In what manner would O2 therapy induce worsening mismatch and thus a further elevation in CO2 in a chronically hypercapnic patient?
a. By improving blood flow to poorly venti-lated alveoli
b. By decreasing blood flow to poorly venti-lated alveoli
c. Causing bronchoconstriction, which worsens gas flow to low areas
d. Causing bronchodilation, which improves gas flow to poorly ventilated alveoli
ANS: A
Oxygen breathing causes more blood flow to be directed to poorly ventilated alveoli, which takes blood flow away from well-ventilated alveoli. The key point is that when already un-der-ventilated alveoli receive additional blood flow, blood PCO2 rises further. These events can occur without a fall in overall minute ventilation.
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