Department of Physiology: CVS Physiology-Critical thinking

1. Can you tell why the cardiac output increases: a. soon after eating b. during a hot water bath? c. during exposure to a high ambient temperature d. during pregnancy e. during exercise f. in anxiety and excitement g. in hypoxia h. in hyperthyroidism i. in anaemia

2. For the determination of cardiac output by Fick’s principle, why is it better to collect the venous blood sample from the right ventricle than from the right atrium?

3. For the .determination of cardiac output by Fick’s principle, which is the ideal site for collecting the arterial blood sample?

4. Can you think of a real life situation resembling a heart-lung preparation?

5. What is the genesis of Korotkow’s sounds heard during measurement of blood pressure?

6. In spite of being so thin, why don’t the capillaries normally rupture?

7. Why is an injury to the jugular vein in the neck life-threatening?

8. Why is injury to subdural venous sinuses dangerous?

9. Can you explain why:

a. electrical stimulation of the carotid sinus nerve or aortic nerve produces a fall in blood pressure?

b. sectioning of the sino-aortic nerves produces a rise in blood pressure?

10. What do you think will be the effect of clamping the external and internal carotid arteries above the level of the carotid sinus?

11. Why do some people get bradycardia or even a fainting fit if they wear a tight collar?

12. Explain why the walls of the ventricles are thicker than the walls of the atria.

13. In most tissues, peak blood flow occurs during systole and decreases during diastole. In heart tissue, however, the opposite is true, and peak blood flow occurs during diastole. Explain this difference.

14. Explain why it is more efficient for contraction of the ventricles to begin at the apex of the heart than at the base.

15. Predict the consequences for the heart’s pumping effectiveness if numerous ectopic foci in the ventricles produce action potentials.

16. A patient has tachycardia. Would you recommend a drug that prolongs or shortens the plateau of cardiac muscle cell action potentials?

17. Many endurance-trained athletes have a decreased resting heart rate, compared with that of nonathletes. Explain why an endurance-trained athlete’s resting heart rate decreases rather than increases.

18. A doctor lets you listen to a patient’s heart with a stethoscope at the same time that you feel the patient’s pulse. Once in a while, you hear two heartbeats very close together, but you feel only one pulse beat. Later, the doctor tells you that the patient has an ectopic focus in the right atrium. Explain why you hear two heartbeats very close together. The doctor also tells you that the patient exhibits a pulse deficit (the number of pulse beats felt is fewer than the number of heartbeats heard). Explain why a pulse deficit occurs.

19. Explain why it is sufficient to replace the ventricles, but not the atria, in artificial heart transplantation.

20. A friend tells you an ECG revealed that her son has a slight heart murmur. Should you be convinced that he has a heart murmur? Explain.

21. An experiment on a dog was performed in which the mean arterial blood pressure was monitored before and after the common carotid arteries was partially clamped (at time A). The results are graphed here: Explain the change in mean arterial blood pressure. (Hint: Baroreceptors are located in the internal carotid arteries, which are superior to the site of clamping of the common carotid arteries.)

22. During hemorrhagic shock (caused by loss of blood), blood pressure may fall dramatically, although the heart rate is elevated. Explain why blood pressure falls despite the increase in heart rate.

23. What is the physiological significance of AV delay?

24. What is the applied significance of knowing that upstroke of the action potential depends on sodium influx in myocardial cells but it depends on calcium influx in nodal tissue?

25. Does skeletal muscle follow all or none law?

26. How is it that repeated stimulation of cardiac muscle gives an all or none response in one experiment and staircase phenomenon in another experiment?

27. Why is the sequence of repolarization in ventricles different from the sequence of depolarization?

28. Why is sinus arrhythmia accentuated in voluntary hyperventilation and breath holding, and why is it abolished during exercise?

29. Why is ventricular fibrillation more dangerous than atrial fibrillation?

30 Why is the ventricular rhythm much faster than the idioventricular rhythm in atrial fibrillation?

31. Karen is taking the medication verapamil, a drug that blocks the calcium channels in cardiac muscle cells. What effect should this medication have on Karen’s stroke volume?

32. Vern is suffering from cardiac arrhythmias and is brought into the emergency room of a hospital. In the emergency room he begins to exhibit tachycardia and as a result loses consciousness. Explain why Vern lost consciousness.

33. The following measurements were made on two individuals (the values recorded remained stable for one hour): Person 1: heart rate, 75 bpm; stroke volume, 60 mL Person 2: heart rate, 90 bpm; stroke volume, 95 mL. Which person has the greater venous return? Which person has the longer ventricular filling time?

34. Jolene awakens suddenly to the sound of her alarm clock. Realizing that she is late for class, she jumps to her feet, feels light-headed, and falls back on her bed. What probably caused this reaction? Why doesn’t this happen all the time?

35. People with allergies commonly take antihistamines with decongestants to relieve their symptoms. The container warns that individuals who are being treated for high blood pressure should not take the medication. Why not?

36. Bob is sitting outside on a warm day and is sweating profusely. Mary wants to practice taking blood pressures, and he agrees to play the patient. Mary finds that Bob’s blood pressure is elevated, even though he is resting and has lost fluid from sweating. (She reasons that fluid loss should lower blood volume and, thus, blood pressure.) Why is Bob’s blood pressure high instead of low?

37. If you must stand all day, why do shoes that are loose in the morning feel so tight by evening?

38. What causes varicose veins to develop? Why do some pregnant women develop them and others do not?

39. Automatic external defbrillators (AEDs) can be found in airports and other public places. These are for heart emergencies, such as heart attacks. Should they be used only by a paramedic?

40. Kim Sung was told that her baby was born with a hole in the upper chambers of his heart. Is this something Kim Sung should worry about?

41. Michael was brought into the emergency room suffering from a gunshot wound. He is bleeding profusely and exhibits the following: systolic blood pressure is 40 mmHg; weak pulse of 200 beats per minute; cool, pale, and clammy skin. Michael is not producing urine but is asking for water. He is confused and disoriented. What is his diagnosis and what, specifically, is causing these symptoms?

42. Maureen’s job entails standing on a concrete floor for 10-hour days on an assembly line. Lately she has noticed swelling in her ankles at the end of the day and some tenderness in her calves. What do you suspect is Maureen’s problem and how could she help counteract the problem?

43. Gerald recently visited the dentist to have his teeth cleaned and checked. During the cleaning process, Gerald had some bleeding from his gums. A couple of days later, Gerald developed a fever, rapid heartbeat, sweating, and chills. He visited his family physician who detected a slight heart murmur. Gerald was given antibiotics and continued to have his heart monitored. How was Gerald's dental visit related to his illness?

44. Un-athletic Sylvia makes a resolution to begin an exercise program. She tells you that she wants to make her heart “beat as fast as it can” during exercise. Explain to her why that may not be a good idea.

45. Mr. Perkins is a large, 62-year-old man with a weakness for sweets and fried foods. His idea of exercise is walking to the kitchen for more potato chips to eat while he is watching sports on television. Lately, he's been troubled by chest pains when he walks up stairs. His doctor told him to quit smoking and scheduled a cardiac angiography for next week. What is involved in performing this procedure? Why did the doctor order this test?

46. The stroke volume ejected on the next heartbeat after a premature ventricular contraction (PVC) is usually larger than normal. Can you explain why? (Hint: At a given heart rate, the interval between a PVC and the next normal beat is longer than the interval between two normal beats.)

47. Trained athletes usually have lower resting heart rates than normal (for example, 50 beats per minute in an athlete compared to 70 beats per minute in a sedentary individual). Considering that the resting CO is 5000 mL per minute in both trained athletes and sedentary people, what is responsible for the bradycardia of trained athletes?

48. During fetal life, because of the tremendous resistance offered by the collapsed, non-functioning lungs, the pressures in the right half of the heart and pulmonary circulation are higher than those in the lef half of the heart and systemic circulation, a situation that reverses after birth. Also in the fetus, a vessel called the ductus arteriosus connects the pulmonary artery and aorta as these major vessels both leave the heart. Te blood pumped out by the heart into the pulmonary circulation is shunted from the pulmonary artery into the aorta through the ductus arteriosus, bypassing the nonfunctional lungs. What force is driving blood to ﬂow in this direction through the ductus arteriosus? At birth, the ductus arteriosus normally collapses and eventually degenerates into a thin, ligamentous strand. On occasion, this fetal bypass fails to close properly at birth, leading to a patent (open) ductus arteriosus. In what direction would blood ﬂow through a patent ductus arteriosus? What possible outcomes would you predict might occur as a result of this blood ﬂow?

49. There are two branches of the bundle of His, the right and left bundle branches, each of which travels down its respective side of the ventricular septum. Occasionally, conduction through one of these branches becomes blocked (so-called bundle-branch block). In this case, the wave of excitation spreads out from the terminals of the intact branch and eventually depolarizes the whole ventricle, but the normally stimulated ventricle completely depolarizes a considerable time before the ventricle on the side of the defective bundle branch. For example, if the left bundle branch is blocked, the right ventricle will be completely depolarized two to three times more rapidly than the left ventricle. How would this defect aﬀect the heart sounds?

50. Occasionally a child is born with a defective aortic valve that is both stenotic and insufficient. The abnormally shaped valve leaﬂets neither open nor close properly. List the sequence of sounds that would be heard when listening to the heart with a stethoscope, taking into account the timing and type of murmur(s).

51. During coronary bypass surgery, a piece of vein is often removed from the patient’s leg and surgically attached within the coronary circulatory system so that blood detours, through the vein, around an occluded coronary artery segment. Why must the patient wear, for an extended period after surgery, an elastic support stocking on the limb from which the vein was removed?

52. A classmate who has been standing still for several hours working on a laboratory experiment suddenly faints. What is the probable explanation? What would you do if the person next to him tried to get him up?

53. A drug applied to a piece of excised arteriole causes the vessel to relax, but an isolated piece of arteriolar muscle stripped from the other layers of the vessel fails to respond to the same drug. What is the probable explanation?

54. Children who suﬀer from protein malnutrition because their diets are high in starch and low in protein (as in poor countries with limited food supply) often develop kwashiorkor. This condition is characterized among other things by a pronounced, protruding belly caused by a ﬂuid-filled abdominal cavity (called ascites), although the rest of the body is “skin and bones.” What causes the markedly distended abdomen?

55. Why is the risk for developing deep venous thrombosis (DVT) (abnormal formation of blood clots, especially in the deep veins of the legs) increased during a long airplane ﬂight? What can you do while on board to decrease your risk?