born, raised and currently living at \>2500 m * healthy subjects currently living at \<1000 m (low altitude controls) Exclusion criteria: * Pulmonary hypertension from other causes, in particular from left ventricular failure as judged clinically and by echocardiography * excessive erythrocytosis * other coexistent disorders that may interfere with the cardio-respiratory system and sleep * regular use of medication that affects control of breathing * heavy smoking