Heart Rate Variability in White Coat Hypertension and Essential Hypertension

Inclusion Criteria: * age 30-70 years * office BP \>150/95 mmHg and 24-h ambulatory BP =/\>135/85 mmHg * office BP \>150/95 mmHg and 24-h ambulatory BP \<135/85 mmHg * office BP \<150/95 mmHg and 24-h ambulatory BP \<135/85 mmHg Exclusion Criteria: * Clinical signs of disease of the heart, lungs, liver, kidneys, brain or endocrine organs * neoplastic disease * daily use of medicine * alcohol abuse * abnormal laboratory screening including blood-hemoglobin, blood-white cell count, plasma-creatinine, plasma-alanine-amino-transaminases, plasma-albumin, plasma-sodium, plasma-potassium, urinary glucose, urinary albumin; electrocardiogram * pregnancy * unwillingness to participate