Hypertension or high blood pressure is a medical condition where the blood pressure is chronically elevated. While it is formally called arterial hypertension, the word "hypertension" without a qualifier usually refers to arterial hypertension. more...
Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure.
Blood pressure is a continuous variable, and risks of various adverse outcomes rise with it. A blood pressure of less than 120/80 mmHg is defined as "normal" in adults. Hypertension is usually diagnosed on finding blood pressure of 140/90 mmHg or above, measured on both arms on three occasions over a few weeks.
Recently, the JNC VII (The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure) has defined blood pressure 120/80 mmHg to 140/90 mmHg as "prehypertension". Prehypertension is not a disease category. Rather, it is a designation chosen to identify individuals at high risk of developing hypertension (JNC VII).
In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered a risk factor and may warrant treatment.
- Age. Over time, the number of collagen fibres in artery and arteriole walls increases, making blood vessels stiffer. With the reduced elasticity comes a smaller cross-sectional area in systole, and so a raised mean arterial blood pressure.
- High salt intake
- Sedentary lifestyle
- Tobacco smoking
- Alcohol abuse
- High levels of saturated fat in the diet
- Obesity. In obese subjects, losing a kilogram of mass generally reduces blood pressure by 2 mmHg.
- Low birth-weight
- Diabetes mellitus
- Various genetic causes
While most forms of hypertension have no known underlying cause (and are thus known as "essential hypertension" or "primary hypertension"), in about 5% of the cases, there is a known cause, and thus the hypertension is secondary hypertension.
The mechanisms behind the factors associated with inessential hypertension are generally fully understood, and are outlined at secondary hypertension. However, those associated with essential hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
- Inability of the kidneys to excrete sodium, resulting in natriuretic factor (note: the existence of this substance is theoretical) being secreted to promote salt excretion with the side-effect of raising total peripheral resistance.
- An overactive renin / angiotension system leads to vasoconstriction and retention of sodium and water. The increase in blood volume leads to hypertension.
- An overactive sympathetic nervous system, leading to increased stress responses.
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