• Cardiovascular System
  • Physiology

What are the effects of respiratory activity on venous return?

  • Reading time: 1 minute, 51 seconds
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  • Revised on: 2020-07-05

In your quest to study physiology you may at some point asked yourself, what are the effects of respiratory activity on venous return? After the blood has made its way through the arterial system of the body, it must return to the heart by way of the venous system.

But because gravity pulls blood into the legs and away from the heart when a person stands, veins must go against gravitational force to deliver blood back to the heart.

There are two key mechanisms that aid in venous return:

For the essence of this article, we are going to cover how respiratory activity affects venous return.

Like we have mentioned, the process of breathing also promotes the flow of venous blood in the thoracic and abdominal cavities.

During inhalation, the chest expands and the diaphragm moves downward reducing the pressure in the chest cavity. As a result of this respiratory activity, the pressure within the chest cavity averages 5 mm Hg less than atmospheric pressure and the pressure in the abdominal cavity to rise.

The rising abdominal pressure squeezes the inferior vena cava, forcing blood upward toward the thorax.

The lower pressure in the thorax helps draw blood toward the heart.

Valves in the veins in the legs ensure that blood doesn’t flow backward

As the venous system returns blood to the heart from the lower regions of the body, it travels through the chest cavity, where it is exposed to this subatmospheric pressure.

Because the venous system in the limbs and abdomen is subject to normal atmospheric pressure, an externally applied pressure gradient exists between the lower veins (at atmospheric pressure) and the chest veins (at 5 mm Hg less than atmospheric pressure).

This pressure difference squeezes blood from the lower veins to the chest veins, promoting increased venous return.

This mechanism is called the respiratory pump because it results from respiratory activity.

Increased respiratory activity, as well as the effects of the skeletal muscle pump and venous vasoconstriction, all enhance venous return during exercise.

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