Causes Of Essential Hypertension
High Blood Pressure Puts Load On, And Gradually Destroys Every Vital System
High Blood Pressure - Types and How To Get It Measured?
High blood pressure is a chronic medical condition in which the blood pressure of arteries in our body, is elevated.
Measurement of Blood Pressure:
Blood pressure should be measured with a well-calibrated sphygmomanometer with a cuff of proper size (the bladder width within the cuff should encircle at least 80% of the arm circumference) after the individual has been resting comfortably, back supported in the sitting or supine (lying down) position for at least 5 minutes, and at least 30 minutes after smoking or having a cup of coffee. Since blood pressure readings in many individuals are highly variable - especially in the office setting - the diagnosis of high blood pressure is made only after elevation is noted in three readings on different occasions over a period of several months unless the elevations are severe or associated with symptoms.
There are two basic forms or types of high blood pressure, which include the following:
- Essential Hypertension - Speaking on a literal basis, individuals with arterial high blood pressure and no definable cause, are said to have a primary, essential, or idiopathic hypertension. In these people generalized or functional abnormalities may be the cause of high blood pressure, even if the abnormalities are discrete.
- Secondary Hypertension - Individuals in whom a specific structural organ or gene defect is responsible for high blood pressure, are defined as having a secondary form of hypertension.
The major factors that lead to essential hypertension include the following:
Grades of Hypertension
Systolic Blood Pressure (mm Hg)
Diastolic Blood Pressure (mm Hg)
more than or equal to 100
Isolated Systolic Hypertension
more than or equal to 140
1. Heredity - A Common Cause of Essential Hypertension
Genetic factors play a very important role in increasing the blood pressure of an individual which reflects in the form of familial aggregation of this condition.
Several single-gene disorders have been associated with high blood pressure. Inheritance of this condition is believed to be Multifactorial (though there have been some studies against this concept), that is, a number of different genetic defects along with environmental stressors, together lead to an elevation in arterial blood pressure.
One possible mechanism involves a reduction in vascular compliance due to the stiffening of arteries.
A number of environmental factors have been implicated in the development of high blood pressure, which include salt intake, obesity, occupation, alcohol intake, family size, and crowding.
Dietary Guideline for Americans 2010 recommends that everyone age 2 and above should consume less than 2300 mg of sodium each day. Some groups of people should further limit sodium intake to 1500 mg daily; this restriction is meant especially for adults >51 years age; and anyone with high blood pressure, diabetes, or kidney diseases.
Obesity is associated with an increased intravascular blood volume and an increased cardiac output. Weight reduction leads to a modest reduction in blood pressure.
Excess alcohol intake raises blood pressure by increasing plasma catecholamines. High blood pressure may be difficult to control in individuals who consume more than 40 gms of ethanol (2 drinks) daily or "drink in binges".
Cigarette smoking raises blood pressure, again by increasing plasma adrenaline levels.
Aerobic exercises lower blood pressure in previously sedentary individuals, but extremely strenuous exercises in an already active person may have a lesser effect.
Polycythemia (Increase in the number of red blood cells above normal) increases blood viscosity and may raise the blood pressure.
Low potassium intake causes high blood pressure (Recommended intake is 90 m mol/day).
Parts Of A Sphygmomanometer
3. Salt Sensitivity - A Cause of High Blood Pressure
Blood pressure in only approximately 60% of hypertensives is particularly responsive to the level of sodium intake.
The cause of this special sensitivity to salt varies, with medical conditions like Primary Aldosteronism, Bilateral Renal Artery Stenosis, Renal Parenchymal Disease, and Low Renin Essential Hypertension, accounting for about half of the cases.
In the remainder, other contributing factors like chloride intake, calcium intake, a generalized cellular membrane defect, insulin resistance, and non-modulation play an important role.
4. Role of Renin in Raising the Blood Pressure
A normal person has two kidneys, each of which comprises of functional units known as nephrons.
Renin is a protein degrading enzyme secreted by the juxtaglomerular cells of the kidneys in response to a number of stimuli that include -
- Reduced renal perfusion (a decreased blood supply to the kidneys).
- Diminished intravascular blood volume (particularly related to low dietary sodium intake).
- Increased sympathetic nervous system activity and raised blood Adrenaline levels.
- Increased arteriolar stretch
- Reduced blood potassium levels.
Renin acts on the enzyme Angiotensinogen to cleave off the peptide Angiotensin-I. This peptide is then acted upon by Angiotensin Converting Enzyme (ACE) to create another peptide Angiotensin-II that directly leads to constriction of blood vessels causing an increase in blood pressure and also stimulates the adrenal glands to release hormone aldosterone.
Sodium or salt intake normally modulates both these responses in a way that, with, sodium restriction, adrenal responses are enhanced (and more aldosterone is released)while renal blood vessel responses are reduced (blood vessels do not get constricted). Sodium loading has the opposite effect.Based on the renin activity, there are three categories of hypertensives, which include -
- Low Renin Essential Hypertensives.
- Non-Modulatory Essential Hypertensives
- High Renin Essential Hypertensives.
Measurement of Toe Blood Pressure with A Photo Plethysmography Unit
5. Sodium Ion Versus Chloride or Calcium
Some investigators have suggested that, along with sodium, the chloride ion component is equally important, as chloride free sodium salts have failed to increase blood pressure in salt-sensitive hypertensives in a few studies (but this concept is still under investigation).
A low calcium intake in the diet can lead to high blood pressure (as whatever the calcium circulating in the blood gets absorbed into the cells including cells of the arterial wall and increases their reactivity and constricting tendency).
6. Cell Membrane Defect
Another postulated mechanism for salt-sensitive high blood pressure is a generalized defect in the cell membranes. There is an abnormality in the sodium/potassium ion transport across the membranes in many, perhaps all cells of the body, particularly the cells of smooth muscles of arterial walls.
The defect leads to an abnormal accumulation of sodium and calcium ions in the muscle cells resulting in increased responsiveness to blood vessel constricting agents.
This defect has been proposed to be present in 35-50% individuals with high blood pressure.
7. Insulin Resistance
Insulin Resistance (reduced sensitivity of target organs to hormone insulin) and the resultant increased blood insulin levels can lead to an increase in blood pressure by the following mechanisms:
- Increased insulin levels lead to salt retention by the kidneys and increase sympathetic nervous system activity.
- Insulin leads to increase in the thickness of smooth muscle layer of blood vessels constricting their lumen and in turn increasing blood pressure.
- Insulin modifies ion transport across cell membranes causing increased Calcium levels in cells of blood vessel walls and kidneys. This in turn leads to constriction of blood vessel walls and salt retention by the kidneys. The increased salt concentration leads to an expansion in the intravascular blood volume and an increase in blood pressure.
8. Stress and Sympathetic Nervous System Activity
Severe mental stress leads to activation of sympathetic nerves thus increasing blood levels of Adrenaline and other catecholamines, that cause an increase in blood pressure, increased heart rate, and an elevated output from the heart.
9. Vitamin-D deficiency Can Cause Essential Hypertension
Vitamin-D deficiency is associated with cardiovascular risk factors. Such individuals have higher than average systolic and diastolic blood pressure levels.
Vitamin-D inhibits renin secretion and its activity. It, therefore, acts as a negative endocrine regulator of the Renin-Angiotensin System. Hence, a deficiency of vitamin-D leads to an increase in renin secretion and the consequent essential hypertension.
Factors That Adversely Affect the Course or Prognosis of High Blood Pressure
- Youth - The younger the person is when hypertension is first noted, the greater is the reduction in life expectancy if high blood pressure is left untreated.
- Male gender - Females with high blood pressure fair better than their male counterparts with similar readings on the scale. Prevalence of high blood pressure in premenopausal females is substantially less than that in age-matched males or postmenopausal women. Compared with their counterparts with normal blood pressure, women with high blood pressure run the same relative risk of a cardiovascular event as males do.
- Persistent diastolic blood pressure >115 mm Hg
- Diabetes mellitus
- Increased Blood Cholesterol
- Excess alcohol intake
- Evidence of end-organ damage
- Cardiac - Heart enlargement, ECG signs of ischemia, Heart attack, Heart failure
- Eyes - Retinal hemorrhages, Papilledema
- Renal - Impaired function of kidneys
- Nervous System - Stroke, Transient ischemic attacks
Course of Essential Hypertension
Although exceptions have been reported, most untreated adults with high blood pressure will develop a further increase in blood pressure with time.
Even individuals who have a relatively mild disease, that is, without the evidence of end-organ damage, if left untreated for 7-10 years, have a high risk of developing significant complications, such as an increased hardening of arterial wall and end organ damage, such as enlargement of heart, congestive heart failure, retinopathy, stroke or brain attacks, and/or kidney damage.
In my next Hub, I shall be discussing about secondary causes of high blood pressure.
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