The Cardiovascular System: Cardiac Output
1.
Define Cardiac Output (CO).
Volume of blood pumped out of the left ventricle in 1 minute (L/min)
2.
Write the equation for CO.
Q = SV x HR
3.
Define Stroke Volume (SV).
Amount of blood ejected from left ventricle in single beat
4.
Write the equation for SV.
SV = LVEDV – LVESV
5.
Write the normal values (include correct units) for the following:
a. HR (heart rate) = 72 bpm
b. SV (stroke volume) = 70 mL
c. EDV (end diastolic volume) = 120 mL
d. ESV (end systolic volume) = 50 mL
6.
Given the values for HR and SV, calculate cardiac output:
SV = 70 mL  0.07 L (BE SURE TO CONVERT THE UNITS: mL  L)
Q = HR x SV
= 72bpm x 0.07 L
= 5 L/min
7.
Explain how the following factors affect HR, SV, and CO by placing arrows (, , or  for no change)
under them.
a.  SNS
HR
SV
CO
↑
↑
↑
Increased Sympathetic Nervous System (SNS) - Increased sympathetic stimulation (due
to fright, anger, etc.) increases the heart rate. It also increases stroke volume by
increasing contractility, which results in more complete ejection of blood from the heart
(lower ESV)
b. Venous return

↑
↑
Cardiac muscle fibers are stretched by increased blood volume returning to the heart
(increased venous return and EDV). Increased stretch results in greater force of
contraction, which increases stroke volume.
c. Exercise
↑
↑
↑
Elite Athletes

↑
↑
Exercise activates the sympathetic nervous system, increasing heart rate, contractility,
and stroke volume. Both the higher heart rate and squeezing action of skeletal muscles on veins increase
venous return, contributing to increased stroke volume.
d.  Calcium

↑
↑
Excess calcium can lead to spastic heart contractions, an undesirable condition. Calcium
also increases stroke volume by enhancing contractility.
e.  HR

↑
↑
Slow Heart Rate - Slow heart rate allows for more time for ventricular filling, increasing
EDV and therefore stroke volume.
8.
Why would stroke volume increase with an increase in the sympathetic nervous system or an increase in
calcium?


9.
Why would stroke volume increase when heart rate slows down?

10.
Excess calcium can lead to spastic heart contractions, an undesirable condition. Calcium also
increases stroke volume by enhancing contractility.
Increased Sympathetic Nervous System (SNS) - Increased sympathetic stimulation (due to
fright, anger, etc.) increases the heart rate. It also increases stroke volume by increasing
contractility, which results in more complete ejection of blood from the heart (lower ESV)
Slow Heart Rate - Slow heart rate allows for more time for ventricular filling, increasing
EDV and therefore stroke volume. (SV = LVDEV – LVSEV)
If stroke volume is 75 ml/beat and heart rate is 80 beats/min, how many of the soda bottles would equal
the correct volume ?
75 mL  0.075 L
Q = SV x HR
= 0.075 L x 80 bpm
= 6 L/min