Arterial stiffening and isolated systolic hypertension in ageing
With age, the large arteries lose elasticity (their ability to stretch and recoil) and become less compliant (they stretch less when filled), so systolic blood pressure rises.
Remember
Systolic blood pressure rises with age mainly because the large arteries become stiffer and less compliant, and the extra load then strains the left ventricle.
Memory aid
stiff pipes give higher pressure peaks
Think of a stiff pipe in place of an elastic artery: it cannot absorb the pulse, so the pressure peak is higher.
In young people the large arteries, the aorta included, are elastic. Each beat of blood stretches them, and they then recoil (spring back), which smooths the pressure.
With age the large arteries lose elasticity and become less compliant, which means they stretch less when filled. They cannot absorb each pulse of blood, so the systolic pressure peaks higher.
The result is commonly a raised systolic pressure with a relatively normal or even low diastolic pressure. This pattern is called isolated systolic hypertension, the commonest type of high blood pressure after the age of 50. The stiff arteries also lose the recoil that normally supports diastolic pressure, so diastolic pressure can fall. The gap between the two, the pulse pressure, widens.
The heart has to pump against this extra load, called afterload. Like any muscle working against a heavier weight, the left ventricle strains and, over time, thickens. This thickening of the muscular wall is left ventricular hypertrophy.
Cardiac output falls with each decade, so a stronger pump is not why blood pressure rises with age. The age-related rise in blood pressure comes mainly from a structural change in the wall of the artery, not from a hormonal or rhythm problem.
Key facts
- Arterial change
- large arteries lose elasticity and become less compliant with age.
- Pressure pattern
- systolic pressure rises, often with a normal or lower diastolic pressure, which is called isolated systolic hypertension.
- Pulse pressure
- the gap between systolic and diastolic pressure widens with arterial stiffness.
- Effect on the heart
- higher afterload strains the left ventricle and can cause hypertrophy.
- Cardiac output
- it falls with each passing decade, so a stronger pump is not why blood pressure rises with age.
- Age
- isolated systolic hypertension is the commonest type of high blood pressure after the age of 50.
Exam traps
- A stronger, higher-output heart is not the change behind the age-related rise in blood pressure, because cardiac output falls with age.
- A more compliant left ventricle does not explain a high systolic pressure in the arteries, because the compliance of the left ventricle falls with age and it becomes stiffer.
- Narrowing of the small arteries (arteriolar vasoconstriction) raises resistance (the opposition to blood flow in the circulation), but that affects the diastolic pressure more than the gap between systolic and diastolic, which widens because of loss of elasticity in the large arteries.
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