Atlas of pathophysiology, 2 Edition

Part II - Disorders

Renovascular Hypertension

Renovascular hypertension is a rise in systemic blood pressure resulting from stenosis of the major renal arteries or their branches or from intrarenal atherosclerosis. The narrowing or sclerosis may be partial or complete, and the resulting blood pressure elevation may be benign or malignant. Approximately 5% to 10% of patients with high blood pressure display renovascular hypertension.

Age Alert

Renovascular hypertension is most common in persons under age 30 or over age 50.

Causes

In 95% of all patients with renovascular hypertension

·   Atherosclerosis (especially in older men)

·   Fibromuscular diseases of the renal artery wall layers, such as medial fibroplasia and, less commonly, intimal or subadventitial fibroplasia

Other causes

·   Arteritis

·   Anomalies of renal arteries

·   Embolism

·   Trauma

·   Tumor

·   Dissecting aneurysm

Pathophysiology

Stenosis or occlusion of the renal artery stimulates the affected kidney to release the enzyme renin, which converts the plasma protein angiotensinogen to angiotensin I. As angiotensin I circulates through the lungs and liver, it's converted to angiotensin II, which causes peripheral vasoconstriction, increased arterial pressure and aldosterone secretion and, eventually, hypertension.

Signs and symptoms

·   Elevated systemic blood pressure

·   Headache, light-headedness

·   Palpitations, tachycardia

·   Anxiety, mental sluggishness

·   Decreased tolerance of temperature extremes

·   Retinopathy

·   Significant complications: heart failure, myocardial infarction, stroke, renal failure

Diagnostic test results

·   Renal scan testing that includes administration of an angiotensin-converting enzyme inhibitor such as captopril, renal angiography, and renal ultrasound with Doppler evaluation shows evidence of renal stenosis.

·   Excretory urography shows slow uptake in one or both kidneys.

·   Complete blood count reveals anemia.

·   Blood chemistries show abnormal electrolyte levels and elevated blood urea nitrogen and creatinine.

Treatment

·   Symptomatic measures: antihypertensives, diuretics, sodium-restricted diet

·   Balloon catheter renal artery dilation in selected cases to correct renal artery stenosis without risks and morbidity of surgery

·   Insertion of renal artery stents

·   Surgery to restore adequate circulation and to control severe hypertension or severely impaired renal function:

§  renal artery bypass, endarterectomy, arterioplasty

§  as a last resort, nephrectomy

P.371

RENOVASCULAR HYPERTENSION

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Mechanism of renovascular hypertension

1.     Renal artery stenosis causes reduction of blood flow to the kidneys.

2.     Kidneys secrete renin in response.

3.     Renin combines with angiotensinogen in the liver to form angiotensin I.

4.     In the lungs, angiotensin I is converted to angiotensin II, a vasoconstrictor.

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