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Definition of cardiac output Q stroke volume SV and heart rate HR CV variables part 1
This is sarah wilkinson from humber college and the university of guelphhumber. In this new series of tutorials of key cardiovascular variables, I am going to be giving the definition of cardiac output, stroke volume and heart rate. In the next set of tutorials, I will cover the regulation of heart rate and then I will be discussing factors that affect stroke volume.
These are preload, contractility and after load. Let’s get started on our basic definitions of these three variables. Let’s start with cardiac output. We can think about cardiac output as the total volume of blood being pumped from the heart ventricle in one minute. If we look down here, this is our left ventricle.
The cardiac output will how much blood leaves this ventricle every minute. We can think about cardiac ouput as the speed of blood flow through the body. At rest, an average cardiac output is about 5 litres per minute. Smaller people will have a lower cardiac output,.
And larger people have a larger cardiac output. During maximal exercise, cardiac out put will be 4 to 7 times higher than rest. In an untrained individual, we will it between 18 to 20 litres per minute. And in some elite endurance athletes, it will.
Be much, much higher. Cardiac output will equal stroke volume times heart rate. We will start out by discussing what heart rate is followed by stroke volume. We have all experienced taking our heart rate. There is a number of different ways we can do this.
We can do it by wearing a ‘polar’ watch or my manually palpating an artery Essentially what heart rate is, is counting the number of times the heart pumps in one minute. As you can see here, the heart is contracting a particular number of times per minute.
This can be sped up. Or slowed down. An average resting heart rate range is between 60 to 100 beats per minute. A lower resting heart rate can indicate a higher cardiovascular fitness.
Coming back to our cardiac output. It is equal to stroke volume times heart rate. Let’s have a look at the second variable that determines cardiac output. We can think about stroke volume as the volume of blood ejected from the heart with each beat. The arrows depict her the amount of blood leaving the heart in every beat.