Cardiac output


Cardiac output (HMV) is defined as the volume of blood that the heart pumps into the body's circulation per minute.
Alternatively, the term body time volume is used, but the term cardiac output is more common.
The cardiac output is used as a measure of the pumping function of the heart, i.e. it describes the ejection capacity of the heart or, for short, the cardiac output. A similar term for cardiac output is cardiac output, which, however, is not related to a specific time unit.

How can you calculate or measure cardiac output?

The Cardiac output is the product of Heart rate (HF), which can be determined by the pulse and the Stroke volume.

The Cardiac output so is the same Heart rate times the stroke volume (HMV = HR x stroke volume). To put it simply, the stroke volume is the volume that is ejected from the left ventricle during a heartbeat.

To determine the cardiac output, it is therefore necessary to determine the stroke volume. However, this is complicated and time-consuming, but there are several methods of stroke volume to determine.
You can measure the stroke volume with the so-called Thermodilution method to calculate. Here is a Swan-Ganz catheter into the pulmonary arteries through a vein in the neck over the right half of the heart. Cold fluid is then injected into the right atrium and the catheter measures the change in temperature. In the course of the process, the measurement data from the catheter can be used to measure the temperature drop and the further temperature curve, the cardiac output.
A simpler, but also less precise one method is the Echocardiography, so the heart ultrasound. The stroke volume can be calculated using measurements of the diameter of the outflow path of the left ventricle, which are calculated using the circular area formula to form a three-dimensional area.
You can also use the Oxygen concentration calculate the cardiac output in venous blood, arterial blood and oxygen uptake from the lungs. The cardiac output results from the volume of oxygen absorbed from the lungs per unit of time divided by the oxygen concentration in the arterial blood, which must first be subtracted from the oxygen concentration in the mixed venous blood. This ultimately corresponds to that Blood flow through the lungswhat about the Equate cardiac output leaves.
In addition, there are a few other methods that can be used to determine stroke volume.

Normal values ​​of the cardiac output

The cardiac output is given in the unit volume per minute, as the name suggests. At a healthy adults is that Cardiac output 3.5-5 liters per minute. The Values ​​fluctuate depending on the individual circumstances and the current requirements. A pregnant woman, for example, has a higher cardiac output than before her pregnancy because she has to take care of the fetus in the abdomen.

Cardiac output in athletes

At Athletes the cardiac output is increased, with exercise it is possible that the cardiac output increases to 30 liters / minute.
On the one hand, control mechanisms outside the heart are responsible for this. At the location of the central Cardiovascular regulation in the Brain stem the body receives signals from the vessels in the body. Adapted to these signals, reactions are sent out to the body.
The contraction force of the heart increases, which increases the heart rate and the heart muscle cells can be excited more quickly.
On the other hand, the heart also reacts quickly to an increased need for transport. For this purpose, the Heart muscle stretched more at firstwhich allows more blood to flow from the body to the heart and consequently more blood to be expelled.
The one common to athletes Enlargement of the heart chambers and the hypertrophy (This is an increase in the volume of the cells) of the heart muscle means that they have a higher cardiac output not only under load but also at rest.

What is the cardiac output like in a marathon runner?

In an adult, the cardiac output is about 5 liters per minute at rest.
This value can briefly quadruple under load.

Heavily endurance trained hearts can even pump over 30 liters per minute. However, the heart can only maintain such high values ​​for a short period of time.
A marathon runner's heart beats about 150 times per minute.
About 100 ml of blood are pumped out of the heart per stroke.

If you multiply the number of beats per minute by the stroke volume, you get the cardiac output. In this case it is 15 liters per minute.

If the runner ran the marathon within four hours, the heart would have to pump 3,600 liters of blood within this time. For top athletes, the value is probably even higher.

Cardiac output at rest

In Quiet the body's need to be supplied with fresh blood and oxygen is lower than during exercise or with athletes. Overall, that beats Heart quieter in peace, the Pulse is lower and the Cardiac output is less. Even so, it is enough to supply the body with sufficient blood and oxygen.

Kidney and cardiac output

The kidney become 20-25% of cardiac output made available. The kidneys do not need the oxygen contained in the blood to a large extent, but they do filters the blood and absorbs components or releases others back into it.
In addition to blood washing, the kidney is also for the Fluid excretion in the form of urine responsible. She adapts this to the needs of the body.
However, do influence each other Kidney and heart precisely for these two reasons each other. In case of a Renal failure for example, less fluid is excreted that The preload and afterload are high. The heart therefore has to move more blood, the cardiac output increases, which in the long term leads to negative changes in the heart.

Control of cardiac output

The has an influence on the cardiac output Contractility, the Preload and the Afterload. The contractility describes the ability of the muscle to contract.
With Preload is this volume meant which is present in the chambers after the chambers have been completely filled.
The Afterload however, refers to that volumethat occurs after the contraction of the heart muscle still in the heart has remained.
Anatomical conditions of the heart are also important. These include the size of the heart chamber, the thickness of the heart wall and the function of the valves.

What is the influence of adrenaline?

The release of adrenaline increases the cardiac output and thus the cardiac output.

Adrenaline affects several pumping properties of the heart.
First of all, it speeds up the heart rate. The heart's own pacemaker cells become more active and send signals more frequently. In addition, the resulting signal is transmitted more quickly via the heart muscle.
The force with which the heart contracts also increases. In addition, after contracting, the heart relaxes faster under the effect of adrenaline. This enables a more rapid succession of strokes.

Because of the harder work, the heart muscle needs a higher supply of nutrients and oxygen. This is why the so-called coronary vessels expand with adrenaline. They serve to supply the heart muscle.