USMLE Forum - Largest USMLE Community

a 68 yr old man was diagnosed with abdominal aortic anurysm sec to atherosclerosis.
Which of the following physiologic observations helps to account for the fact that 75% of the aneurysms of this patient's type are found in the
abdomen and only 25% principally involve the thorax?
/ A. Diastolic pressure is greater in the abdominal aorta in the supine position
/ B. Negative intrathoracic pressure reduces aortic wall tension in the thorax
/ C. The average blood flow in the abdominal aorta is greater than that in the thoracic aorta
/ D. The average blood pressure in the abdominal aorta is higher than that in the thoracic aorta
/ E. The average degree of turbulence in the thoracic aorta is higher than that in the abdominal aorta

My choice is B

bbb

B??

The correct answer is D. Increased blood pressure is a strong risk factor for atherosclerosis, and humans pay a price for their erect sitting and standing postures. In these postures, the abdominal aorta experiences the weight of a column of blood added to the pressure produced by the heart. In the supine posture, the pressures in the thoracic and abdominal aorta are similar. So, if an average daily pressure is taken, the abdominal aorta tends to have a significantly higher pressure than does the thoracic aorta.
Diastolic pressure (choice A) is actually greater in the thoracic aorta compared to the abdominal aorta in the supine position. However, the systolic blood pressure is greater in the abdominal aorta.
A negative intrathoracic pressure (choice B) would tend to increase transmural pressure across the wall of the thoracic aorta, and thereby increase wall tension and promote the development of aneurysms.
Blood flow (choice C) in the abdominal aorta is less than that in the thoracic aorta, because some blood leaves the aorta through its thoracic branches.
Higher turbulence (choice E) tends to predispose for atherosclerosis, and the flow in the abdominal aorta, with its many branches, tends to be more turbulent than that in the thoracic aorta; this problem is exacerbated as atherosclerotic disease advances.

good Q,thanks