USMLE Step 1 Physiology Review 56 05 Left-Ventricular P-V Loop (1_2)

USMLE Step 1 Physiology Review 56 05 Left-Ventricular P-V Loop (1_2)

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Play USMLE Audio MP3 56 05 Left-Ventricular P-V Loop (1_2) Below

Begin 56 04 Valve lesions & murmurs – valvular stenosis (2_2) Transcription

Now for some questions on the left ventricular pressure volume loop. Ventricular pressure and volumes change during the cardiac cycle. The resulting graph of these changes is a loop. The graph provides a lot of information about the function and integrity of the ventricles. Afterload impedes what?

  • The shortening of muscle fibers and therefore ejection in the heart

Afterload is the force that a ventricle must overcome while contracts during systolic ejection. Therefore the afterload for ventricles is what?

  • Arterial pressure

How does arterial pressure behave normally throughout most of the ejection phase of the cardiac cycle?

  • It increases progressively. The normal ventricle can maintain a normal stroke volume in response to increasing arterial pressure but a failing ventricle cannot.

Student doctor please pause the tape and summarize the information discussed on the first ventricular pressure volume loop.

  • The first question was about afterload and what it impedes. Ventricular pressure and volumes change during the cardiac cycle. The resulting graph of these changes is a loop. The graph provides a lot of information about the function and integrity of the ventricles. Afterload impedes the shortening of muscle fibers and therefore ejection in the heart. Afterload for the ventricles is the force that a ventricle must overcome while contracts during systolic ejection. Therefore the afterload for ventricles is arterial pressure. Arterial pressure normally increases progressively throughout most of the ejection phase of the cardiac cycle. The normal ventricle can maintain a normal stroke volume in response to increasing arterial pressure but a failing ventricle cannot.

Now back to more questions about the left ventricular pressure volume loop. The VEDV affects the stroke volume because of what mechanism?

  • The Frank-Starling mechanism

What is the VEDV?

  • It is the volume of blood in the ventricles after the end of diastole and is referred to as the Ventricular end diastolic volume.

At any one level of contractility according to the Frank-Starling mechanism, what happens to the strength of contraction as the VEDV increase?

  • The strength of contraction increases

The size of the pressure volume loop is the representation of what?

  • Cardiac work

Cardiac work is proportional to what two aspects of pressure and volume?

  • The pressure generated by ventricular contraction and stroke volume

Systolic pressure of the right ventricle is about what fraction of the systolic pressure of the left ventricle?

  • One seventh

Since both ventricles pump about the same stroke volume the cardiac work accomplished by the right ventricle is about what fraction of the work of the left ventricle?

  • One seventh.

Student doctor please pause the tape and summarize the information discussed on the first ventricular pressure volume loop.

  • The first question was about the Frank-Starling mechanism. The VEDV affects the stroke volume because of the Frank-Starling mechanism. The VEDV is the volume of blood in the ventricles after the end of diastole and is referred to as the Ventricular end diastolic volume. At any one level of contractility according to the Frank-Starling mechanism, the strength of contraction increases as the VEDV increases. The size of the pressure volume loop is the representation of Cardiac work. Cardiac work is proportional to the pressure generated by ventricular contraction and stroke volume. Systolic pressure of the right ventricle is about one seventh of the systolic pressure of the left ventricle. Since both ventricles pump about the same stroke volume, the cardiac work accomplished by the right ventricle is about one seventh of the work of the left ventricle.

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