Use the Oxygen-Hb dissociation curve below to assist in the following questions:

From the Hb-oxygen dissociation curve, going from an alveolar pO2 of 100 torr to 300 torr, additional loading of hemoglobin will
[ Select ]
be insignificant
triple
. This is an argument
[ Select ]
in favor of
against
giving the “normal person” pure oxygen for the purpose of increasing oxygen delivery to tissues.

Question

Use the Oxygen-Hb dissociation curve below to assist in the following questions:

From the Hb-oxygen dissociation curve, going from an alveolar pO2 of 100 torr to 300 torr, additional loading of hemoglobin will 
[ Select ]
be insignificant
triple
 . This is an argument 
[ Select ]
in favor of
against
 giving the “normal person” pure oxygen for the purpose of increasing oxygen delivery to tissues.

BlackTom AI · Accepted Answer

The oxyhemoglobin dissociation curve plateaus above about 60–80 torr, so increasing alveolar/arterial PO2 from 100 to 300 torr produces very little additional hemoglobin saturation.

1) Relevant concepts:
- The sigmoid O2–Hb dissociation curve: steep at low PO2, flat/plateaued at high PO2.
- O2 content of arterial blood (CaO2) has two components: hemoglobin-bound O2 and physically dissolved O2. Hemoglobin O2 capacity ≈ 1.34 ml O2/g Hb × [Hb] (g/dL). Dissolved O2 ≈ 0.003 ml O2/dL blood per mmHg PO2 (Henry’s law).  
2) Step-by-step reasoning and calculations:
- At a normal alveolar/arterial PO2 ≈ 100 torr, Hb saturation is ≈ 97%. At PO2 ≈ 300 torr the curve is essentially at its plateau, ≈ 100% saturation. The increment in saturation is only ≈ 3 percentage points.  
- If [Hb] = 15 g/dL, full O2 capacity = 1.34 × 15 ≈ 20.1 ml O2/dL. A 3% increase in saturation = 0.03 × 20.1 ≈ 0.6 ml O2 per 100 ml blood from extra Hb loading (intermediate step shown).  
- Dissolved O2 increases by 0.003 ml/dL/mmHg × ΔPO2 (200 mmHg) = 0.003 × 200 = 0.6 ml O2/dL.  
- Total extra O2 carried when raising PO2 100 → 300 torr ≈ 0.6 (from Hb) + 0.6 (dissolved) ≈ 1.2 ml O2 per 100 ml blood — a small absolute increase compared with total CaO2 ≈ 20 ml/dL.  
3) Why the correct answer is correct:
- The first blank: “be insignificant” — the Hb-bound increase is tiny because the curve is already near the plateau at 100 torr; thus additional hemoglobin loading is minimal.  
- The second blank: “in favor of” — although Hb loading is insignificant, raising inspired O2 to 100% does increase dissolved O2 and produces a small net rise in arterial O2 content. That small but real increase supports (is an argument in favor of) giving oxygen if the explicit goal is to increase total oxygen delivery to tissues. In other words, the curve shows Hb saturation changes are minor, but pure O2 still modestly raises total CaO2 via dissolved O2.  
4) Why other options are incorrect:
- “Triple” (or a large increase) is incorrect because the plateau means large increases in PO2 do not produce large changes in Hb saturation.  
- Choosing “against” would assert no benefit at all; but there is a measurable (albeit small) increase in dissolved O2 and total CaO2, so it can be an argument in favor for increasing delivery in some circumstances.

Conclusion: Additional hemoglobin loading will be be insignificant, and this is an argument in favor of giving the “normal person” pure oxygen to increase oxygen delivery (answer matches the provided choices).

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