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Energy Expenditure

Energy Expenditure. Direct Calorimetry. All metabolic processes produce heat Human calorimeter - closed system Monitored heat output. Direct Calorimetry. Indirect Calorimetry. Estimate energy expenditure from O 2 uptake 5 kcal/L of O 2 consumed is liberated. Closed-Circuit Spirometry.

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Energy Expenditure

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  1. Energy Expenditure

  2. Direct Calorimetry • All metabolic processes produce heat • Human calorimeter - closed system • Monitored heat output

  3. Direct Calorimetry

  4. Indirect Calorimetry • Estimate energy expenditure from O2 uptake • 5 kcal/L of O2 consumed is liberated

  5. Closed-Circuit Spirometry • Closed system of 100% O2 - Rebreathe • Canister of KOH absorbs expired CO2 • O2 consumption = VO2i - VO2f • Effective for resting and light exercise

  6. Open-Circuit Spirometry • Inhale ambient air w/ constant composition (20.93% O2, 0.03% CO2, 79.04% N2) • O2 consumption = inspired O2 - expired O2

  7. Open-Circuit Spirometry • Portable • Bag Technique • Computerized Instrumentation

  8. Open-Circuit Spirometry

  9. Respiratory Quotient (RQ) Assumption: Exchange of O2 and CO2 measured at the lungs reflects the actual gas exchange from nutrient catabolism in the cell • steady-rate conditions

  10. Respiratory Quotient (RQ) • Determine magnitude & type of food metabolized • % contribution of lipids and CHO • Chemical composition of various CHO, fats, and proteins varies

  11. Respiratory Quotient (RQ) • Quantity of CO2 produced / O2 consumed • RQ = VCO2 / VO2 • Varies depending on the composition

  12. Respiratory Quotient (RQ) • RQ = CO2 produced / O2 consumed • CHO • C6H12O6 + 6 O2 6 CO2 + 6 H2O • RQ = 6 CO2 / 6 O2 = 1.0

  13. Respiratory Quotient (RQ) • Lipid - C16H32O2 + 23 O2 16 CO2 + 16 H2O • RQ = 16 CO2 / 23 O2 = 0.696 • RQ  0.70

  14. Respiratory Quotient (RQ)

  15. Respiratory Quotient (RQ) Protein (Albumin) C72H112N2 O22S + 77 O2 63 CO2 + 38 H2O + SO3 + 9 CO(NH2)2 • RQ = 63 CO2 / 77 O2 = 0.818 • RQ  0.82

  16. Respiratory Quotient (RQ) However, impossible to determine proteins contribution to RQ. Why? • Not completely oxidized • As a result ...

  17. Calulate the Nonprotein RQ • Ignore protein oxidation • Calculate only CHO and Fat oxidation

  18. Limitations of RQ • Cannot calculated protein use accurately • Assume body’s O2 content remains constant and CO2 exchange is proportional to its release from cells • At or near exhaustion   CO2 20 excess lactate • production of glucose in liver from AA and fats  RQ < 0.70

  19. Respiratory Exchange Ratio (RER) • RQ assumption holds true only in steady-rate conditions • Identical calculation to RQ • reflects gas exchange only

  20. Calulate the Nonprotein RQ • For each gram of excreted N (urea): - 4.8 L CO2 is produced - 6.0 L O2 is consumed If a subject: - consumes 4.0 L O2 - produces 3.4 L CO2 - excretes 0.13 g of N

  21. Nonprotein RQ • Determine CO2produced: - 4.8 L CO2/g * 0.13 g = 0.62 L • Determine O2consumed: - 6.0 L O2/g * 0.13 g = 0.78 L • Determine nonprotein CO2 produced: - 3.4 L - 0.62 L = 2.78 L

  22. Nonprotein RQ • Determine nonprotein O2 consumed: - 4.0 L - 0.78 L = 3.22 L • Overall nonprotein RQ: - 2.78 / 3.22 = 0.86 • Determine thermal equivalents (table)

  23. How much food was metabolized for energy? • Known: 3.22 L O2 consumed • Calculated nonprotein RQ: 0.86 • Table look-up - 0.62 g CHO/L O2 - 0.25 g lipid/L O2

  24. How much food was metabolized for energy? • Grams of CHO metabolized: - 3.22 L x 0.62 g/L = 2.00 grams • Grams of lipid metabolized: - 3.22 L x 0.25 g/L = 0.80 grams

  25. How much food was metabolized for energy? • How many calories were metabolized? - CHO: 2 g * 4 kcal/g = 8.0 kcal - lipid: 0.8 g * 9 kcal/g = 7.2 kcal - total: 15.2 kcal • typically assume: 40:60 lipid to CHO ratio (4.825 kcal/L O2)

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