Objectives: To compare the response of polycythemia in terms of hematocrit decrease in patients treated with positive airway pressure (CPAP) versus patients not treated with CPAP.

Methodology: Randomized, parallel-group, nonblinded, controlled clinical trial.

Patients diagnosed with OSA in a respiratory polygraphy (RP) and who meet all the inclusion criteria and none of the exclusion criteria will undergo sleepiness and quality of life questionnaires, anthropometric measurements and blood tests and will be randomized to a CPAP treatment group or control group, maintaining this treatment for 12 months. A visit will be made at 12 weeks ,24 weeks and 52 weeks to check compliance with CPAP in the treatment group and to carry out questionnaires on physical activity and quality of life, anthropometric measurements, blood tests including hemoglobin and hematocrit as well as parameters related to coagulation and platelet function and changes in medication as well as adverse effects.

Efficacy variables: blood count, hemoglobin, haematocrit, erythropoietin, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), mean platelet volume (MPV), platelets, coagulation, erythrocyte range of distribution (ADE), glucose, creatinine, glomerular filtration rate, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma glutamyltransferase (GGT), Total bilirubin, hypoxic burden, Epworth score, EuroQol- 5D questionnaire.

Inclusion Criteria:

• Subjects from 18 to 80 years old.
• Diagnosis of polycytemia defined as hematocrit > 49% in men and > 48% in women. ç
• Diagnosis of moderate or severe sleep apnea, defined by an apnea-hypoapnea index >15. - Patients able to read and understand informed consent and give their signed consent.

Exclusion Criteria:

• Smokers or former smokers with pack-year index (IPA>30) or chronic obstructive pulmonary disease diagnosed by spirometry (FEV1/FVC post-bronchodilator below the lower limit of normal or z score < 1.645).
• Patients with central sleep apnea or periodic breathing
• Patients with oxygen saturation <92% or pO2< 60 mmHg at rest during wakefulness. - Evidence of severe heart failure (LVEF<50) or pulmonary hypertension.
• Patients with primary polyglobulia (polycythemia vera). It will be done prior to the inclusion in the study blood levels of erythropoietin (EPO) and determination of the mutation of the JAK2 V617F gene. Patients with normal or elevated EPO levels (normal limits 2.9- 25.9 mU/ml) and no JAK2 V617F gene mutation
• Patients with any active neoplasm will be included in the study. - Patients with chronic kidney disease (Glomerular Filtration Rate (GFR) <60 mL/min/1.73 m2).
• Patients with any active neoplasia.- Patients with chronic kidney disease (Glomerular Filtration Rate (GFR) <60 mL/min/1.73 m2).
• Need for periodic bleeding according to hematology guidelines.
• Treatment with diuretics.
• Treatment with antiplatelets or anticoagulants.
• Systolic blood pressure ≥ 180 mmHg or diastolic blood pressure ≥ 110 mmHg at the baseline visit.
• Stroke, transient ischemic attack, acute coronary syndrome or hospitalization due to worsening heart failure, in the previous 30 days .
• Professional drivers, high-risk profession or respiratory failure (according to criteria of the clinical path of diagnosis and treatment of sleep-related respiratory disorders).
• High daytime sleepiness (Epworth sleepiness scale > 16)
• Previous treatment with CPAP- Participation in another clinical trial within 30 days prior to randomization.