Erythrocytapheresis for Chronic Mountain Sickness

Inclusion: 1. High-altitude residents or long-term dwellers (defined as continuous residence at ≥2,500 meters above sea level for ≥1 year), with no history of travel to low-altitude areas in the preceding 2 months and no planned travel to low-altitude areas during the study period; 2. Aged more than 18 years, any gender; 3. Diagnosed with CMS per the Qinghai CMS Criteria: Hemoglobin (Hb): Men: ≥210 g/L Women: ≥190 g/L At least one symptom/sign: headache, dizziness, dyspnea and/or palpitations, sleep disturbances, fatigue, localized cyanosis, burning sensation in palms/soles, venous dilatation, muscle/joint pain, loss of appetite, poor concentration or memory changes. CMS score ≥6; 4. Women of childbearing potential: negative pregnancy test (serum/urine) at screening. No pregnancy plans during the study period; 5. Willing to sign informed consent and able to comply with study procedures. Exclusion: 1. Hematocrit \<60%; 2. Patients with polycythemia due to: polycythemia vera, underlying cardiopulmonary diseases (e.g. COPD, chronic bronchitis, bronchiectasis, pulmonary fibrosis, heart disease), or other causes including malignancy; 3. Patients with active pneumonia, acute/chronic pulmonary embolism, or severe organ dysfunction (including cardiac, hepatic, or renal failure); 4. patients with contraindications to study procedures: erythrocytapheresis, pulmonary function tests, incremental shuttle walk test et al, including conditions such as pneumothorax, impaired consciousness, severe arrhythmia, or significant coagulation disorders et al.; 5. recent CMS-specific treatments (within the past 6 months): drug therapy, phlebotomy, or erythrocytapheresis; 6. pregnant or breastfeeding women; 7. current participation in other clinical trial (observational studies permitted).