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PH-CV04

Hypertension

How cardiac output and arteriolar resistance set blood pressure, why it stays high in essential and secondary hypertension, and how remodelled small vessels and a thickened heart lead to damage in the heart, brain, kidneys and eyes.

By the end, you can

  • Explain how cardiac output and peripheral resistance set arterial pressure, and how the kidneys set its long-term level.
  • Distinguish essential from secondary hypertension and give examples of secondary causes.
  • Describe hyaline and hyperplastic arteriolosclerosis and how they raise resistance further.
  • Explain why the left ventricle hypertrophies and what that costs.
  • Relate small-vessel damage to the consequences in the heart, brain, kidney and retina.
  • Recognise the classifications, key thresholds, tests and appearances of hypertension, and explain how each main drug class lowers pressure through output, resistance or salt and water.

What it is

Hypertension is arterial blood pressure that stays above the level at which the risk of damage to the heart, brain, kidneys and vessels clearly rises. It is essential (primary) when no single cause is found, as in most people, and secondary when a specific disease or medicine causes it.

4 types to tell apart
Essential (primary) hypertension
Many small genetic and lifestyle influences together reset the kidney’s handling of salt and raise arteriolar resistance.
Secondary hypertension
A specific cause, such as kidney disease, renal artery narrowing or excess aldosterone, raises the pressure.
Isolated systolic hypertension
Raised systolic with normal diastolic pressure, mainly from stiff large arteries in older adults.
Severe (accelerated or malignant) hypertension
Very high pressure with acute damage to small vessels and to organs such as the retina, kidney and brain.

Normal function

How blood pressure is set

Mean arterial pressure depends on two things: cardiac output, the blood the heart pumps each minute, and total peripheral resistance, how hard it is to push that blood through the small vessels. Pressure = cardiac output × resistance.

Most resistance lies in the arterioles. Their walls are mostly , and small changes in its tone change the radius, and so the resistance, greatly. The releases nitric oxide, which relaxes the muscle; sympathetic nerves and angiotensin II contract it.

Baroreceptors in the carotid sinus and aortic arch correct short-term swings within seconds. Over days the kidneys set the level: when pressure rises they excrete more sodium and water (pressure natriuresis), lowering blood volume and pressure again.

Point to it on the model
What sets arterial pressureSchematic
  1. Heart rate
    Stroke volume
  2. multiply
    NormalCardiac output
    NormalPeripheral resistanceSet mainly by arteriole radius
  3. multiply
    NormalMean arterial pressure
  4. sensed by baroreceptors and kidneys
    Reflexes and pressure natriuresisReturn pressure towards its set level

In established hypertension the set level itself is raised; most people have a normal output and raised resistance.

This explains