Airflow was measured using nasal thermistors, and a nasal pressure transducer. Abdominal and thoracic movements were assessed by respiratory inductive plethysmography. Oximetry was measured using a disposable finger probe (oximeter flex sensor 8000 J, NONIN, Plymouth, Massachusetts, United States) placed on the index finger. Snoring sounds, heart rate also were recorded. Body position was monitored using body position sensor. Apnea was defined as a cessation of airflow lasting for more than 10 sec., and hypopnea as a discrete reduction (two thirds) of airflow and/or abdominal ribcage movements lasting for more than 10 sec. and associated with a decrease of more than 4% in oxygen saturation. Trained PSG technicians and sleep physicians using the criteria of Rechtschaffen and Kales, and in close concordance with scoring updates given by the American Academy of Sleep Medicine analyzed all studies. The apnea-hypopnea index (AHI) was defined by the total number of apneas and hypopneas per hour of sleep. The severity of OSA was determined as: mild (AHI 5-15), moderate (AHI 15 - 30) and severe (AHI ≥ 30) (21) on the basis of AHI Design of the study First visit Patients with previously diagnosed RAH and with suspected OSA (medical history, the Epworth scale assessment) were referred from an outpatient clinic to the hospital ward. After admission numerous laboratory tests and imaging, such as aldosterone and Plasma renin activity levels (ARO), both before and after tilting, creatinine, urea, GFR, sodium and potassium levels, pro B-type natriuretic peptide (BNP), thyrotrophin (TSH), free triiodothyronine (FT3), free thyroxine(fT4), 24-hour urine collection for electrolytes, as well as abdominal ultrasound examinations, computed tomography of the abdomen and Doppler ultrasound of the renal arteries, were performed to exclude secondary causes of arterial hypertension (other than primary hyperaldosteronism). What is more, office BP was measured three times at admission and afterwards 24-hours ABPM examination was conducted. All participants underwent also transthoracic echocardiography. After aforementioned diagnostics and after confirming RAH based on 24-hour ABPM, patients were referred to the Department of Pulmonology to perform polysomnography.