Cardiac Output: Function, Tasks, Role & Diseases

In medicine, cardiac output is the volume of blood pumped from the heart through the entire circulatory system in one minute. It thus represents the unit of measurement for the heart‘s pumping function and is also referred to as cardiac output. Cardiac output is obtained by multiplying the heart rate by the cardiac output.

What is cardiac output per minute?

In medicine, cardiac output is the volume of blood pumped from the heart throughout the circulatory system in one minute. All multicellular organisms require an efficient system that supplies the cells with everything they need. Energy can be stored in the cells, oxygen or carbon dioxide must be delivered or removed respectively. This circulation is ensured by the power of the heart. Switched cells that require more or less power and energy must also be supplied in the same way. The heart is therefore regulated over a wide power band. This is done by a current or pulse beat, which can be measured. The stroke volume times the heart rate gives the cardiac output, abbreviated HMV.

Function and task

Control of the cardiovascular system arises from blood pressure. As soon as a person moves faster, the oxygen demand in the muscles increases, the blood pressure decreases and must be increased again. As a result, the cardiovascular system in the “medulla oblongata” increases the so-called sympathetic tone. The medulla oblongata is the caudal part of the brain that serves as the transition from the spinal cord to the brain stem. Sympathetic tone functions as an alarm response in the body, characterized by a rise in blood and an increased heart rate. The reaction leads to a vasoconstriction, via alpha receptors, in organs that are not needed at that moment, such as the skin or certain tracts of the kidney. The return flow in the veins is also increased, while the pumping capacity of the heart is increased via beta receptors. In this process, the sinus node, Purkinje fibers, His bundle, and one right and two left tawara legs form the conduction system of the heart and tend to depolarize spontaneously. The sinus node is particularly active at the resting rate of about sixty impulses per minute. Activation of the sympathetic nervous system drives the sinus node to successive rapid depolarizations, acting “positively chronotropic,” in increased stroke frequency; “positively inotropic,” in increased contractile force; “positively dromotropic,” in increased speed of stimulus conduction; and “positively bathmotropic,” in increased excitation of the muscle cell membrane. In short, short-term control of the circulation occurs through regulation of vascular cross-sections by the central nervous system. Pressure volume can be measured during heart rate. Stroke volume, in turn, is brought about by increasing the filling pressure of blood to the heart and by increasing contractility. The stroke volume is then multiplied by the stroke frequency, which is also higher under the influence of the sympathetic nervous system. While the body is at rest, the cardiac output in a healthy and adult human is around five liters per minute. The cardiac index in its lower normal limit is 2.5 liters per minute. It is the parameter for the general assessment of cardiac performance and is calculated as the quotient of cardiac output per minute and body surface area. This measurement plays an important role in hemodynamics and for recording circulatory data for patients who are in the intensive care unit. Under higher stress, on the other hand, the cardiac output can increase sixfold. Especially during athletic activity or competitive sports, the cardiac output sometimes exceeds thirty liters per minute. The measurement is carried out in various ways. In clinical practice, it can only be recorded indirectly. For example, by means of echocardiography, from which in turn the stroke volume and heart rate can be roughly estimated. Here, the diameter of the left ventricular outflow tract is measured as a 2D image. Another measurement method is the somewhat more complex thermodilution. A measured amount of cold fluid is injected into the patient and the temperature of the blood is recorded via a thermal probe. This can be done through the Swan-Ganz catheter, which is advanced through a vein in the neck through the right side of the heart until it reaches the pulmonary artery.Cardiac output is then determined using a heating coil. A cardiac catheter is also necessary for dye dilution procedures. Another method is to measure cardiac output using magnetic resonance imaging or impedance cardiography. The latter is performed as a noninvasive measurement.

Diseases and medical conditions

If the pumping capacity of the right or left ventricle decreases, a reduced cardiac output occurs. This can be triggered by hypothyroidism, for example, but also by structural cardiac changes, as in ischemia, by tachycardia, bradycardia, or by valvular damage. Cardiac output also decreases in the presence of arterial hypertension or inhibited filling conditions of the ventricles. This occurs, for example, in thoracic deformities, stiffening of the heart walls, or cardiac tamponade, where fluid accumulation interferes with overall cardiac action and impedes contraction movements. This, in turn, can be caused by hemorrhage following a heart attack or pericarditis, an inflammation of the pericardium. With an increased cardiac output, a person usually suffers from anemia, fever or hyperthyroidism. The cardiac output also increases during pregnancy, as more blood is needed by the organism to supply the uterus and placenta. Similarly, the volume may increase during septic shock, even if there is impaired blood flow to the organs. Cardiac output also increases with the use of certain cardiac rhythm-accelerating drugs.