0:00 Hello in this video we're going to talk about cardiac output. 0:11 So cardiac output is defined as the amount of blood ejected by the heart in one 0:18 minute. 0:18 So here is a heart in systole and the ventricles are contracting, ejecting 0:25 blood out to the 0:26 aorta and the pulmonary trunk. 0:29 The cardiac output is defined by the amount of blood ejected by each ventricle 0:35 in one 0:35 minute. 0:37 And there are two factors that are used to calculate the cardiac output. 0:41 These are your heart rate and stroke volume. 0:44 Your heart rate is essentially your conduction system of the heart. 0:47 Your heart rate is how many beats per minute, so beats over minute. 0:52 The other factor is your stroke volume. 0:54 The other factor is your stroke volume, which is the volume of blood pumped by 0:58 each ventricle 0:59 with each beat. 1:01 So this is mils per beat. 1:07 So therefore, cardiac output is equal to stroke volume multiplied by heart rate 1:13 . 1:13 And stroke volume is mils per beat and heart rate is beats per minute. 1:18 So as an example, a normal stroke volume would be about 70 mils per beat and 1:24 heart rate about 1:25 75 beats per minute. 1:27 Cross the beats out and your cardiac output is 5,250 mils per minute. 1:35 And this is about 5 liters per minute, which is about right because the amount 1:39 of blood 1:39 passing through the heart each minute is about 4 to 6 liters. 1:44 So the heart rate and stroke volume is used to calculate cardiac output. 1:48 But there's another 3 factors which influence stroke volume. 1:53 And so in total, there are 4 determinants of cardiac output. 1:57 Let's take a look at these. 1:59 So the first determinant, which we already talked about, is heart rate, which 2:03 is your 2:04 conduction system. 2:06 This is how many beats per minute. 2:09 And there are things that can influence your heart rate, known as chronotropic 2:13 factors. 2:14 So you can have positive chronotropes, which increase your heart rate and 2:18 negative chronotropes, 2:19 which decrease your heart rate. 2:21 An example of positive chronotropes is your sympathetic stimulation. 2:26 Your adrenaline, nor adrenaline, epinephrine, nor epinephrine, these guys will 2:30 increase 2:30 your heart rate. 2:31 Some drugs can also increase your heart rate, such as atropine. 2:36 Negative chronotropes decrease your heart rate. 2:38 This is your parasympathetic activity. 2:40 So this is your acetylcholine. 2:43 Some drugs, such as adenosine, can also decrease your heart rate. 2:47 The next 3 determinants of cardiac output are the things that influence your 2:51 stroke volume. 2:53 The first being preload. 2:56 Your preload is essentially the amount of blood entering the ventricles during 3:01 diastole. 3:01 So it's also known as, I guess, your end diastolic volume. 3:06 Again, the preload is the amount of blood, the volume entering the ventricles. 3:10 And this is during diastole. 3:14 Preload can be influenced by, therefore, venous return, the blood volume, and 3:19 also atrial 3:20 contraction. 3:22 And the preload, again, occurs during diastole, because this is when your vent 3:26 ricles are being 3:26 filled with blood. 3:29 The next determinant of cardiac output, the third one, is afterload, which 3:33 essentially 3:34 occurs during systole, when your ventricles are contracting, ejecting blood out 3:39 of the 3:40 aorta and into the pulmonary trunk. 3:44 Your afterload is essentially the resistant the ventricles must overcome to 3:48 circulate the 3:48 blood. 3:50 And so you can imagine things that can increase your afterload. 3:54 These are things such as hypertension, atherosclerosis, and vasoconstriction, 4:00 because these things 4:01 will increase the resistance, and therefore increase afterload. 4:06 The fourth determinant of cardiac output is contractility. 4:09 This is how hard the myocardia must contract for a given preload. 4:14 And there are things that influence contractility. 4:17 These are ionotropic factors. 4:19 There are positive ionotropes which increase contractility, and then there are 4:24 negative 4:24 chronotropes which decrease contractility. 4:27 So positive ionotropes, again, is your sympathetic stimulation, nor adrenaline, 4:32 or nor epinephrine. 4:34 Some drugs such as dobutamin can also increase contractility, making it a more 4:38 powerful contraction. 4:40 Negative ionotropes are things such as your parasympathetic stimulation, so you 4:44 're acetylcholine 4:45 again, and some drugs can also decrease contractility, such as your beta 4:50 blockers and calcium channel 4:51 blockers. 4:57 So those are the four determinants of cardiac output, your heart rate, preload, 5:00 afterload, 5:01 and contractility.
