Calculating Oxygen Exchange Rate: A Step-by-Step Guide

Given Data

• Respiratory rate: 16 breaths/min
• Tidal volume: 1.5 L/breath
• Inspired O₂ fraction (FᵢO₂): 0.20 (20%)
• Expired O₂ fraction (FₑO₂): 0.16 (16%)

Step-by-Step Calculation

1. Minute ventilation (V̇E): 16 breaths/min × 1.5 L/breath = 24 L/min.
2. O₂ inspired per minute (V̇ᵢO₂): 24 L/min × 0.20 = 4.8 L O₂/min.
3. O₂ expired per minute (V̇ₑO₂): 24 L/min × 0.16 = 3.84 L O₂/min.
4. O₂ consumption (V̇O₂): V̇ᵢO₂ – V̇ₑO₂ = 4.8 – 3.84 = 0.96 L O₂/min.
5. CO₂ production (V̇CO₂): Assuming respiratory quotient (RQ) = 0.8 (mixed diet), V̇CO₂ = RQ × V̇O₂ = 0.8 × 0.96 = 0.768 L CO₂/min.
6. Respiratory Quotient (RQ): V̇CO₂ / V̇O₂ = 0.768 / 0.96 = 0.8.

Interpretation

• RQ 0.8 indicates mixed carbohydrate/fat oxidation.
• V̇O₂ 0.96 L/min ≈ 335 kcal/hr (using 4.8 kcal/L O₂), consistent with light activity.