Medical Physiology 2005

Problem Set 6:  Cardiac Physiology

 

 

1.  Consider 3 drugs:  dobutamine (a b1 agonist); nifedipine (a Ca2+ channel blocker) and, and digitalis (a cardiac glycoside).  When applied to ventricular cardiac myocytes:

·        Describe any changes to the action potential that would occur in the presence of these drugs.  Explain.

·        Describe any changes in the contraction of these cells in the presence of these drugs.  Explain.

·        Assuming that this stimulation occurs independent of any pacemaking regions, describe any changes to cardiac output that would occur as a result of these drugs.  Explain.

 


2.  The figure shown below indicates how pressure changes over time within the left ventricle (solid line), aorta (upper dotted line), and left atrium (lower dotted line) for a normal healthy adult.  

 

Using the letters indicated in the figure, describe:

a.   When atrial systole occurs?

b.   Where does the x-descent occur?

c.   Where is the 2nd heart sound?

d.   Between which two points does the T wave of the EKG occur?

e.   Where is ventricular volume the least?

f.    Between which two points does isovolumetric contraction occur?

g.   The rapid filling phase follows which point?

h.   How would this record change in the event of an aortic stenosis?

i.    How would this record change in the event of an incompetent aortic valve?

 

 

3.  In an experimental animal the O2 uptake is 50 ml/min. A sample of arterial blood contains 0.20 ml O2/ml blood, a sample from the vena cava contains 0.15 ml O2/ ml blood and a sample from the pulmonary artery contains 0.16 ml O2/ ml blood. What is the animal's cardiac output?

 

4.  The figure shown below is a pressure-volume loop from a normal, healthy adult.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Based on this information:

a.   What is EDV?

b.   What is the SV?

c.   What is the ejection fraction?

d.   What is the cardiac output?

e.   When does the 1st heart sound occur?

f.    When does the 2nd heart sound occur?

g.   Over what interval is the velocity of contraction highest?

 

5.  Draw a Frank-Starling curve for a normal healthy adult heart, being sure to label the axes.  In particular:

a.   Which is the dependent and which is the independent variable?

b.   Add a second curve for the same heart under sympathetic stimulation.  Show how, for a given preload, cardiac output changes in response to the sympathetic stimulation..

c.   Add a third curve for an individual experiencing congestive heart failure.  Show how, for a given preload, cardiac output changes in response to this pathology.

 

6.  Draw a vascular function curve for a normal healthy adult heart, being sure to label the axes.  In particular:

a.   Which is the dependent and which is the independent variable?

b.   Add two additional curves showing the effects of transfusion and hemorrhage, respectively.   Show how, for a given cardiac output, CVP changes in response to these alterations in fluid volume. 

c.   Add two additional curves showing the effects of vasoconstriction and vasodilation, respectively.  Show how, for a given cardiac output, CVP changes in response to these changes in vascular tone. 

 

7.  The figure shown below is a pressure-volume loop from a normal, healthy adult.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Using these data for comparison, draw the PV loop of the same heart experiencing a significant increase in preload.  [Assume that no change occurs in afterload.]  In particular comment on how this increase in preload affects:

a.   stroke volume

b.   ejection fraction

c.   contractility

d.   wall tension within the ventricle

e.   stroke work

 

8.  Using the normal PV loop shown in question 7 for comparison, draw the PV loop of the same heart experiencing a significant increase in afterload.  [Assume no compensatory changes in preload].

a.   What happens to stroke volume as a result of this change?

b.   What happens to ejection fraction?

c.   Does cardiac efficiency change?

d.   If we now assume that compensatory changes occur, what will happen and how will this affect the PV loop?

 

9.  Using the normal PV loop shown in question 7 for comparison, draw the PV loop of the same heart under sympathetic stimulation.

a.   What happens to the peak pressure within the ventricle?

b.   What happens to stroke volume?

c.   What happens to ejection fraction?

d.   What happens to the stroke work?

e.   How would this PV loop you have drawn differ from the PV loop of an individual experiencing increased sympathetic stimulation accompanying exercise?  Explain any cardiovascular events that make this circumstance different than a simple increase in sympathetic supply to the heart.

 

10.  CASE STUDY:  A 44-year old man presents with symptoms of dyspnea, chest pains, and fatigue and weakness, all of which increase upon exertion.  From his history, you learn that 9 months ago, he experienced a myocardial infarction localized to his left ventricle due to coronary artery disease, which was corrected at that time with by-pass surgery.  Since then, his symptoms have developed progressively.  Upon physical exam, you note his respiration and heart rates are elevated, his skin is pale, and his jugular veins are distended.  Upon auscultation of the lungs, you detect rales, and you detect a third heart sound.  A pressure-volume loop from this patient (dotted curve), taken shortly after his myocardical infarction, is shown below in comparison with a normal pressure volume loop (solid curve).  Assume that the patient’s pressure-volume loop represents the uncompensated status of this patient.


 

 

 

a.   Prior to compensation, what has changed in this patient’s PV loop (compared to normal) and how has this affected stroke volume and ejection fraction?  What other cardiac parameters are affected?

 

 


 

b.  The PV loop shown above indicates one compensatory mechanism that occurs in this patient.  Explain what has occurred and the likely mechanism that resulted in this change.  How does this compensatory change affect this patient’s cardiac performance parameters?


 

 

c.  The PV loop shown above indicates a second compensatory mechanism that occurs in this patient.  Explain what has occurred and the likely mechanisms that result in this change.  How does this compensatory change affect this patient’s cardiac performance parameters?

d.   With regard to the compensatory mechanisms involved with part c, explain any deleterious consequences (if any) for this patient, and how these provide the rationale for treatment options.

e.   Explain this patient’s symptoms.