Cardiac output: assessment according to the principle of changes in oxygen concentration
Venous blood oxygen concentration is measured through a catheter inserted from the brachial vein, through the subclavian vein, and into the right atrium, and finally the right ventricle and pulmonary artery.
In experimental animals, tubes can be inserted into the aorta, pulmonary artery, and major blood vessels of the heart to assess cardiac output through a flowmeter.
Alternatively, an electromagnetic flowmeter or an ultrasonic flowmeter placed in the aorta or pulmonary artery can be used to calculate cardiac output.
In humans, except for a few special cases, most of the cardiac output is calculated through the direct method without surgery. The two commonly used methods are the oxygen concentration method and the indicator method.
Cardiac output can be assessed through echocardiography, a method that uses sound waves transmitted through the chest wall and oesophagus to evaluate the size of the heart chambers as well as the speed of blood flow from the right heart to the aorta.
Blood flow will be calculated through the speed of blood flow through the aorta, the cross-sectional area of the aorta is assessed by measuring the diameter of the vessel wall under ultrasound guidance. Cardiac output is now calculated by heart rate and blood flow.
Figure. Principle of changing oxygen concentration to calculate cardiac output
The figure shows 200 ml of oxygen being taken up by the lungs every minute to enter the circulatory system.
The oxygen concentration in the right heart is 160 ml/l and in the left heart is 200 ml/l. Thus, each litre of blood passing through the lungs carries an additional 40 ml of oxygen.
The volume of pulmonary oxygen required to enter the circulation every minute is 200 lm, divided by 200 by 40 gives 5 litres of blood. Therefore, the required pulmonary blood flow in 1 minute is 5 litres or cardiac output. Based on the above principle, we have the formula:
Cardiac output (ml/min) = [Volume of pulmonary blood absorbed (ml/min)]/[Difference in arterial oxygen concentration (ml/L of blood)]
Applying the above principle to the calculation of cardiac output in humans, the venous blood oxygen concentration is measured through a catheter inserted from the brachial vein, through the subclavian vein, and into the right atrium, and finally the right ventricle and the right ventricle. pulmonary artery. Measurement of arterial blood oxygen concentration is assessed through an artery of the body. Pulmonary oxygen concentration is measured through the difference in air concentrations during inhalation and exhalation, by means of an oximeter.