Oxygen and Carbon Dioxide Physiology

Only % of total O₂ in blood is dissolved in plasma; the remaining __% is bound to hemoglobin

2%, 98%

The concentration of dissolved O₂ in plasma is calculated using the formula:
CdO₂ = ____ × PO₂

0.003

Why is dissolved O₂ such a small contributor to total blood oxygen content?

O₂ has low solubility in plasma

The formula for O₂ bound to hemoglobin is CHbO₂ = ____ × 1.34 × ____

[Hb], SO₂ (decimal)

Why is hemoglobin the main carrier of oxygen rather than plasma?

Hb has a massive carrying capacity, whereas plasma dissolves very little O₂

Calculate dissolved oxygen content if PO₂ = 80 mmHg

CdO₂ = 0.003 × 80 = 0.24 mL/dL

Calculate O₂ bound to Hb if [Hb] = 14 g/dL and SO₂ = 90%

CHbO₂ = 14 × 1.34 × 0.90 = 16.9 mL/dL

Calculate CaO₂ if CdO₂ = 0.26 and CHbO₂ = 18.5.

CaO₂ = 0.26 + 18.5 = 18.76 mL/dL

Calculate CvO₂ if CdO₂ = 0.12 and CHbO₂ = 14.6

CvO₂ = 0.12 + 14.6 = 14.72 mL/dL

Calculate C(a–v)O₂ if CaO₂ = 20 and CvO₂ = 15

C(a–v)O₂ = 20 – 15 = 5 mL/dL (normal)

Formula for O₂ Extraction Ratio (O₂ER)

O₂ER = C(a–v)O₂ / CaO₂

Calculate O₂ER if CaO₂ = 19 and C(a–v)O₂ = 5

O₂ER = 5 / 19 = 0.26 (26%)

Each hemoglobin molecule consists of ___ heme groups and ___ globin chains.

4, 4

What does the Fe²⁺ molecule inside the heme group do?

Reversibly binds O₂

Define cooperative binding

Binding of one O₂ increases affinity for the next; release of one O₂ promotes additional release

Which state has higher affinity for oxygen: Tense (T) or Relaxed (R)?

Relaxed (R)

Define P50

The PO₂ at which Hb is 50% saturated (≈ 27 mmHg normally)

What does a RIGHT shift indicate?

↓ affinity for O₂ → easier unloading → ↑ P50

What does a LEFT shift indicate?

↑ affinity for O₂ → harder unloading → ↓ P50

Name 4 causes of a rightward shift

↑ CO₂, ↑ H+ (↓ pH), ↑ temperature, ↑ 2,3-DPG

Name 4 causes of a leftward shift

↓ CO₂, ↓ H+, ↓ temperature, ↓ 2,3-DPG

Why do shifts affect the dissociation portion more than the top?

Because tissues rely on small PO₂ changes dramatically altering unloading

At rest, PvO₂ ≈ ___ mmHg and saturation ≈ ___%.

40 mmHg, 75%

During exercise, PvO₂ may drop to ___ mmHg and tissues extract up to ___%

20 mmHg, 70%

State the Bohr Effect

↑ CO₂ or ↑ H+ decreases Hb affinity for O₂ → promotes unloading in tissues

In alkalosis, O₂ affinity ______

Increases (left shift)

CO₂ is carried in 3 forms

dissolved in plasma

Carbamino compounds

Bicarbonate (HCO₃⁻)

The majority of CO₂ is transported as

Bicarbonate (HCO₃⁻)

State the CO₂ hydration reaction

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

How does Le Chatelier’s Principle apply in tissues?

Increased CO₂ pushes the reaction right → more HCO₃⁻ + H⁺

How does Le Chatelier’s Principle apply in lungs?

Removal of CO₂ pulls reaction left → HCO₃⁻ + H⁺ → CO₂ + H₂O

What is the chloride shift?

Movement of Cl⁻ into RBCs as HCO₃⁻ leaves to maintain electrical neutrality

Why is deoxygenated Hb a better buffer?

It binds H⁺ more effectively than oxygenated Hb

What happens if RBCs did NOT take in chloride during HCO₃⁻ export?

RBC interior would become excessively positive → inhibits transport

Define the Haldane Effect

Oxygenated Hb has reduced affinity for CO₂, promoting unloading of CO₂ in lungs

Where does the Haldane Effect matter?

In the alveoli, where O₂ loading promotes CO₂ release

What is the relationship between Bohr and Haldane?

• Bohr = tissues (↑CO₂/H+ → ↓O₂ affinity → unload O₂)

• Haldane = lungs (↑O₂ → ↓CO₂ affinity → unload CO₂)

Which effect enhances oxygen unloading in tissues?

Bohr Effect

Which effect enhances CO₂ unloading in lungs?

Haldane Effect

Why is CaO₂ primarily influenced by Hb rather than PO₂?

Because Hb carries 98% of O₂; dissolved O₂ is tiny

Explain why anemia lowers CaO₂ even if PaO₂ and SaO₂ are normal

Less Hb available → less O₂ bound despite normal saturation

Why do septic patients have LOW O₂ extraction ratios?

Cells cannot use O₂ effectively (cytopathic hypoxia)

Why does HbF shift the curve left?

Higher affinity improves placental oxygen transfer

In CO poisoning, why is CaO₂ severely reduced?

CO binds strongly to Hb → reduces available binding sites + increases affinity → less O₂ released

PO₂ = 100 mmHg

Formula: CdO₂ (mL O₂ / dL) = 0.003 × PO₂ (mmHg)

CdO₂ = 0.003 × 100 = 0.300 mL/dL

Note: small contributor to total O₂

Formula: CHbO₂ (mL/dL) = [Hb] (g/dL) × 1.34 × SO₂ (decimal)
[Hb] = 15 g/dL, SO₂ = 98% = 0.98

CHbO₂ = 15 × 1.34 × 0.98 = 19.698 → 19.70 mL/dL

Note: 1.34 mL O₂/g Hb is the carrying constant

Formula: C O₂ = CdO₂ + CHbO₂

Example (arterial): CdO₂ = 0.30, CHbO₂ = 19.70

CaO₂ = 0.30 + 19.70 = 20.00 mL/dL

Note: Use same formula for venous (CvO₂) with venous values.

PvO₂ = 40 mmHg, [Hb] = 15 g/dL, SvO₂ = 75% = 0.75

CdO₂ = 0.003 × 40 = 0.12 mL/dL

CHbO₂ = 15 × 1.34 × 0.75 = 15.075 → 15.08 mL/dL

CvO₂ = 0.12 + 15.08 = 15.20 mL/dL

Formula: C(a–v)O₂ = CaO₂ − CvO₂

Example: CaO₂ = 20.00, CvO₂ = 15.20

C(a–v)O₂ = 20.00 − 15.20 = 4.80 mL/dL

Note: Normal ≈ 4–6 mL/dL

Formula: O₂ER = C(a–v)O₂ / CaO₂ (or VO₂ / DO₂)

Example: C(a–v)O₂ = 4.80, CaO₂ = 20.00

O₂ER = 4.80 / 20.00 = 0.24 → 24%

Note: Normal ≈ 25%

Formula: DO₂ (mL/min) = Cardiac Output (L/min) × CaO₂ (mL/dL) × 10

Example: CO = 5.0 L/min, CaO₂ = 20.00 mL/dL

DO₂ = 5.0 × 20.00 × 10 = 1000 mL/min

Note: DO₂ units = mL O₂ per minute

Formula: VO₂ (mL/min) = CO (L/min) × C(a–v)O₂ (mL/dL) × 10

Example: CO = 5.0 L/min, C(a–v)O₂ = 4.80 mL/dL

VO₂ = 5.0 × 4.80 × 10 = 240 mL/min

Note: VO₂ ≈ 200–250 mL/min at rest.

Formula: O₂ER = VO₂ / DO₂

Example (use prev results): VO₂ = 240, DO₂ = 1000

O₂ER = 240 / 1000 = 0.24 (24%) — matches content-based calc.

Given: PaO₂ normal → CdO₂ ≈ 0.30. Compare [Hb] 15 vs 8 g/dL, SO₂ = 0.98.

[Hb]=15 → CHbO₂ = 15×1.34×0.98 = 19.70; CaO₂ = 0.30 + 19.70 = 20.00 mL/dL

[Hb]=8 → CHbO₂ = 8×1.34×0.98 = 10.51; CaO₂ = 0.30 + 10.51 = 10.81 mL/dL

Note: PaO₂/SaO₂ can be normal but CaO₂ halved — oxygen content depends on Hb.