The key difference between stroke volume and cardiac output is that stroke volume is the amount of blood pumped in each heartbeat while cardiac output is the amount of blood pumped by the heart per minute.
The heart is a muscular organ of our circulatory system, which pumps blood throughout our body. Thereby, it delivers oxygen and necessary nutrients for body tissues. It also collects deoxygenated blood from our body tissues and hands over to our lungs in order to purify them. When considering the heart functioning, there are three important measurements namely cardiac output, stroke volume, and heart rate. Cardiac output is the product of stroke volume and heart rate (cardiac output = stroke volume x heart rate). Hence, cardiac output refers to the total amount of blood pumped by the heart per one minute. On the other hand, stroke volume refers to the amount of blood pumped by each heartbeat. The aim of this article is to discuss the difference between stroke volume and cardiac output while explaining the individual terms.
CONTENTS
1. Overview and Key Difference
2. What is Stroke Volume
3. What is Cardiac Output
4. Similarities Between Stroke Volume and Cardiac Output
5. Side by Side Comparison – Stroke Volume vs Cardiac Output in Tabular Form
6. Summary
What is Stroke Volume?
Stroke volume refers to the volume of blood pumped by each heartbeat. In simple words, it is the amount of blood ejected from each ventricle due to the contraction of the heart muscles. Furthermore, it is the difference between end diastolic volume and end systolic volume. Stroke volume expresses in millimetres (ml). In a healthy person of 70 kg, normal stroke volume is about 70 ml. Normally, stroke volume increases when doing exercises.
Figure 01: Stroke Volume
Several different factors affect the stroke volume. Among them, preload, afterload, and contractility are three primary factors that greatly affect the stroke volume. Furthermore, heart rate also affects the stroke volume. Apart from that, the factors that change the end diastolic volume and end systolic volume also change the stroke volume. Increased end diastolic volume or decreased systolic volume increase the stroke volume. On the other hand, increased systolic volume decreases the stroke volume.
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: 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). Similar to stroke volume, cardiac output also depends on the heart rate, preload, afterload and contractility. In 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 Stroke Volume and Cardiac Output?
- Stroke volume and cardiac output are two different amounts of the blood pumped from the heart.
- Both stroke volume and cardiac output cannot be measured non-invasively.
- Also, the heart rate, contractility, preload, and afterload affect both values.
- Besides, these values change when a person is doing exercises.
What is the Difference Between Stroke Volume and Cardiac Output?
Stroke volume and cardiac output are two types of measurements that relate to the efficiency of the heart. Stroke volume tells the amount of blood ejected from a ventricle at each heartbeat. On the other hand, cardiac output tells the total amount of blood pumped from the heart per minute. Hence, this is the key difference between stroke volume and cardiac output. Furthermore, stroke volume can be measured by subtracting end systolic volume from the end diastolic volume while the cardiac output can be measured by multiplying stroke volume and heart rate. Therefore, the method of calculation is another difference between stroke volume and cardiac output.
Moreover, one other difference between stroke volume and cardiac output is the unit of measurement. That is; the stroke volume is measured in millilitres while cardiac volume is measured in litres per minute. Also, the value of stroke volume in a healthy individual weighing 70 kg is 70 ml while the cardiac volume is 5 litres/minute. Therefore, this is also a difference between stroke volume and cardiac output.
Summary – Stroke Volume vs Cardiac Output
Stroke volume is the amount of blood ejected per heartbeat from each ventricle. It can be calculated by subtracting the end-systolic volume from the end-diastolic volume. On the other hand, cardiac output is the total amount of blood pumped from the heart per minute. It is a product of the stroke volume and the heart rate. Stroke volume expresses in millilitres while cardiac output expresses in litres per minute. The same factors such as heart rate, preload, afterload and contractility affect both volumes. An individual weighing 70 kg has about 70 ml of stroke volume and 5 L/minute of cardiac output. This is the summary of the difference between stroke volume and cardiac output.
Reference:
1. King, Jordan. “Physiology, Cardiac Output.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, 27 Oct. 2018. Available here
Image Courtesy:
1.”2035 Factors in Stroke Volume”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