Blood pressure is the pressure exerted by the blood against the walls of the arteries through which it flows. Blood pressure is highest each time the heart contracts and pumps out blood into the arteries.
The reading at this time is called systolic, as systole means heart contraction. The blood pressure falls to its lowest level when the heart is relaxing.
This reading is called diastolic, as diastole means heart relaxation. Both these blood pressure readings are generally recorded as the higher systolic pressure over the lower diastolic pressure, for example, 125/85.
Since there is no dividing line between normal and high blood pressure, arbitrary levels have been established to define those who have an increased risk of developing a heart or blood vessel (cardiovascular) disorder and/or will clearly benefit from medical therapy.
For example, patients with a diastolic pressure greater than 90 mm Hg will have a significant reduction in disease and mortality with adequate treatment.
These, then, are patients who have hypertension and who should be considered for treatment.
The level of systolic pressure is also important in assessing arterial pressure’s influence on heart disease.
Males with normal diastolic pressures (less than 82 mm Hg) but elevated systolic pressures (more than 158 mm Hg) have a 2 ½ fold increase in their cardiovascular mortality rates when compared with individuals with similar diastolic pressures but whose systolic pressures are normal (less than 130 mm Hg).
Even though in an adult, hypertension is usually defined as a pressure greater than or equal to 150/90, in men, less than 45 years of age, a pressure greater than or equal to 130/90 mm Hg may be elevated.
Individuals can be classified as being normotensive if arterial pressure is less than levels noted above, and as having sustained hypertension if the diastolic pressure always exceeds these levels.
Arterial pressure fluctuates in most persons, whether they are normotensive or hypertensive.
Those who are classified as having labile hypertension are patients who sometimes have arterial pressures within the hypertensive range. These patients are often considered to have borderline hypertension.
Blood Pressure Regulation
The degree of blood pressure is regulated by various factors. The kidneys participate in this regulation.
Stimuli from the nervous system and the consequent body responses, particularly the hormonal secretions of various endocrinal glands of the body are the important ones.
These factors influence the blood pressure level by controlling the relaxation or contraction of the smaller arteries called arterioles.
If the arterioles relax readily, the blood forced out by the heart can be accommodated in the vessels easily without heightening the blood pressure.
But if the arterioles do not relax readily then as the blood is forced into them by the heart, the pressure in them rises and remains high even in diastole. This progressive lack of relaxation of blood vessels increases blood pressure over a period of time.
In most cases of hypertension, the cause is not clearly discernible. These cases are called Idiopathic Hypertension or Essential Hypertension – though the last is a misnomer, as there is nothing essential about this high blood pressure.
Symptoms and Signs: The vast majority of patients suffering from hypertension, has no symptoms referable to their blood pressure elevation and will be identified only in the course of a physical examination.
When symptoms do bring the patient to the physician, they fall into three categories. They are related to:
The elevated pressure itself,
The hypertensive vascular disease, and
The underlying disease – in the case of secondary hypertension.
Though popularly considered a symptom of elevated arterial pressure, headache is characteristic only of severe hypertension; most commonly it is localized to the back of the head, is present when the patient awakens in the morning, and subsides spontaneously after several hours.
Other possibly related complaints include dizziness, palpitation, and easy fatigue.
Complaints referable to vascular disease include epistaxis, blood in urine, blurring of vision owing to retinal changes, episodes of weakness or dizziness due to transient cerebral ischaemia, angina pectoris, and dyspnoea due to heart failure.
Examples of symptoms related to the underlying disease in secondary hypertension are varied.
Insurance statistics show that, in general, expectation of life is considerably reduced in those who have high blood pressure compared with those who have high blood pressure compared with those in whom the pressure is within the normal range.
However, it does not follow that all who have high blood pressure necessarily have a bad prognosis.
The condition is mild if the heart is not enlarged, the retina of the eyes (fundi), show no abnormalities and there is no protein in urine (proteinuria) or evidence of impaired kidney function. Many such patients live a life of normal span free from related illness.
On the whole, women seem to withstand hypertension better than men.
Young men, in particular, who when first seen have high diastolic pressures together with secondary manifestations in the fundi or heart, require optimal control of the blood pressure without delay.
Consequences of Hypertension:
As the blood vessels do not relax to receive the blood from the heart, the heart has to work harder against this resistance.
This strains the heart, so that it ultimately fails to perform its function of pumping the blood to all parts of the body.
Hypertension accelerates the process of hardening and narrowing of the blood vessels.
The coronary arteries leading to less blood and less oxygen being supplied to the heart muscle (myocardium) and myocardial infarction or angina;
Cerebral arteries leading to brain strokes, and
Renal arteries leading to less blood going through the kidney arteries for purification, and subsequent collection of waste products in the blood, the condition called uraemia.
Hypertension enhances atherogenesis by directly producing injury via mechanical stress on endothelial cells at specific high pressure sites in the arterial tree.
In addition, hypertension allows more lipoproteins to be transported through the lining cells of the arteries into their walls by altering their permeability.
High blood pressure is found in about 50 per cent of men and in about 75 per cent of women with coronary heart disease.
In the Framingham study in the USA, it was found that a blood pressure reading of greater than 160/90 mm. Hg produced a three-fold increase in risk of heart attack for men between 50 and 59 years of age, and a six-fold increase in risk for women of the same age.
An increase in coronary heart disease occurred at each successive level of blood pressure, with a seven-fold increase in those with blood pressure, with a seven-fold increase in those with blood pressure over 180 compared to those with pressure under 120 systolic.
Experimentally induced hypertension increased the severity of atherosclerosis in laboratory animals such as rabbits, dogs, chicks and rats.