Preload | Cardiology

[Music] hi I'm dr. mark here in this video we're going to take a look at preload and see how preload influences cardiac output remember cardiac output is the amount of blood our heart pumps out every minute and it's around about five liters every minute now preload it's one of the factors that influences stroke volume what stroke volume stroke volume is the amount of blood our heart pumps out every contraction so you obviously multiply that by how many times we or our heart beats per minute and we get our Kanak output all right preload what is it well first thing I need to drop is a heart and when we have our heart we're also going to have some blood vessels but the only one I'm going to draw up here is going to be the a order now I want you to think about this your heart's going to contract that's called systole when it contracts it ejects blood and then it relaxes and that's called diastole and that's when it fills with blood we're gonna talk right now about diastole the heart is relaxed and it begins to fill up with blood what you'll find is right at the very end of diastole okay so it's right at the end of filling immediately before the heart contracts in systole to eject the blood you've got the end diastolic volume that's this right here and that is going to be the maximum filling of the heart but it's also the maximum stretching of the walls of the ventricles of the heart just before contraction this is actually preload preload is the maximum stretch of the walls of the ventricles or the musculature of the ventricles just before they contract to eject the blood you're probably thinking why is this important for us to understand cardiac output and the reason is because the preload or the maximum stretch of the walls of the ventricles is proportional to the amount of blood that gets ejected out of the heart this is called the frank-starling mechanism the frank-starling mechanism and it basically states the more you stretch or fill the heart with blood the stronger that contractions going to be and the more blood gets ejected that means the higher the preload so the higher the stretch the greater the stroke volume the greater the stroke volume the greater the cardiac output so preload is directly proportional to cardiac output more filling more contraction more ejection okay now things that can affect preload include well the major thing that affects preload is venous return so obviously you're gonna have your inferior superior vena cava that's returning deoxygenated blood from the body back to the heart and if you have a greater filling you're go and have a greater preload if you have a greater preload you're also gonna have a greater stroke volume and a greater cardiac output but think about this if the heart rate starts to pump faster faster faster faster there's less time for dynasty diastole so that's less time for filling which means a reduced preload and also a reduced cardiac output so you may think but wait a minute an increased heart rate should increase cardiac output and that's true but if the heart rate increases too quickly there's less time fulfilling and a smaller ejection fraction so a smaller stroke volume so it is complex but all you need to be aware of is for preload it is the maximum stretch on the walls of the ventricles immediately before contraction the greater the stretch the greater the ejection the greater the ejection the greater the cardiac output that's preload

Channel: Dr Matt & Dr Mike

Views: 40,153

Keywords: preload, afterload, cardiac output, heart rate, stroke volume, cardiology, cardiovascular physiology, heart physiology, medicine, nursing

Id: IVSDvEEWgxE

Length: 3min 49sec (229 seconds)

Published: Wed Jun 26 2019