Understanding venous return
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Cardiac output can increase fivefold to adapt to changing metabolic needs. Since normal contraction empties the heart of nearly all its blood, simply increasing the force or rate of contraction cannot explain the dramatic increase in cardiac output. Instead, the circulation mobilizes a large volume of blood from the compliant veins. The venous system stores two-thirds of the blood volume and serve as an adjustable reservoir [1, 2]. The Starling law explains that cardiac output is intrinsically coupled to the rate of blood return to the heart . To increase cardiac output, the circulation increases venous return—the rate of blood flowing from the systemic veins into the right atrium. This review will discuss the mechanisms that regulate venous return.
A pressure gradient drives blood from the veins into the heart. The normal right atrial pressure at rest is 0 mmHg [1, 3, 4, 5]. Contraction empties the heart and maintains this normal (low) right atrial pressure. The mean systemic...
KeywordsCardiac Output Venous Return Atrial Pressure Cardiac Tamponade Ventricular Afterload
Conflicts of interest
The authors declare they have no financial conflict of interest.
There were no human or animal subjects used for this study and there is no requirement for institutional review approval.
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