Ischaemia
What happens when arterial inflow falls short of a tissue’s needs: why flow falls, why some tissues and zones suffer first, how speed of onset and collaterals decide the outcome, and why narrowed arteries cause pain on exertion.
By the end, you can
- Define ischaemia and distinguish it from hypoxia with normal blood flow and from venous congestion.
- Explain the causes of reduced arterial inflow: narrowing, occlusion, spasm, compression, low perfusion pressure and redistribution.
- Explain angina and intermittent claudication as a mismatch between oxygen supply and demand.
- Explain why tissues differ in tolerance and why the subendocardium and watershed zones suffer first.
- Relate speed of onset, collateral circulation and duration to infarction, atrophy or recovery.
- Recognise the classic appearances, watershed areas, staging systems and tests of ischaemia, and explain how revascularisation, fibrinolysis, antithrombotic drugs and lowering demand act on the mechanism, and why time matters.
What it is
Ischaemia is arterial blood flow too low for a tissue’s needs. It deprives cells of oxygen and glucose and lets waste products (carbon dioxide, lactate, hydrogen and potassium ions) build up, so it injures faster than low oxygen alone. Many European curricula call it local (arterial) anaemia: the tissue is pale because less blood reaches it, although the blood itself is normal.
3 types to tell apart
- Acute ischaemia
- Sudden occlusion (an embolus, thrombosis on a plaque, injury to an artery): no time for collaterals to develop, so tissue dies unless flow returns.
- Chronic ischaemia
- Gradual narrowing, usually by atherosclerosis: collaterals enlarge, and the tissue suffers pain on exertion, atrophy and fibrosis.
- Relative (demand) ischaemia
- Flow is enough at rest but cannot rise to meet extra demand, as in angina and intermittent claudication.
US spelling: ischaemia → ischemia, anaemia → anemia.
Normal function
Flow matched to demand
Arteries deliver blood; the small arterioles set how much each tissue receives. Within a wide range of pressures, arterioles adjust their tone to keep flow steady (autoregulation), and when a tissue works harder its metabolites (adenosine, carbon dioxide, hydrogen and potassium ions, nitric oxide) dilate them, so flow rises to match demand.
In the heart, the run on the surface and their dive through the muscle. The is reached last and is squeezed during each contraction, so it fills mainly in diastole.
Neighbouring arterial territories are often linked by small collateral vessels. Some organs have two supplies (lung, liver), whereas others depend on single end arteries (kidney, spleen, retina) or on arteries whose collaterals are too small to help quickly (heart, brain).
Underlying change · Step 1 of 4
Why arterial inflow falls
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Enough at rest, too little on effort
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Which tissues and zones suffer first
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Speed, collaterals and the outcome
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .