Coronary blood flow regulation — MCQs

A peripheral artery is found to have 50% stenosis (50% reduction in cross-sectional area). Therefore, compared to a normal artery with no stenosis, by what factor has the flow of blood been decreased?

During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?

In the coronary steal phenomenon, vessel dilation is paradoxically harmful because blood is diverted from ischemic areas of the myocardium. Which of the following is responsible for the coronary steal phenomenon?

A 27-year-old man is brought to the emergency department after a motorcycle accident 30 minutes ago. He was found at the scene of the accident with a major injury to the anterior chest by a metallic object that was not removed during transport to the hospital. The medical history could not be obtained. His blood pressure is 80/50 mm Hg, pulse is 130/min, and respiratory rate is 40/min. Evaluation upon arrival to the emergency department reveals a sharp metal object penetrating through the anterior chest to the right of the sternum at the 4th intercostal space. The patient is taken to the operating room immediately, where it is shown the heart has sustained a major injury. Which of the following arteries supplies the part of the heart most likely injured in this patient?

A 60-year-old male engineer who complains of shortness of breath when walking a few blocks undergoes a cardiac stress test because of concern for coronary artery disease. During the test he asks his cardiologist about what variables are usually used to quantify the functioning of the heart. He learns that one of these variables is stroke volume. Which of the following scenarios would be most likely to lead to a decrease in stroke volume?

A 54-year-old man is brought to the emergency department 1 hour after the sudden onset of shortness of breath, severe chest pain, and sweating. He has hypertension and type 2 diabetes mellitus. He has smoked one pack and a half of cigarettes daily for 20 years. An ECG shows ST-segment elevations in leads II, III, and avF. The next hospital with a cardiac catheterization unit is more than 2 hours away. Reperfusion pharmacotherapy is initiated. Which of the following is the primary mechanism of action of this medication?

During a clinical study evaluating the effects of exercise on muscle perfusion, 15 healthy individuals perform a 20-minute treadmill run at submaximal effort. Before and after the treadmill session, perfusion of the quadriceps muscle is evaluated with contrast-enhanced magnetic resonance imaging. The study shows a significant increase in muscle blood flow per unit of tissue mass. Which of the following local changes is most likely involved in the observed change in perfusion?

A 32-year-old man presents to his primary care physician because he has been experiencing intermittent episodes of squeezing chest pain and tightness. He says that the pain is 8/10 in severity, radiates to his left arm, and does not appear to be associated with activity. The episodes started 3 months ago and have been occurring about twice per month. His past medical history is significant for migraines for which he takes sumatriptan. Physical exam reveals no abnormalities and an EKG demonstrates sinus tachycardia with no obvious changes. An angiogram is performed to evaluate coronary artery blood flow. During the angiogram, a norepinephrine challenge is administered and blood flow is observed to decrease initially; however, after 2 minutes blood flow is observed to be increased compared to baseline. Which of the following substances is most likely responsible for the increased blood flow observed at this later time point?

A 35-year-old man presents to the physician’s clinic due to episodic chest pain over the last couple of months. He is currently pain-free. His chest pain occurs soon after he starts to exercise, and it is rapidly relieved by rest. He recently started training for a marathon after a decade of a fairly sedentary lifestyle. He was a competitive runner during his college years, but he has only had occasional exercise since then. He is concerned that he might be developing some heart disease. He has no prior medical issues and takes no medications. The family history is significant for hypertension and myocardial infarction in his father. His vital signs include: pulse 74/min, respirations 10/min, and blood pressure 120/74 mm Hg. The ECG test is normal. The physician orders an exercise tolerance test that has to be stopped after 5 minutes due to the onset of chest pain. Which of the following contributes most to the decreasing cardiac perfusion in this patient's heart?

A 44-year-old man is brought to the emergency department 45 minutes after being involved in a high-speed motor vehicle collision in which he was the restrained driver. On arrival, he has left hip and left leg pain. His pulse is 135/min, respirations are 28/min, and blood pressure is 90/40 mm Hg. Examination shows an open left tibial fracture with active bleeding. The left lower extremity appears shortened, flexed, and internally rotated. Femoral and pedal pulses are decreased bilaterally. Massive transfusion protocol is initiated. An x-ray of the pelvis shows an open pelvis fracture and an open left tibial mid-shaft fracture. A CT scan of the head shows no abnormalities. Laboratory studies show: Hemoglobin 10.2 g/dL Leukocyte count 10,000/mm3 Platelet count <250,000/mm3 Prothrombin time 12 sec Partial thromboplastin time 30 sec Serum Na+ 125 mEq/L K+ 4.5 mEq/L Cl- 98 mEq/L HCO3- 25 mEq/L Urea nitrogen 18 mg/dL Creatinine 1.2 mg/dL The patient is taken emergently to interventional radiology for exploratory angiography and arterial embolization. Which of the following is the most likely explanation for this patient's hyponatremia?