USMLE Step 1 Physiology Review 55 14 Cardiac Cycle (4_4)

USMLE Step 1 Physiology Review 55 14 Cardiac Cycle (4_4)

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Begin 55 14 Cardiac Cycle (4_4) Transcription

 

Now we will talk about Diastole. The closure of what marks the beginning of iso-volumetric relaxation?

 

  • The closure of semilunar valves, the aortic and pulmonic valves

 

 What happens to ventricular pressure during the brief 0.04sec iso-volumetric relaxation?

 

  • Ventricular pressure plummets.

 

 Ventricular volume remains constant for a period of time marked by two events, what are those events?

 

  • Ventricular volume remains constant from the closure of the semilunar valves to the opening of the AV valves.

 

 What happens when the ventricular volume falls below the atrial?

 

  • The AV valves open

 

 What feature in the atrial pressure tracing marks this event?

 

  • The V Peak

 

 Okay ventricular pressure plummets, the ventricles relax, the AV valves opens and what happens to ventricular volume which corresponds to the V peak on the atrial pressure tracing?

 

  • Ventricular volume rapidly increases

 

 Where is the blood coming from to fill the ventricle when the AV valves open?

 

  • From the atrial that are full from venous return.

 

 Student doctor, please pause the tape and describe the information about Diastole discussed since the last summary.

 

  • The first question was about what marks the beginning of iso-volumetric relaxation. The closure of semilunar valves marks the beginning of iso-volumetric relaxation. During the brief 0.04sec iso-volumetric relaxation, ventricular pressure plummets. Ventricular volume remains constant from the closure of the semilunar valves to the opening of the AV valves. When the ventricular volume falls below the atrial, the AV valves open.  The V Peak in the atrial pressure tracing marks this event. Okay ventricular pressure plummets, the ventricles relax, the AV valves opens and ventricular volume rapidly increases which corresponds to the V peak on the atrial pressure tracing. The blood coming from the atrial that are full from venous return fill the ventricle when the AV valves open.

 

 Now back to question about Diastole. The rate of ventricular filling tails off and with very slow heart rates ventricular filling actually ceases because the ventricles reach their volume limit. What is this period of cessation called?

 

  • Diastasis

 

 Increased heart rate leads to a shortened cardiac cycle. What two aspects of the cardiac are most affected by a shortening of the cardiac cycle?

 

  • Diastasis and the reduced filling phase

 

 Increases in heart rate up to a 140-150beats per min do not significantly affect cardiac output. What levels must heart rate exceed for there to be a noticeable decrease in cardiac output? 

 

  • 180-200beats per min

 

 Since ventricular filling is reduced by a shortening of cardiac cycle, what aspect of ventricular volume will be reduced?

 

  • The Ventricular end diastolic volume, the VEDV

 

 

And what does VEDV stand for?

 

  • Ventricular end diastolic volume

 

 Since VEDV is reduced what other aspect of ventricular volume would be reduced?

 

  • Stroke volume

 

 Student doctor, please pause the tape and describe the information about Diastole discussed since the last summary.

 

  • The first question was about Diastasis. The rate of ventricular filling tails off and with very slow heart rates ventricular filling actually ceases because the ventricles reach their volume limit. This period of cessation is called Diastasis. Increased heart rate leads to a shortened cardiac cycle. Diastasis and the reduced filling phase are most affected by a shortening of the cardiac cycle. Increases in heart up to a 140-150beats per min do not significantly affect cardiac output. The heart rate must exceed 180-200beats per min for there to be a noticeable decrease in cardiac output.  Since ventricular filling is reduced by a shortening of cardiac cycle, ventricular end diastolic volume, or VEDV is reduced. Since VEDV is reduced, Stroke volume is reduced as well.

 

 What heart sound is not normally audible in adults but may be heard in children?

 

  • S3

 

 What part of the cardiac cycle does the third heart sound correspond with?

 

  • The rapid passive filling.

 

 The fourth heart sound, S4, corresponds to what event in the cardiac cycle?

 

  • The atrial contraction.

 

 Is S4 normally heard?

 

  • No

 

 In what situation or in what kinds of people is S4 occasionally heard?

 

  • People with congestive heart failure

 

 What kind of rhythm is audible in people with congestive heart failure?

 

  • A triple sound or a gallop rhythm.

 

 Student doctor, please pause the tape and describe the information discussed about Diastole since the last summary.

 

  • The first question was about the third heart sound.  The third heart sound or S3 is not normally audible in adults but may be heard in children. Third heart sound corresponds with the rapid passive filling.The fourth heart sound, S4, corresponds with atrial contraction.  S4 is not normally heard.  S4 is occasionally heard in people with congestive heart failure. A triple sound or a gallop rhythm is audible in people with congestive heart failure.

 

****END OF TRANSCRIPTION****

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55-14 Cardiac Cycle (4/4)

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