USMLE Step 1 Physiology Review 56 06 Left Ventricular P-V Loop (2_2)

USMLE Step 1 Physiology Review 56 06 Left Ventricular P-V Loop (2_2)

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Play USMLE Audio MP3 56 06 Left Ventricular P-V Loop (2_2) Below

Begin 56 06 Left Ventricular P-V Loop (2_2) Transcription

What two variables provide an accurate reflection of myocardial oxygen consumption? (you may want to pause the tape here)

  • First the differences in oxygen content between the coronary artery and venous blood. Second coronary blood flow.

What are the two factors that affect cardiac work?

  • First, hypertension; Second, myocardial oxygen supply

What are the two kind of hypertension?

  • First, pulmonary hypertension; Second, systemic hypertension

Pulmonary hypertension is also referred to as?

  • Right sided hypertension

Systemic hypertension is also referred to as?

  • Essential hypertension

Almost always what is the cause of pulmonary hypertension?

  • Chronic lung disease

For the heart to work properly it needs a continuous supply of oxygen, how do you calculate the oxygen delivery to any tissue? (Please pause the tape)

  •  You take the arterial oxygen content and multiply it by the blood flow.

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

  • The first question was about variables that provide a reflection of oxygen consumption. The differences in oxygen content between the coronary artery and venous blood and coronary blood flow provide an accurate reflection of myocardial oxygen consumption. Hypertension and myocardial oxygen supply are the two factors that affect cardiac work. The two kind of hypertension are pulmonary hypertension or Right sided hypertension and systemic hypertension or Essential hypertension. Chronic lung disease almost always is the cause of pulmonary hypertension.  For the heart to work properly it needs a continuous supply of oxygen. To calculate the oxygen delivery to any tissue, you take the arterial oxygen content and multiply it by the blood flow.

Now back to some more questions. For the following questions please refer to the graph of the left ventricular pressure volume loop (You will find the graph in your outline). What is the key concept behind the ventricular pressure volume loop?

  •  Counterclockwise movement in the loop.

Where is the ESV in the graph? (Remember ESV stands for End Systolic volume.

  • The upper left hand corner.

Look at the line of the graph that goes down, ventricular pressure plummets while ventricular volume remains unchanged. What phase of the cardiac cycle is represented by this part of the loop?

  • Iso-volumetric relaxation.

At the lower left corner of the loop, what is happening to the heart in this part of the loop?

  • The mitral valve is opening

And what happens during the phase across the bottom where the line slowly rises?

  • Ventricular filling

What happens at the beginning of that ventricular filling phase?

  • Rapid filling

What happens at the end of that ventricular filling phase?

  • Slow filling

What happens at the lower right corner of the graph?

  • The mitral valve closes

Student doctor please pause the tape and summarize the information on the left ventricular pressure volume loop discussed since the last summary.

  • The first question was about the key concept behind the graph. The key concept behind the ventricular pressure volume loop is Counterclockwise movement in the loop. The ESV, End Systolic volume, in the graph is in the upper left hand corner. The line of the graph that goes down shows that ventricular pressure plummets while ventricular volume remains unchanged. Iso-volumetric relaxation is represented by this part of the loop. At the lower left corner of the loop, the mitral valve is opening. Ventricular filling occurs during the phase across the bottom where the line slowly rises. Rapid filling occurs at the beginning of that ventricular filling phase and slow filling at the end of that ventricular filling phase. The mitral valve closes at the lower right corner of the graph.

Now back to more questions on the pressure volume loop. After the mitral valve closes, the ventricular pressure increases precipitously while ventricular volume remains constant, what is happening to the heart in this part of the graph?

  • Iso-volumetric contraction

What part of the cardiac cycle is represented at the upper right hand corner of the loop, just before volume starts decreasing?

  • VEDV that is Ventricular end diastolic volume

What is happening to the heart as we follow the top part of the loop back across to the left?

  • Systolic ejection

Student doctor please pause the tape and summarize these last three points about the left ventricular pressure volume loop.

  • After the mitral valve closes, the ventricular pressure increases precipitously while there is no change in ventricular volume. Iso-volumetric contraction is occurring in this part of the graph. VEDV or Ventricular end diastolic volume is represented at the upper right hand corner of the loop, just before volume starts decreasing. As we follow the top part of the loop back across to the left, systolic ejection occurs in this part of the graph.

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