<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Relate heart rate to cardiac output
  • Describe the effect of exercise on heart rate
  • Identify cardiovascular centers and cardiac reflexes that regulate heart function
  • Describe factors affecting heart rate
  • Distinguish between positive and negative factors that affect heart contractility
  • Summarize factors affecting stroke volume and cardiac output
  • Describe the cardiac response to variations in blood flow and pressure

The autorhythmicity inherent in cardiac cells keeps the heart beating at a regular pace; however, the heart is regulated by and responds to outside influences as well. Neural and endocrine controls are vital to the regulation of cardiac function. In addition, the heart is sensitive to several environmental factors, including electrolytes.

Resting cardiac output

Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle in one minute. To calculate this value, multiply stroke volume (SV)    , the amount of blood pumped by each ventricle, by heart rate (HR)    , in contractions per minute (or beats per minute, bpm). It can be represented mathematically by the following equation:

CO = HR × SV

SV is normally measured using an echocardiogram to record EDV and ESV, and calculating the difference: SV = EDV – ESV. SV can also be measured using a specialized catheter, but this is an invasive procedure and far more dangerous to the patient. A mean SV for a resting 70-kg (150-lb) individual would be approximately 70 mL. There are several important variables, including size of the heart, physical and mental condition of the individual, sex, contractility, duration of contraction, preload or EDV, and afterload or resistance. Normal range for SV would be 55–100 mL. An average resting HR would be approximately 75 bpm but could range from 60–100 in some individuals.

Using these numbers, the mean CO is 5.25 L/min, with a range of 4.0–8.0 L/min. Remember, however, that these numbers refer to CO from each ventricle separately, not the total for the heart. Factors influencing CO are summarized in [link] .

Major factors influencing cardiac output

This figure lists the different factors affecting the heart rate and stroke volume. It also shows how they both affect the cardiac output.
Cardiac output is influenced by heart rate and stroke volume, both of which are also variable.

SVs are also used to calculate ejection fraction    , which is the portion of the blood that is pumped or ejected from the heart with each contraction. To calculate ejection fraction, SV is divided by EDV. Despite the name, the ejection fraction is normally expressed as a percentage. Ejection fractions range from approximately 55–70 percent, with a mean of 58 percent.

Exercise and maximum cardiac output

In healthy young individuals, HR may increase to 150 bpm during exercise. SV can also increase from 70 to approximately 130 mL due to increased strength of contraction. This would increase CO to approximately 19.5 L/min, 4–5 times the resting rate. Top cardiovascular athletes can achieve even higher levels. At their peak performance, they may increase resting CO by 7–8 times.

Since the heart is a muscle, exercising it increases its efficiency. The difference between maximum and resting CO is known as the cardiac reserve    . It measures the residual capacity of the heart to pump blood.

Questions & Answers

what is scrotum
Dakshit Reply
a bag of skin near the penis which contains the testicles
its me Sardar from kpk pakistan
Why are you on my digits
how does it work?
Uriah Reply
I want to know the fertilization process in human
Nana Reply
Which plane divides the body into right and left parts
sagittal plane
Thank you
Homestatic regulations usually involves a (n) _ that detects a particular stimulus, and a(n) _that respond to the stimulus by communicating with a (n) _whose activity has an effect on the same stimulus.
A cell is producing proteins to be transported out of that cell. They will be processed on ribosomes that are
what are diseases in the bood
Azoyenime Reply
right hypochondriac rision how meain word
Ganesh Reply
Diabetes insipidus or diabetes mellitus would most likely be indicated by ________.
oral cavity how miean
Ganesh Reply
oral cavity how mean what
seems to me every one is here a doctor and worse part is that even they donot know what to ask.
they know what to ask the problem is how to ask it.too much broken english.
dear George ongeche I think if they ask these kind questions and telling themselves as HCPs or medical student's .these are the basic ones go ask something more interesting .
what is blood red
Ahmad Reply
what is human anatomy?
Arpita Reply
tell me what is human anatomy?
what is Openstax?
arpita jana I think it's not the forum to ask such basic question...
study of structure of an object in this case human body.
what are deferent between trasemicacid and vitamin k
Ubah Reply
This medication is used to treat heavy bleeding during your menstrual period. Tranexamic acid works by slowing the breakdown of blood clots, which helps to prevent prolonged bleeding. It belongs to a class of drugs known as antifibrinolytics
In the body, vitamin K plays a major role in blood clotting. So it is used to reverse the effects of “blood thinning” medications when too much is given; to prevent clotting problems in newborns who don’t have enough vitamin K; and to treat bleeding caused by medications including salicylates, sulfo
Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding. Unlike many other vitamins, vitamin K is not typically used as a dietary supplement. Vitamin K is actually a group of compounds. The most important of these compounds appears to be vitamin K1 and vitamin K2. Vitami
how much tha total vertebrea bone
26 vertebrea bone
wathe is blood function
dhena Reply
Blood, fluid that transports oxygen and nutrients to the cells and carries away carbon dioxide and other waste products. ... It is a tissue because it is a collection of similar specialized cells that serve particular functions. These cells are suspended in a liquid matrix (plasma), which makes the 
how tissue carries waste matrial
how many bone in human body?
Islam Reply
what is endocrin? plese help many people.
heart layers
endoceime is the inner layer of heart
What is buffer?
Peer Reply
a buffer is a solution that resists a chemical change.
Yup it also balances the solutions
most common side effect reported by users emergency contraceptive pill
Shivvir Reply
spotting .breakbrough bleeding .weightgain.breast tenderness.mood alteration. headache
How many systems are in the body?
Irvin Reply
names the systems pls
name the systems pls
integumentary system, lymphatic system, skeletal system, digestive system, cardiovascular system, reproductive system, respiratory system, urinary system, endocrine system
approximately 11 system
what's the meaning of Acidphosphacidic
Tiwa Reply
most common source of phosphoric acid is an 85% aqueous solution; such solutions are colourless, odourless, and non-volatile. The 85% solution is a syrupy liquid, but still pourable. Although phosphoric aciddoes not meet the strict definition of a strongacid, the 85% solution is acidic 
What is osteoblast and what is osteoclast?
osteoblast is the bone forming cells osteoclast is the bone dissolving cells

Get the best Anatomy & Physiology course in your pocket!

Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?