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Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 mL of O 2 per L. Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is: Cardiac Output = (125 mL O 2 /minute × 1.9) / (200 mL O 2 /L − 150 mL O 2 /L) = 4.75 L/min
Here Q is the cardiac output of the heart, C a O 2 is the arterial oxygen content, and C v O 2 is the venous oxygen content. (C a O 2 – C v O 2) is also known as the arteriovenous oxygen difference. The Fick equation may be used to measure V̇O 2 in critically ill patients, but its usefulness is low even in non-exerted cases. [8]
Major factors influencing cardiac output – heart rate and stroke volume, both of which are variable. [1]In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols , ˙, or ˙, [2] is the volumetric flow rate of the heart's pumping output: that is, the volume of blood being pumped by a single ventricle of the heart, per unit time (usually measured ...
In order to do so oxygen consumption (VO 2) may be measured using a spirometer to detect gaseous concentrations in exhaled air compared to inhaled air, while cardiac output can be determined using a Doppler ultrasound. [3] Arterial blood will generally contain an oxygen concentration of around 20 mL/100 mL. [1]
Cardiomyopathy and heart failure cause a reduction in cardiac output, whereas infection and sepsis are known to increase cardiac output. Hence, the ability to accurately measure CO is important in physiology, as it provides for improved diagnosis of abnormalities, and can be used to guide the development of new treatment strategies.
CO reflects the hemodynamic flow and hence the transport of oxygen; its clinical applications by non-invasive continuous hemodynamic monitoring are especially useful for some medical specialties like anaesthesiology, emergency care and cardiology, for example to prevent hypoperfusion and to guide fluid administration.
One shortcoming of measuring pulse oximetry alone is that administration of supplemental oxygen (ie. via nasal cannula) can delay desaturation in a patient if they stopped breathing, therefore delaying medical intervention. Capnography provides a rapid way to directly assess ventilation status and indirectly assess cardiac function.
Impedance cardiography (ICG) is a non-invasive technology measuring total electrical conductivity of the thorax and its changes in time to process continuously a number of cardiodynamic parameters, such as stroke volume (SV), heart rate (HR), cardiac output (CO), ventricular ejection time (VET), pre-ejection period and used to detect the impedance changes caused by a high-frequency, low ...