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Old 05-22-2010
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Heart Increased coronary blood flow in aortic stenosis

A 48-year-old man complaining of chest pain is brought to the emergency room. Physical examination followed by echocardiography demonstrates aortic stenosis. His coronary blood flow is increased. Which of the following is the most likely explanation for the increased coronary blood flow in this individual?
A. Decreased left ventricular oxygen consumption
B. Decreased left ventricular pressure
C. Decreased left ventricular work
D. Increased cardiac tissue adenosine concentration
E. Increased cardiac tissue oxygen concentration
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Old 05-22-2010
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Default D

D. Increased cardiac tissue adenosine concentration

adenosine stimulates A1 & A2 adenosine receptors...inhibit adenyl cyclase...so increases ATP...
this ATP stimulate K+ channels....hyperpolarises smooth mus. surrounding blood vessels...leading to vasodilatation
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Old 05-22-2010
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Blood flow through the coronary circulation is regulated almost entirely by the
metabolic requirements of the cardiac muscle. When the oxygen consumption of the heart increases, a larger
than normal proportion of the adenosine triphosphate (ATP) in the heart muscle cells degrades to adenosine.
The adenosine then dilates the coronary blood vessels, increasing oxygen delivery to an adequate level. In this
way, the coronary blood flow increases in direct proportion to the oxygen consumption of the heart.
In aortic stenosis, the left ventricular pressure (choice B) becomes excessively high because the resistance of
the aortic valve orifice is higher than normal. This increase in left ventricular pressure increases the work load
on the left ventricle (choice C) because the heart now pumps blood with an elevated left ventricular pressure.
The increased work load on the heart requires a greater consumption of oxygen (choice A). Under these
conditions of increased cardiac work and increased oxygen consumption, one expects the cardiac tissue
oxygen concentration (choice E) to be lower than normal.

Qbank explanation
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Cardiovascular-, Pathology-, Physiology-, Step-1-Questions

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