Central blood volume is the portion of blood volume located in the pulmonary circulation and the left side of the heart. It affects the central venous pressure and the filling of the left ventricle during the relaxation phase of the heart (diastole).
What is central blood volume?
Central blood volume is the portion of blood volume that is in the pulmonary circulation and the left side of the heart. Central blood volume is the amount of blood that is in the pulmonary circulation and the left side of the heart. Medical definitions also speak of the volume of blood between the pulmonary valve and the aortic valve; both are heart valves, of which humans have a total of four. In the pulmonary circulation, also known as the small circulation, the heart pumps blood from the right ventricle through the pulmonary trunk into the right and left pulmonary arteries and from there on into the finer blood vessels to the capillaries and alveoli. The oxygenated blood then returns to the heart, now flowing in reverse in progressively larger veins. On average, the central blood volume of an adult contains about 500 to 600 ml of blood.
Function and purpose
Central blood volume affects central venous pressure as well as the filling of the left ventricle during the relaxation phase of the heart muscle. Central venous pressure is the medical term for the blood pressure in the right atrium of the heart and in the superior vena cava. The superior vena cava is powerful and combines in itself the blood from two other large veins: the right and left brachiocephalic veins. This blood originates from the arms, neck and head and flows through the superior vena cava into the right atrium of the heart. The point where the two veins flow into the superior vena cava is called the venous angle and is located at the level of the first rib. Central venous pressure can be measured through a central venous catheter. Originally, physicians used central venous pressure as an indicator of the total amount of blood that is in the blood vessels, i.e., intravascular volume status. Today, however, this measure is generally considered outdated: Reviews of this assumption found that central venous pressure does not predict intravascular blood volume reliably enough. However, central venous pressure appears to be useful for estimating preload. Preload is the force exerted on the myocardial fibers of the ventricles at the end of the relaxation phase of the heart (diastole). As a result, the fibers stretch at most until they reach the maximum resting length of the cardiac muscle fibers. Furthermore, the central blood volume influences the filling of the left ventricle during diastole. From the left ventricle, blood travels to other parts of the human organism via the great circulation or systemic circulation. Furthermore, central blood volume is involved in the regulation of blood circulation.
Diseases and ailments
Various disease patterns may occur in connection with central blood volume. One of these is postural orthostatic tachycardia syndrome (POTS), which may be due to a disorder in the autonomic nervous system, at least in some patients. Typical symptoms include palpitations with equal or slightly elevated blood pressure, increased perspiration, feelings of weakness, nausea, dizziness, and/or loss of consciousness. Anxiety symptoms and visual disturbances may also occur in the setting of POTS. In many cases, symptoms manifest after prolonged standing. If a person changes position – for example, when standing up – a mechanism for regulating blood circulation normally takes effect. This adaptation enables the organism to continue supplying all areas of the body with blood and thus oxygen and nutrients even in the changed position. A whole series of syndromes and diseases is characterized by the failure of this regulation. In postural orthostatic tachycardia syndrome, too, the individual symptoms result from such a misregulation, which also affects the central blood volume. If POTS occurs as a result of another underlying disease, treatment usually focuses on the underlying disease, as far as possible. In other forms of POTS, treatment may include strengthening the leg muscles to prevent blood stasis in the leg veins or increased fluid intake with sufficient salt.In addition, drug therapy options exist, but like all treatment options, these depend on individual circumstances. Another clinical picture in which central blood volume can play a role is hypovolemia. As such, medicine refers to a volume deficiency of the entire blood. Hypovolemia can increase heart rate, decrease blood pressure, and lead to pale, cold hands, the latter usually due to poorer blood flow to the extremities. Decreased central venous pressure may also occur. Treatment of hypovolemia depends on the underlying cause and, moreover, generally focuses on compensating for the lack of volume. Hypervolemia, on the other hand, is characterized by increased blood volume. It can manifest as increased central venous pressure, palpitations, elevated blood pressure, edema, and jugular vein influence congestion. Among others, hypervolemia is possible in pregnant women and recipients of blood transfusions. It is also possible that the increase in blood volume is due to the body holding too much water. This condition is also known as hyperhydration and may be due to, for example, kidney failure, cirrhosis of the liver, heart failure, high levels of water consumption, or drinking seawater. Treatment for hypervolemia also depends on the presenting cause.