Blood pressure (BP) is measured using an instrument called a sphygmomanometer. This has an inflatable cuff which goes around your upper arm, a small pump to push air into the cuff and a column of mercury (or a dial) to record the pressure within the cuff.
As the cuff is inflated with air, the person measuring your BP usually feels for a pulse (brachial artery) in the crook of your elbow. While the pressure within your artery stays higher than that in the cuff, blood can be felt pulsing through. Once the pressure in the cuff becomes greater than that in your artery, the vessel is squashed flat and blood stops flowing through it at that point. By inflating the cuff to an initial pressure that is higher than the expected systolic pressure, then listening with a stethoscope over your brachial artery as the pressure is slowly released, the point at which blood manages to squirt through again with each pulse can be heard distinctly as a tapping sound. The pressure registering in the cuff at this point is taken as your systolic BP. The cuff is then slowly deflated further while listening over your artery. The tapping sounds become louder, then change to a dull whooshing noise before disappearing. The point at which blood can no longer be heard whooshing through the vessel is taken as your diastolic BP. The pulsing noise heard in the artery between these two pressures is a result of turbulence as the cuff impinges on the vessel and deforms its walls. We therefore know that the blood pressure in the artery is the same as that in the cuff at the point where the sounds disappear, as turbulence is no longer occurring. BP can also be measured with modern digital cuffs that fit around the wrist.
BP is measured according to the length of a column of mercury it can support. It is therefore expressed in millimetres of mercury (mmHg). BP is written down as the higher pressure (systole) over the lower figure (diastole).
A typical 20-year-old may have a BP of around 120/70 mmHg.
BP naturally tends to rise with age and a fit 50-year-old may have a BP of around 135/85 mmHg.
The pulse pressure – the difference between the systolic and diastolic pressures – is normally around 50 mmHg.
If your BP is consistently higher than 140/90, then you are suffering from high blood pressure, or hypertension.
How Blood Pressure is Controlled
Blood pressure is normally controlled and kept within safe limits by the body in a number of ways, including:
changing the rate at which the heart pumps
widening or constricting small arteries
altering the amount of blood pooled in the veins
varying the amount of salt and fluids filtered from the circulation via the kidneys.
These factors are controlled by nerve signals from the brain, and by several different hormones. As a result, normal BP varies naturally throughout the day, going up and down in response to your emotions and level of activity. It is lowest during sleep (usually at around 3am) and highest in the morning from just before you wake until around 11 am. If you have high blood pressure, however, your BP will remain high all the time, even at rest.
Hypertension
As many as one in five adults have high blood pressure, known medically as hypertension. This means that blood is forced through their system under a constantly high pressure. Hypertension is diagnosed when systolic pressure is consistently greater than 140 mmHg and diastolic pressure consistently greater than 90 mmHg. A systolic blood pressure between 140–160 mmHg and diastolic values between 90–95 mmHg are sometimes referred to as mild hypertension.
In hypertension, the body’s systems for correcting high or low blood pressure don’t seem to work properly so blood pressure is maintained at an elevated level compared to normal. Little is known about how or why this happens, but the condition seems to be readily reversible once diet and lifestyle changes are introduced, together with any necessary anti-hypertensive drug treatment.
SYMPTOMS
Unfortunately, people with high blood pressure usually notice very little in the way of symptoms, although a few may develop a pounding sensation in their ears or a splitting headache. As a result, hypertension is often referred to as the silent killer, as it usually creeps up on you without any obvious warning. Even if your blood pressure is dangerously high, you may feel relatively well. If symptoms do occur, they tend to be non-specific, such as a headache or getting up at night to pass urine more often than normal. Your blood pressure has to be severely raised before you develop dizziness or visual disturbances. It is therefore a good idea for adults to have their blood pressure checked on a regular basis, every year or so – especially if high blood pressure runs in their family. This is because a high blood pressure that remains undiagnosed and untreated can lead to a number of potentially serious complications.
WHY HIGH BLOOD PRESSURE IS HARMFUL
Hypertension is not a disease in itself, but a clinical sign that you are at increased risk of a number of serious health problems. As blood is forced through your system at high pressure, your artery walls receive a pounding. This which can both over-stretch important blood vessels as well as damage their linings. If left untreated, this can trigger premature hardening and furring up of the arteries (atherosclerosis) and increase the risk of a number of health problems. If your blood pressure remains constantly high, this can lead to:
peripheral vascular disease – when arteries supplying blood to the limbs become hardened and furred up so circulation is reduced
impotence – when the blood supply to the penis is affected
failing sight – when blood vessels in the eyes are affected
kidney failure – when blood vessels in your kidneys are damaged
heart failure – when your heart finds it difficult to pump blood against the high pressure in your circulation; this typically causes breathlessness as fluid builds up in your lungs
angina (heart pain) – when the excess workload on the heart increases its oxygen and nutrient needs beyond those provided by its blood supply
a heart attack – when the coronary arteries are damaged enough to trigger a sudden blockage of blood supply to the heart muscle (e.g. due to a blood clot)
a stroke – when blood vessels in the brain are damaged enough to cause a disruption in blood supply to brain cells, – either due to a sudden blood clot, or to a haemorrhage.
Research shows that for a man in his 40s:
each rise in systolic blood pressure of 10mmHg increases his risk of heart disease by 20 per cent
the risk of having a stroke is 30 times higher if he has high blood pressure than for someone with normal BP.
This all sounds rather frightening, but the good news is that early diagnosis and treatment can control your blood pressure and keep you healthy. It is vitally important that your hypertension is well controlled, by taking your tablets exactly as prescribed. A number of relatively simple dietary and lifestyle changes can also help to reduce the risk of high blood pressure, lower a BP that is already raised and reduce the risk of complications such as coronary heart disease. If these changes were to reduce your diastolic BP by as little as 5 mmHg, they would decrease your risk of coronary heart disease by 16 per cent, and if they succeeded in reducing your average blood pressure by 10 mmHg, this would reduce your risk of premature death by as much as a third. You really can eat to beat the unwanted effects of high blood pressure.
UNDIAGNOSED HYPERTENSION
Ideally, all adults should have their blood pressure measured regularly, at least once every three years, or more often as your doctor recommends. If your blood pressure is found to be high, you will have it measured several times before your doctor decides whether or not to prescribe any anti-hypertensive drugs. This is to make sure your blood pressure remains consistently high and is not just going up as a result of visiting the surgery. Once you start taking blood pressure treatment, you may be on it for life – but you will probably live longer as a result.
Unfortunately, an estimated one in two people with high blood pressure are undiagnosed, and of those that are picked up and treated, at least another half do not have acceptable blood pressure control. This is mostly because the condition rarely makes you feel ill, and having to take one, two or even three tablets per day to treat something that is not an illness, but a risk factor for other diseases, is understandably frustrating. However, early diagnosis and successful treatment of high blood pressure is vital for continued long-term health.
Types of High Blood Pressure
Ninety per cent of people with high blood pressure, have no obvious single cause and are said to have primary, or essential, hypertension. The remaining one in ten people with high blood pressure have an identifiable underlying factor, such as kidney problems, a hormone imbalance or drug side-effects, and are said to have secondary hypertension.
Malignant hypertension refers to the most dangerous type of high blood pressure in which pressures go very high, often very quickly. This can damage internal organs over a short period of time and is sometimes also referred to as accelerated hypertension. It is treated as a medical emergency because if diastolic pressure remains above 120 mmHg for a prolonged period of time, the linings of small blood vessels (arterioles) are damaged and start to leak. When looked at under the microscope, the blood vessel walls have literally started to crumble (fibrinoid necrosis). This lets protein-rich fluid, and sometimes whole blood, seep out of the blood stream to build up in the tissues. As well as interfering with blood supply to that part of the body, the leakages cause damage, inflammation and scarring – commonly to the kidneys, backs of the eyes and in the brain. This is known as target organ damage. Damage to the kidneys also results in the release of hormones that put the blood pressure up even more, so a vicious cycle builds up. Treatment aims to bring BP down slowly over several days so that the body can adjust to lower pressures again.
To differentiate it from malignant hypertension, primary high blood pressure is often referred to as benign essential hypertension.
Refractory hypertension refers to high blood pressure that does not respond to standard first-line anti-hypertensive drug treatments. Although this is uncommon, referral to a specialist is needed so that investigations and treatment with other drugs can be started.
CHAPTER 2 Causes, Diagnosis and Treatment of High Blood Pressure (#ulink_20c31778-6207-5fba-a84a-592c7ae718c1)
Blood pressure naturally tends to rise with age, so that high blood pressure is more common in middle life and beyond. Some people, especially males, may develop it in their 20s or even earlier, however. Blood pressure is also known to vary with race – those of African origin tend to have higher blood pressures than Caucasians, for example.
Causes of Essential Hypertension
Several factors are thought to be involved in the development of primary, or benign essential hypertension. These include inherited factors (high blood pressure runs in some families), developmental factors (occurring during embryonic life in the womb) and environmental factors such as diet and lifestyle, which you can address to help lower a high blood pressure.
INHERITED FACTORS
Essential hypertension is thought to result from inherited genes that may trigger high blood pressure as a result of one or more abnormalities involving:
sensitivity of the blood pressure monitors (baroreceptors) throughout the circulation
altered secretion of, or sensitivity to, hormones (e.g. anti-diuretic hormone, renin, aldosterone) or other chemicals that help to regulate normal blood pressure
dilation or constriction of blood vessels in response to pressure changes