Atlas of pathophysiology, 2 Edition

Part II - Disorders

Cardiovascular disorders

Hypertension

Hypertension, an elevation in diastolic or systolic blood pressure, occurs as two major types: primary (essential), which is the most common, and secondary, which results from renal disease or another identifiable cause. Malignant hypertension is a severe, fulminant form of either type. Hypertension is a major cause of cerebrovascular accident, cardiac disease, and renal failure.

Causes

Risk factors for primary hypertension

·   Family history

·   Advancing age

·   Race (most common in blacks)

·   Obesity

·   Tobacco use

·   High intake of sodium or saturated fat

·   Excessive alcohol consumption

·   Sedentary lifestyle, stress

Causes of secondary hypertension

·   Excess renin

·   Mineral deficiencies (calcium, potassium, and magnesium)

·   Diabetes mellitus

·   Coarctation of the aorta

·   Renal artery stenosis or parenchymal disease

·   Brain tumor, quadriplegia, head injury

·   Pheochromocytoma, Cushing's syndrome, hyperaldosteronism

·   Thyroid, pituitary, or parathyroid dysfunction

·   Hormonal contraceptives, cocaine, epoetin alfa, sympathetic stimulants, monoamine oxidase inhibitors taken with tyramine, estrogen replacement therapy, nonsteroidal anti-inflammatory drugs

·   Pregnancy

Pathophysiology

Arterial blood pressure is a product of total peripheral resistance and cardiac output. Cardiac output is increased by conditions that increase heart rate or stroke volume, or both. Peripheral resistance is increased by factors that increase blood viscosity or reduce the lumen size of vessels.

Several mechanisms may lead to hypertension, including:

·   changes in the arteriolar bed causing increased peripheral vascular resistance

·   abnormally increased tone in the sympathetic nervous system that originates in the vasomotor system centers, causing increased peripheral vascular resistance

·   increased blood volume resulting from renal or hormonal dysfunction

·   arteriolar thickening caused by genetic factors, leading to increased peripheral vascular resistance

·   abnormal renin release, resulting in the formation of angiotensin II, which constricts the arteriole and increases blood volume.

Prolonged hypertension increases the workload of the heart as resistance to left ventricular ejection increases. To increase contractile force, the left ventricle hypertrophies, raising the oxygen demand and workload of the heart. Cardiac dilation and failure may occur when hypertrophy can no longer maintain sufficient cardiac output. Because hypertension promotes coronary atherosclerosis, the heart may be further compromised by reduced blood flow to the myocardium, resulting in angina or myocardial infarction. Hypertension also causes vascular damage, leading to accelerated atherosclerosis.

The pathophysiology of secondary hypertension is related to the underlying disease.

Signs and symptoms

·   Generally produces no symptoms

·   Systolic blood pressure consistently over 139 mm Hg

·   Diastolic blood pressure consistently over 89 mm Hg

·   Occipital headache

·   Epistaxis possibly due to vascular involvement

·   Bruits

·   Dizziness, confusion, fatigue

·   Blurry vision

·   Nocturia

·   Edema

Clinical Tip

Many older adults have a wide auscultatory gap — the hiatus between the first Korotkoff's sound and the next sound. Failure to inflate the blood pressure cuff high enough can lead to missing the first Korotkoff's sound and underestimating the systolic blood pressure. To avoid missing the first sound, palpate the radial artery and inflate the cuff 20 mm beyond disappearance of the pulse beat.

Diagnostic test results

·   Serial blood pressure measurements show elevation.

·   Urinalysis shows protein, casts, red blood cells, or white blood cells, suggesting renal disease; presence of catecholamines associated with pheochromocytoma; or glucose, suggesting diabetes.

·   Blood chemistry reveals elevated blood urea nitrogen and serum creatinine levels suggestive of renal disease, or hypokalemia indicating adrenal dysfunction.

·   Excretory urography may reveal renal atrophy, indicating chronic renal disease.

·   Electrocardiography detects left ventricular hypertrophy or ischemia.

·   Chest X-rays show cardiomegaly.

·   Echocardiography reveals left ventricular hypertrophy.

Treatment

·   Lifestyle modifications to reduce risk factors

·   Diuretics

·   Angiotensin-converting enzyme inhibitors

·   Alpha-receptor blockers

·   Alpha-receptor agonists

·   Beta-adrenergic blockers

·   Treatment of underlying cause

·   Nitroprusside or an adrenergic inhibitor such as propranolol

P.59

BLOOD VESSEL DAMAGE IN HYPERTENSION

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