Hypertension, or high blood pressure, is one of the commonest disorders in the population which over time can lead to serious ill health. It is a particularly sinister condition in that it is often asymptomatic until organ damage has occurred, by which point the effects can be irreversible. Blood pressure (BP) is the measurable pressure at which blood is flowing through a large artery, and hypertension can have negative consequences throughout the body.
Hypertension is very common in the developed world, and varies between ethnic groups; about 20-30% of the adult population of developed countries currently have hypertension, with the percentage rising to 40-45% among black Africans 1. BP tends to rise with age due to changes in the elasticity of arteries and the deposition of fat in the artery walls, but patients can aim to keep their BP within a healthy range even into old age by eating healthily, exercising regularly and not smoking.
Measuring Blood Pressure
BP can be measured using a device called a sphygmomanometer, which is an inflatable pressure cuff attached to a measuring unit to measure the pressure within the compressed artery. There are manual sphygmomanometers, which are used along with a stethoscope to listen for pressure changes, and electronic sphygmomanometers which automatically inflate and measure arterial pressure.
Figure 1: a manual sphygmomanometer with hand pump and pressure dial 2
The pressure cuff is usually placed around the upper arm, covering the brachial artery. It is then inflated until the pulse of blood stops and the vessel is compressed. An electrical sphygmomanometer will do this automatically, but with a manual device the medic must inflate the cuff until a pulse is no longer felt at the wrist (the radial pulse), then place the diaphragm of the stethoscope over the brachial artery and listen for certain sounds as they deflate the cuff. These sounds are called Korotkoff sounds, and they are produced by turbulent blood flow as the artery opens up again 3.
Two pressures within the artery can be measured, the systolic and diastolic pressure. The systolic pressure is the highest pressure in the blood produced when the ventricles of the heart contract, and the diastolic pressure is the lowest pressure which occurs during the relaxed filling phase of the heart. These pressures correlate with the Korotkoff sounds; the pressure at which the sounds begin is roughly the systolic pressure, and when they disappear marks the diastolic pressure 3.
One phenomenon to be aware of when measuring a patients BP is white coat hypertension; this is where a person’s BP is 10mmHg (systolic) or 5mmHg (diastolic) higher in a medical setting than when measured at home. This can be due to a number of reasons, including anxiety about seeing the doctor, feeling nervous or worried about their health, or simply from rushing to get to their appointment. Because of this, it is recommended that ideally 3 different blood pressure readings are taken during the consultation and the average taken from those, and to allow 5 minutes for the patient to rest before taking their blood pressure 4.
Definition of Hypertension
Because BP differs naturally between individuals, it could be quite hard to define hypertension, but because there is a clear positive correlation between rising blood pressure and risk of complications certain boundaries have been outlined to define the different stages of hypertension 1. There are variations between guidelines, but the values outlined by the British Hypertension Society can be seen below in figure 2. BP is traditionally measured in mmHg (millimetres of mercury).
Figure 2: the classifications of different grades of hypertension; the higher the BP, the more severe the consequences. Numbers shown in mmHg 1
Hypertension can be classified as essential (primary) or secondary. About 80-90% of hypertension cases are essential, meaning the exact cause is unknown; often it is multifactorial, and due to environmental, genetic and hormonal factors. In general essential hypertension is caused by a process called atherosclerosis, which is the build-up of fatty streaks and plaques in the arterial wall. As these plaques build up, they cause the artery to narrow, which ultimately causes a pressure increase within the circulation 1.
Figure 3: a diagram showing the breakdown of primary and secondary hypertension
The main risk factor for atherosclerosis is obesity as it generally comes hand in hand with a high blood lipid concentration (hyperlipidaemia). This means fat deposition occurs faster than normal. Other environmental factors which can cause hypertension include excessive alcohol or caffeine consumption, smoking, a high sodium (salt) intake and, to a certain extent, long-term stress 1.
Figure 4: a diagram showing broadly how BP rises as atherosclerosis increases
Genetic factors also play a role; hypertension tends to run in families, and a person’s risk of hypertension is higher if their parents had the condition 1.
Secondary hypertension makes up 10-20% of cases, and this is where the main cause of hypertension can be identified. Secondary causes of hypertension include:
*Hormonal Causes – Cushing’s syndrome, thyroid disease, adrenal tumours producing high levels of adrenaline
*Renal (Kidney) Causes – narrowing of the renal arteries, renal disease
*Drugs – Steroids, oral contraceptive pill, non-steroidal anti-inflammatory drugs (NSAID’s) such as aspirin or ibuprofen 1
In varying ways, these conditions or drugs cause the blood pressure to rise; for example, high levels of adrenaline from an adrenal tumour cause the muscular narrowing of arteries (vasoconstriction), which produces a rise in BP. Interestingly, eating large amounts of liquorice can also cause secondary hypertension.
Complications of Hypertension
Primary hypertension is often asymptomatic, so patients can be unaware that their BP is high for many years without regular monitoring. Unfortunately, when a patient begins to suffer from symptoms caused by their hypertension, such as headaches, long-term damage to organs may have already occurred. The organs that are particularly at risk of damage from long-standing, untreated hypertension are the arteries themselves, the kidneys, heart, brain and eyes. The kidneys are easily damaged as they continually filter the blood through tubules which can be damaged by high blood pressure. The eyes and brain are vulnerable due to their small, thin arteries; damage to these delicate arteries can result in bleeding into the organs, causing a stroke or affecting vision.
Figure 5: the main complications of long-term hypertension 5
Hypertension and its complications can dramatically alter people’s lives; the severe consequences of untreated hypertension can lead to kidney failure, heart failure, strokes and blindness. Once this end-organ damage has occurred it is largely irreversible, and severe disability can occur from a condition that initially had no symptoms. It is essential to emphasise how important monitoring and controlling your BP is to patients; if hypertension is discovered in the early stages, lifestyle changes and drug therapy can bring the blood pressure down to normal, preventing the occurrence of serious, life-changing consequences.
A patient with hypertension may have a history of headaches or visual changes, but in most cases hypertension is asymptomatic. On examination elevated BP is normally the only abnormal sign, but it is important to look for any secondary causes of hypertension before diagnosing primary hypertension. Examining the eyes, a process called fundoscopy, is essential to make sure no damage has occurred to the retina at the back of the eye 5.
The most accurate way of measuring a patients BP at home is by doing ambulatory blood pressure monitoring; a device worn by the patient measures their blood pressure over 24 hours whilst standing, walking, sitting and sleeping and takes an average reading. This method can be used to overcome white coat hypertension by measuring BP in the patient’s own home 5
It is also important to check kidney function by doing a urine dipstick; the presence of blood or protein in the urine can be a sign of hypertensive kidney damage, indicating that the patient needs drug therapy to lower their BP as soon as possible 5.
The management of hypertension depends on how severe the person’s hypertension is, their age and ethnic background, how long they have been hypertensive for and whether they have any organ damage. The primary management of hypertension is lifestyle change; if the patient can lower their BP themselves through weight loss, quitting smoking, exercise and lowering their sodium, caffeine, alcohol and fat intake sometimes drug therapy is not necessary.
When a patient has a BP >160 systolic and/or >100 diastolic, drug therapy is normally recommended along with lifestyle changes. Drug therapy is also first-line treatment when the hypertension has caused organ damage, regardless of the blood pressure reading 6.
Anti-hypertensive drugs work in various ways to reduce the BP and thus lower the risk of organ damage. For example, calcium channel blockers cause the muscle within arterial walls to relax and widen, reducing resistance and pressure. ACE Inhibitors (Angiotensin Converting Enzyme inhibitors) block angiotensin converting enzyme which plays a role in the kidneys control of BP. This leads to increased loss of sodium and water from the kidneys, causing blood volume and pressure to fall. Diuretic drugs work in a similar way, increasing sodium and water excretion from the kidneys. Another drug class, beta-blockers, can also be used to lower the heart rate, and thus lower BP 6.
NICE (National Institute for Health and Care Excellence) guidelines have been published on the drug treatment of hypertension to make sure patients get the best treatment for their age and condition; these guidelines can be seen in figure 6 below. Patients are normally started on just one drug (monotherapy), but often they need two or more to control their BP 7.
Figure 6: NICE guidelines on the drug treatment of hypertension. Note that the guidelines differ depending on the patients age and ethnic background 7, 8.
All drugs come with side-effects, and unfortunately anti-hypertensives are no different. For example, ACE inhibitors can cause a dry cough, headache and drowsiness 9, and calcium channel blockers may cause headache, constipation and oedema (fluid gathering in tissues) 10. Because of these issues, it is important that patients on anti-hypertensives have regular medication reviews to make sure they are not suffering from serious side-effects, and to make sure their BP has not dropped too low. The aim of treatment is to bring the blood pressure down to <140/90, or <130/80 if diabetic 6.
When hypertension is detected early and controlled well, the outlook for the patient is generally good as long as they have no other illnesses. With appropriate control, the risk of developing organ damage and other complications can fall to the level of a person with normal BP.
Hypertension is a major problem in the developed world, and the prevalence of this condition continues to increase each year along with the rise in obesity. Drug therapy can be very effective at bringing BP down to normal levels, but it is important that patients also make the lifestyle changes necessary, or they will continue to be at risk of other conditions such as diabetes. Measuring the BP is an essential part of any normal examination, so it is very important for medics to be able to take BP properly and to understand hypertension and its complications.
1. Kumar P, Clark M, Kumar and Clarks Clinical Medicine 8th Edition (2012). Sunders Elsevier, pp. 777-778
2. Manual Sphygmomanometer Image http://www.mountainside-medical.com/manual-blood-pressure-monitor-with-nylon-cuff.html Accessed: 23/07/15
3. Taking BP http://www.osceskills.com/e-learning/subjects/blood-pressure-measurement/ Accessed: 23/07/15
4. White Coat Hypertension http://www.bloodpressureuk.org/BloodPressureandyou/Medicaltests/Whitecoateffect
5. Kumar P, Clark M, Kumar and Clarks Clinical Medicine 8th Edition (2012). Sunders Elsevier, pp. 779-780
6. Longmore M, Wilkinson IB, Baldwin A, Wallin E. Oxford Handbook of Clinical Medicine 9th Edition. Oxford University Press (2014) pp. 133-134
7. Treatment of Hypertension http://www.nice.org.uk/guidance/cg127/chapter/1-recommendations Accessed: 27/07/15
8. Treatment Diagram http://www.guidelinesinpractice.co.uk/sep_06_minhas_hypertension_sep06#.VbZnjvlViko Accessed: 27/07/15
9. ACEI Side Effects http://www.rxlist.com/ace_inhibitors-page2/drugs-condition.htm
10. CCB Side Effects http://www.rxlist.com/calcium_channel_blockers_ccbs-page3/drugs-condition.htm Accessed: 27/07/15