USMLE Step 1 Physiology Review 55 12 Cardiac Cycle (2_4)

USMLE Step 1 Physiology Review 55 12 Cardiac Cycle (2_4)

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Play USMLE Audio MP3 55 12 Cardiac Cycle (2_4) Below

Begin 55 12 Cardiac Cycle (2_4) Transcription

Now we will talk about systole. What is the term for the volume of blood in the ventricle just before the onset of ventricular contraction?

  • Ventricular end diastolic volume or VEDV for short.

What is the normal VEDV for the left ventricle?

  • 120 to 140mL

What term describes the volume of blood remaining in the ventricle at the end of ejection?

  • Ventricular end systolic volume or VESV for short

What is the normal VESV?

  •  40-70mililiters

The volume of blood ejected with each beat is called the?

  • Stroke volume

If you knew the VEDV and the VESV, how would you derive the stroke volume?

  • Stroke volume equals VEDV minus VESV or that is stroke volume equals Ventricular end Diastolic volume minus Ventricular end Systolic volume.

What is the term for the amount of blood equal to the stroke volume divided by the VEDV?

  •  Ejection fraction.

Student doctor please pause the tape and summarize the information about systole discussed so far.

  • Ventricular end diastolic volume or VEDV for short is the term for the volume of blood in the ventricle just before the onset of ventricular contraction. The normal VEDV for the left ventricle is 120 to 140mL. Ventricular end systolic volume or VESV for short describes the volume of blood remaining in the ventricle at the end of ejection. The normal VESV is 40-70mililiters. The volume of blood ejected with each beat is called the stroke volume. Stroke volume equals VEDV minus VESV. Ejection fraction is the stroke volume divided by the VEDV.

Okay back to some more questions. Before the end of the QRS complex there is a precipitous rise in which one of the curves?

  • The ventricular pressure curve

This rise in ventricular pressure far exceeds the atrial pressure, what is caused by this atrial-ventricular pressure difference?

  • The closure of the AV valves.

What are the names of the two Atrial-Ventricular valves or the two AV valves?

  •  The Mitral and the tricuspid valves.

With the closure of the AV valves what phase of the Cardiac cycle has just finished?

  •  Atrial systole and Ventricular filling

The closure of the AV valves is a major reason for which heart sound?

  • The first heart sound or S1.

The S1 is a low frequency sound that signals the onset of what?

  • Ventricular systole.

Student doctor please pause the tape and summarize the information about systole discussed since the last summary.

  • The first question was about the precipitous rise in ventricular pressure after the QRS complex. Before the end of the QRS complex there is a precipitous rise in the ventricular pressure curve. This rise in ventricular pressure far exceeds the atrial pressure, the atrial-ventricular pressure difference causes closure of the AV valves which are the Mitral and the tricuspid valves. The closure of the AV valves marks the end of Atrial systole and Ventricular filling. The closure of the AV valves is a major reason for the first heart sound or S1. The S1 is a low frequency sound that signals the onset of ventricular systole.

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