Types And Causes Of Hypertension

Essential or primary hypertension is defined as a medical condition denoted by consecutive high (above 140/90 mmHg) blood pressure readings in the absence of a known causal disease.14 It is the result of elevated arterial pressure associated with increased cardiac output, total peripheral resistance, or both.15 Unfortunately, mystery exists about the causes and treatment of this form, even though 95% of all hypertensive patients have essential hypertension.9 Primary hypertension affects approximately one-third of the world's adult population.4

Secondary hypertension is the sudden onset of high blood pressure in children or people over the age of 50.9 A mere 5% of those with hypertension have the secondary type.9 Systemic arterial hypertension is one of the most common cardiovascular diseases of industrialized populations. It affects approximately 20% of adults in these societies, and the percentage is higher among the elderly and blacks.15 Males were at higher risk to develop hypertension, but greater risks for women have been noted in the past decade.16 Malignant hypertension is the most severe form. It progresses rapidly and proves fatal within 5 years for 90% of its patients.9

Essential hypertension can result from narrowed arteries, from circulation of a greater-than-normal volume of blood through the body, or a combination of both factors.12 Arteriosclerosis is a narrowing of the smaller arteries recognized as a major pathophysiological change in essential hypertension.17 In order to function well, arteries must have elasticity. Serotonin occurs naturally in the body and is believed responsible for causing constriction of the large arteries while causing arterioles and large veins to vasodilate.18

The sympathetic nervous system or insulin resistance can also cause hypertension.19 Abnormal renin that triggers angiotensin21 and oxidation that produces aldosterone21 are further risk factors.19 Other causes of clinical variable hypertension are physiologic variables.22 The first is vascular tone, which establishes the elastic properties of veins and arteries, vessel diameter, and vascular resistance.22 Additional variables causing high blood pressure are inotropic state and heart rate.22 Hypertension can result also from the use of drugs, medications, and other substances such as oral contraceptives, nonsteroidal anti-inflammatory drugs, licorice, cocaine, and amphetamines.23

Obesity and diet factors are other issues considered as causes for hypertension because 50% of obese people have hypertension.9 Possible dietary causes for hypertension include high intake of salt and fats.24 Processed foods and many snack foods are high in sodium content. Although modern society embraces the fast food concept, fast foods may not be as healthy as we want or need. Actions to promote awareness of the risks associated with this type of daily dietary intake have met with resistance. "The possible loss of income to the salt and soft-drink industries that might follow moderate sodium reduction has led to the formation of lobbying operations in several countries that work against efforts to reduce sodium intake." 25

An elevated level of dietary salt (NaCl) is thought to be a cause of hypertension. By the late 1940s, the role of dietary salt as a cause of hypertension had been studied and debated for over 100 years.26 "The prevalence of hypertension and its consequences is [sic] linearly linked to dietary salt intake in societies throughout the world."27

Endothelial cells are important mediators of vasoconstriction and vasodilatation. This mediation is brought about by the production of nitric oxide (a vasodilator) by the endothelium.2829 Inhibition of platelet aggregation relaxation are some ways nitric oxide can affect the body.30 Alterations in L-arginine, a compound that forms nitric oxide, can lead to a decrease in nitric oxide production and high blood pressure. While not directly related to nitric oxide, cyclooxygenase (COX) can cause vascular damage by producing superoxide anions and prostanions31 (see Figure 10.1).

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