Vascular compliance and capacitance !
- Concept
- Exam priority: medium
Arteries are elastic and cushion each beat; veins are so stretchy that they hold most of the body's blood.
Updated 2026-11-01
Also called: Vascular distensibility
See it in 3D: Thoracic aorta · Ascending aorta · Great saphenous vein
What it is
Compliance is how much volume a vessel gains for each mmHg of pressure. The large elastic arteries stretch in systole and give the blood back in diastole, turning pulsatile flow into continuous flow. Veins, far more compliant, act as a reservoir: a small change in tone moves large volumes toward the heart.
Key facts
- Windkessel effect: the aorta stores elastic energy in systole and returns it in diastole, keeping coronary and peripheral flow going.
- Delayed compliance (stress relaxation): after a sudden rise in volume, pressure rises then falls over minutes as smooth muscle stretches.
- Arterial stiffness speeds the pulse wave: the reflected wave returns in systole and adds load to the left ventricle.
- Leg veins carry high hydrostatic pressure when standing; their valves and the muscle pump keep blood from pooling.
Equations
- ΔV
- change in volume
- ΔP
- change in pressure
Distensibility is ΔV / (ΔP × starting V).
- SV
- stroke volume
- Carterial
- arterial compliance
More volume or less compliance → a wider pulse pressure.
Approximate distribution of blood volume
| Parameter | Value |
|---|---|
| Systemic veins, venules and venous sinuses | ≈60–70% |
| Systemic arteries | ≈13–15% |
| Pulmonary circulation | ≈9% |
| Heart | ≈7% |
| Systemic capillaries | ≈5–7% |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Clinical notes
- Isolated systolic hypertension of older adults reflects a stiff aorta more than high peripheral resistance.
- In varicose veins incompetent valves and a stretched wall let blood pool in the legs: heaviness, edema and skin changes.
- Loss of compliance of the ventricle (not the vessels) underlies heart failure with preserved ejection fraction.
Test yourself
Think of the answer, then tap the question to see it.
Why does an older adult with a stiff aorta have high systolic but normal or low diastolic pressure?
A stiff aorta cannot cushion the ejected volume (systolic rises) or return elastic energy in diastole (diastolic falls): the pulse pressure widens.
Why is venoconstriction so effective at sustaining cardiac output in hemorrhage?
Veins hold most of the blood and are very compliant: a small rise in tone shifts a large volume toward the heart and raises venous return.
What is stress relaxation of a vessel and what does it achieve?
After a sudden rise in volume, pressure rises then falls over minutes as smooth muscle stretches; it lets the system absorb moderate transfusions or losses.
How would pulse pressure change if stroke volume stays the same but arterial compliance halves?
It would widen, because pulse pressure is roughly stroke volume divided by arterial compliance.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Systolic, diastolic, mean and pulse pressure
- Venous return and the Guyton curves
- Physiology of hypertension
- Central venous pressure and the jugular pulse
- Flow, pressure and resistance: Poiseuille and turbulent flow
Related conditions
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 20.1 Structure and Function of Blood Vessels (OpenStax (Rice University), 2022); 20.2 Blood Flow, Blood Pressure, and Resistance (OpenStax (Rice University), 2022); Varicose Veins (StatPearls (NCBI Bookshelf), 2023); Essential Hypertension (StatPearls (NCBI Bookshelf), 2023); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 15). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.