Cardiovascular Problem Set A

Purpose: Questions 1-13: Practice with physical factors that determine flow, specifically, Poiseuille's flow-equation; effect of adding or subtracting resistances in series; effect of adding or subtracting resistances in parallel.

INSTRUCTIONS: Use information in the following figure to answer questions 1 - 2.

1. Assuming that flow is streamlined in both tubes, flow in tube X will be:

• A. 16 times that of Y
• B. 8 times that of Y.
• C. 4 times that of Y.
• D. 2 times that of Y.
• E. equal to that of Y.

2. If flow in tube X is 1 ml/minute, what is the resistance to flow in tube X?

• A. 20 mmHg/ml/min.
• B. 80 mmHg/ml/min.
• C. 100 mmHg/ml/min.
• D. 100 ml/min./mm Hg
• E. not determinable with the information given.

INSTRUCTIONS: Use information in the following figure to answer questions 3 & 4.

3. Given the conditions in the above figure, and assuming that flow in X and in Y is streamlined, flow in X is:

• A. 3 times that of Y.
• B. equal to that of Y.
• C. 1/3 that of Y.
• D. Flow of X and Y can not be compared based on the information given.

4. X and Y have been rearranged as shown in the following figure, but ΔP was held constant. Flow through the new system will be:

• A. equal to that of X in question 3.
• B. equal to that of Y in question 3.
• C. equal to that of X plus Y in question 3.
• D. 3/4 that of X in question 3.
• E. 4/3 that of Y in question 3.

INSTRUCTIONS for questions 5 - 10: In answering these questions, assume that the pressure gradient across the systemic circuit is held constant even if the perturbation alters total systemic resistance. Also, since you have not yet studied compensatory cardiovascular reflexes, assume they do not exist when choosing your answer.

• Answer A, if the perturbation increases total peripheral resistance.
• Answer B, if the perturbation decreases total peripheral resistance.
• Answer C, if the perturbation has no effect on total peripheral resistance.

PERTURBATIONS:

5. As a result of pregnancy, blood flow through a woman's uterus greatly increases.

6. A large release of catecholamines produces marked vasoconstriction of the splanchnic circulation.

7. A male experimental subject lies on his back and raises one leg. This maneuver causes most of the venous blood in that leg to drain into his abdominal veins. While the leg is still raised, a tourniquet is tightened on the upper thigh of the raised leg thus preventing blood from entering or leaving that leg. The leg (with blood flow still impeded) is then lowered.

8. Surgical production of an arterio-venous fistula in the wrist.

9. Pronounced anemia reducing the hematocrit to half the normal value. (Assume blood flow remains streamlined).

10. Streptococcal infection causes the aortic valve to become stenotic ( its opening is narrowed).

INSTRUCTIONS for question 11: One best answer.

11. In response to a low partial pressure of alveolar O₂ (as occurs at high altitudes), precapillary vessels of the pulmonary circuit constrict. Also, after a few weeks, production of red blood cells increases causing hematocrit to increase. Which of the following is most likely to occur as a result of these changes? (Assume in answering this question that compensatory cardiovascular reflexes maintain normal flow of blood through the lung.)

• A. Pressure in the pulmonary artery increases.
• B. Resistance to flow in the systemic circuit remains constant.
• C. Pressure in the pulmonary vein increases.
• D. Increased turbulence develops in the large systemic arteries.
• E. Turbulence develops in the large systemic veins.

INSTRUCTIONS for questions 12 and 13: Answer true or false:

12. If turbulence develops in a portion of the vasculature where it did not previously exist, a greater ΔP is necessary to maintain normal flow across the affected area.

13. DELETED.

Purpose of questions 14-15: The importance of the La Place relationship in determining tension in the vessel wall:

INSTRUCTIONS for questions 14: Based on information in the following figure select the one best answer.

14. In the above figure, tension in the walls of two vessels, X & Y, of equal length and with equally thick walls is plotted as a function of transmural pressure. Based on this information, vessel X:

• A. has a smaller diameter than Y.
• B. has a larger diameter than Y.
• C. is more compliant than Y.
• D. is displaying less active contraction than Y.
• E. has less collagen in its wall than Y.

15. An aortic aneurysm is more likely to burst than a normal aorta because:

• A. transmural pressure in the distended region is greater than normal.
• B. wall tension in the distended region is greater than normal.
• C. intraluminal pressure in the distended region is greater than normal.

15 continued: In what plane of the vessel does wall tension act? Choose one:

• A. at right angles to the circumference of the vessel.
• B. on the circumference of the vessel.
• C. on the long axis of the vessel.

Purpose: Questions 16-18: The importance of compliance as a characteristic of blood vessels:

INSTRUCTIONS: Use the figure below to answer question 16-18.

16. As transmural pressure is increased from 25 to 35 mmHg, vessel _______ is most compliant, and as transmural pressure is increased from 75 to 100 mmHg, vessel _______ is most compliant.

• A. X X
• B. X Y
• C. Y Y
• D. Y X

17. Vessel X is typical of a _________, and vessel Y is typical of a __________.

• A. large artery large vein
• B. large vein large artery
• C. arteriole large vein
• D. capillary venule

18. Starting at a volume corresponding to a transmural pressure of 25 mm Hg, the volume in each vessel is increased by 10%. In response to this increase in volume, the walls of which vessel (X or Y in the figure above) store the most potential energy?

Purpose of questions 19-23: Practice in determining resistance in vascular circuits, and in determining transmural pressures

INSTRUCTIONS: The figure below contains information necessary to solve questions 19-23. The hand-written numbers at various points within the vascular circuit are mean blood pressures in mmHg. Note that all are greater than atmospheric. The intrathoracic pressure (also referred to as intrapleural pressure) is less than atmospheric. Consider the cardiac output to be 5.0 L/min.

Figure is modified from Circulatory Physiology (2nd edition) by J.J. smith and J.P. Kampine. Williams and Wilkins 1984.

19. What is the resistance to flow in the systemic circuit of this individual?

20. What is the resistance to flow in the pulmonary circuit of this individual?

21. What is the transmural pressure across the wall of the pulmonary artery? Contrast this to intraluminal pressure in the pulmonary artery. During inspiration, intrapleural pressure decreases. What effect does this have on transmural pressure in the right atrium? What effect does this have on venous return to the right atrium and right ventricle?

22. Assuming the mean intraluminal pressure of the pulmonary veins is 8 mmHg, what is the transmural pressure across the walls of the pulmonary veins?

23. What is the transmural pressure across the wall of a systemic capillary?

INSTRUCTIONS FOR NUMBER 24: Select the correct choice given in parentheses:

24. "Blood pressure" as measured by an indwelling arterial catheter is actually a measure of (osmotic pressure) (intraluminal pressure) (transmural pressure).

DIRECTIONS 25-27: Select the one best answer.

25. The mean arterial pressure of a person who is standing up is highest at the: (Hint: consider the effect of gravity.)

• A. femoral artery
• B. dorsalis pedis artery ( an artery in the feet)
• C. radial artery (an artery in the arms)
• D. cerebral artery
• E. aorta

25. Continued. Would the answer change if the question referred to systolic arterial pressure?

26. A pattern of turbulent rather than laminar flow in a systemic artery:

• A. is more likely to occur in the aorta than in the femoral artery.
• B. is less likely to occur when there is a reduction in blood viscosity, as in anemia.
• C. results in a lower pressure gradient for a given flow.
• D. is associated with flow in distinct layers.

27. Over a period of 15 minutes, a normal human adult is given an intravenous infusion of 0.5 liters of whole blood. At the end of the infusion, the largest percentage of this infused blood will be in the subject's (pulmonary vasculature, left ventricle, systemic arteries, systemic capillaries, systemic veins, right ventricle) Choose one.

Purpose of questions 28-32: More practice with Poiseuille.

Indicate which of the following statements are true and which are false.

28. The blood volume of the systemic veins is approximately equal to the blood volume of the entire pulmonary circulation.

29. Doubling the radius of a vessel will alter resistance more than doubling the length of a vessel.

30. The large pressure drop that occurs between the beginning and the end of the arterioles is related to the large resistance in these vessels.

31. As blood flows from the aorta peripherally to the arterioles, total cross sectional area of the vessels decreases.

32. Adding a resistance in series will always increase the overall resistance in the circuit.

33. Adding the new circuit shown with dotted lines in the figure below will (increase) (decrease) (not change) the resistance to flow between points A and B.

34. What percentage of cardiac output is pulmonary blood flow?

A. 0.5%

B. 10%

C. 50%

D. 75%

E. 100%

The following case is modified from R.S. Alexander, Case studies in medical physiology, Little Brown and Co, Boston, 1977. The case will be discussed as part of the first cardiovascular problem set, but you may wish to review it as you learn more cardiovascular physiology.

A 27-year-old unemployed male appeared at the clinic complaining of throbbing headaches. His blood pressure was 184/52, his pulse was 70 beats/min and chest examination demonstrated an enlarged heart. On auscultation, a high pitched systolic murmur and an accentuated second heart sound (S2) were heard over the base of the heart. In completing the physical examination, a scar was seen on the inner aspect of the thigh. Palpation revealed a strong "thrill" in the area of the scar. The patient initially dismissed this scar as an "accident", but on closer questioning, admitted that it was the result of a gunshot wound. The bullet had not lodged in the tissue, and he was able to treat the wound with first-aid measures. At the time of the incident, he had not sought medical attention, because he did not wish to reveal the circumstances under which he received the wound. The patient was admitted to surgical service.

1. What is the patient's pulse pressure and mean arterial pressure? How do these values compare to normal?
2. What is a thrill? What causes a thrill? What might be causing the thrill in this patient? (Additional measurements reveal that the patient's right atrial pressure is 6 mmHg, and his cardiac output is about twice normal.)
3. Knowing the above, the patient's stroke volume is (normal, about half the normal value, about twice the normal value)? The patient's systemic peripheral resistance is (normal, about half normal, about twice normal)?
4. What is the cause of the high pitched systolic murmur over the base of the heart?
5. What causes the second heart sound (S2) to be "accentuated" (louder than normal)?
6. What caused the patient's heart to enlarge?
7. What might be the cause of the patient's throbbing headaches?