Difference Between Cardiac Cycle and Cardiac Output

The key difference between cardiac cycle and cardiac output is that cardiac cycle is the series of pressure changes that take place within the heart during the period that begins with the contraction of the atria and ends with ventricular relaxation while cardiac output refers to the total amount of blood pumped by the heart into the circulation per one minute.

The heart is a muscular organ which pumps blood throughout our body. It delivers oxygen and necessary nutrients for body tissues and collects deoxygenated blood from them and sends to our lungs for purification. Our heart beats as a consequence of a series of pressure changes occurring within the heart. Due to these pressure changes, blood moves through the chambers of the heart and throughout the body via blood vessels. The cardiac cycle is the period that begins with the contraction of atria and ends with ventricular relaxation. Cardiac output is a measurement of the total amount of blood pumped by the heart to fulfil the body’s demand per one minute.

CONTENTS

1. Overview and Key Difference
2. What is Cardiac Cycle 
3. What is Cardiac Output
4. Similarities Between Cardiac Cycle and Cardiac Output
5. Side by Side Comparison – Cardiac Cycle vs Cardiac Output in Tabular Form
6. Summary

What is Cardiac Cycle?

The cardiac cycle is the series of events or pressure changes taking place within one heartbeat. In a healthy individual, the cardiac cycle runs for 0.8 seconds to complete its cycle. There are two major phases of the cardiac cycle. Those are diastole and systole. During the diastole, ventricles undergo relaxation, and the heart refills with the blood. In systole, the ventricles contract and pump blood into the circulation. Therefore, the cardiac cycle completes its one cycle, beginning from the ventricle relaxation to pumping blood throughout the body. In other words, the cardiac cycle is the time from ending one heartbeat to the beginning of the next heartbeat.

Figure 01: Cardiac Cycle

The cardiac cycle begins with refilling of the upper chambers of the heart due to relaxation of atria and ventricles. During this time, the right atrium receives blood from the superior and inferior venae cavae and the coronary sinus. The left atrium receives blood from the pulmonary veins. Then the blood flows from atria to ventricles via the tricuspid and mitral valves. Ventricle muscles contract and build a pressure inside ventricles, which drives blood to enter into the pulmonary trunk and the aorta. Finally, ventricles undergo relaxation.

What is Cardiac Output?

Cardiac output is the total amount of blood pumped from the heart per minute. In other words, it is the amount of blood given by the heart in response to the body’s need for oxygen. Hence, it is an important measurement since it tells the efficiency of the heart to fulfil the body’s demand for perfusion. Cardiac output is low when a person has heart failure. Hence, low cardiac output is a good indication of a heart problem.

Figure 02: Factors Affecting Cardiac Output

Cardiac output is expressed in litres per minute. It can be evaluated by multiplying the stroke volume and heart rate (the number of the heartbeat). Cardiac output depends on the heart rate, preload, afterload and contractility. In a normal healthy individual weighing 70 kg, cardiac output is about 5 L/minute. It changes when a person begins to exercise. It can go up to 20 or 35 L/minute at the peak of exercise.

What are the Similarities Between Cardiac Cycle and Cardiac Output?

• The heart is the organ that is related to the cardiac cycle and cardiac output.
• Both cardiac cycle and cardiac output depend on the heartbeat.

What is the Difference Between Cardiac Cycle and Cardiac Output?

The cardiac cycle is the series of events taking place from the beginning of one heartbeat to the beginning of next. Meanwhile, the cardiac output is the total amount of blood pumped by the heart into circulation per minute. So, this is the key difference between cardiac cycle and cardiac output. Furthermore, the cardiac cycle has two major phases as systole and diastole, while cardiac output depends on stroke volume and heart rate. Therefore, this is also a difference between cardiac cycle and cardiac output.

Moreover, the cardiac cycle runs for 0.8 seconds while the cardiac output is 5 L/minute in an adult.

Summary – Cardiac Cycle vs Cardiac Output

The cardiac cycle is the events occurring within the heart from the beginning of one heartbeat to the beginning of the next heartbeat. Generally, the cardiac cycle completes its one cycle within 0.8 seconds. In contrast, cardiac output is the amount of blood heart pumps through the circulatory system per minute. In a healthy adult, cardiac output is 5 litres per minute. Both cardiac cycle and cardiac output depend on the heartbeat. So, this summarizes the difference between cardiac cycle and cardiac output.

Reference:

1. King, Jordan. “Physiology, Cardiac Output.” StatPearls [Internet]., U.S. National Library of Medicine, 7 May 2019, Available here.
2. Pollock, Joshua D. “Physiology, Cardiac Cycle.” StatPearls [Internet]., U.S. National Library of Medicine, 5 May 2019, Available here.

Image Courtesy:

1. “2027 Phases of the Cardiac Cycle” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2.”2031 Factors in Cardiac Output” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia

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