SECTION III THE CARDIONASOULAR SYSTEM Thrarboangiitis Obliterans A 50-year-old man went to see his physician because of pain in the calf muscles of both legs when he walked noderate distances,especially uphill:the pain would subside when he rested.The pain had been insidious in onset and had recently occurred more frequently,even after shorter walks.The patient had smoked three packs of cigarettes a day for the past 34 years.Physical exanination was essentially normal except for the absence of dorsalis pedis and posterior tibial pulses in both feet. X-ray examinations revealed arterial calcification of lower leg arteries and significant obstruction of the arteries abowe the knees. 1.Is the main resistance to blood flow in the patient's legs the same as in a healthy person? 2.Is the vascular spooth muscle functioning normally in this patient? 3.How would the arterioles of this patient respoed to stimulation of sympathetic nerve fibers to the legs? 4.Which ion is of greatest inportance in contraction of the vascular snooth 1scle？ 5.What is autoregulation of blood flow,and does it operate in this patient's legs? 6.In which vascular beds is the mogenic nechanisn for blood flow regulation most important in healthy individuals?In this patient? 7.How may the endothelium be involved in the local regulation of blood flow in healthy people?In this patient? 8.Why does he experience calf ruscle pain in response to noderate walking? 9.What is metabolie regulation of blood flow,and how does it apply in this patient? 10.How are his basal tone.active hyperemia:and reactive hyperemia affected?
SECTION III THE CARDIOVASCULAR SYSTEM Thromboangiitis Obliterans A 50-year-old man went to see his physician because of pain in the calf muscles of both legs when he walked moderate distances, especially uphill; the pain would subside when he rested. The pain had been insidious in onset and had recently occurred more frequently, even after shorter walks. The patient had smoked three packs of cigarettes a day for the past 34 years. Physical examination was essentially normal except for the absence of dorsalis pedis and posterior tibial pulses in both feet. X-ray examinations revealed arterial calcification of lower leg arteries and significant obstruction of the arteries above the knees. 1. Is the main resistance to blood flow in the patient's legs the same as in a healthy person? 2. Is the vascular smooth muscle functioning normally in this patient? 3. How would the arterioles of this patient respond to stimulation of sympathetic nerve fibers to the legs? 4. Which ion is of greatest importance in contraction of the vascular smooth muscle? 5. What is autoregulation of blood flow, and does it operate in this patient's legs? 6. In which vascular beds is the myogenic mechanism for blood flow regulation most important in healthy individuals? In this patient? 7. How may the endothelium be involved in the local regulation of blood flow in healthy people? In this patient? 8. Why does he experience calf muscle pain in response to moderate walking? 9. What is metabolic regulation of blood flow, and how does it apply in this patient? 10. How are his basal tone, active hyperemia; and reactive hyperemia affected?
11.What is the role of the sympathetic nerves in regulating leg blood flow? 12.Bow do resistance and capacitance vessels differ with respect to sensitivity to sympathetie nerve stimulation and to metabolic vasoactive mediators in the healthy person and in this patient? 13.Would sympathetic denervation be helpful in this patient? 14.What effect would a peripheral vasodilator,such as acetylcholine or adenosine,have on this patient? 15.What effect would a peripheral constrictor,such as norepinephrine have? 16.What is responsible for the short-term and long-term maintenance of blood pressure? 17.What would happen to the patient's respiration,blood pressure,and leg blood flow if he breathed a mixture of 10%C0,21 0.and 69%N.? 18.What would happen to his respiration,blood pressure,and leg blood flow if he breathed a nixture of 10%0:and 90%N? 19.Mascle blood vessels are under dual control (neural and local metabolic). Which of these factors predominates at rest and during exercise in the arms and legs of this patient? ANSVER 1.In the normal person.resistance to blood flov is greatest in the arterioles (resistance vessels).Bowever,in this patient the large arteries are severely blocked by disease,whereas the arterioles are probably maximally dilated because of the release of vasodilator metabolites froa the muscle as a result of inadequate blood supply. 2.The vascular smooth muscle of the arteries is damaged by the disease process, but the smooth ruscle of the arterioles is functional but relaxed because of the presence of vasodilator netabolites. 3.The arterioles of this patient would constrict in response to stimulation of the sympathetic nerve fibers to the legs,and they would also constrict in response
11. What is the role of the sympathetic nerves in regulating leg blood flow? 12. How do resistance and capacitance vessels differ with respect to sensitivity to sympathetic nerve stimulation and to metabolic vasoactive mediators in the healthy person and in this patient? 13. Would sympathetic denervation be helpful in this patient? 14. What effect would a peripheral vasodilator, such as acetylcholine or adenosine, have on this patient? 15. What effect would a peripheral constrictor, such as norepinephrine have? 16. What is responsible for the short-term and long-term maintenance of blood pressure? 17. What would happen to the patient's respiration, blood pressure, and leg blood flow if he breathed a mixture of 10% CO2, 21 % O2 and 69% N2? 18. What would happen to his respiration, blood pressure, and leg blood flow if he breathed a mixture of 10% O2 and 90% N2? 19. Muscle blood vessels are under dual control (neural and local metabolic). Which of these factors predominates at rest and during exercise in the arms and legs of this patient? ANSWER 1. In the normal person, resistance to blood flow is greatest in the arterioles (resistance vessels). However, in this patient the large arteries are severely blocked by disease, whereas the arterioles are probably maximally dilated because of the release of vasodilator metabolites from the muscle as a result of inadequate blood supply. 2. The vascular smooth muscle of the arteries is damaged by the disease process, but the smooth muscle of the arterioles is functional but relaxed because of the presence of vasodilator metabolites. 3. The arterioles of this patient would constrict in response to stimulation of the sympathetic nerve fibers to the legs, and they would also constrict in response
to norepinephrine,which is the neurohumor released by the sympathetic nerve endings in the hlood vessels. 4.Calcfum is the fon of greatest importance in contraction of vascular snooth muscle,just as it is for other smooth muscle and for skeletal and cardiac mscle. 5.Autoregulation of blood flow refers to the constancy of blood flow in the face of chanzes in perfusion pressure.In this patient,autoregulation would not operate because the resistance vessels are maximally dilated,even when the arterial pressure is high because the blockage of the leg arteries impairs blood flow. 6.The myogenic mechanisn is most important in the lower extremities,because the arteriolar constriction in response to the large hydrostatic (transmural) pressure (blood pressure plus effects of gravity in the standing position)prevents very high pressure in the leg capillaries and thereby prevents excessive capillary filtration (edema).In this patient,the myogenic nechanism would be overriddem by the metabolic dilation. 7.When stimulated by such agents as acetylcholine or ATP or by shear stress. the endothelfum can symthesize and release mitric oxide,which is a potent vasodilator.In this patient,this could occur in the undamaged sections of the large arteries and in the arterioles and capillaries. &雪ith moderate walking。the leg mscles'need for0ygen1 sincreased,甸t the blood supply,and hence the oxygen supply,is limited by the arterial obstruction. Thus ischemia of the msele occurs and elicits pain.The substance responsible for the pain is not known.but sone evidence suggests it is bradykinin and/or adenosine. 9.Metabolic regulation of blood flow is the adjustment of blood flow to the metabolic (oxygen)requirements of the tissue.Such regulation is mediated by release of endogenous vasodilator netabolites,such as adenosine.In this patient. the nechanism is operating continuously:that is,the inadequate blood flow causes vasodilator release and maxinally dilated arterioles. 10.Basal tone in arterioles is partial contraction,independent of the nerves. Active hyperemia is vasodilation in response to increased metabolic activity. whereas reactive hyperemia is vasodilation that oceurs after release of occlusion
to norepinephrine, which is the neurohumor released by the sympathetic nerve endings in the blood vessels. 4. Calcium is the ion of greatest importance in contraction of vascular smooth muscle, just as it is for other smooth muscle and for skeletal and cardiac muscle. 5. Autoregulation of blood flow refers to the constancy of blood flow in the face of changes in perfusion pressure. In this patient, autoregulation would not operate because the resistance vessels are maximally dilated, even when the arterial pressure is high because the blockage of the leg arteries impairs blood flow. 6. The myogenic mechanism is most important in the lower extremities, because the arteriolar constriction in response to the large hydrostatic (transmural) pressure (blood pressure plus effects of gravity in the standing position) prevents very high pressure in the leg capillaries and thereby prevents excessive capillary filtration (edema). In this patient, the myogenic mechanism would be overridden by the metabolic dilation. 7. When stimulated by such agents as acetylcholine or ATP or by shear stress, the endothelium can synthesize and release nitric oxide, which is a potent vasodilator. In this patient, this could occur in the undamaged sections of the large arteries and in the arterioles and capillaries. 8. With moderate walking, the leg muscles’ need for oxygen is increased, but the blood supply, and hence the oxygen supply, is limited by the arterial obstruction. Thus ischemia of the muscle occurs and elicits pain. The substance responsible for the pain is not known, but some evidence suggests it is bradykinin and/or adenosine. 9. Metabolic regulation of blood flow is the adjustment of blood flow to the metabolic (oxygen) requirements of the tissue. Such regulation is mediated by release of endogenous vasodilator metabolites, such as adenosine. In this patient, the mechanism is operating continuously; that is, the inadequate blood flow causes vasodilator release and maximally dilated arterioles. 10. Basal tone in arterioles is partial contraction, independent of the nerves. Active hyperemia is vasodilation in response to increased metabolic activity, whereas reactive hyperemia is vasodilation that occurs after release of occlusion
of an artery.In this patient,basal tone would be abolished by the petabolites, and because the arterioles are already maximally dilated (even at rest),increased muscle activity or arterial occlusion could not dilate then further. 11.Normally,the sympathetic nerves exert a tomic effect on the resistance vessels and can constrict these vessels when the nerves are reflexly activated.In this patient,there would be little if any tonic action and a limited reflex constriction because of the overriding metabolic effects. 12.Capacitance vessels are more sensitive to syrpathetie nerve stimulat ion than are resistance vessels,but capacitance vessels do not respond well to metabolites, whereas resistance vessels do.In this patient.the resistance vessels would be even less sensitive to sympathetic nerve stimulat ion because of the predominance of the metabolic vasodilation. 13.Sympathetic denervation would not he of much help because sympathetic tone has been overriddem by the action of the vasodilator metabolites. 14.A peripheral vasodilator would decrease arterial blood pressure and increase venous pressure (shift of blood from arterial to venous side of the circulation). Heart rate would reflexly increase via the baroreceptor reflex.The reduced blood pressure would make the leg symptoms worse by reducing an already inadequate blood f10w. 15.A peripheral constrictor would exaggerate the symptoms by comstricting the arterioles of the leg.This would in part be compensated by the elevated arterial blood pressure caused by comstriction of resistance vessels in other parts of the body.Heart rate would decrease reflexly in response to the increased blood pressure. 16.In the short term.the baroreceptor reflex keeps the blood pressure fairly constant,whereas in the long term,the adjustments in salt and vater excretfon (and hence blood volure)by the kidneys are of paramount importance in the regulation of blood pressure.These mechanisas also operate in this patient. 17.Inhalation of Co would (1)increase the rate and depth of respiration by stimulation of the chemoreceptors,(2)increase blood pressure by stimulation of
of an artery. In this patient, basal tone would be abolished by the metabolites, and because the arterioles are already maximally dilated (even at rest), increased muscle activity or arterial occlusion could not dilate them further. 11. Normally, the sympathetic nerves exert a tonic effect on the resistance vessels and can constrict these vessels when the nerves are reflexly activated. In this patient, there would be little if any tonic action and a limited reflex constriction because of the overriding metabolic effects. 12. Capacitance vessels are more sensitive to sympathetic nerve stimulation than are resistance vessels, but capacitance vessels do not respond well to metabolites, whereas resistance vessels do. In this patient, the resistance vessels would be even less sensitive to sympathetic nerve stimulation because of the predominance of the metabolic vasodilation. 13. Sympathetic denervation would not be of much help because sympathetic tone has been overridden by the action of the vasodilator metabolites. 14. A peripheral vasodilator would decrease arterial blood pressure and increase venous pressure (shift of blood from arterial to venous side of the circulation). Heart rate would reflexly increase via the baroreceptor reflex. The reduced blood pressure would make the leg symptoms worse by reducing an already inadequate blood flow. 15. A peripheral constrictor would exaggerate the symptoms by constricting the arterioles of the leg. This would in part be compensated by the elevated arterial blood pressure caused by constriction of resistance vessels in other parts of the body. Heart rate would decrease reflexly in response to the increased blood pressure. 16. In the short term, the baroreceptor reflex keeps the blood pressure fairly constant, whereas in the long term, the adjustments in salt and water excretion (and hence blood volume) by the kidneys are of paramount importance in the regulation of blood pressure. These mechanisms also operate in this patient. 17. Inhalation of CO2 would (1) increase the rate and depth of respiration by stimulation of the chemoreceptors, (2) increase blood pressure by stimulation of
the vasoconstrictor center in the medulla,and (3)have little reflex effect on the leg blood flow because of the local metabolites. 18.In response to hypoxia,(1)respiration would increase by stimulation of the peripheral chemoreceptors (carotid and aortic bodies),(2)blood pressure would probably not change or would increase slightly,and (3)leg blood flow would be unchanged. 19.In the normal person at rest.neural regulation of ruscle blood flow predoninates,but with exercise,the local factors supervene.In this patient the local factors predominate at rest and during exereise
the vasoconstrictor center in the medulla, and (3) have little reflex effect on the leg blood flow because of the local metabolites. 18. In response to hypoxia, (1) respiration would increase by stimulation of the peripheral chemoreceptors (carotid and aortic bodies), (2) blood pressure would probably not change or would increase slightly, and (3) leg blood flow would be unchanged. 19. In the normal person at rest, neural regulation of muscle blood flow predominates, but with exercise, the local factors supervene. In this patient the local factors predominate at rest and during exercise