Isovolumetric Contraction: LV Phases– Cardiac Cycle

by Thad Wilson, PhD

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    This is the classic cardiac cycle. For this, we’re going to start off in isovolumic contraction. So, I know these terms are a little bit difficult, but you must invest the time in to learn them because this is how everyone is going to refer to the various stages of the cardiac cycle and when blood is being pumped out. What does isovolumic mean? Iso meaning the same, volumetric is the volume is the same during a contraction. Isovolumetric contraction. Thus, whatever is being filled, this is the left ventricular end-diastolic volume. What we have is then a depolarization of the left ventricle. And remember, that's the QRS complex from your ECG. At this point, the left ventricular pressure increases, which is the pressure within the left ventricle. The mitral valve closes, and this left ventricular volume then is maintained throughout this particular portion of the cycle. The big thing that looks like that's changing here is that left ventricular pressure is increasing. So, the volume doesn't change, just the pressure. Now, we enter force of ejection. There's going to be a rapid ejection, which is number three. There's going be reduced ejection, which is number four. When does ejection happen? As soon as the aortic valve opens. So, you build up pressure within this left ventricle, you’re squeezing in on this fluid, but the fluid is not traveling anywhere and then, BOOM, pops through the aortic valve. At that point, blood is now ejected into the aorta and then out through the systemic vasculature. What happens here in terms of the ECG? This is at the time when the T wave occurs. And remember from the ECG, the T wave is during ventricular repolarization. The last item to kind of consider is that left ventricular end-systolic volume will be...

    About the Lecture

    The lecture Isovolumetric Contraction: LV Phases– Cardiac Cycle by Thad Wilson, PhD is from the course Cardiac Physiology. It contains the following chapters:

    • LV Systole
    • LV Diastole

    Included Quiz Questions

    1. Phase 5
    2. Phase 1
    3. Phase 3
    4. Phase 7
    1. Ejection
    2. Atrial contraction
    3. Isovolumic Contraction
    4. Passive filling
    5. Isovolumic Relaxation
    1. Phase 3 & 4
    2. Phase 6 &7
    3. Phase 1
    4. Phase 4 &5
    5. Phase 5 & 6

    Author of lecture Isovolumetric Contraction: LV Phases– Cardiac Cycle

     Thad Wilson, PhD

    Thad Wilson, PhD

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