High Blood Pressure

Having high blood pressure (or hypertension as doctors call it) is BAD news! It is a major risk factor for developing heart attacks and strokes at a relatively early stage in life. It also causes other problems such as kidney failure and diabetes to get worse much quicker than they might if the blood pressure was normal.

So what is blood pressure exactly?

We all have a system of pipes or blood vessels which carry blood all around our bodies. The blood carries nutrients (food substances) and oxygen for all our body tissues to use. It also removes from these tissues the waste products and carbon dioxide gas which are produced as these tissues live and do their important jobs. The blood then travels to the kidneys and liver for removal of waste products and also to our lungs where the carbon dioxide gas is transferred to the air we breath out. As we breath in (inhale) air which is rich in oxygen and the blood in the lungs then absorbs this rich supply of oxygen which our tissues need.

The blood travels around our bodies within the complex system of blood vessels because it is pumped by the heart. The heart is a muscular hollow organ with one-way valves which ensure that blood only travels in one direction around the body. As the heart muscle contracts the pressure in its chambers rises and this forces the blood out of the chambers into the largest blood vessel (the aorta). When each heart beat has finished its outer one-way valves snap shut to stop blood flowing back into the heart. The aorta is elastic and with each heart beat it stretches to accommodate the blood pushed into it from the heart's chambers. There is always some resistance to the flow of blood in the smaller vessels in the body's tissues and the pressure inside the aorta slowly drops as the blood flows through the blood vessels leading away from the heart and to the body's tissues.

When doctors measure blood pressure with their "sphygmomanometers" (s'fig-mo-man-o-meters) they listen to sounds from the heart valves snapping shut with each heart beat. They pump up the cuff to a pressure higher than the highest the heart generates in the aorta and then slowly release the air from the cuff. They watch the meter on the machine as they listen for the heartbeat sounds to appear. When the sounds are first heard the pressure on the meter is approximately matches the pressure in the aorta. They then continue to allow air to escape from the cuff while they listen for the sounds to disappear. When the sounds disappear they note the pressure on the machine which approximately matches the lowest pressure in the aorta just before the next heart beat.

These two pressures (upper and lower) are called the "systolic" and "diastolic" pressures respectively and a doctor will tell you that your blood pressure is, for example, "125 on 85" (written as 125/85 by convention). Nowadays it's considered that pressures higher than 140/90 are too high for adults. High blood pressure usually creeps up over a long period of time and the slow rise over years allows the body to become accustomed to high levels without causing any symptoms. Occasionally if blood pressure rises very quickly it can cause headaches, dizziness, tiredness and lots of other more minor symptoms in some people. However, it is quite uncommon for high blood pressure to make one feel different or unwell.

Of course one's blood pressure isn't always the same all the time. For example, at rest one's blood pressure is usually much lower than when one is anxious or doing hard physical activity. At night when one is asleep one's blood pressure may be very low. Our bodies have complex mechanisms for controlling the pressure in our blood vessels so that whatever we are doing there is always enough blood flowing to the brain and to other essential organs. Under the control of these mechanisms the muscle layers within our blood vessels can tighten up (which makes the blood vessels narrower) or they can relax (which makes the blood vessels open up wider). These actions respectively increase and decrease the resistance to the flow of blood and therefore the pressure in the large blood vessels with rise and fall respectively.

Usually when one has high blood pressure, both the diastolic (lower) and the systolic (higher) readings are too high. However for some people only the systolic blood pressure is too high and this is called isolated systolic hypertension. Some people only have high blood pressure readings when they go to visit their doctor. When their blood pressure is measured in their homes by a visiting nurse their blood pressure readings are normal - they are said to have "white-coat hypertension" (because doctors once used to wear white coats at work!)

So what's so bad about having high blood pressure?

It's easy to understand why high blood pressure is dangerous by thinking of a man-made pumping system. If a pump has to pump fluid against a high pressure it's predictable that it will wear out quicker than if it has to work at a lower pressure. Also, if the pressure within a plumbing system is very high, there's a higher risk that a leak will happen than if the pressure is at a lower level.

In humans, the heart is the pump which can become worn out (that's called "heart failure") and one can spring a leak in various places such as the brain (this catastrophe is called a "cerebral hæmorrhage" or stroke).

It is now well known that the risk of heart failure and stroke rises in direct proportion with blood pressure and that lowering blood pressure will lower the risks of these problems.

How does one lower blood pressure?

LIFESTYLE CHANGES - Doctors usually recommend that people with high blood pressure should have less beer and whisky if they are drinkers (wine doesn't seem to cause problems unless patients are overweight), have less salt in their diet, lose some weight, do more exercise (eg. get a dog which needs a daily walk) and try to lower the amount of stress in their lives. In other words, measures which alter the lifestyle are recommended first. Then they review the situation after a few weeks to months to see if there is an improvement in the blood pressure.

MEDICATIONS - If there is no change or not enough change occurs then doctors usually recommend that medications be used. There are many different medications to choose from and there is no way any doctor can be certain which drug is best for a particular patient. It's literally trial and error. Most people tolerate most drugs well and most drugs work well for most patients. However there are always some patients who have troubles with side-effects or who need more than one drug to get enough benefit. It can take a number of weeks and quite a number of tries before one's blood pressure is satisfactorily controlled with minimal or no side-effects.

What happens if one stops taking the blood pressure tablets?

For most people the blood pressure gradually rises to the pre-treatment level. Unfortunately some people have a rapid and massive rise in their blood pressure almost as if they'd suddenly taken their hand off a compressed spring and let it bounce up very high and quickly. If this happens with blood pressure it can rise to such a dangerous level that a lifethreatening stroke can happen! Not a good thing!

So the important take-home messages are -