|
Blood pressure is the amount of force required for the heart to circulate blood through the body. Systolic blood pressure represents the maximal blood pressure during systole, and diastolic blood pressure the minimum pressure at the end of ventricular diastole. Arterial blood pressure can be defined hemodynamically as the product of cardiac output and total peripheral resistance. Cardiac output is the main determinant of systolic pressure while peripheral resistance largely determines the level of diastolic pressure.
Under normal physiologic conditions, the blood pressure stays within narrow limits. It may reach a peak during emotional or physical stress, and falls the lowest during sleep. Generally, blood pressure tends to be lower in women than men, it tends to be higher in blacks than whites, and it rises with age.
Hypertension is a cardiovascular disease characterized by elevation of blood pressure above arbitrary values considered normal for people of similar racial and environmental background.(1) Hypertension affects the vasculature of all major organs (heart, brain, kidneys), and myocardial infarction and congestive heart failure account for the majority of deaths secondary to hypertension.
The Sixth Joint National Committee on the Detection, Evaluation, and Treatment of High Blood Pressure (JNC-VI) classifies hypertension in adults as follows:(2)
| Optimal |
<120 |
<80 |
| Normal |
<130 |
<85 |
| High Normal |
130-139 |
85-89 |
| Hypertension |
| Stage 1 |
140-159 |
90-99 |
| Stage 2 |
160-179 |
100-109 |
| Stage 3 |
>180 |
>110 |
Because arterial blood pressure is a continuous variable, it is impossible to define a cut point below which is normal and above which is abnormally high. Nevertheless, evidence from epidemiologic studies clearly indicates a strong correlation between blood pressure and morbidity and mortality.(3) The higher the pressure, the more likely an individual is to experience a stroke, myocardial infarction, angina, heart failure, renal failure, or early death from a cardiovascular cause.(4)
Isolated systolic hypertension is the term used to describe a diastolic pressure less than 90 mm Hg and systolic blood pressure of greater than 140 mm Hg. It is believed to result from the pathophysiology of aging and indicates an increased risk of cardiovascular morbidity.
Hypertensive crisis is defined as a marked increase in diastolic blood pressure and can be divided into the categories of hypertensive emergency or hypertensive urgency. A hypertensive emergency exists if elevation of BP is accompanied by an acute target organ injury. Examples of this may be intracranial hemorrhage, acute left ventricular failure wi
|
