What Is Cardiac Output

Cardiac output is the total amount of blood that is pumped through the heart at a given time.  This can be in liters or deciliters per minute. Cardiac output changes from time to time depending on what you are doing. During rest, the output remains constant but increases appreciably during exercises. Scientists have come up with ways of determining the cardiac output at any given time. They use the formulae stroke volume (SV) multiplied by heart rate (HR). In regards to this, the cardiac output changes when the heart rate changes. This explains why the cardiac output is higher during exercises compared to when you are resting.Factors that affect cardiac output

  •     Change in stroke volume
  •     Levels of catecholamine
  •     Myocardial infarction
  •     Chronic high blood pressure
  •     Kidney disease
  •     Heart and liver disease
  •     Medications
  •     Poisons

Some of these factors raise the cardiac output while others lower it. Presence of most of these factors has a direct influence on the stroke volume and heart beat and therefore increases or decreases the cardiac output depending on the effect. If the stroke volume and heart rate are increased, the cardiac output increases and when lowered, the cardiac output goes down.How to measure cardiac output:Using the fick principle; this method involves measuring the amount of oxygen at different times. It is based on the fact that the red blood cells consume oxygen. The amount of oxygen is measured initially and then after sometime to determine the change in the level of oxygen. This method is usually done on two arteries; peripheral artery and pulmonary artery.Dilution methods: this is a method in which an indicator is injected into the body. The rate at which the indicator is absorbed reflects the cardiac output.

Doppler ultrasound method:

This strategy is based on that Doppler Effect is generated when blood passes through the heart. An instrument is used to measure the ultrasound waves caused by the Doppler shift. Doppler shift can be measured through Echocardiography, Transcutaneous Doppler: USCOM and Transoesophageal Doppler: TOD. The three different strategies use different mechanisms to measure Doppler shift. Despite that, they have the same results; the higher the Doppler shift the higher the cardiac output and the lower the Doppler shift the lower the cardiac output. Doppler shift increases when you are exercising or working because there is more blood pumped from the heart.Pulse pressure method:

This method measures the pressure in the arteries at specified times and used to create wave like graphs which are used to determine the cardiac performance. Usually, high pressure is recorded when there is more blood being pumped and indicated high cardiac output. The cardiac output remains low when there is lower pressure because there is less blood being pumped.

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