USMLE Step 1 Physiology Review 55 11 Cardiac Cycle (1_4)

USMLE Step 1 Physiology Review 55 11 Cardiac Cycle (1_4)

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Play USMLE Audio MP3 55 11 Cardiac Cycle (1_4) Below

Begin 55 11 Cardiac Cycle (1_4) Transcription

Now let’s talk about the Cardiac cycle. What two kinds of events does the cardiac cycle include?

  • Electrical and mechanical.

Which events precede and initiate which?

  • The electrical events precede and initiate the mechanical event

The following questions refer to the graph included with the outline, we will work through and identify different features on the graph, work with the tape and soon you will be able identify the different curves peaks and troughs from their shapes and relative position on the graph

What is the wave form at the very bottom of the graph that is labeled A?

  • EKG

What is the information provided by the next wave form up it is labeled B?

  • Heart sounds

The next wave form which is labeled C and is a dash line provides information about what?

  •  Ventricular pressure

The next wave form which is labeled D and is just above ventricular pressure provides information about what?

  • Atrial pressure

What is another term for this wave form?

  • The Jugular Venous pulse

The next wave form that is labeled E provides information about what?

  • Ventricular volume

The wave form which is labeled F and is a bold line provides information about what?

  • Aortic pressure.

Student please pause the tape and summarize the information discussed this far on the cardiac cycle

  • The Cardiac cycle includes electrical and mechanical events. The electrical events precede and initiate the mechanical events. The wave form at the very bottom of the graph that is labeled A is an EKG. The next wave form the one labeled B provides a graphic picture of Heart sounds. The next wave form which is labeled C and is a dash line provides information about Ventricular pressure. The next wave form which is labeled D and is just above ventricular pressure provides information about atrial pressure. Another term for this wave form is the Jugular Venous Pulse. The next wave form that is labeled E is Ventricular volume. The wave form which is labeled F and is a bold line is Aortic pressure.

The first thump in the EKG corresponds to what?

  • The P wave

After the P wave in the EKG there is sharp negative wave referred to by what letter?

  • Q

Immediately after the Q wave there is a sharp positive peak in the EKG, this peak is referred to by what letter?

  • R

What is the negative wave immediately following the R wave?

  • The S wave

123These three waves are referred to collectively as what?

  • The QRS complex

Look at the wave form that correspond to atrial pressure the one labeled D,  there is a slight rise in this wave form that occurs immediately after the P wave in the EKG. This rise or peak is called the A peak what causes the slight peak?

  • Atrial contraction.

What is the function of atrial contraction?

  •  Atrial contraction increases the volume of blood in the ventricles

When are the effects of atrial contraction especially important?

  • when the heart rate is rapid and there is less time for ventricular filling

What is the term for the pressure of the blood in the ventricle at the end of atrial contraction?

  • Ventricular End Diastolic Pressure or VEDP.

Student doctor please pause the tape and summarize the information discussed on the Cardiac cycle since the last summary.

  • The first question was question was about the first hump in the EKG. The first hump in the EKG is the P wave. After the P wave in the EKG, there is sharp negative wave called the Q wave. Immediately after the Q wave, there is a sharp positive peak in the EKG, called the R wave. The negative wave immediately following the R wave is the S wave. These three waves are referred to collectively as the QRS complex. In the wave form that corresponds to atrial pressure the one labeled D, there is a slight rise in the wave that corresponds to the atrial pressure that occurs immediately after the P wave in the EKG. This rise or peak is called the A peak, and is causes by atrial contraction. Atrial contraction increases the volume of blood in the ventricles. The effects of atrial contraction are especially important when the heart rate is rapid and there is less time for ventricular filling. The term for the pressure of the blood in the ventricle at the end of atrial contraction is Ventricular End Diastolic Pressure or VEDP.

What is the next peak after the A peak in the Jugular venous pulse?

  • The c peak

What cause the c peak in the jugular venous pulse?

  • Right ventricular contraction

What is another term for the c peak?

  • Carotid pulse

The next peak after the c peak in the jugular venous pulse is referred to as the v peak what causes the v peak?

  • Atrial pressure against the closed tricuspid valve.

What heart sound roughly corresponds with the a peak in the jugular venous pulse?

  • S4, which is the very first one on the sound curve, although it is conventionally referred to as the fourth heart sound.

What causes the S4 sound?

  • High atrial pressure filling a stiff ventricle.

Student doctor, please pause the tape and summarize the information discussed on the Cardiac cycle since the last summary.

  • The first question was about the a peak or a wave in the jugular venous pulse. The next peak after the A peak in the Jugular venous pulse is the c peak, also referred to as the carotid pulse which is cause by right ventricular contraction. The next peak after the c peak in the jugular venous pulse is referred to as the v peak which is caused by atrial pressure against the closed tricuspid valve. The heart sound that roughly corresponds with the a peak in the jugular venous pulse is S4, which is the very first one on the sound curve, although it is conventionally referred to as the fourth heart sound. High atrial pressure filling a stiff ventricle causes the fourth heart sound.

****END OF TRANSCRIPTION****

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