Central venous pressure (CVP) is a measure of the mean pressure within the thoracic vena cava, which is the largest vein in the body and responsible for returning blood from the systemic circulation to the heart. CVP is a major determinant of the filling pressure and cardiac preload, and like any fluid pump, the heart depends on an adequate preload to function effectively. Low venous return translates into a lower preload and a drop in overall cardiac output, a relationship described by the Frank-Starling Mechanism. CVP is an important physiological parameter, the correct measure of which is a clinically relevant diagnostic tool for heart failure patients. In addition to other vitals such as heart rate and mean arterial pressure, accurate measures of central venous pressure through simple diagnostic instrumentation would provide physicians with a clear picture of cardiac functionality, and allow for more targeted treatment. Recent literature has also shown that measuring CVP can be an important hemodynamic indicator for the early identification and treatment of more widespread conditions, such as sepsis (Rivers, Nguyen, Havstad, & Ressler, 2001). With over five million patients (American Heart Association, http://www.americanheart.org/presenter. jhtml) in the U.S. presenting with heart failure-like symptoms annually, a current challenge for physicians is to obtain a quick and accurate measure of a patient’s central venous pressure in a manner that poses minimum discomfort.
Key Terms in this Chapter
Cardiac Output: Total volume of blood ejected from left side of the heart into systemic circulation per minute.
Cardiac Preload: Initial stretch of cardiac muscle before the systolic contraction phase; preload directly affects stroke volume and cardiac output through the Frank-Starling mechanism.
Sphygmomanometer: An instrument for measuring arterial blood pressure, also known as a blood pressure cuff.
Ultrasound Imaging: Procedure by which high-frequency sound waves are reflected off internal tissues or organs to produce echoes, which are analyzed to form an image of body tissues, called a sonogram; ultrasound is commonly used in fetal monitoring, and more recently used in cardiology and radiology.
Frank-Starling Mechanism: Pioneering work of Otto Frank and Ernest Starling that provides a framework for relating cardiac muscle length, tension, and activation to parameters such as preload and cardiac output.
Plethysmograph: Instrument used to measure changes in volume of a vessel or organ.
Intravenous Cannulation: Insertion of a flexible tube or cannula into the venous compartment to allow for passage of a catheter; a procedure commonly performed when inserting a central intravenous line.
Compliance: Ratio of change in blood volume to change in intraluminal pressure; highly compliant vessels will respond to increased blood flow by distending, whereas low compliance vessels are more rigid, and will have increased pressure with more blood flow; compliance is regulated by the sympathetic nervous system, and affected by collagen build-up and short-term changes in vascular tone.
Central Venous Pressure (CVP): Mean pressure inside the thoracic vena cava, near the right atrium of the heart; primary determinant of cardiac preload, and sensitive to changes in blood volume and venous compliance.
Heart Failure: Pathological condition whereby the heart has reduced cardiac output, leading to backup of blood volume in the venous system and increased central venous pressure; causes include coronary artery disease, valvular disease, and myocardial infarction.