Hypertension
Questions Received:
Responses:
How do you define hypertension, and what are the agreed normal values?
14th September 1999
Hypertension means that a person's blood pressure is elevated above what might be considered "normal" for their age and weight. Mosby's Medical, Nursing and Allied Health Dictionary gives the following definition:
Hypertension - [Gk. hyper + L. tendre, to stretch] A common, often asymptomatic disorder characterised by elevated blood pressure persistently exceeding 140/90mm Hg.
According to Oates (1996) "hypertension is somewhat arbitrarily defined as blood pressure in excess of 140/90 mm Hg on more than one occasion." Cripps (1994) suggested that although it is difficult to give precise definitions of degrees of severity of hypertension, a rough working guide is as follows:
Mild hypertension, bp 130/90 to 140/100 mm Hg
Moderate hypertension, bp 140/100 to 160/120 mm Hg
Severe hypertension, bp above 160/120 mm Hg
Hypertensive emergency, diastolic bp above 130 mm Hg or if there is encephalopathy, whatever the bp
These values apply to adults in the age range 20 - 65 years (approximately). The diastolic pressures are phase V pressures. If there is severe retinopathy or nephropathy, hypertension should be considered to be severe, whatever the bp.
Souhami and Moxham (1990) point out that a definition of hypertension should be able to take into account new information derived from the results of therapeutic trials and determine "the level of blood pressure above which investigation and treatment do more good than harm."
There is little doubt about the consequences of hypertension, for example left ventricular hypertrophy (enlargement), ischaemic heart disease, stroke, and renal insufficiency. Shaper et al (1985) found that a systolic blood pressure of more than 160 mmHg carries nearly three times the risk of a major coronary event compared to a systolic blood pressure of 130 mmHg. Brown (1997) states that "hypertension is the commonest indication in the Western world for chronic, lifelong treatment because of the incontrovertible evidence that such treatment substantially reduces the risk of stroke. About 20% of adults over 40 have a blood pressure > 140/90 mmHg, with a risk of stroke at least 100% higher than subjects of the same age with a blood pressure of 125/75 mmHg."
References
Brown, M.J. (1997) Science, medicine, and the future - hypertension. British Medical Journal, 314 (26 April).
Cripps, T.R. (1994) The drug therapy of cardiovascular disorders. In: Oxford Textbook of Clinical Pharmacology and Drug Therapy (2nd edition) edited by D.G. Grahame-Smith and J.K. Aronson. Oxford: Oxford University Press (Chapter 23, p 256).
Fox K. (1996) Hypertension and heart disease. Nursing Standard, 10(23), 52 (28 Feb).
Jordan, S., and Torrance, C. (1998) Hypertension (Systems and Diseases series, part 4) Nursing Times, 94(3), 50-53 (21 Jan).
Mosby's Medical, Nursing and Allied Health Dictionary (5th.edition) (1998) Edited by K. N. Anderson. St. Louis: Mosby-Year Book, Inc.
Oates J. (1996) Antihypertensive agents and the drug therapy of hypertension. In Goodman and Gilman's: The Pharmacological Basis of Therapeutics. Edited by J. Hardman, L. Limbard, Molinoff, P. et al. New York: Mc Graw - Hill.
Shaper, A.G. et al (1985) Risk factors for ischaemic heart disease: the prospective phase of the British Regional Heart Study. Journal of Epidemiology and Community Health, 39(1), 97-209.
Souhami R.L., and Moxham J. (1990) Systemic blood pressure and hypertension. In:Textbook of Medicine. Edinburgh: Churchill Livingstone (Chapter 13, p 437).
I am doing a project about heart disease and I know that a major risk factor is hypertension, but why is this so?
28th October 2004
Hypertension increases the risk of heart disease by putting extra stress on the heart and blood vessels. Healthy arteries expand and contract elastically with each heartbeat. With sustained hypertension, the arterial walls become thickened and less elastic, and this increases their resistance to blood flow. The lining of the vessels becomes damaged and there is accelerated formation of atherosclerotic plaques in the walls of the vessels. The plaques bulge into the lumen of the vessel and may trigger the formation of blood clots which further reduce blood flow. The heart has to work harder and harder to maintain sufficient blood flow through the narrowed and hardened arteries. The left ventricle in particular may become distended and hypertrophied.
A point of exhaustion may be reached where the heart can no longer keep up this work rate and it fails. If the wall of an artery becomes weakened by plaque-formation it may begin to balloon outwards due to the high pressure of the blood within, forming an aneurysm. If the aneurysm ruptures, there will be massive internal bleeding and this may result in death. Aneurysm, stroke, angina pectoris, myocardial infarction and renal problems are all more likely if there is hypertension, particularly if blood cholesterol levels are high too.