High Blood Pressure: In-Depth Report

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High Blood Pressure: In-Depth Report

* Review Date: 4/14/2006
* Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of high blood pressure.

Alternative Names:
Hypertension

Causes

Hypertension is referred to as essential (primary) when the doctor is unable to identify a specific cause. It is by far the most common type of high blood pressure. The causes of this type are unknown but are likely to be a complex combination of genetic, environmental, and other factors.

Genetic Factors. A number of genetic factors or interactions between genes play a major role in essential hypertension. Experts think that the chromosomes (13 and 18) house the genes responsible for blood pressure regulation, although pinning down the range of specific genes involved in hypertension is more difficult.

Abnormalities in the Angiotensin-Renin-Aldosterone System. Genes under intense study are those that regulate a group of hormones known collectively as the angiotensin-renin-aldosterone system. This system influences all aspects of blood pressure control, including blood vessel contraction, sodium and water balance, and cell development in the heart.

Experts believed that this system evolved millions of years ago to protect early humans during drought or stress by retaining salt and water and narrowing blood vessels to ensure adequate blood flow and repair injured tissue. With industrialization, however, this system wreaks havoc on modern humans by intensifying the effects of high-salt diets and sedentary lifestyle. Of particular importance in these harmful responses are the hormone aldosterone and a peptide (which are components of proteins) called angiotensin II.

Inherited Abnormalities in the Sympathetic Nervous System. Studies suggest that some people with essential hypertension may inherit abnormalities of the sympathetic nervous system . This is the part of the autonomic nervous system that controls heart rate, blood pressure, and the diameter of the blood vessels.

Insulin Resistance and Type 2 Diabetes. Hypertension is strongly associated with diabetes, both type 1 and type 2. Kidney damage is generally the cause of high blood pressure in type 1 diabetes. Obesity and insulin resistance are the factors associated with hypertension in type 2 diabetes, the more common type. People with type 2 diabetes generally have normal or high levels of insulin, a critical hormone in the metabolism of sugar. However, they are unable to use the insulin, the condition called insulin resistance . Without insulin, blood glucose (sugar) levels rise, the hallmark of diabetes.

Some research indicates that obesity is the one common element linking insulin, type 2 diabetes, and high blood pressure. Obesity is common in both type 2 diabetes and hypertension. Oddly, however, studies have found a stronger association between hypertension and insulin resistance in thin patients as well as overweight people with type 2 diabetes. Some research indicates that insulin resistance may cause sodium retention, a contributor to high blood pressure.

In any case, regardless of the causal connections, people who have both insulin resistance or full-blown diabetes plus hypertension have a significantly greater chance for heart attack, kidney disease, and stroke than people who have only high blood pressure.

Obesity. Obesity on its own has a number of possible effects that could lead to hypertension. It may blunt certain actions of insulin that open blood vessels, and it may cause structural changes in the kidney and abnormal handling of sodium. It is also associated with alterations in the systems that regulate blood flow.

Low Levels of Nitric Oxide. The gas nitric oxide can be produced in the body, where it affects the smooth muscles cells that line blood vessels; it helps keep them relaxed, flexible. It may also help prevent blood clotting. Low levels of nitric oxide have been observed in people with high blood pressure (particularly in African Americans) and may be an important factor in essential hypertension.
Secondary Hypertension

Secondary hypertension has recognizable causes, which are usually treatable or reversible.

Medical Conditions. A number of medical conditions can cause secondary high blood pressure:

* Kidney disease is the most common cause of secondary hypertension, particularly in older people.
* Sleep apnea, a disorder in which breathing halts briefly but repeatedly during sleep, is now highly associated with hypertension. A weak but still higher than normal association with high blood pressure has even been observed in those who snore or have mild sleep apnea. The relationship between sleep apnea and hypertension has been thought to be largely due to obesity, but major studies are finding a higher rate of hypertension in people with sleep apnea regardless of their weight. Treating sleep apnea with a device known as nasal continuous positive airway pressure (CPAP) may have modest benefits blood pressure as well.

*Other medical conditions that contribute to temporary hypertension are pregnancy, cirrhosis, and Cushing's disease.

Medications. Certain prescription and over-the-counter drugs can cause temporary high blood pressure. They include:

* Corticosteroids.
* Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, may cause secondary hypertension as well as other complications. In one important study, women who used an NSAID for 5 or more days a month had a significantly higher risk for hypertension. The more often they used them, the higher the risk. A 2005 study found that NSAIDs increase the risk for kidney failure, and that the risk is significantly greater for patients with hypertension. Patients who took diuretics along with NSAIDs had 11.6 times the risk of developing acute kidney failure compared to non-NSAID users. The relative risk for calcium channel blockers and NSAIDs was 7.8. The researchers advised that NSAIDs should be used with caution in patients with hypertension or heart failure.
* Cold medicines containing pseudoephedrine have also been found to increase blood pressure in hypertensive people, although they appear to pose no danger for those with normal blood pressure.
* Oral contraceptives ("the pill") increase the risk for high blood pressure, particularly in women who are older, obese, smokers, or some combination. Stopping the pill nearly always reduces blood pressure, although a recent study suggested that oral contraceptives may produce a small but significant increase in diastolic pressure that persists in some older women who have been off the pill for years.

Alcohol, Cigarettes, and Coffee

* An estimated 10% of hypertension cases are caused by alcohol abuse (three or more alcohol drinks a day), with heavier drinkers having higher pressure. Women may be more sensitive than men to the blood pressure effects of alcohol. Moderate drinking (one or two drinks a day) has benefits for the heart and may even protect against some types of stroke. In particular, red wine may have chemicals that help blood pressure.
* Smoking. Smoking is a major risk factor. One study reported that smokers have blood pressures up to 10 points higher than nonsmokers.
* Caffeine. In healthy people with normal blood pressure, drinking a couple of cups of coffee a day is unlikely to do any harm. A high intake of coffee may be harmful in people with hypertension and may even increase their risk for stroke.

Other Causes of Secondary High Blood Pressure

* Stress
* Intense workouts (snow shoveling, jogging, speed walking, tennis, heavy lifting, heavy gardening)


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