Cardiac Output

Introduction

The muscular organ of the human body known as the heart acts as a pump. The heart pumps continuously from birth to death. The heart, the muscular organ is divided into four-chambers i.e. two upper receiving chambers and two lower distributing chambers. The different parts of the heart include a wall of the heart, four chambers, valves, blood vessels, and the electrical conduction system. Cardiac output is the amount of blood pumped by the heart per minute. In this tutorial, we will learn about cardiac output in depth.

What is Cardiac Output?

Cardiac output is the amount of blood pumped by the heart per minute. In other words, we can say that it is the function of heart rate and stroke volume. The stroke volume is the quantity of blood expelled by the left ventricle in one compression. Cardiac output determines the effectiveness of the human heart. The cardiac output of an individual differs depending on the size of the heart. An adult person per minute pumps approximately 5 litres of blood during a resting period.

But in the case of exercise, the heart may pump more so that body cells will get an adequate amount of oxygen. The supply of oxygen and nutrients to the body cells is the crucial function of the blood. If the heart pumps less blood or more blood that leads to heart failure or any other heart-related alignment. Heart rate and stroke volume are the two important components of cardiac output.

Factors Determining Cardiac Output

Factors determining cardiac output are listed below:

Venous return

• The total quantity of blood that transports to the heart through veins from different parts of the body.

• The cardiac output is directly equivalent to venous return at certain intervals of time depending on certain factors.

• The venous return depends on the respiratory pump, muscle pump, gravity, and venous pressure.

Force of contraction

• The stroke volume and cardiac output are correlated to the contraction force.

• As the force of contraction increases these two important factors of cardiac output also increase.

Heart rate

• Heart rate directly correlates with cardiac output.

• As the heart rate increases, cardiac output also increases.

• As the heart rate decreases, the cardiac output rate also decreases.

Peripheral resistance

• It is resistance in the circulatory system.

• That utilises to generate blood pressure and flow of blood.

• Peripheral resistance is the load against which the heart has to pump blood.

• Peripheral resistance is inversely correlated with cardiac output.

Cardiac Output Formula

The cardiac output can be calculated based on the heart rate and stroke volume. That can be formulated as

Cardiac output = Heart rate × Stroke volume

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Cardiac Output Calculation and Measurement

To calculate the cardiac output, we have to use the cardiac output formula. For example, if 75 bpm is the heart rate and 75ml is stroke volume what will be the cardiac output?

Cardiac output = Heart rate × Stroke volume

                         = 75 × 75

                         = 5625 ml/min or 4.9 liters per minute.

There are several methods to measure cardiac output that are listed below:

• Pulmonary artery catheter: In this method, the health care professional will insert this instrument into the artery.

• Echocardiogram: In this method, the sound wave is used. Sound waves make an image of the heart and flow of blood through the heart.

• Arterial pulse waveform analysis: In this method, cardiac output is calculated from shock waves. A shock wave is generated by the blood flow.

• Doppler ultrasound: It is similar to an echocardiogram. From Doppler ultrasound, one can easily determine the blood flow through the heart and blood vessels. It reveals the obstruction of the heart and blood vessels.

Apart from these Transcutaneous and Transoesophageal tests are used to measure cardiac output. If the heart is unable to pump enough blood to the tissue or cells it may lead to heart failure. Low output leads to sepsis, heart failure, or heart disease.

Sometimes due to sepsis, there is a tremendous drop in blood pressure as well as organ failure that leads to high cardiac output. High output also can result due to insufficient oxygen-carrying blood cells, anaemia, and hyperthyroidism. Because of these reasons the heart pumps blood faster.

Cardiac Index

Cardiac index is the analysis of cardiac output depending on the size of an individual. The cardiac index is estimated by dividing the cardiac output by an individual surface area of the body. The cardiac index normal range is from 2.5 to 4 L/min/m².

Significance

Heart rate and stroke volume are the two integrated parts of cardiac output. The event of the cardiac cycle is represented by the heart rate that the heart beats per minute. The stroke volume is the amount of blood that is ejected during ventricular ejection.

Conclusion

Cardiac output is the amount of blood pumped by the heart per minute. In other words, we can say that it is the function of stroke volume and heart rate. The stroke volume is the quantity of blood expelled by the left ventricle in one compression. Cardiac output determines the efficiency of the human heart.

FAQs

Q1. What are the causes of heart disease?

Ans: Heart diseases are kind of diseases that affect both arteries and the heart. The plaque accumulation in the arteries and blood vessels leads to heart disease. Sometimes due to our lifestyle, smoking, consumption of excessive alcohol, food habits, lack of exercise, and due to some comorbid conditions like hypertension affect the heart and blood vessels.

Q2. What do you understand about heart failure?

Ans: Heart diseases are of different types; heart attacks and heart failure are the most common among them. This occurs when the heart muscles are weak or damaged and are unable to pump the amount of blood needed by the body.

Q3. What is anemia?

Ans: Anemia is caused due to low hemoglobin percentage in the blood. In other words, we can say anemia is caused due to low percentage of red blood cells. It is one of the most common diseases. Anemia can be inherited through genes from parents to offsprings and other medical conditions. Women are also at high risk as they lose blood through the menstrual cycle. A person who suffer from anemia also suffers with fatigue and shortness of breath,

Q4. What is hyperthyroidism?

Ans: Hyperthyroidism is caused due to over secretion of thyroxine hormone from the thyroid gland. It increases the rate of metabolism and as a result of this, the affected person will lose weight. Hyperthyroidism also causes an irregular and rapid heartbeat. Health care professionals give anti-thyroid medication drugs to treat hyperthyroidism.

Q5. What is sepsis?

Ans: It is a serious life-threatening medical condition. A person suffer with sepsis, when the body fights the infection and spoils its own tissue. As the disease progress it spreads to the organs. As a result, organs fail to function properly. The symptoms include weakness, faintness, irregular heartbeat, shortness of breath, etc.