Hmv

In 1870, Adolf Eugen Fick first described a method for measuring the CO2 content in humans (Kobe 2019).

At the beginning of the 20th century, Ernest Starling recognized that the heart can only pump out what flows to it. Arthur Guyton and Solbert Permutt later developed this method further. This made it possible to show that mechanical properties of the circulation are important determinants of the HRV (Magder 2016).

Thermodilution, another method for measuring HMV, was introduced in 1970 (Kobe 2019).

HMV (cardiac output) is the volume of blood ejected from the left ventricle per minute (Hajdugal 2020). It is the product of stroke volume and heart rate and is a decisive factor for oxygen supply (Saugel 2021).

The lower value of the HMV in relation to the body surface area is > 2.5 l / min / m2 at rest (Herold 2022). There is no direct standard value, as the HMV depends on height, weight, gender, age and metabolic status. In healthy adults, values between 6 - 8 l / min are generally found at rest (Krakow 2005). Under stress, however, the HMV can increase fourfold (Krist 2024).

• The formula for HMV is: cardiac output (l / min) = heart rate x stroke volume (Krist 2024).

Influence on the HMV:

- Contractility

- preload

- Afterload

- Size of the ventricle

- Heart wall thickness

- Function of the valves (Krist 2024)

The HMV can now be determined using numerous methods (Saugel 2021). The best known are the Fick method and the thermodilution method. Both examination methods are performed during a cardiac catheterization (Kasper 2015). Another way of determining the HMV is the angiographic method (Krakow 2005).

• Fick method

The Fick method is based on the fact that cardiac output is equal to pulmonary output (Speckmann 2019).

Oxygen is used as an indicator. The method is based on the principle that the amount of a substance absorbed or released by an organ must be equal to the product of its blood flow (HRV) and the difference in concentration of the substance in the venous and arterial circulation.

The Fick method is considered to be very reliable, particularly in the case of low cardiac output or tricuspid valve insufficiency (Kasper 2015).

• Thermodilution method

A substance - e.g. saline solution - previously injected into the blood is measured. The temperature measurement serves as an indicator (Kasper 2015).

• Angiographic method

This is also carried out during left heart catheterization. A laevocardiogram is used as the measured variable (Krakow 2005). However, this method cannot be used for aortic valve and mitral valve insufficiency . The basic requirements for the angiographic method are:

Complete contrasting

- No extrasystoles may occur during the procedure

- Accurate calibration of the image to determine the left ventricular volumes (Lapp 2005)

Further examination methods for estimating the HMV are:

• Echocardiography

Echocardiography can only be used to estimate the HMV. As direct measurement of the HMV in both the systemic and arterial circulation is only possible to a limited extent in clinical routine, the HMV is generally only estimated using echocardiography (Michel-Behnke 2020).

• Pulse wave analysis

Pulse wave analysis can be performed invasively, minimally invasively and also non-invasively. Pulse wave analysis makes it possible to estimate the HMV based on a continuous analysis of the arterial blood pressure waveform. (Saugel 2021).

• Cardiac MRI

Cardiac MRI is a non-invasive procedure that can be used to determine HMV in addition to stroke volume and ejection fraction (Hajduga 2020).

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