Hypertension

Hypertension is chronically elevated arterial blood pressure. As a cardiovascular pathology topic it is important both as a disease in its own right and as a major driver of injury to the heart, brain, kidneys and vasculature, accelerating atherosclerosis and imposing the pressure overload that leads to hypertrophy, remodelling and ultimately heart failure.

Definition

Hypertension is a sustained elevation of arterial blood pressure above defined thresholds; most cases are primary (essential) hypertension without a single identifiable cause, while a minority are secondary to an identifiable renal, endocrine, vascular or other disorder. Diagnostic thresholds vary across guidelines.

Scope

The entry covers the distinction between primary (essential) and secondary hypertension, the haemodynamic and regulatory factors that set blood pressure, and the end-organ pathology - vascular, cardiac, renal and cerebral - that sustained elevation produces. It is reference description of disease mechanisms and consequences, not clinical management guidance.

Core questions

• What distinguishes primary (essential) from secondary hypertension?
• Which haemodynamic and regulatory factors - cardiac output, vascular resistance, sodium and the renin-angiotensin system - determine blood pressure?
• How does sustained high pressure injure arteries, the heart, kidneys and brain?
• Why is hypertension a major amplifier of atherosclerotic and heart-failure risk?

Key concepts

• Primary (essential) versus secondary hypertension
• Cardiac output and systemic vascular resistance
• Renin-angiotensin-aldosterone system
• Sodium handling and the pressure-natriuresis relationship
• Pressure overload and left-ventricular hypertrophy
• Hypertensive end-organ damage
• Arteriolosclerosis

Mechanisms

Blood pressure is the product of cardiac output and systemic vascular resistance, regulated by neural, renal and hormonal systems including the renin-angiotensin-aldosterone axis and renal sodium handling. In most people hypertension is primary, reflecting the complex interplay of these regulators rather than a single lesion; a minority have secondary hypertension from renal, endocrine or vascular causes. Sustained elevation injures target organs: arterioles undergo hyaline or hyperplastic arteriolosclerosis, large arteries develop accelerated atherosclerosis, the left ventricle hypertrophies under pressure overload and may progress to failure, the kidney develops nephrosclerosis, and the cerebral vasculature is predisposed to haemorrhage and lacunar disease. These end-organ effects explain why hypertension is a leading contributor to cardiovascular and renal disease.

Clinical relevance

Hypertension is one of the most prevalent and impactful cardiovascular risk factors, contributing to ischaemic heart disease, stroke, heart failure and chronic kidney disease. This entry describes its mechanisms and end-organ pathology for reference; it does not provide blood-pressure targets for, or treatment advice about, any individual.

Epidemiology

Hypertension affects a very large share of the adult population worldwide and is a leading modifiable risk factor for cardiovascular and renal disease; analyses of global data have documented its high and rising prevalence across regions and income levels.

History

Once regarded by some as a benign or even necessary compensatory state, hypertension was established through twentieth-century epidemiology and physiology as a major cause of cardiovascular and renal damage. Guyton's integrative analysis of pressure regulation and renal sodium handling shaped mechanistic understanding, and successive consensus guidelines have refined diagnostic thresholds and the framing of cardiovascular risk; thresholds continue to differ across organisations.

Debates

Where to set the diagnostic and treatment thresholds for hypertension

Guidelines differ on the blood-pressure levels that define hypertension and warrant intervention, reflecting differing weightings of trial evidence, risk-based versus threshold-based approaches and population context.

Key figures

• Paul K. Whelton
• Thomas Unger
• Arthur Guyton

Seminal works

• kearney-2005
• whelton-2018

Frequently asked questions

What is the difference between primary and secondary hypertension?

Primary (essential) hypertension, which accounts for the great majority of cases, has no single identifiable cause and reflects the interplay of many regulators of blood pressure; secondary hypertension is caused by an identifiable disorder such as renal, endocrine or vascular disease.

How does high blood pressure damage organs?

Sustained pressure injures small and large vessels (arteriolosclerosis and accelerated atherosclerosis), drives left-ventricular hypertrophy and heart failure, produces nephrosclerosis in the kidney, and predisposes the brain to stroke.