Cardiovascular system

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Hypertension

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Epidemiology of Hypertension:

Affects

worldwide

BP distribution is unimodal and any distinction between normal and abnormal is arbitrary

Hypertension definition: the level of blood pressure above which investigation and treatment do more good than harm

Prevalence of hypertension increases with advancing age

At young ages, the prevalence was

in males than in females; from age 60, however, the trend was reversed, with prevalence higher in women than in men.

Pulse pressure also rises with age, therefore the majority of people older than

yrs old are expected to be hypertensive; by current definitions

The reasons for gender differences in BP are not known, although it has been suggested (but not proven) that

may be responsible for lower BP in younger women

There is an association between hypertension and increased risk of

BP causes disease in the whole population, not jst hypertensive individuals

Pathophysiology of Primary Hypertension:

Classification-

Primary hypertension –

% of cases

Secondary hypertension – 5% of cases

Identifiable causes:

disease, including renal artery stenosis

Tumours secreting aldosterone e.g.

syndrome

Tumours secreting catecholamines

Oral contraceptive pill

Pre-eclampsia - hypertension associated with

Rare genetic causes

Aetiology: Genetics – twin and other studies suggest around

% of variation in blood pressure is attributable to genetic variation

Monogenic (Rare) – causes <1% of hypertension

Complex polygenic (common)- Multiple genes with small effects, may have appositive or negative effect

Environment- Dietary

Obesity, Alcohol and Pre-natal environment (birth weight)

Haemodynamics:

BP=

Typically, established hypertension is associated with:

Uniformly increased

Reduced arterial

Normal cardiac output

Elevated PVR is accounted for by:

Active narrowing of arteries –

Structural narrowing of arteries – growth and remodelling

Loss of capillaries -

Candidate causes:

Kidney-

Key role in BP regulation, relation to salt intake and reabsorption

Sympathetic nervous system

Evidence linking high sympathetic sympathetic activity to the

of hypertension

Endocrine/paracrine factors

The Kidney:

The kidney exerts a major influence on BP – Guton’s concept of ‘infinite gain’ of renal sodium/water/BP regulation

Impaired renal function or blood flow is the commonest secondary cause of hypertension (e.g. renal parenchymal disease, renal artery stenosis),

Most monogenic causes of hypertension affect renal

excretion

Salt intake is strongly linked with blood pressures of human populations. Populations with low salt have low population blood pressures and no rise in BP with age.

The major risks attributable to elevated blood pressure:

coronary heart disease,  stroke and peripheral vascular disease/atheromatous disease

heart failure and atrial

dementia /cognitive impairment and  retinopathy

increase in left

wall mass and changes in chamber size

thickened walls (hypertrophy) of large arteries and acceleration of

arterial rupture or dilations (aneurysms). This can lead to thrombosis or haemorrhage (e.g. strokes)

Retina illustrates microvascular damage in hypertension. There is thickening of the wall of small arteries, arteriolar narrowing, vasospasm, impaired perfusion and increased leakage into the surrounding tissue

microvasculature damage –

reduction in capillary density leads to impaired perfusion and increased

elevated capillary pressure leads to damage and leakage

Renal dysfunction is common in hypertension



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