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PH-FD25

Venous congestion (hyperaemia)

Why blood pools when it cannot drain: how raised venous pressure distends capillaries, drives fluid into tissues and starves cells of oxygen, and how chronic congestion browns the lung, mottles the liver and stains the legs.

By the end, you can

  • Distinguish active (arterial) hyperaemia from passive (venous) congestion by cause, colour and effect.
  • Explain how raised venous pressure causes oedema, cyanosis and tissue hypoxia.
  • Relate left- and right-sided heart failure and local venous obstruction to the organs they congest.
  • Describe the gross and microscopic changes of chronic congestion in the lung (brown induration) and liver (nutmeg liver).
  • Explain why long-standing congestion leads to haemosiderin deposits, atrophy and fibrosis.
  • Recognise the classic appearances of the congested lung, liver, spleen, kidney and leg and the tests examiners ask about, and explain how diuretics, venodilators, compression and relieving the cause act on the mechanism.

What it is

Hyperaemia and congestion both mean an increased volume of blood in a tissue’s vessels. In active (arterial) hyperaemia, arterioles dilate and more oxygenated blood flows in, as in exercise or inflammation. In passive (venous) congestion, blood cannot drain away, because the heart fails or a vein is obstructed; deoxygenated blood pools, the tissue turns blue-red, and if congestion lasts the tissue is damaged.

4 types to tell apart
Active hyperaemia
Arterioles dilate and inflow rises: physiological (exercise, digestion, blushing) or inflammatory. The tissue is red and warm.
Acute passive congestion
Drainage fails suddenly (acute left heart failure, a fresh venous thrombosis): distended vessels and oedema, with little lasting damage if it is relieved.
Chronic passive congestion
Venous pressure stays high for months or years: chronic hypoxia, small haemorrhages, haemosiderin, atrophy and fibrosis.
Local and generalised
An obstructed vein congests the territory it drains; heart failure congests the lungs (left side) or the systemic organs (right side).

US spelling: hyperaemia → hyperemia.

Normal function

Blood drains back at low pressure

Blood leaves the capillaries through venules and veins, which hold most of the blood volume at low pressure. The and return systemic blood to the ; four pulmonary veins, such as the , return blood from the lungs to the .

Return is helped by valves in the limb veins, by contracting muscles that squeeze the deep veins, and by the fall in chest pressure during breathing. Each atrium can only empty if the ventricle beyond it fills and pumps well.

In the capillaries, hydrostatic pressure pushes fluid out, and the oncotic pressure of plasma proteins draws most of it back; lymph returns the small remainder. Venous pressure therefore sets the pressure at the end of every capillary bed it drains.

Point to it on the model