# 19.4 Cardiac physiology

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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] .

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.

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what is ankylosis
master gland Kon si h
Pituitary gland
KUNDAN
pituitary gland because it give harmonies and control other gland
ABDULLAH
glands often secrete hormones which play an important role in maintaining homeostasis.
KUNDAN
pituitary gland
Aftab
pituitary gland is master gland because it present in biran and secrtehormones and play other gland of human body and function its gland so that also called master gland.
ABDULLAH
pituitary glandis the master gland of our body
how do you study for A&P? lab and lecture?
depends how your lab exams and lecture exams are structured. but either way, you want to study two weeks before any of the exams. study in a way that you would be teaching it to someone. lec is mostly physio. and a lil' anatomy. lab is all anatomy and motion- so memorization is key.
Berlin
record the lectures in both cases. read the lessons for that class day. have questions. go to office hours. this will help you in A&P- if anything the teacher would give you a little bit of points for making so much of an effort
Berlin
When one is suffering from motion sickness what area of the brain may trigger emesis?
that is the sign of stroke. if the patient have a stroke. the left side of body is weakness, the affected right of cerebrum but if right side of the body is weakness surely in left side!
Larry
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Sentamu
Fatima hw a u
Sentamu
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Shubham
any one elaborate fr me foramens of the skull and features which they transmit
Sentamu
icant undrestand plz
try to read I hop you will understand
state and explain 20 radiology uses
what are chemicals in anatomy and physiology?
what can I do to find it easy for me in anatomy and physiology course
Mike
study up on the basics of the periodic chart, learn bones and muscles attachments, and learn muscles. Those take the longest to memorize. After that it should be a little easier.
Toni
what are the two types of body cells
what is malnutrition
Claire
malnutrition refers to faulty nutrition resulting from malabsorption,poor diet or overeating. Sometimes too these food do not contain all the six food nutrients in their right proportion.
Yakubu
thank you
Claire
welcome
Yakubu
Will u be malnourished?
Baigwa
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Budumari
gabriel
Nothing! Radiology it means the study or using of radiation in medical science it can be 1.diagnose or treatment diagnosed radiology! x- ray. ultrasound. ct-scan. mammogram. MRI. 2. treatmen- radiation oncology, like Cobalt 60. and nuclear medicine
Larry
what is X-ray?
Nissar
X-ray is type of light that make it possible to see inside any object. as human body
KUNDAN
How the nervous system develops
From the cells at the back of an embryo
Mma
breifly explain anatomy of thorax
How many region the rib is divided
Konneh
how many bon of human being
Nura
206
John
how to study for the skeletal system
ryaisha
and anatomy
ryaisha
I really need sources immediately
ryaisha
I printed out all the different bones. Put them in the see through protective sheaths and got dry erase markers. I could right on them and erase to help me learn to spell the names of markings and bones.
Toni
Or go to a book store, Barnes and Noble(doesn't have to be this) and they have coloring books for anatomy. \$16. Really helpful.
Toni
okay thanks and are what study tools you use to study the materials and get a better understanding
ryaisha
*what are
ryaisha
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Roopa
I prefer diagrams, pictures that lay out each step with the information in each step. For Example: how action potential creates muscles to move. A pictured diagram gives me a better understanding of how each piece plays a role in each step of the process.
Toni
Also for basics, such as memorizing vocab. Flash cards are great. Don't become discouraged if you don't get them all right the first times through. The more you go through them, your brain will remember pieces of information from each and help you to pull out the information 😉
Toni
okay thanks
ryaisha
what is the functions of the lips in human
could I say sensation?
Sovilace
kissing
Obrian
for protection
Omar
Lips assist in speech and eating
Cindy
Too many easy questions. Which bones are the axial and appendicular? What are the abbreviations for TEE, TTE, AED, A-Mode, B-Mode, and LTH? What is the difference between hypothalamus and thalamus? Where is the parathyroid located? How many True Ribs do we have?
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Inam
what is anatomy
anatomy is scientific study of body structures and how they relate to each other
Skeater