Introduction of Hypertension

 Hypertension

Blood pressure is the force with which blood pushes against the artery walls as it travels through the body. Like air in a balloon, blood fills arteries to a certain capacity—and just as too much air pressure can cause damage to a balloon, too much blood pressure can harm healthy arteries. Blood pressure is measured by two methods—systolic pressure and diastolic pressure. Systolic pressure measures cardiac output and refers to the pressure in the arterial system at its highest. Diastolic pressure measures peripheral resistance and refers to arterial pressure at its lowest. Blood pressure is normally mea sured at the brachial artery with a sphygmomanometer (pressure cuff) in millimeters of mercury (mm Hg) and given as systolic over diastolic pressure.

A blood pressure reading thus appears as two methods. The upper method is the systolic pressure, which is the peak force of blood as the heart pumps it. The lower method the diastolic pressure, which is the pressure when the heart is filling or relaxing before the next beat. Normal blood pressure for an adult is 120/70 (on average), but normal for an individual varies with the height, weight, fitness level, age, and health of a person.
 
What Is Hypertension?

Hypertension, or high blood pressure, is defined as a reading of 140/90 on three consecutive measurements at least six hours apart. The definition varies for pregnant women, where hypertension is defined as 140/90 on two consecutive measurements six hours apart. Consistently high blood pressure causes the heart to work harder than it should and can damage the coronary arteries, the brain, the kidneys, and the eyes. Hypertension is a major cause of stroke.

Classification

Category    Systolic, mm Hg          Diastolic, mm Hg
________________________________________
Optimal                  <120     and       <80
Normal                   <130     and         <85
High normal         130–139     or          85–89

Hypertension           
Stage 1 (mild)            140–159      or    90–99
Subgroup: borderline   140–149       or    90–94
Stage 2 (moderate)       160–179    or    100–109
Stage 3 (severe)            180            or     110

Isolated systolic hypertension  140   and    <90
Subgroup: borderline            140–149    and    <90

Types of Hypertension

Hypertension is classified as either primary (or essential) hypertension or secondary hypertension. Primary hypertension has no specific origin but is strongly associated with lifestyle. It is responsible for 90 to 95 percent of diagnosed hypertension and is treated with stress management, changes in diet, increased physical activity, and medication (if needed). Secondary hypertension is responsible for 5 to 10 percent of diagnosed hypertension. It is caused by a preexisting medical condition such as congestive heart failure, kidney failure, liver failure, or damage to the endocrine (hormone) system.

Primary Hypertension
BP is a quantitative trait that is highly variable1 ; in population studies, BP has a normal distribution that is slightly skewed to the right. There is a strong positive and continuous correlation between BP and the risk of CVD (stroke, myocardial infarction, heart failure), renal disease, and mortality, even in the normotensive range. This correlation is more robust with systolic than with diastolic BP.2 There is no specific level of BP where cardiovascular and renal complications start to occur; thus the definition of hypertension is arbitrary but needed for practical reasons in patient assessment and treatment.

The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI) defined and classified hypertension in adults, as shown in above The diagnosis of hypertension is made when the average of 2 or more diastolic BP measurements on at least 2 subsequent visits is  90 mm Hg or when the average of multiple systolic BP readings on 2 or more subsequent visits is consistently  140 mm Hg. Isolated systolic hypertension is defined as systolic BP  140 mm Hg and diastolic BP <90 mm Hg. Individuals with high normal BP tend to maintain pressures that are above average for the general population and are at greater risk for development of definite hypertension and cardiovascular events than the general population. With the use of these definitions, it is estimated that 43 million people in the United States have hypertension or are taking antihypertensive medication, which is  24% of the adult population. This proportion changes with (1) race, being higher in blacks (32.4%) and lower in whites (23.3%) and Mexican Americans (22.6%); (2) age, because in industrialized countries systolic BP rises throughout life, whereas diastolic BP rises until age 55 to 60 years and thus the greater increase in prevalence of hypertension among the elderly is mainly due to systolic hypertension; (3) geographic patterns, because hypertension is more prevalent in the southeastern United States; (4) gender, because hypertension is more prevalent in men (though menopause tends to abolish this difference); and (5) socioeconomic status, which is an indicator of lifestyle attributes and is inversely related to the prevalence, morbidity, and mortality rates of hypertension. Essential, primary, or idiopathic hypertension is defined as high BP in which secondary causes such as renovascular disease, renal failure, pheochromocytoma, aldosteronism, or other causes of secondary hypertension or mendelian forms (monogenic) are not present. Essential hypertension accounts for 95% of all cases of hypertension. Essential hypertension is a heterogeneous disorder, with different patients having different causal factors that lead to high BP. Essential hypertension needs to be separated into various syndromes because the causes of high BP in most patients presently classified as having Known Etiological Factors in Essential Hypertension

Although it has frequently been indicated that the causes of essential hypertension are not known, this is only partially true because we have little information on genetic variations or genes that are overexpressed or underexpressed as well as the intermediary phenotypes that they regulate to cause high BP.4 A number of factors increase BP, including (1) obesity, (2) insulin resistance, (3) high alcohol intake, (4) high salt intake (in salt-sensitive patients), (5) aging and perhaps (6) sedentary lifestyle, (7) stress, (8) low potassium intake, and (9) low calcium intake.5 6 Furthermore, many of these factors are additive, such as obesity and alcohol intake.


Secondary Hypertension

Secondary hypertension accounts for approximately 5-10% of all cases of hypertension, with the remaining being primary hypertension.  Secondary hypertension has an identifiable cause whereas primary hypertension has no known cause (i.e., idiopathic).

There are many known conditions that can cause secondary hypertension. Regardless of the cause, arterial pressure becomes elevated either due to an increase in cardiac output, an increase in systemic vascular resistance, or both. When cardiac output is elevated, it is generally due to either increased neurohumoral activation of the heart or increased blood volume. 

Patients with secondary hypertension are best treated by controlling or removing the underlying disease or pathology, although they may still require antihypertensive drugs.

Some causes for secondary hypertension are listed below:

Renal artery stenosis

Chronic renal disease

Primary hyperaldosteronism

Stress

Sleep apnea

Hyper- or hypothyroidism

Pheochromocytoma

Preeclampsia