energy expenditure. direct calorimetry zall metabolic processes produce heat zhuman calorimeter -...
TRANSCRIPT
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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
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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)
Energy % kcalRER Kcal/L O2 CHO FATS0.71 4.69 0.0 1000.75 4.74 15.6 84.40.80 4.80 33.4 66.60.85 4.86 50.7 49.30.90 4.92 67.5 32.50.95 4.99 84.0 16.01.00 5.05 100.0 0.0
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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 accuratelyAssume 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
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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: 40:60 lipid to CHO ratio (4.825 kcal/L O2)