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Cardiovascular Physiology Concepts

Richard E. Klabunde, PhD


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Central Venous Pressure


Venous pressure is a term that represents the average blood pressure within the venous compartment. The term "central venous pressure" (CVP) describes the pressure in the thoracic vena cava near the right atrium (therefore CVP and right atrial pressure are essentially the same). CVP is an important concept in clinical cardiology because it is a major determinant of the filling pressure and therefore the preload of the right ventricle, which regulates stroke volume through the Frank-Starling mechanism.

A change in CVP (ΔCVP) is determined by the change in volume (ΔV) of blood within the thoracic veins divided by the compliance (Cv) of the veins according to the following equation:

ΔCVP = ΔV / Cv

venous complianceTherefore, CVP is increased by either an increase in venous blood volume or by a decrease in venous compliance. The latter change can be caused by contraction of the smooth muscle within the veins, which increases the venous vascular tone and decreases compliance. The effects of increased venous blood volume and decreased venous compliance on CVP are illustrated in the figure. Point A represents a control operating point on a compliance curve for a large vein. If the volume of blood within the vein is increased, then the operating point will shift up and to the right (from A to B) along the same compliance curve. This will lead to an increase in pressure that is determined by the change in volume and the venous compliance (slope of the curve). Venous pressure is also increased if venous smooth muscle contraction is enhanced (e.g., by sympathetic nerve stimulation). When this occurs, the venous compliance decreases (dashed red line), and the new operating point C will reflect a smaller venous volume but at a greater venous pressure.

It is important to note for a proper conceptual understanding that the compliance of the large thoracic veins (especially the vena cava) does not undergo large changes. Instead, the major site for venous compliance changes is smaller veins located outside of the thorax. These smaller veins can undergo large changes in compliance. When the compliance of veins decreases (e.g., by sympathetic nerve stimulation) causing venoconstriction, the pressure within the veins increases and this is transmitted up to the thoracic veins, which increases their volume and pressure.

In the body, venous compliance and venous volume are not static, but dynamic, with many factors influences these two variables, such as cardiac output, respiratory activity, contraction of skeletal muscles (particularly legs and abdomen), sympathetic vasoconstrictor tone, and hydrostatic forces (i.e., gravity). Venodilator drugs, which are often used in the treatment of acute heart failure and angina, relax venous vessels (increase their compliance) and lower central venous pressure. All the above factors influence central venous pressure by either changing thoracic venous blood volume or venous compliance. These factors or mechanisms are summarized in the following table:

Factors Increasing Central Venous Pressure

Primarily a change in compliance (C) or volume (V)
Decreased cardiac output V
Increased blood volume V
Venous constriction C
Changing from standing to supine body posture V
Arterial dilation V
Forced expiration (e.g., Valsalva) C
Muscle contraction (abdominal and limb) V, C

Revised 01/30/2023




DISCLAIMER: These materials are for educational purposes only, and are not a source of medical decision-making advice.