Hypertension

Introduction

Hypertension is defined as a consistent elevation of arterial pressure above the normal range expected for a particular age group.

it is now identified as one of the most significant risk factors for cardiovascular (CV) disease in the United States.

Increasing awareness and diagnosis of hypertension, and improving control of BP with appropriate treatment, are considered critical public health initiatives to reduce CV morbidity and mortality.

 Data from 2003 to 2006 indicate that of the population of Americans with hypertension 77.6% are aware that they have hypertension, only 67.9% are on some form on

antihypertensive treatment, and only 44.1% of all patients have controlled

BP.

EPIDEMIOLOGY

Approximately 31% of Americans (74.5 million people) have elevated BP, defined as greater than or equal to 140/90 mm Hg.

BP values increase with age, and hypertension (persistently elevated BP values) is very common in the elderly.

during a 5-year period between 1995 and 2000 in Saudi Arabia The prevalence of hypertension was 26.1% in

crude terms. For males, the prevalence of hypertension was 28.6%, while for females; the prevalence was significantly lower at 23.9% (p<0.001).

ETIOLOGY

In most patients, hypertension results from unknown pathophysiological etiology (essential or primary hypertension ).

This form of hypertension cannot be cured, but it can be controlled.

A small percentage of patients have a specific cause of their hypertension ( secondary hypertension ).

There are many potential secondary causes that either are concurrent medical conditions or are endogenously induced. If the cause can be identified, hypertension in these patients can be mitigated or potentially be cured.

Hypertension

Arterial BP is hemodynamically generated by the interplay between blood flow and the resistance to blood flow. It is mathematically defined as the product of cardiac output (CO) and total peripheral resistance (TPR) according to the following equation:

BP = CO x TPR

Arterial BP = Cardiac Output (CO) x Systemic vascular resistance (SVR)

Cardiac Output = stroke volume x beats per min

Systemic vascular resistance = force opposing the movement of blood within the blood vessels

stroke volume = The volume of blood pumped by one ventricle during one contraction.

Primary or essential hypertension

Over 90% of individuals with high BP have essential hypertension

Genetic factors may play an important role in the development of essential hypertension

several theories have been proposed to explain the mechanism of its occurrence. Involving: chronic increases in fluid volume, enhanced sympathetic activity or abnormal salt and water excretion by the kidneys

A number of key physiologic changes have also been observed in the kidneys of patients with essential hypertension that may contribute to the development of the disorder.

These renal changes include increased resistance to renal blood flow, decreased renal blood flow with disease progression and inadequate excretion of fluid and electrolytes at normal blood

pressures.

Diagnosis and classification

Hypertension is termed the silent killer because most patients do not have symptoms.

The primary physical finding is elevated BP.

The diagnosis of hypertension cannot be made based on one elevated BP measurement

The average of two or more measurements taken during two or more clinical encounters should be used to diagnose hypertension.

 This BP average should be used to establish a diagnosis, and then classify the stage of hypertension using

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TABLE 19-3. Classification of Blood Pressure in Adults

(Age ≥18 Years)

Risk Factors for the Development of Essential Hypertension

A number of genetic, environmental and dietary factors are associated with an increased risk for the development of essential hypertension:

Familial history of hypertension Increasing ageRace and gender: incidence of hypertension is

significantly higher in black menHigh dietary salt intake

HyperinsulinemiaHeavy alcohol consumptionObesityCigarette smokingLow dietary intake of potassium, calcium and

magnesium

Blood Pressure Measures

Systolic blood pressure = the pressure in the arteries when the ventricles are contracting

Diastolic blood pressure = the pressure in the arteries when the ventricles are relaxed

Mean arterial pressure = average blood pressure in the arteries, estimated as diastolic blood pressure + one third of the pulse pressure

Pulse pressure = systolic blood pressure – diastolic blood pressure

Methods for Measuring Blood Pressure

Sphygmomanometer (blood pressure cuff) — indirect measure

Intra-arterial catheter — direct measure

Manifestations of essential hypertension

Although a small percentage of patients with essential hypertension may present with frequent headaches, most are asymptomatic.

As a result, essential hypertension may go undetected and untreated for a number of years.

Unless diagnosed early by blood pressure screening and treated appropriately, chronic essential hypertension can progressively damage tissue and organs.

Hypertension-Associated Target-Organ Damage

chronic essential hypertension can progressively damage tissue and organs, including:

1- Blood vessels — Prolonged high blood pressure in the arteries and arterioles will cause the walls of the blood vessels to thicken to compensate for the excess stress.

The chronic increased forces that the blood vessel walls are exposed to also predispose them to atherosclerosis and aneurysm. As a result, untreated essential hypertension puts patients at a greater risk of coronary artery disease, cerebrovascular disease and renal vascular disease.

The risk for atherosclerosis is exacerbated in hypertensive patients who have high serum cholesterol, are obese, have diabetes or who smoke.

2- Heart — Chronic elevation of arterial pressure means the heart must now pump blood out against a continually elevated afterload. As compensation for this increased afterload, left ventricular hypertrophy occurs.

The hypertrophied ventricle will require increased blood, oxygen and nutrient supplies and will be at greater risk for arrhythmia.

When the ventricular enlargement reaches a certain point, contractile function will no longer be supported and pump failure (congestive heart failure, CHF) will ensue.

3- Kidneys — Chronically elevated pressure can damage the renal vasculature and compromise renal blood flow, oxygen delivery and filtration. As a result, renal insufficiency can occur that may eventually progress to renal failure

Decreased renal blood flow can lead to activation of the

renin–angiotensin system and contribute to a cycle of increasing blood pressure and decreasing renal function.

Hypertension-induced renal injury is exacerbated in patients with diabetes.

4- Eyes — Vision can suffer in a patient with chronic hypertension as a result of increased arteriolar pressure in the eyeball or from vascular sclerosis, both of which can damage the retina and eye as a whole.

Secondary hypertension

Fewer than 10% of patients have secondary hypertension where either a comorbid disease or drug (or other product) is responsible for elevating BP

One of the most common causes of secondary hypertension is renal artery stenosis, which is a narrowing of the renal arteries due to atherosclerosis.

As a result of the reduced renal blood flow that accompanies the narrowed blood vessels, the kidney responds by activating the renin–angiotensin system that in turn leads to vasoconstriction and salt and water retention.

Causes of secondary hypertension can include: - renal artery stenosis- Hyperaldosteronism (excess aldosterone production)- Pheochromocytoma (tumor of the adrenal medulla).

Secondary hypertension caused by renal artery stenosis may be effectively treated by ACE inhibitors or may be resolved with angioplasty or surgical intervention to reopen the occluded renal blood vessels

Malignant hypertension

In a small percentage of patients with chronic essential hypertension, dramatic increases in blood pressure (greater than 120 to 130 mmHg diastolic pressure) may occur suddenly.

These sudden increases in blood pressure are termed malignant hypertension and are especially dangerous because dramatic increases in pressure may damage the retina or kidneys and lead to cerebral edema and stroke.

Malignant hypertension requires immediate medical treatment with powerful intravenous vasodilators such as diazoxide or sodium nitroprusside.

Hypertensive Emergency : Elevated BP , there is evidence of end-organ damage

Hypertensive Urgency : elevated BP but without evidence of end-organ damage

Hypotension

Hypotension is an abnormally low blood pressure. One common form of hypotension is orthostatic hypotension (also called postural hypotension ) that occurs upon standing.

The act of standing initiates a series of reflex responses in the body that are designed to prevent pooling of blood in the lower extremities and a decrease in blood pressure. These reflexes include vasoconstriction in the lower limbs and a reflex increase in heart rate.

Causes of Orthostatic Hypotension

Aging — Associated with reduced baroreceptor responses, decreased cardiac output and reduced vascular responsiveness

Decreased blood or fluid volume — Caused by dehydration, diarrhea, diuretic use

Autonomic nervous defects — An inability to initiate vasoconstriction and increased heart rate reflexes

Prolonged bed rest

Drug-induced — Examples: antihypertensive drugs, calcium channel blockers, vasodilators

Idiopathic — Cause is not known

Manifestations

Dizziness (syncope)

Decreased cardiac output

Reduced brain blood flow

Pooling of blood in the extremities

Falls and injuries, particularly in elderly individuals

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