Chapter 7  ·  Module 1

Understanding Hypertension

Definition, Pathophysiology & Hemodynamic Framework

Blood Pressure Classification (ACC/AHA 2017)

Diagnostic Thresholds

Blood Pressure Categories

Category Systolic (mm Hg) Diastolic (mm Hg) Status
Normal Below 120 Below 80 Normal
Elevated 120–129 Below 80 Watch
Stage 1 Hypertension 130–139 80–89 Stage 1
Stage 2 Hypertension 140 or above 90 or above Stage 2
Hypertensive Crisis Above 180 and/or above 120 Emergency

Renin-Angiotensin-Aldosterone System Pathway

Stimulus

Low Renal Perfusion

or low sodium delivery; beta-1 stimulation

→

Kidney

Renin Released

from juxtaglomerular cells

→

Liver Product

Angiotensinogen

cleaved to Angiotensin I

→

Lung (ACE)

Angiotensin II

angiotensin converting enzyme cleaves angiotensin I

→

AT1 Receptor Effects

Vasoconstriction + Aldosterone + SNS + Remodeling

raises BP, retains sodium

Pharmacological Targets

Where Drugs Act on RAAS

  • Angiotensin converting enzyme inhibitors: block angiotensin converting enzyme, prevent angiotensin II formation
  • Angiotensin receptor blockers: block angiotensin II type 1 receptor directly
  • Aldosterone antagonists (spironolactone, eplerenone): block mineralocorticoid receptor in collecting duct
  • Beta-blockers: reduce renin release via beta-1 blockade

Sympathetic Nervous System

SNS Contributions to Hypertension

  • Increased heart rate and contractility: raises cardiac output
  • Arteriolar vasoconstriction: raises total peripheral resistance
  • Renal sodium retention via tubular alpha-adrenoceptors
  • Renin release stimulation via beta-1 receptors
  • Feed-forward loop with renin-angiotensin-aldosterone system

Target Organ Damage

Cardiac

Heart

  • Left ventricular hypertrophy
  • Heart failure with preserved ejection fraction
  • Coronary artery disease
  • Atrial fibrillation

Cerebrovascular

Brain

  • Ischemic and hemorrhagic stroke
  • Lacunar infarcts
  • Hypertensive encephalopathy
  • Cognitive impairment

Renal

Kidney

  • Hypertensive nephrosclerosis
  • Progressive chronic kidney disease
  • Microalbuminuria (early marker)
  • Reciprocal: kidney disease worsens hypertension

Other

Vessels & Eyes

  • Hypertensive retinopathy
  • Aortic aneurysm and dissection
  • Peripheral arterial disease
  • Endothelial dysfunction (systemic)

Hemodynamic Drug Class Map

BP = Cardiac Output × Total Peripheral Resistance

Drug Classes by Hemodynamic Target

Target

Reduce Cardiac Output

Beta-blockers

Reduce heart rate, contractility, renin

Diuretics

Reduce preload via natriuresis

Target

Reduce Total Peripheral Resistance

Calcium channel blockers

Arteriolar vasodilation

Angiotensin converting enzyme inhibitors / Angiotensin receptor blockers

Block renin-angiotensin-aldosterone system vasoconstriction

Alpha-1 blockers

Block sympathetic vasoconstriction

Direct vasodilators

Hydralazine, minoxidil — arteriolar relaxation

Target

Reduce Both

Combined alpha-beta blockers

Labetalol, carvedilol — cardiac output and peripheral resistance

Centrally acting agents

Clonidine, methyldopa — reduce sympathetic outflow