Blood pressure is a continuous variable with a reasonably normal, or bell-shaped-curve, distribution across the general population. High blood pressure has been classically defined as a diastolic pressure of greater than 90 mm Hg, a systolic pressure greater than 140 mm Hg, or both. The higher the blood pressure, the greater the risk of a cardiovascular events; conversely, the lower the blood pressure, the lower the cardiovascular risk. It is important to stress that isolated systolic hypertension, a systolic pressure of greater than 140 mm Hg with a diastolic pressure of less than 90 mm Hg, is abnormal and requires attention.
The diagnosis of hypertension should not be based on measurements taken at a single office visit. Elevated readings should be confirmed at a second or third visit to establish the diagnosis, and any factors that might elevate blood pressure should be excluded. For example, the patient should refrain from smoking for at least 30 min prior to blood pressure measurement. The blood pressure should be measured, with a cuff of the appropriate size, after at least 5 min of rest in a seated or supine position. The cuff should cover approximately one third of the length of the upper arm and should completely or almost completely encircle the arm. Too small a cuff may overestimate the true blood pressure because it may only partially compress the artery, requiring a higher pressure for total occlusion. The measurements should be made twice in both arms, for a total of four measures. The average of the two measurements in the arm with the higher values is used as the baseline value of blood pressure. Systolic blood pressure is indicated by the phase 1 Korotkoff sound (onset) and diastolic pressure by phase 5, or disappearance, in adults. In children, phase 4, or muffling, has been suggested as the best indicator of diastolic pressure.
The blood pressure obtained in the physician's office, however, does not always accurately represent that experienced by the patient during routine daily living. About 20–30% of patients with mildly elevated office blood pressure may have a hyperadrenergic response to having their blood pressure measured. This hyperreactivity is called white-coat, pseudo-, or office hypertension and may be related to anxiety from merely being in the physician's office or clinic. If the blood pressure is measured in a nonthreatening situation by a friend or relative or with an automated device, the blood pressure in these individuals may be normal. Blood pressure hyperreactivity should be suspected in patients who have persistently elevated blood pressure in the office and normal pressure measurements out of the office or in patients who have hypotensive symptoms but remain hypertensive in the office despite therapy. It has not been clearly established whether the blood pressure in these individuals is truly normal or whether they have an early or different form of hypertension. Several studies have found alterations in cardiac structure and function that are somewhere between those found in normotensive subjects and those found in hypertensive patients. No large outcome studies are available.
The best way to evaluate a patient with suspected white-coat hypertension is to use an automated ambulatory blood pressure device that measures the blood pressure periodically throughout the day and night. The patient quickly becomes accustomed to the small, light-weight, portable device, and a representative series of recordings can be obtained. The accuracy of these devices allows separation of those patients with true elevations of blood pressure from those who are hyperreactors. The devices are also useful in evaluating patients with episodic hypertension and those with borderline blood pressure elevations who already have evidence of involvement of the heart, kidneys, or vasculature. Automated blood pressure monitoring can be used to evaluate the duration and effectiveness of antihypertensive medication; correlate blood pressure with damage to the heart, kidneys, or blood vessels; and determine the prognosis. Its value in routine evaluation of hypertensive patients has not been clearly established, however.
Sabtu, 05 Juli 2008
Pathophysiology & Etiology
Until recently, high blood pressure was synonymous with hypertension; now, however, data suggest that there is considerably more to hypertension than increased blood pressure. Several metabolic and functional abnormalities have even been observed in the children of hypertensive patients prior to blood pressure elevation that are similar to, but of a lesser magnitude than, those found in their parents. Hypertension is also associated with insulin resistance and glucose intolerance. Insulin levels are consistently higher in hypertensive patients than in normotensive controls. This condition of hyperinsulinemia is worsened by thiazide diuretics, especially in the presence of b-blocker therapy. Hyperinsulinemia produces a proliferation of vascular smooth muscle and fibrous tissue and adversely affects the serum lipid profile.
Renin and angiotensin levels are also important factors in determining both the response to therapy and the prognosis. Hypertensive patients with high renin levels have a greater incidence of myocardial infarction than do similar patients with lower levels. Normotensive young adults with a family history of hypertension have been found to have thicker left ventricular (LV) walls and alterations of LV diastolic filling in comparison with control subjects. Although not frankly abnormal, these latter two findings are similar to but less severe than those observed in hypertensive patients. Renal reserve also appears diminished in the children of hypertensive parents.
Hypertension, therefore, is a multisystem disorder with involvement of the cardiovascular, neuroendocrine, and renal systems with a strong genetic component.
A. NATURAL HISTORY
Blood pressure gradually increases throughout childhood and adolescence. The best predictor of the level of future blood pressure is the relative level of blood pressure of a child in relation to his or her peers. During childhood and adolescence, body weight is a major determinant of blood pressure, with heavier children having higher blood pressures. High blood pressure is uncommon under the age of 20; if present, it is usually associated with renal insufficiency, renal artery stenosis, or coarctation of the aorta. The initial presentation of high blood pressure usually occurs in the third to the sixth decade, and blood pressure may fluctuate significantly during the early course of the disease. The prevalence of high blood pressure increases with age and is greater in men than women. In the elderly population, this reverses, and more women than men have high blood pressure.
Everyone should be screened for the presence of high blood pressure; testing should be done routinely in the physician's office or at one of the larger community screening activities. These activities are typically targeted at those at greater risk of high blood pressure: older individuals, individuals with previously high-normal blood pressures, blacks, sedentary individuals, and those with a family history of hypertension.
Burt VL, Whelton P, Rocella EJ, et al: Prevalence of hypertension in the U. S. adult population. Results of the Third National Health and Nutrition Examination Survey, 1988–91. Hypertension 1995;25:305.
B. ETHNIC AND SOCIOECONOMIC FACTORS
Blacks have both an earlier onset and a greater prevalence of high blood pressure than do whites, Asians, and Native Americans at all ages. Over the age of 50 years, hypertension is prevalent in more than 40% of black males, compared with approximately 27% in white males. Severe high blood pressure (diastolic BP at least 115 mm Hg) is five times more common in black men than in white men and seven times more common in black women than in white women. Blacks therefore tend to have more serious complications, especially strokes, from high blood pressure. Other factors also affect the prevalence of high blood pressure. Among all ethnic groups, less-educated individuals have a greater prevalence of high blood pressure than do more highly educated individuals, especially in lower socioeconomic groups.
The level of blood pressure elevation is directly related to total cardiovascular risk, and the presence of other cardiovascular disease risk factors, especially diabetes or dyslipidemia, is synergistic with high blood pressure.
Renin and angiotensin levels are also important factors in determining both the response to therapy and the prognosis. Hypertensive patients with high renin levels have a greater incidence of myocardial infarction than do similar patients with lower levels. Normotensive young adults with a family history of hypertension have been found to have thicker left ventricular (LV) walls and alterations of LV diastolic filling in comparison with control subjects. Although not frankly abnormal, these latter two findings are similar to but less severe than those observed in hypertensive patients. Renal reserve also appears diminished in the children of hypertensive parents.
Hypertension, therefore, is a multisystem disorder with involvement of the cardiovascular, neuroendocrine, and renal systems with a strong genetic component.
A. NATURAL HISTORY
Blood pressure gradually increases throughout childhood and adolescence. The best predictor of the level of future blood pressure is the relative level of blood pressure of a child in relation to his or her peers. During childhood and adolescence, body weight is a major determinant of blood pressure, with heavier children having higher blood pressures. High blood pressure is uncommon under the age of 20; if present, it is usually associated with renal insufficiency, renal artery stenosis, or coarctation of the aorta. The initial presentation of high blood pressure usually occurs in the third to the sixth decade, and blood pressure may fluctuate significantly during the early course of the disease. The prevalence of high blood pressure increases with age and is greater in men than women. In the elderly population, this reverses, and more women than men have high blood pressure.
Everyone should be screened for the presence of high blood pressure; testing should be done routinely in the physician's office or at one of the larger community screening activities. These activities are typically targeted at those at greater risk of high blood pressure: older individuals, individuals with previously high-normal blood pressures, blacks, sedentary individuals, and those with a family history of hypertension.
Burt VL, Whelton P, Rocella EJ, et al: Prevalence of hypertension in the U. S. adult population. Results of the Third National Health and Nutrition Examination Survey, 1988–91. Hypertension 1995;25:305.
B. ETHNIC AND SOCIOECONOMIC FACTORS
Blacks have both an earlier onset and a greater prevalence of high blood pressure than do whites, Asians, and Native Americans at all ages. Over the age of 50 years, hypertension is prevalent in more than 40% of black males, compared with approximately 27% in white males. Severe high blood pressure (diastolic BP at least 115 mm Hg) is five times more common in black men than in white men and seven times more common in black women than in white women. Blacks therefore tend to have more serious complications, especially strokes, from high blood pressure. Other factors also affect the prevalence of high blood pressure. Among all ethnic groups, less-educated individuals have a greater prevalence of high blood pressure than do more highly educated individuals, especially in lower socioeconomic groups.
The level of blood pressure elevation is directly related to total cardiovascular risk, and the presence of other cardiovascular disease risk factors, especially diabetes or dyslipidemia, is synergistic with high blood pressure.
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