Hypertension

What is Hypertension?

What is blood pressure?

Your blood pressure is the force exerted by your heart, against the resistance created by the arteries, to keep blood flowing through your body. Your blood pressure is high (hypertension) when the force is excessive. Blood pressure is the pressure exerted by the blood, on the walls of the arteries. Your heart functions as a muscular pump, which contracts rhythmically and squirts blood into your arteries. From there your blood is channelled to your entire body, through a circulatory system of smaller vessels. In this way, oxygen is delivered to all your living tissue.

The resistance offered by these arteries and the smaller arterioles is very significant. Constriction of the muscle in the artery wall causes it to narrow, which increases the resistance and hence the pressure within. This can be compared to taking a garden hose and reducing the opening at the nozzle. Pressure in a hose, can of course also be raised by increasing the amount of water flowing from the tap. Similarly, the amount of circulating blood, and the strength of the heart muscle contractions, can also influence your blood pressure.

If your blood pressure is too high, your heart must work much harder to maintain adequate blood flow to your body.

The terminology

If your blood pressure is recorded as 120/80, the number on top is the systolic pressure, and the bottom number the diastolic. It is measured in millimetres of mercury. 120/80mm Hg also happens to be the optimal blood pressure.

Systolic pressure is the pressure generated by each heartbeat. This occurs during the contraction of the heartmuscle, which is called a systole.

Diastolic blood pressure is the pressure between the heartbeats when the heart is resting. Systolic pressure is obviously always higher than diastolic blood pressure.

Pulse pressure is the difference between the two readings. If any of these are significantly elevated, it increases the risk for heart disease, stroke or kidney damage.

Essential to life

Blood pressure is essential to life. In fact when a person dies of so-called "shock" it usually implies events that cause a fatal drop in blood pressure. This leads to inadequate perfusion of vital organs like the brain and kidneys. Starved from their life-giving source of oxygen, these organs cannot function anymore. Blood pressure varies during the day.

Considerable variation occurs in all people, depending on the demands of the body. When doing exercise, the muscles require more oxygen, and with the increase in heart rate and pumping action as result, the blood pressure is raised. Anxiety, when being startled or feeling threatened, also raises the blood pressure through the effects of the "fight or flight" response. Experiencing pain can also raise pressure dramatically. Alcohol, nicotine and caffeine intake can cause transient elevations of blood pressure.

Some people have high blood pressure only in a clinical setting, so-called white coat hypertension, with normal readings otherwise.

Blood pressure rises when you are active and falls when you are inactive. During restful sleep, the inactivity reduces the demand for oxygen and therefore blood pressure is usually lowest at night and highest during arousal in the morning.

The causes of hypertension

There are two types of hypertension, namely primary and secondary hypertension.

Primary hypertension: More than 90% of hypertension cases have no known or identifiable cause. This type of hypertension is called primary or essential hypertension.

Secondary hypertension:In some cases, another disease or a medication may cause hypertension. This is called secondary hypertension. Treating the underlying cause can sometimes cure this type of hypertension. Secondary hypertension may be caused by:

• Kidney problems - these account for a large percentage of secondary hypertension. Normally the kidneys play an important role in fluid and blood pressure control.
• Coarctation of the aorta - an inborn, abnormal narrowing of the primary blood vessel supplying blood to the body from the heart
• Prescription and non-prescription drug usage
• Recreational drug usage - ecstacy and cocaine can cause hypertensive crisis and death
• Excessive alcohol intake - implicated in about 10% of secondary hypertension
• Sleep apnoea - Research indicates a connection between obstructed breathing during sleep and hypertension. The effect persists during the waking hours.
• Pheochromocytoma - a tumour of the adrenal gland (secretes various hormones, including those that affect blood pressure)
• Thyroid dysfunction - both over- and under-performance (hypo- and hyperthyroidism)
• Cushing's syndrome and aldosteronism - disorders of the outer layer of the adrenal gland resulting in various hormonal imbalances.

If hypertension occurs with any of the following factors, it may indicate that the hypertension is secondary:

• Age below 35
• Abrupt onset
• Lack of family history of essential hypertension
• Severity (180/110 mm Hg or higher)
• History of blood vessel disease, such as blockages in arteries in the neck or heart (carotid or coronary arteries)
• Lack of response to usual drug treatment
• Sudden increase of blood pressure that has been controlled by medications (provided you did not stop taking your medications)