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Free USMLE STEP1 Exam Braindumps (page: 104)

Page 42 of 213
PDF with 845 Questions

A 71-year-old man was admitted to the hospital after getting very dizzy upon rising from the toilet seat. At that time his pulse was racing and he remembers that his stool looked very different than usual. Over the last 4 or 5 weeks before the incident, the patient self-medicated with high-dose ibuprofen three times a day to control some pain in his hips. What is the mechanism of action for nonsteroidal anti-inflammatory drugs (NSAIDs) to cause gastrointestinal (GI) bleeding?

  1. they inhibit arachidonic acid synthesis
  2. they inhibit bradykinin synthesis
  3. they inhibit cyclooxygenase
  4. they inhibit histamine synthesis
  5. they promote prostaglandin synthesis

Answer(s): C

Explanation:

NSAIDs inhibit cyclooxygenase and consequently inhibit (not promote, choice E) synthesis of prostaglandins. In the stomach, prostaglandins have a cytoprotective effect through inhibition of acid secretion, enhancement of mucosal blood flow, and stimulation of bicarbonate and mucus secretion.
Inhibiting these processes can cause stomach ulcers and bleeding such as described in the case.
Arachidonic acid (choice A) is not directly affected by NSAIDs--it is turned into prostaglandin by
the action of cyclooxygenases. NSAIDs do not regulate bradykinin and histamine synthesis (choices B and D).



A 52-year-old man has a history of anginal pain that until recently was responsive to nitrates. He is now evaluated for possible angioplasty. The graph in below figure shows the ECG of this patient. Blood flow across the mitral valve is largest around which indicated point in this ECG tracing?

  1. A
  2. B
  3. C
  4. D
  5. E

Answer(s): E

Explanation:

The most rapid filling of the ventricles occurs in early diastole, immediately after opening of the atrioventricular valves. This happens after the repolarization phase (T wave) and resulting relaxation of the cardiac ventricular muscle. Excitation of the atria (choice A) also results in increased blood flow into the ventricles, occurring around choice B. However, the flow at that time is less than during early diastole.
Ventricular contraction begins with the QRS complex (choice C) and lasts until the end of the T wave (choice D). During this time, the mitral and tricuspid valves are closed.



The graph in below figure shows the pressurevolume curve of the left ventricle of this patient (shaded area). The pressurevolume curve of a normal subject is shown for comparison (broken lines). Compared to normal, which term best describes this patient's heart?

  1. decreased afterload
  2. decreased preload
  3. decreased stroke volume
  4. increased force of contraction
  5. increased preload

Answer(s): D

Explanation:

Note that the end-diastolic volume of this patient is the same as that of a normal subject. Because the patient's stroke volume is larger than that of a normal subject, the force of contraction must also be larger.
This could be due to increased sympathetic tone or to the fact that the patient took inotropic medications.
The volume remaining after the ventricular contraction is correspondingly smaller compared to normal.
Preload (choices B and E) equals end-diastolic volume and is the same in the patient and normal subjects.
Afterload (choice A) is equal to arterial pressure. Both afterload and stroke volume (choice C) are larger in this patient compared to normal.



The graph in below figure shows the jugular vein pressure curve of this patient. If the first heart sound occurs between letters C and D, which part of the curve represents the atrial contraction?

  1. peak A
  2. peak C
  3. peak D
  4. trough B
  5. trough E

Answer(s): B

Explanation:

below figure shows the jugular vein pressure curve. Pressure in the jugular vein reflects atrial pressure and is highest during the atrial contraction (named the "a wave"). The "v wave" (choice A) represents the rise in atrial pressure before the tricuspid valve opens during diastole. The "y notch" (choice D) is due to the fall in atrial pressure during the ventricular filling phase. The "c wave" (choice C) is due to the rise in atrial pressure produced by the bulging of the tricuspid valve during isovolumetric contraction of the right ventricle. The "x notch" (choice E) coincides with the ventricular ejection phase.



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