This article contains cardiac output, cardiac output formula and normal cardiac output. Vertebrates circulate blood (a fluid connective tissue) in the body to transport essential and nonessential products. Blood comprises red blood cells (RBCs/ erythrocytes), white blood cells (WBCs/ leukocytes) and platelets (thrombocytes). The human circulatory system consists of a muscular pumping organ (heart). About 70 mL of blood pumps out by one of the ventricles during a cardiac cycle. The cardiac cycle is formed by events in the heart which are cyclically repeated. The volume of blood pumped by each ventricle/ minute is termed “cardiac output”.
The Cardiac output formula = heart rate X stroke volume.
Structure and Working of the Human Heart
The human heart is between the lungs above the diaphragm and under the breastbone in the thoracic cavity. It is a hollow, fibro-muscular, pulsatile 4 chambered organ. It resembles a conical or pyramidal shape. The broad upper part is called the base, and the lower, narrow part is the apex. The apex is slightly directed to the left and is present between the fifth and sixth ribs. An average human heart is about 12 cm in length, and 9 cm in breadth. The heart is a muscular organ, big as our fist. Its weight varies from 280-340 gm in males with an average of 300 gm and females from 230-280 gm.
Cardiac Cycle
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The heartbeat rate in an average human adult at rest is about 72 beats/min. Therefore, the time taken per one beat is roughly 0.8 sec.
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The sequence of events occurring in the heart per beat is called the cardiac cycle. The same event is repeated in each beat.
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Each cardiac cycle consists of one systole and one diastole.
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Atrial systole initiates the cycle and lasts for 0.1 sec, followed by atrial diastole, lasting for the next 0.7 sec.
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Thus the total duration is 0.8 sec. At the end of the atrial systole, the ventricular systole starts, lasting 0.3 sec.
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This is immediately followed by ventricular diastole. Its duration is 0.5 sec.
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Thus, the total ventricular cycle is also 0.8 sec.
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The cardiac cycle duration may vary with changing conditions such as age, temperature, excitation, sex, size of heart, etc.
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The cardiac cycle is the contraction and relaxation cycle of the atria and ventricles in one heartbeat.
The Cardiac Cycle Process
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At first, the heart’s four chambers are in a relaxed state.
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As the tricuspid and bicuspid valves are open, blood from the pulmonary veins and vena cava flows into the left and the right ventricle, respectively, through the left and the right atria.
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This causes the closing of semilunar valves.
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The SAN now generates an action potential that causes the atrial systole.
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The action potential is conducted by the AVN and AV bundle. This causes contraction of the ventricular muscles contraction.
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Now ventricular systole occurs, and the atria undergo relaxation (diastole).
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Ventricular systole increases ventricular pressure. This causes the closure of tricuspid and bicuspid valves due to attempted backflow of blood into the atria.
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As the ventricular pressure increases, the semilunar valves guarding the pulmonary artery (right side) and the aorta (left side) are forced open.
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It allows the blood in the ventricles to flow through these vessels into the circulatory pathways.
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The ventricles now relax (ventricular diastole), and the ventricular pressure falls, preventing blood backflow into the ventricles.
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Now, the tricuspid and bicuspid valves are pushed open by the atria’s pressure, emptying into them.
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Now the blood moves freely to the ventricles, which causes relaxation of the ventricles and atria.
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This cyclically repeated sequential event in the heart is the “cardiac cycle”.
Cardiac Output
The volume of blood pumped by each ventricle/minute is called c.o. (cardiac output). The same amount/volume of blood is pumped by each ventricle/ cardiac cycle. The cardiac output is determined by multiplying the heart rate and blood volume ejected by each ventricle during each beat (stroke volume).
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Cardiac output= heart rate X stroke volume.
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The normal value of heart rate is 72/min, and stroke volume is 80 mL/beat.
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So, the cardiac output formula = 72 beat/min X 0.08 L/beat = 5.5L/min.
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Conditions like exercises, emotions and fever might increase cardiac output.
Conclusion
The right atrium has a thin wall because it transfers blood to nearby chambers. The superior vena cava, inferior vena cava, and the coronary sinus open into the right atrium and pour deoxygenated blood. Superior vena cava carries deoxygenated blood from the upper region. The inferior vena cava drains the blood from the lower regions of the body. However, the coronary vein opens into the coronary sinus. The cardiac output is also increased by “adrenal medullary hormones”. The formula for cardiac output is the product of heart rate X stroke volume. We can calculate the cardiac output using the formula outlined in the article.