q5 - guest1

[ArchivalUser]

Patient A is suffering from carbon monoxide (CO) poisoning and patient B has iron deficiency anemia. Assume
that CO is binding 50% of the available O2-binding sites on the hemoglobin, and that the anemic patient has 50%
of the normal amount of hemoglobin. Patient A is more at risk of tissue hypoxia because CO causes


A. a decrease in diffusing capacity

B. a decrease in the P50 of Hb for O2

C. a greater decrease in the concentration of arterial oxygen

D. a reduced rate of O2 binding to available Hb

E. arterial hypoxemia, while anemia does not

[ArchivalUser]

BBBBBBB

[ArchivalUser]

BBB?

[ArchivalUser]

B?

[ArchivalUser]

confused between B & cc i will go 4 CCCC

[ArchivalUser]

Aimhigh Oxygen saturation is normal in case of CO toxicity i guess...

[ArchivalUser]

Explanation:

The correct answer is B. The P50 is defined as the partial pressure of oxygen necessary to bind 50% of
available hemoglobin. CO will decrease the P50 of Hb for O2. Another way of stating this is that CO left-shifts
the oxygen-hemoglobin dissociation curve. CO is deadly because it not only binds hemoglobin with a greater
affinity than does O2 (240 times better), it also left-shifts the curve, thereby making it more difficult to unload O2
in peripheral tissues.

CO will not diminish the diffusing capacity of the lung (choice A). CO is routinely used to measure diffusing
capacity.

The concentration of oxygen in arterial blood will be approximately the same for both cases (choice C). If
anything, the concentration will be slightly greater in the patient with CO poisoning because CO2 left-shifts the
curve, and therefore the available binding sites of Hb for O2 will be slightly more saturated.

CO does not change the rate of O2 binding to Hb (choice D). It does, however, bind to hemoglobin with a 240
times greater affinity than does oxygen.

Neither of these conditions will cause arterial hypoxemia (choice E).