Central venous pressure is the blood pressure in the superior vena cava and right atrium of the heart. It is used in medicine as an indicator of blood volume. If venous pressure is too high or too low, it may indicate various heart and lung diseases, among others.
What is central venous pressure?
Central venous pressure is the blood pressure in the superior vena cava and right atrium of the heart. In medicine, central venous pressure means that blood pressure that prevails in the superior vena cava. The so-called superior vena cava is located in the thoracic cavity and blood from the arms, neck and head flow together in it. The place where the blood vessels join is called the venous angle or angulus venosus. One venous angle exists on each side of the body. Doctors measure the central venous pressure with the aid of a venous catheter. The patient lies still during the measurement. The examiner inserts a thin plastic tube into the vein. The catheter enters the vein below the right collarbone and travels through the vein to the heart area. This measurement allows for very accurate results. Doctors can also administer medications through the catheter. In particular, the body can use electrolyte solutions and cardiac medications optimally in this way.
Function and task
In the past, physicians used central venous pressure as a measure to estimate the total blood and fluid volume of the organism. However, this approach is widely considered outdated. Instead, modern medicine uses venous pressure to predict preload. Preload is the force that causes the muscle fibers of the ventricles of the heart to stretch. Preload occurs at the end of diastole, which is the end of the slackening phase of the heart muscle. Central venous pressure depends on both blood volume and vascular tone. Vascular tone influences blood pressure and refers to the total peripheral resistance in the blood vessels. Above all, hormones and the movements of the muscles located on the outside of the blood vessels influence vascular tone. In addition to these two factors, the pressure in the right atrium of the heart also plays a major role in central venous pressure. On the other hand, the pressure acting mechanically on the veins in the chest (intrathoracic pressure) influences the central venous pressure. In a healthy person, the central venous pressure should be between 0 and 9 mmHg. When measured with the aid of a fluid column, the fluid rises by up to 12 cm. This displayed value is the arithmetic mean of the central venous pressure. In addition, diagnosticians can also display the course of the venous pressure over time in the form of a curve. The venous pressure follows certain phases that repeat cyclically. They depend on the heartbeat: When the heart muscle contracts, the heart pumps blood from its chambers into the venous system. Further bodily fluid flows in from the arteries. These transport the oxygen-rich blood toward the heart after the red blood cells have bound it to themselves in the lungs. The cycle of venous pressure itself has different phases. First, the A wave appears, indicating the contraction of the atrium of the heart. This is followed by the C wave – during which a heart valve closes the atrium and bulges out. The subsequent X-sink means that the atrium relaxes as the contraction of the smooth muscle of the heart subsides. During the V wave, blood subsequently flows into the right atrium of the heart. Finally, the Y-sink appears in the progression curve of central venous pressure, during which the body releases blood from the heart and pumps it into the vein with pressure. Subsequently, the cycle repeats at the next heartbeat.
Diseases and ailments
Abnormalities in central venous pressure can indicate various diseases and syndromes. For example, volume deficiency leads to abnormal findings when central venous pressure is measured. Volume deficiency, or hypovolemia, is the medical term for a condition in which there is too little blood in the circulation. A volume deficiency may indicate a loss of blood, even if the bleeding is not due to external injury. Central venous pressure thus also provides an indirect indicator of the presence of internal bleeding. Medicine distinguishes between absolute and relative volume deficiency.In absolute volume deficiency, blood loss is the reason for the syndrome; in relative volume deficiency, on the other hand, weaknesses in the cardiovascular system cause blood to be incorrectly distributed throughout the organism and thus unable to adequately supply all parts of the body. In addition to volume deficiency, abnormal central venous pressure may also indicate a specific weakening of the heart muscle, known as right heart failure. Because doctors measure central venous pressure in the vein in front of the right atrium of the heart, it is particularly sensitive to changes in cardiac activity on the right side. Right heart failure can be caused by various underlying diseases and congenital or acquired malformations. Furthermore, disturbances of the water-electrolyte balance potentially manifest themselves in the central venous pressure: the ratio of fluid and electrolytes is disturbed. The cause of such an imbalance is, for example, overhydration, which is also known as hyperhydration. In this case, the water content of the human body rises above the normal level – either due to abnormal fluid intake or due to disorders of the heart or kidneys. Hormonal disorders can also cause hyperhydration.
