Cardiovascular Problem Set C

The following figure contains a "cardiac function" curve wherein cardiac output (CO on the Y axis) is plotted as a function of central venous pressure (P_cv on the X axis). [Right atrial pressure is often used as a measure of P_cv]. The figure also contains a "venous return" curve, i.e., a plot of venous return as a function of right atrial pressure. The circled intersection of the bold dashed-line venous return curve and the bold solid-line cardiac function curve represents the steady state relationship between the normal heart and vasculature of a resting human standing or sitting upright.

1. If the heart of the normal subject (depicted in the above figure) were to suddenly cease contracting, the central venous pressure would (within a few minutes) be ______ mmHg. This pressure is referred to as the ________________ pressure.

INSTRUCTIONS FOR QUESTIONS 2- 12: From the graph above, select the letter that best fits the condition described.

2. Rapid withdrawal of 0.5 L of blood from a normal subject causes a shift toward point ______, but within a few minutes (because of compensatory mechanisms) a shift toward point ______ begins. List at least four of these compensatory mechanisms.

3. Effect of rapid intravenous infusion of 1 L of plasma to a normal subject.

4. A normal person walks into a swimming pool and begins to float leisurely on his/her back. As a result there is an immediate shift toward point ______.

REPEAT OF FIGURE FROM PREVIOUS PAGE.

5. For this question (#5) only, consider the circled intersection to represent the operating equilibrium of a woman who is lying supine. Upon suddenly being raised to an upright position, her cardiovascular equilibrium will first move toward______. Then compensatory mechanisms will move it toward ______. List at least 4 of these compensatory mechanisms.

6. In a hypersensitive person, release of histamine into the circulation following a bee sting causes enormous venodilation. As a result, the immediate shift is toward point ______.

7. Mild exercise in a normal subject produces a shift toward point ______, and then toward point ______.

8. Suddenly infusing an effective dose of norepinephrine intravenously to the normal subject produces a shift toward point ______, and then toward point ______.

9. The plasma volume of a female patient is depleted by the administration of a diuretic. She is then given a β1 adrenergic blocking agent. As a result, her heart and vasculature will now function at point ______.

10. Deleted

11. Deleted

12. Electrical stimulation (in the normal subject) of the afferent fibers that arise from the carotid sinus baroreceptors produces a shift toward point ______.

Being able to place a catheter into the pulmonary artery has made it possible for the critical care specialist to monitor several important cardiovascular parameters including preload of the left ventricle. In this procedure, a multi-lumened catheter is inserted into a large vein (femoral or jugular) and advanced to the right atrium. A small balloon at the end of the catheter is inflated (about 1.0 ml) and the blood flow in the atrium and right ventricle carries the catheter into the pulmonary artery. The catheter is then advanced until it wedges in a small branch of a pulmonary artery, causing the catheter to occlude the vessel. As a result of this occlusion, the pressure at the end of the "wedged" catheter reflects the pressure in the pulmonary vein, because the pulmonary capillaries in the occluded region are "back-filled" from the pulmonary vein. Pulmonary vein pressure reflects left atrial pressure, which in turn reflects left ventricular end-diastolic pressure and the latter reflects left ventricular end-diastolic volume i.e., the preload of the left ventricle. After recording "wedge" pressure for a few seconds, the catheter is pulled back (Why?) until pulmonary artery pressure is again recorded . Openings of the other channels in the multi-lumened "Swan-Ganz" catheter allow the recording of right atrial pressure (i.e. preload of the right heart), and right ventricular pressure. Also, the catheter allows blood be withdrawn from (or fluids to be injected into) the right atrium, and a thermister within the catheter allows blood temperature to be measured.

The figure below diagramatically represents pressures obtained from a Swan-Ganz catheter as it is advanced toward the heart and the pulmonary artery. Select answers for the questions 13 - 20 from letters in this figure.

Time ----→

13 - 16. The pressures recorded at times A, B, C, and D represent respectively pressures in the (13)______________, (14)______________, (15)______________, and (16)______________.

17. The pressure recorded at letter ______________is the best measure of filling pressure for the right ventricle.

18. The pressure recorded at time ______________ is the best measure of filling pressure for the left ventricle.

19. Cardiac output can be measured with a multiple channel Swan- Ganz catheter. To do so by the thermodilution technique, cold isotonic saline is injected into the ______________, and the temperature of the blood measured in the ______________. When using this technique, the more the blood in the pulmonary artery is cooled by the injection of cold isotonic saline, the (more, less ) is the cardiac output.

20. INSTRUCTIONS; Chose one best answer:

In the previous figure, mean left atrial pressure is (equal to, less than, greater than) mean right atrial pressure. Is this relationship unusual?

20.5 Suppose the Swan-Ganz catheter is properly wedged into a small branch of pulmonary artery, and blood sample is withdrawn from the tip of the wedged catheter. The O2 content (ml 02/100 ml blood) would be closest to that of the patient’s

• A. pulmonary artery.
• B. pulmonary vein.
• C. right atrium.
• D. right ventricle.

Use information in the following records to answer question 21. (Assume the patient's body surface area is 2 square meters.) CI = cardiac index; PCW = pulmonary capillary wedge pressure.

Choose the one best answer:

21. Based on the records shown above, the patient has:

• A. inadequate left ventricular filling pressure.
• B. a heart rate of less than 60 beats per minute.
• C. a cardiac output of less than 2.5 liters per minute.
• D. a stroke volume of about 30 ml.
• E. an abnormally small right ventricular preload.

22-26 For each of the following conditions, will pulmonary capillary wedge pressures most likely be normal, below normal, or above normal?

• 22. mitral stenosis.
• 23. stenosis of the pulmonic valve.
• 24. mitral insufficiency with regurgitation.
• 25. a thrombus lodges in the left anterior descending coronary artery and reduces flow to the left ventricular myocardium to one third of normal.
• 26. traumatic abdominal injuries cause bleeding into the abdominal cavity.

27. Mean pulmonary arterial pressure is approximately 1/8 that of mean aortic pressure because:

• A. right ventricular stroke volume is less than left ventricular stroke volume.
• B. resistance in the pulmonary circuit is 1/8 of the resistance in the systemic circuit.
• C. pulmonary blood volume is 1/8 that of systemic blood volume.
• D. intrathoracic pressure is subatmospheric.
• E. right ventricular compliance is greater than left ventricular compliance.
• F. pulmonary blood flow is 1/8 that of systemic blood flow.

28. Electrical stimulation of the parasympathetic fibers in the distal end of a cut vagus nerve in the neck would be expected to:

• A. produce a positive inotropic effect on the left ventricle.
• B. increase the interval between successive R waves in the electrocardiogram.
• C. decrease the P-R interval in the electrocardiogram.
• D. increase the frequency of afferent impulses from the baroreceptors of the carotid sinus.
• E. cause an immediate increase in cerebral blood flow.

29. In an experimental animal with a catheter in the pulmonary artery, mean pulmonary arterial pressure (PAP) is 20mmHg, pressure in a wedged branch of the pulmonary artery is 5 mmHg, and mean intrapleural pressure is -5 mmHg. Cardiac output is 30 ml/second.

The pulmonary vascular resistance would be:

• A. 15 mmHg/30 ml per second
• B. 25 mmHg/30 ml per second
• C. 30 ml per second/15mmHg
• D. 30 ml per second/25 mmHg
• E. 20 mmHg/30 ml per second

30. The average output of the right and left heart must be maintained equal with great precision over long periods of time, or blood will accumulate in the systemic or pulmonary circulation. The most important factor in maintaining the two outputs equal is:

• A. the length-tension relationship of cardiac muscle (Starling's law)
• B. sympathetic nervous outflow to the heart
• C. parasympathetic nervous outflow to the heart
• D. the baroreceptor system
• E. humoral sympathomimetic agents

31. Use the following data to calculate the cardiac output, stroke volume, and cardiac index of an individual in a supine position.