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On fred link, the q about the CXR, can anyone explain each X-ray? Like what we are looking at?

http://www.usmle.org/pdfs/step-1/2014samples_step1.pdf


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98. A previously healthy 26-year-old patient develops shortness of breath over several hours during a mountain
climb at 5000 m (16,404 ft). There is no history of trauma. On examination, the point of cardiac apical
impulse is not displaced and there are widespread crackles throughout both lung fields. Which of the
following x-rays of the chest shown best represents this patient?

Answer A hypoxemia due pulomnary congestion

1. Recognize that this patient is making a "rapid ascent" up the mountain 16,000ft/(several hrs)
2. Then look at your GojanRR (It took me a while to find it) p172
3. The patient has "High Altitude Pulmonary Edema"
4. Rapid onset hypoxemia within the lung causes massive intrapulmonary shunting (vasoconstriction to push blood to other areas with better perfusion).
5. However, there are no such areas with better ventilation at this altitude and our patient is probably running to the peak.
6. All of the capillary beds coming from the right ventricle are vasoconstricted when the right ventricle contracts, therefore the right ventricle will pump harder to overcome the resistance and a exudate will cross into the lung parenchyma.
7. The CXR in plate A is showing bilateral infiltrates so this is what I would pick.

I hope this helps you! Good luck!

Thank you ....