Updated: 12/16/2016

Oxygen-Hemoglobin Dissociation Curve

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Overview 
Oxygen-Hemoglobin Dissociation Curve
  • Oxygen-hemoglobin dissociation curve
    • sigmoidal shape is characteristic of positive cooperativity
      • binding of 1 O2 molecule to 1 subunit of deoxyhemoglobin increases affinity for O2 in adjacent subunits
    • P50 is PO2 at which hemoglobin is 50% saturated
      • ↑ P50↓ hemoglobin affinity for O2
        • 50% saturation achieved at higher-than-normal P50
      • ↓ P50↑ hemoglobin affinity for O2
        • 50% saturation achieved at lower-than-normal P50
  • Loading and unloading of oxygen 
    • in lungs
      • PaO2 ≈ 100 mm Hg
      • hemoglobin % saturation ≈ 100%
      • facilitates maximal O2 loading into arterial blood in lungs
    • in peripheral tissues
      • PvO2 ≈ 40 mm Hg
      • hemoglobin % saturation ≈ 75%
      • facilitates O2 unloading into peripheral tissues
  • Shift to right
    • mechanism
      • ↑ P50 ↓ hemoglobin affinity for O2↑ O2 unloading
    • causes
      • ↑ PCO2, ↓ pH (Bohr Effect)
        • ↑ PCO→ ↑ H+ → ↓ pH
          • CO2 + H2 H2CO3 H+ + HCO3-
            • ↑ PCO2 equilibrium reaction shifts right
              • Le Chatelier's principle
        • CO2, H+ bind hemoglobin and stabilize low O2 affinity T (taut) state
          • ↓ hemoglobin affinity for O2 ↑ O2 unloading
            • e.g., exercise ↑ PCO2, ↓ pH
              • ↑ O2 unloading ensures O2 delivery meets O2 demand in skeletal muscle
      • ↑ temperature
        • e.g., ↑ tissue metabolism ↑ temperature
      • ↑ 2,3-bisphosphoglycerate (2,3-BPG)
        • high altitude hypoxemia ↑ synthesis of 2,3-BPG
        • 2,3-BPG binds hemoglobin and stabilizes low O2 affinity T (taut) state
          • ↓ hemoglobin affinity for O2 ↑ O2 unloading
  • Shift to left 
    • mechanism
      • ↓ P50↑ hemoglobin affinity for O2 ↓ O2 unloading
    • causes
      • ↓ PCO2, ↑ pH (Bohr Effect)
        • ↓ PCO→ ↓ H+ → ↑ pH
        • CO2, H+ stabilizes high O2 affinity R (relaxed) state
          • ↑ hemoglobin affinity for O2 → ↑ O2 loading
        • conversely, O2  decreases Hb affinity for CO2/H (Haldane effect)
      • ↓ temperature
        • ↓ tissue metabolism → ↓ temperature
      • ↓ 2,3-bisphosphoglycerate (2,3-BPG)
      • hemoglobin F
        • fetal hemoglobin
        • 2 α subunits and 2 γ subunits (α2γ2)
          • ↑ affinity for O2, ↓ affinity for 2,3-BPG
            • facilitates O2 delivery from mother to fetus
 

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Questions (1)

(M1.PL.14.25) A 67-year-old male is brought in by EMS after being found unconscious on the first floor of a burning building. On exam, his respiratory rate is 14 breaths/min with scattered wheezes. He has no evidence of any burns, but dark soot is caked around much of his face (see Figure A). Suspecting inhalational injury, you expect this man's oxygen-hemoglobin curve will be: Tested Concept

QID: 100090
FIGURES:
1

Unchanged, due to the fact that carbon monoxide (CO) is largely unbound and dissolved in plasma

0%

(0/71)

2

Shifted right, due to strong competition between CO and O2 for binding

15%

(11/71)

3

Shifted left, due to carbon monoxide binding

75%

(53/71)

4

Shifted left, due to metabolic acidosis in tissues

3%

(2/71)

5

Shifted right, due to decreased affinity for oxygen

1%

(1/71)

M 1 D

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