1. Definition
Venous return is the flow of blood from the veins back to the right atrium of the heart, driven by factors like the pressure gradient between veins and the heart, muscle contractions, and venous valves. It directly influences cardiac output and preload.
2. Influencing Factors
- Blood volume – Increased blood volume boosts venous return, while dehydration or blood loss reduces it.
- Venous tone – The contraction of smooth muscle in the venous walls (venoconstriction) increases venous return by reducing venous capacity.
- Skeletal muscle pump – Muscle contractions, particularly in the legs, squeeze veins and push blood toward the heart, enhancing venous return.
- Respiratory pump – During inhalation, decreased intrathoracic pressure facilitates the return of blood to the heart.
- Gravity and body position – Lying down or elevating the legs increases venous return, while standing decreases it.
- Sympathetic nervous system activity – Increases venoconstriction and enhances venous return.
- Right atrial pressure – Lower right atrial pressure promotes venous return, while higher pressure impedes it.