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Definition of cardiac output (Q), stroke volume (SV) and heart rate (HR)- CV variables part 1 - YouTube
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This is Sarah Wilkinson from Humber College
and the University of Guelph-Humber.
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In this new series of videos of key
cardiovascular variables,
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I am going to be giving the definition of
cardiac output, stroke volume and heart rate.
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In the next set of videos,
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I will cover the regulation of heart rate
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and then I will be discussing factors
that affect stroke volume.
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These are preload, contractility and after load.
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Let's get started on our basic definitions
of these three variables.
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Let's start with cardiac output.
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We can think about cardiac output as
the total volume of blood being
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pumped from the heart ventricle in
one minute.
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If we look down here, this is our left ventricle.
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The cardiac output will how much blood
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leaves this ventricle every minute.
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We can think about cardiac ouput
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as the speed of blood flow through the body.
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At rest, an average cardiac output is about
5 litres per minute.
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Smaller people will have a lower cardiac output,
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and larger people have a larger cardiac output.
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During maximal exercise, cardiac out put
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will be 4 to 7 times higher than rest.
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In an untrained individual, we will it
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between 18 to 20 litres per minute.
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And in some elite endurance athletes, it will
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be much, much higher.
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Cardiac output will equal
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stroke volume times heart rate.
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We will start out by discussing what heart rate
is followed by stroke volume.
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We have all experienced taking our heart rate.
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There is a number of different ways we can do this.
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We can do it by wearing a 'Polar' watch
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or my manually palpating an artery
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Essentially what heart rate is, is counting
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the number of times the heart pumps in one minute.
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As you can see here, the heart is contracting
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a particular number of times per minute.
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This can be sped up.
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Or slowed down.
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An average resting heart rate range
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is between 60 to 100 beats per minute.
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A lower resting heart rate can indicate
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a higher cardiovascular fitness.
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Coming back to our cardiac output.
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It is equal to stroke volume times heart rate.
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Let's have a look at the second variable
that determines cardiac output.
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We can think about stroke volume as
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the volume of blood ejected from the heart
with each beat.
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The arrows depict her the amount of
blood leaving the heart in every beat.
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Sometimes, more blood is ejected from the
heart with one heart beat.
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That is a higher stroke volume.
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An average resting stroke volume is
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between 60 to 70 millilitres per beat.
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The amount of blood in the heart ejected in
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one single contraction.
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We know that there is a much higher resting
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stroke volume seen in endurance athletes.
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While it is relatively easy to measure heart rate,
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it is more challenging to measure stroke volume.
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To measure stroke volume, an ultrasound of
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the heart needs to be taken.
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What we see here is an image of ultrasound
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I am going to show you what it looks like for
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an ultrasound technician.
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Here you can see, the two ventricles
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and the two atria
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and the valves between the atria
and the ventricles
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What an ultrasound technician would
be able to do,
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is measure the volume of blood leaving the
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heart via the aorta.
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To review, the cardiac output is the
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total amount of blood flowing from the heart
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in one minute.
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It is going to be determined by multiplying
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heart rate, which is the number of
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contractions per minute by
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stroke volume, which is the blood ejected
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with each beat of the heart.
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In the next set of videos, I am going to
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discuss how heart rate can change from resting
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values of 60 to 100 beats per minute
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and increase during exercise
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or decrease during relaxation.
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In a future video, I will also be discussing
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how stroke volume is regulated.
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