Energy Expenditure

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Energy Expenditure
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Direct Calorimetry

• All metabolic processes produce heat
• Human calorimeter - closed system
• Monitored heat output

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Direct Calorimetry
4
Indirect Calorimetry

• Estimate energy expenditure from O2 uptake
• 5 kcal/L of O2 consumed is liberated

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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

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Open-Circuit Spirometry

• Inhale ambient air w/ constant composition
  (20.93 O2, 0.03 CO2, 79.04 N2)
• O2 consumption inspired O2 - expired O2

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Open-Circuit Spirometry

• Portable
• Bag Technique
• Computerized Instrumentation

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Open-Circuit Spirometry
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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

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Respiratory Quotient (RQ)

• Determine magnitude type of food metabolized
• contribution of lipids and CHO
• Chemical composition of various CHO, fats, and
  proteins varies

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Respiratory Quotient (RQ)

• Quantity of CO2 produced / O2 consumed
• RQ VCO2 / VO2
• Varies depending on the composition

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Respiratory Quotient (RQ)

• RQ CO2 produced / O2 consumed
• CHO
• C6H12O6 6 O2 ? 6 CO2 6 H2O
• RQ 6 CO2 / 6 O2 1.0

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Respiratory Quotient (RQ)

• Lipid
• - C16H32O2 23 O2 ? 16 CO2 16 H2O
• RQ 16 CO2 / 23 O2 0.696
• RQ ? 0.70

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Respiratory Quotient (RQ)
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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

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Respiratory Quotient (RQ)

• However, impossible to determine proteins
  contribution to RQ. Why?
• Not completely oxidized
• As a result ...

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Calulate the Nonprotein RQ

• Ignore protein oxidation
• Calculate only CHO and Fat oxidation

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Limitations of RQ

• Cannot calculated protein use accurately
• Assume bodys 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 lt 0.70

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Respiratory Exchange Ratio (RER)

• RQ assumption holds true only in steady-rate
  conditions
• Identical calculation to RQ
• reflects gas exchange only

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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

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Nonprotein RQ

• Determine CO2 produced
• - 4.8 L CO2/g 0.13 g 0.62 L
• Determine O2 consumed
• - 6.0 L O2/g 0.13 g 0.78 L
• Determine nonprotein CO2 produced
• - 3.4 L - 0.62 L 2.78 L

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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)

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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

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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

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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 4060 lipid to CHO ratio (4.825
  kcal/L O2)