A&P-Cardiac Output

Know the ejection fraction formula

SV/EDVx100%

Be able to calculate stroke volume

SV=EDV-ESV

Understand how afterload affect stroke volume (and therefore cardiac output)

afterload is the resistance in arteries to the ejection of blood by the ventricles. the greater the afterload, the more difficult it is to eject blood from the heart, and the lower the stroke volume will be. Afterload is generally a factor only as we age.

Understand how preload affect stroke volume (and therefore cardiac output)

an increase in venous return (the volume of blood flowing back to the heart through the superior and inferior vena cava) increases the cardiac preload (stretch of the myocardium). which in return increases end-diastolic volume (EDV) and finally the stroke volume therefore, the greater the venous return, the greater the stroke volume.

Imagine a person with a resting heart rate pf 70 beats/minute and a resting stroke volume of 70 mL/beat. calculate the cardiac output for this person at rest

cardiac ouput=70 (beats/min) x 70 (mL/beat)=4900 mL/minute or 4.9 L/min *(remember 1L=1000mL)

How does stroke volume affect cardiac output?

if the heart contracts more strongly, then it can pump more blood per beat. the heart fills up with more blood during diastole and the heart contracts more strongly during systole.

What are the two variables that can affect the control of heart rate?

the SA node of the heart is innervated by the sympathetic and parasympathetic nerve fibers. during rest the PNS fibers release AcH which acts to slow the SA node and reduce heart rate. any situation that increases activity of the sympathetic division will result in release of NE, which speeds up the SA and AV nodes to increase the conduction rate of action potentials

How does filling the heart with more blood cause increased stroke volume?

the amount of blood that returns to the heart o fill it during diastole is called venous return. an increase in venous return results in greater filling of the ventricles during diastole. stretching the muscles of the heart optimize the length-tension of cardiac muscle fibers, resulting in stronger contractility leading to greater stroke volume.

How do stroke volume and heart rate affect one another?

the difference is that the slower heart has a longer filling time, and thus the EDV is increased. this automatically leads to increases tension development in the myocardium, and thus higher stroke volume. on the other hand, if the stroke volume is reduced, then heart rate can compensate to establish the necessary cardiac output.

Understand how contractility affect stroke volume (and therefore cardiac output)

the stronger the contractility, the less ESV but more SV and CO. the weaker the contractility, the more ESV there is, the less SV and CO

Define systole and diastole, and understand what is happening in the heart during both of these phases

-systole refers to contraction of a heart chamber. the chamber is moving the blood -diastole refers to relaxation of a heart chamber. the chamber is filling with blood

Define cardiac output, heart rate, and stroke volume

CO is the amount of blood pumped by the left ventricle in 1 minute heart rate (HR) is the number of beats per minute (bpm). stroke volume (SV) is the volume of blood ejected during one beat and is expressed as milliliters per beat

Know how to calculate cardiac output, and how changes in heart rate and stroke volume affect it

CO=HRxSV an decrease/increase in HR and SV can influence the amount of blood being pumped

Know the difference between EDV and ESV and how they affect stroke volume

EDV=end diastolic volume ESV=end systolic volume increases/decreases affect SV