What is hypertension
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Here is a thorough overview of hypertension drawn from Harrison's Principles of Internal Medicine 22E, Park's Textbook of Preventive and Social Medicine, the latest 2025 AHA/ACC guidelines, and supporting textbooks.
Hypertension (High Blood Pressure)
Definition
Hypertension is a condition in which blood pressure (BP) is persistently elevated above normal levels. Defining it is inherently arbitrary because BP in a population is distributed as a continuous, bell-shaped curve with no natural cut-off between normal and high. The dividing line is therefore set operationally, based on the level above which cardiovascular risk rises meaningfully and treatment clearly benefits patients.
- Based on average of 2+ readings, on 2+ occasions, in adults not on antihypertensive drugs
Classification (WHO / ESH-ESC)
| Category | Systolic (mmHg) | Diastolic (mmHg) | |
|---|---|---|---|
| Optimal | < 120 | and | < 80 |
| Normal | 120-129 | and/or | 80-84 |
| High normal | 130-139 | and/or | 85-89 |
| Grade 1 HTN (Mild) | 140-159 | and/or | 90-99 |
| Grade 2 HTN (Moderate) | 160-179 | and/or | 100-109 |
| Grade 3 HTN (Severe) | ≥ 180 | and/or | > 110 |
| Isolated systolic HTN | ≥ 140 | and | < 90 |
When systolic and diastolic values fall in different categories, the higher category is used. - Park's Textbook of Preventive and Social Medicine, p.735
Note: The 2025 AHA/ACC guidelines (PMID 40811516) may update the numeric thresholds slightly. Earlier 2017 ACC/AHA guidelines defined hypertension as ≥ 130/80 mmHg.
Types
1. Primary (Essential) Hypertension
The vast majority (~90-95%) of adults have primary hypertension with no identifiable anatomic cause. It is a multifactorial condition driven by:
- Genetic factors - polygenic inheritance; family studies show a heritable component
- Dietary factors - excessive sodium intake, insufficient potassium, poor diet quality
- Obesity - overweight/obese BMI strongly correlates with higher BP
- Physical inactivity
- Alcohol consumption
- Environmental exposures - heavy metals (lead, mercury, cadmium), air pollution (PM2.5 linked to ~3-5 mmHg rise in SBP), cold climates
- Psychosocial stress
- Harrison's Principles of Internal Medicine 22E, block30
2. Secondary Hypertension
A minority of patients (~5-10%) have an identifiable underlying cause. Secondary hypertension should be considered when there is:
- Treatment-resistant hypertension
- Abrupt worsening of previously controlled BP
- Disproportionate target-organ damage for the BP level
- Abnormal labs such as unprovoked hypokalemia, proteinuria, or LV hypertrophy
Common causes include:
- Renovascular disease (renal artery stenosis)
- Primary aldosteronism (adrenal over-production of aldosterone)
- Obstructive sleep apnea
- Chronic kidney disease
- Pheochromocytoma
- Thyroid disorders
- Drug-induced (NSAIDs, oral contraceptives, decongestants)
- Harrison's Principles of Internal Medicine 22E
Pathophysiology
Blood pressure = Cardiac Output x Peripheral Vascular Resistance. Hypertension arises when one or both of these are chronically elevated through various mechanisms:
- RAAS activation - angiotensin II causes vasoconstriction and aldosterone-driven sodium/water retention
- Sympathetic nervous system overactivity - increased heart rate and vascular tone
- Endothelial dysfunction - reduced nitric oxide, impaired vasodilation
- Renal sodium retention - impaired pressure-natriuresis relationship
- Vascular remodeling - thickening and stiffening of arterial walls over time
Target Organ Damage
Sustained hypertension damages multiple organs. The extent does not always correlate directly with BP level - some patients show damage at moderate pressures, while others tolerate markedly elevated BP with little damage. Organs affected include:
| Organ | Damage |
|---|---|
| Heart | LV hypertrophy, heart failure, coronary artery disease |
| Brain | Stroke, lacunar infarcts, hypertensive encephalopathy |
| Kidneys | Nephrosclerosis, chronic kidney disease, proteinuria |
| Eyes | Hypertensive retinopathy |
| Arteries | Accelerated atherosclerosis, aortic aneurysm |
Cardiovascular Risk
Hypertension is a major independent risk factor for:
- Stroke
- Coronary artery disease / myocardial infarction
- Heart failure
- Peripheral arterial disease (2.5-fold risk increase in men; 3.9-fold in women) - Textbook of Family Medicine 9e
- Chronic kidney disease
The relationship between BP and cardiovascular risk is continuous - even within the "normal" range, lower is generally better.
Diagnosis
BP measurement should be done properly:
- Patient seated, arm at heart level, appropriate cuff size
- Average of 2+ readings on 2+ separate visits
- Supplemented by ambulatory blood pressure monitoring (ABPM) to exclude white-coat hypertension and detect masked hypertension
Management Overview
Lifestyle Modifications (all patients)
- Reduce dietary sodium (target < 2.3 g/day)
- Increase potassium intake (fruits, vegetables)
- DASH diet
- Weight loss if overweight
- Regular aerobic exercise (≥150 min/week)
- Limit alcohol
Pharmacological Treatment
First-line drug classes:
- Thiazide diuretics (e.g., chlorthalidone, hydrochlorothiazide)
- ACE inhibitors (e.g., enalapril, ramipril)
- Angiotensin receptor blockers / ARBs (e.g., losartan, irbesartan)
- Calcium channel blockers (e.g., amlodipine)
Drug choice depends on comorbidities: ACE inhibitors/ARBs are preferred in diabetic nephropathy and proteinuric kidney disease; beta-blockers are preferred when heart failure or post-MI is present. ACE inhibitors may also offer benefits against atherosclerotic vascular disease beyond BP lowering alone. - Textbook of Family Medicine 9e
Latest Guidelines
The 2025 AHA/ACC/AANP et al. Guideline (published in Circulation and Hypertension, PMID 40811497 and 40811516) is the most current authoritative guidance on hypertension prevention, detection, evaluation, and management in adults. If you need specific thresholds, drug algorithms, or target BP goals, this 2025 guideline supersedes prior recommendations.
In summary: Hypertension is a persistent elevation in blood pressure that silently damages the heart, brain, kidneys, and vessels over time. Most cases are primary (no single cause) and are driven by lifestyle and genetic factors. Effective management combines lifestyle changes with antihypertensive medications tailored to the individual patient's risk profile and comorbidities.
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