Peripheral venous pressure, gravity and the blood reservoirs
- Concept
- For completeness
Standing makes the weight of blood push hard on leg veins. Valves and muscle squeezes keep it moving, and big veins store spare blood.
Also called: Hydrostatic pressure, Venous pump, Blood reservoirs
See it in 3D: Leg veins · Great saphenous vein · Inferior vena cava · Spleen · Liver · Portal vein
What it is
Peripheral venous pressure is a few mmHg above right atrial pressure in a lying person, but gravity adds the weight of the blood column when standing. Venous valves and the muscle pump keep leg pressure low during walking. Veins also act as a reservoir: the liver, abdominal veins, skin and lungs hold blood that sympathetic venoconstriction can return to the circulation, and the spleen stores and filters red cells.
Key facts
- Veins are compressed where they cross the first rib, enter the chest and run through the abdomen, so peripheral pressure is a few mmHg above central.
- When right atrial pressure rises above ≈ 4–6 mmHg, the compression points open and peripheral venous pressure rises in step.
- Neck veins collapse above the clavicle in a sitting person: visible distension means a raised central venous pressure.
- The spleen has a venous sinus store and red-pulp cords; it removes old or abnormal red cells and, in some species much more than in humans, contracts to release stored cells.
How it works, step by step
- When a person stands, the column of blood from the heart to the feet adds ≈ 90 mmHg to arterial and venous pressure at the ankles.
- Leg veins distend and pool blood; venous return falls until reflexes and the muscle pump act.
- Each contraction of calf muscles squeezes deep veins; valves let blood move only toward the heart.
- Between contractions valves close, so the column is broken into short segments and pressure stays low.
- If valves fail or a person stands still, pressure stays high, capillary filtration rises and edema forms.
- Sympathetic venoconstriction of reservoirs can return several hundred mL to the central circulation after blood loss.
Reference values
| Parameter | Value |
|---|---|
| Right atrial pressure | ≈ 0 mmHg |
| Peripheral venous pressure, lying down | ≈ 4–7 mmHg above right atrial |
| Foot venous pressure, standing still | ≈ +90 mmHg |
| Foot venous pressure, walking | < 25 mmHg |
| Sagittal sinus pressure, standing | ≈ −10 mmHg |
| Blood held in systemic veins | ≈ 64% of total |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Clinical notes
- Varicose veins and chronic venous insufficiency: failed valves keep standing pressure high, causing edema, skin changes and ulcers.
- Cirrhosis with ascites raises intra-abdominal pressure and portal pressure, adding to leg edema.
- Long immobility (flights, bed rest) removes the muscle pump; slow flow favours deep vein thrombosis.
Test yourself
Think of the answer, then tap the question to see it.
Why is venous pressure at the feet ≈ 90 mmHg in a person standing still?
The weight of the continuous blood column from the heart to the feet (≈ 120 cm × ≈ 0.77 mmHg/cm) adds hydrostatic pressure.
Why is there a risk of air embolism when a dural sinus is opened in a sitting patient?
Sinus pressure is negative above the heart, and the bony walls keep the sinus from collapsing, so air can be sucked in.
How does walking lower foot venous pressure?
Calf muscle contractions push blood upward and the venous valves stop it falling back, breaking the hydrostatic column into short segments.
Why does pregnancy often cause leg edema and varicose veins?
The uterus raises intra-abdominal pressure and compresses the inferior vena cava and iliac veins, raising leg venous and capillary pressure.
Connections
See it in 3D6
The structures of Durgical's 3D anatomy where it happens.
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: Varicose Veins (StatPearls (NCBI Bookshelf), 2024); Venous Insufficiency (StatPearls (NCBI Bookshelf), 2025); Neuroanatomy, Dural Venous Sinuses (StatPearls (NCBI Bookshelf), 2024); Anatomy, Abdomen and Pelvis, Spleen (StatPearls (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.