Venous return

Venous Return

Starling's Law of the Heart and Right Atrial Pressure

Venous return is the rate of blood flow back to the heart. It is a crucial component of the cardiovascular system, as it influences the cardiac output and overall hemodynamics. Venous return is determined by several factors, including the venous pressure, the right atrial pressure, and the venous compliance.

Physiology of Venous Return

Venous return is primarily driven by the pressure gradient between the peripheral veins and the right atrium. This gradient is influenced by the mean systemic filling pressure, which is the average pressure in the systemic circulation when the heart is stopped and the blood is evenly distributed.

Factors Affecting Venous Return

Several factors can affect venous return:

• Venous Tone: The tone of the venous system can alter the capacity of the veins to hold blood, thus affecting venous return.
• Blood Volume: An increase in blood volume can increase venous return by raising the mean systemic filling pressure.
• Muscle Pump: The contraction of skeletal muscles, particularly in the legs, can help propel blood back to the heart.
• Respiratory Pump: During inspiration, the pressure in the thoracic cavity decreases, which can enhance venous return by increasing the pressure gradient.

Vascular Function Curve

Relationship with Cardiac Output

Venous return and cardiac output are closely linked. According to the Frank-Starling law of the heart, the heart will pump out whatever volume of blood it receives. Therefore, an increase in venous return will lead to an increase in cardiac output, provided the heart is functioning normally.

Starling Curve

The Starling curve illustrates the relationship between right atrial pressure and cardiac output. As venous return increases, right atrial pressure rises, leading to an increase in cardiac output until a plateau is reached.

Vascular Function Curve

The vascular function curve represents the relationship between venous return and right atrial pressure. It shows that as right atrial pressure increases, venous return decreases, due to the reduced pressure gradient.

Cardiac and Vascular Function Curves

Combined Cardiac and Vascular Function Curves

The intersection of the cardiac and vascular function curves represents the equilibrium point where venous return equals cardiac output. This point is crucial for understanding the balance of the cardiovascular system.

Venous Return Curves

Venous Return Curves

Venous return curves can demonstrate the effects of different physiological conditions, such as changes in blood volume or venous tone. These curves help in understanding how various factors can shift the equilibrium point of the cardiovascular system.

Related Pages

• Cardiac output
• Frank-Starling law of the heart
• Hemodynamics
• Vascular resistance