NBME Cardio Question 2

[bludeviled]

5) A 72-year-old woman comes to the physician because of an episode of acute substernal chest pain that occurred while she was rushing to catch a bus. She has basilar crackles at both lung bases. S1 is normal and S2 is decreased. A grade 3/6 systolic murmur is heard best at the
upper right sternal border and radiates to the neck. The following data obtained during cardiac catheterization were taken before and during exercise:

Aortic pressure (mm Hg)
Control 130/70
Exercise 160/80

L ventricular End-diastolic volume (mL) :
Control 140
Exercise 165

L ventricular End-systolic volume (mL) :
Control 50
Exercise 58

Heart rate (/min):
Control 85
Exercise 120

While exercising, the patient has shortness of breath but no chest pain. Which of the following is the most likely cause of the shortness of breath?
A) Decreased cardiac output during exercise
B) Decreased pulmonary blood flow
C ) Increased aortic pressure
D ) Increased end-diastolic pressure of the left ventricle during exercise
E ) Tachycardia
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Murmur sounds like Aortic stenosis, so does she have trouble getting blood out and thus A) decreased Cardiac output during exercise?
but CO = 90 for control and CO =107 in exercise, so this may not be the best answer

Also i thought AS usually came with decreased pulse pressures. Her values seem rather normal. regardless I would want to go with D) or with B) - her bilateral crackles could mean pneumonia or something and cause decreased perfusion?

What does everyone else think?

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[crys20]

d- increased EDV is consis with a systolic murmor and shortness of breath. Increase EDV--. increases pulm hypertension and therefore decreases ability for enough blood to flow through lungs with the increased pressure so not enough O2 is getting to her causing shortness of breath. Edv is due to the systolic murmor, whatever its cause.
by the way i read the first answer choice as simply saying " dec CO during exc" that never happens. CO is always increased and the finding also show this. so i would elim both A and B immediatly since both are impossible.

 

[Myostatin]

a = clearly wrong from given info
b = systemic and pulmonic flow must be equal over any appreciable length of time, so must be wrong
c, e = neither would cause shortness of breath by themselves

d = crakles @ bases @ rest + systolic murmur rads to carotids + chest pain w/ exercise is most c/w late aortic stenosis. Although if pt. was having crackles at rest, in AS the BP during exercise would be expected to drop or stay constant 2/2 to outlflow obstruction and reduced systemic resistance. In any case, if lv end diastolic volume is increased in exercise, this means that the left heart preload is increased, preload ~ volume, which tells you that D must be right regardless of the underlying process, which is most likely AS.