Autonomic Regulation of Blood Pressure and Heart Rate During Orthostasis and Exercise in Healthy and Hypertensive Individuals

Inclusion Criteria: * Healthy volunteers aged 18-35 years without known acute or chronic disease, non-smokers, body mass index (BMI) 20-24.9 kg/m², and negative orthostatic test * Participants aged ≥60 years with arterial hypertension followed at the Department of Hypertension * Hypertension group: controlled arterial hypertension, negative orthostatic test, without diabetes mellitus * Hypertension with orthostatic hypotension group: controlled arterial hypertension and positive orthostatic test indicating orthostatic hypotension * Hypertension with orthostatic hypertension group: controlled arterial hypertension and positive orthostatic test indicating a rise in blood pressure during orthostatic testing * Hypertension with diabetes mellitus group: controlled arterial hypertension and diabetes mellitus without previously diagnosed autonomic dysfunction * Ability to provide written informed consent Exclusion Criteria: * Dementia, neurodegenerative disease, or cognitive impairment preventing understanding of study procedures * Known cardiovascular disease including heart failure (NYHA II-IV), myocardial infarction within the previous 6 months, clinically significant arrhythmias, or peripheral arterial occlusive disease * Uncontrolled arterial hypertension * Change in antihypertensive therapy within the previous 4 weeks * Presence of a cardiac pacemaker * Treatment with antiarrhythmic drugs (class I, III, or IV), digoxin, alpha-receptor blockers, or other medications known to significantly affect heart rate variability or autonomic function * Advanced renal failure (eGFR \<30 mL/min/1.73 m²) or advanced liver failure * Active malignancy * Body mass index ≥35 kg/m² * Acute illness within the previous 4 weeks * Current smoking * Inability to safely perform exercise testing on a cycle ergometer * Severe psychiatric disorders without stable treatment * Pregnancy or breastfeeding * Participation in another clinical study * Refusal or inability to provide written informed consent