# Stroke volume, ejection fraction, and cardiac output

00:00 / 00:00

10 pages

of complete

### USMLE® Step 1 style questions USMLE

of complete

A patient is participating in a clinical trial and takes a drug that improves cardiac contractility. At baseline, the patient’s end-diastolic volume is 120 ml, ejection fraction is 60%, and heart rate is 60/min. After taking the medication, the patient’s end-diastolic volume is 100 ml, ejection fraction is 70%, and heart rate is 70/min. Which of the following best characterizes the increase in cardiac output after taking the new medication?

### External References

#### First Aid

2024

2023

2022

2021

cardiac output p. 289

#### Anemia

cardiac output and p. 290

#### Cardiac output p. 289

equation for p. 735

exercise and p. 686

in pregnancy p. 651

variables in p. 289

V /Q mismatch and p. 685

#### Exercise

cardiac output p. 289

### Transcript

Watch video only

#### Contributors

The main job of the heart is to pump oxygenated blood with nutrients through the arteries to the body’s tissues and receive back deoxygenated blood full of waste products through the veins.

Now, let’s zoom into the left ventricle. There’s a moment when the left ventricle is fully relaxed. It occurs at the end of filling or diastole, also called the end-diastolic point, and the volume of blood within the left ventricle is called the end-diastolic volume, and it’s about 120 milliliters. Then the left ventricle contracts, forcing blood through the aorta and into the whole arterial system. After that is another moment when the left ventricle is fully contracted. It occurs at the end of contraction or systole, also called the end-systolic point, and the volume of blood within the left ventricle is called end-systolic volume, and it’s about 50 milliliters. So, end-diastolic volume minus end-systolic volume, gives us the stroke volume, which is the volume of blood that the left ventricle ejects with every heartbeat, or stroke. In this case, the stroke volume is 120 minus 50, which equals 70 milliliters.

Stroke volume is a useful measurement, but it can vary based on the size of a person. For example, a stroke volume of 50 milliliters might be absolutely fine for a small person with a small heart volume, but may be low for a large person with a bigger heart volume. So another helpful measurement is the ejection fraction, which is the stroke volume divided by the end-diastolic volume, Ejection fraction = Stroke Volume / End- Diastolic Volume. In a normal individual that’s 70/120, or about 58%, but it can fluctuate between 50 and 65% and still be considered normal. In other words, at least half of the blood volume in the left ventricle should get pumped out during each heartbeat. In hearts that have a low contractility - a low force of contraction - the ejection fraction can fall below 50%.

### Summary

Stroke volume is the amount of blood the heart pumps with each beat. It is the difference between the end-diastolic volume and the end-systolic volume. The ejection fraction is the proportion of the end-diastolic volume that is pumped out with each beat. It is calculated as stroke volume divided by the end-diastolic volume. Cardiac output is the amount of blood the heart pumps in one minute and is equal to the heart rate multiplied by the stroke volume.

### Sources

1. "Medical Physiology" Elsevier (2016)
2. "Physiology" Elsevier (2017)
3. "Principles of Anatomy and Physiology" Wiley (2014)
4. "VOLUME ELASTICITY CHARACTERISTICS OF THE HUMAN AORTA AND PREDICTION OF THE STROKE VOLUME FROM THE PRESSURE PULSE" American Journal of Physiology-Legacy Content (1948)
5. "Beyond ejection fraction: an integrative approach for assessment of cardiac structure and function in heart failure" European Heart Journal (2015)
6. "Human Anatomy & Physiology" Pearson (2018)

Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.