Clinical meaning
Hypertension is the sustained elevation of systemic arterial blood pressure resulting from increased cardiac output, increased systemic vascular resistance (SVR), or both. The 2017 ACC/AHA guidelines redefined hypertension categories: NORMAL (<120/<80 mmHg), ELEVATED (120-129/<80 mmHg), STAGE 1 HYPERTENSION (130-139/80-89 mmHg), and STAGE 2 HYPERTENSION (≥140/≥90 mmHg). This represented a significant change from the previous JNC 7 threshold of ≥140/90. PRIMARY (essential) hypertension accounts for 90-95% of cases and results from complex interactions between genetic predisposition, sympathetic nervous system overactivity, the renin-angiotensin-aldosterone system (RAAS), endothelial dysfunction, and environmental factors (sodium intake, obesity, physical inactivity, stress). SECONDARY hypertension (5-10%) has identifiable causes including renal artery stenosis (renovascular HTN), primary hyperaldosteronism (Conn syndrome), pheochromocytoma, Cushing syndrome, coarctation of the aorta, obstructive sleep apnea, thyroid disease, and medications (NSAIDs, oral contraceptives, decongestants, stimulants). The pathophysiology of sustained hypertension involves: (1) increased SVR from vascular remodeling (smooth muscle hypertrophy, increased collagen deposition, endothelial dysfunction with reduced nitric oxide availability), (2) RAAS activation (angiotensin II causes direct vasoconstriction, aldosterone causes sodium and water retention, and both promote cardiac and vascular remodeling), (3) sympathetic overactivity (increased norepinephrine...