How are ventilation–perfusion ()ratios distributed throughout the lungs in an erect position?
A. High ratios predominate in the apices, and low ratios prevail in the bases.
B. High ratios occur in the bases, and low ratios are found in the apices.
C. High ratios prevail throughout the lungs.
D. Low ratios predominate throughout the lungs.
?ANS: A ?A. Correct response: In the lungs, ratios decrease from the apex to the base. In other words, the ratios decrease along a vertical gradient from the apex to the bases. When an otherwise healthy person is mechanically ventilated, the distribution of perfusion remains unchanged. However, the overall relationship is less favorable because of the tendency of ventilation to be distributed to the nondependent lung in these patients.
B. Incorrect response: See explanation A.
C. Incorrect response: See explanation A.
D. Incorrect response: See explanation A.
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