Hypertension: contributing factors and vascular changes
THE CONTEXT
Hypertension reflects multiple influences on blood pressure regulation. Most cases have no identifiable specific cause, and sustained hypertension produces structural changes in arteries.
Mechanisms and classification
•
Contributing factors include renal dysfunction, peripheral resistance, vessel tone, endothelial dysfunction, autonomic tone, insulin resistance and neurohumoral factors.
•
In more than 95% of cases, no specific underlying cause is found; these patients have essential hypertension.
•
In about 5% of cases, hypertension is secondary to a specific disease.
Genetic, environmental and developmental influences
•
Hypertension is more common in some ethnic groups, particularly African Americans and Japanese; approximately 40%–60% is explained by genetic factors.
•
Age is a strong risk factor across all ethnic groups.
•
Important environmental factors are high salt intake, heavy alcohol consumption, obesity and lack of exercise.
•
Impaired intrauterine growth and low birth weight are associated with increased risk of hypertension later in life.
Changes in larger arteries
•
In arteries greater than 1 mm in diameter, the internal elastic lamina thickens, smooth muscle hypertrophies and fibrous tissue is deposited.
•
These vessels dilate, become tortuous and develop less compliant walls.
Changes in smaller arteries and atheroma
•
In arteries smaller than 1 mm, hyaline arteriosclerosis affects the wall, the lumen narrows and aneurysms may develop.
•
Widespread atheroma may lead to coronary and cerebrovascular disease, particularly when other risk factors are present.