00:01 Now let's talk a little bit about Atrial Systole. 00:04 We kind of ended on it being the last little kick of volume into the left ventricle. 00:11 It's initiated by the P wave from the ECG. 00:15 It occurs, again, right at the end of ventricular diastole . 00:23 We talked about it also producing a little bit of pressure on its own. 00:27 The pressure that it induces involves squeezing in on the blood that's there right at the end. 00:33 And that again, normally pushes about 10%, into the left ventricle to cause the full filling. 00:41 So someone really doesn't need to have a lot of atrial systole under most circumstances. 00:49 In fact, you could have a cardiac arrhythmia, known as atrial fibrillation, in which you the atrium really don't contribute much to ventricular filling. 01:01 And you can be walking around, and you might not even know that person has this arrhythmia. 01:07 On time though when atrial systole becomes very important around things like during exercise. 01:14 We have large volumes of blood coming back to the heart, and the top part can help squeeze that blood into the left ventricle so that you can get a better contraction out. 01:24 Because that way you can utilize the Frank-Starling mechanism to push more fluid out per stroke without utilizing any more energy. 01:35 Atrial diastole occurs after atrial systole. 01:39 Remember that this atrial kick is what creates the A wave. 01:43 However, during the diastole portion of the atria, these are phases two through seven. 01:49 There are two other waves we need to be concerned about. 01:54 The first of these is known as the C wave. 01:57 The C wave occurs during the contraction of the ventricles. 02:01 This is actually a pressure reverberation that occurs. 02:05 It either occurs during phase two as shown in the graph, or sometimes even a little bit into phase three. 02:14 The other way we need to be concerned about is the V wave. 02:17 The V wave occurs after you start to get blood filling the atria. 02:23 It continues to fill the atria until suddenly the AV valves open and there is a sudden pressure fall. 02:31 That's known as the V wave. 02:35 So in terms of the atrial filling pressures, and the atrial contraction pressures, we can look at A, C, and V being those items that we want to make sure we have good feeling for why they are occurring.
The lecture Atrial Systole and Diastole – Cardiac Cycle by Thad Wilson, PhD is from the course Cardiac Physiology.
In which phase of the cardiac cycle does the a-wave occur in left atrial pressure?
Atrial systole accounts for up to what percentage of ventricular filling during exercise conditions?
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