Energy Expenditure

Direct Calorimetry

All metabolic processes produce heat

Human calorimeter - closed system

Monitored heat output

Direct Calorimetry

Indirect Calorimetry

Estimate energy expenditure from O2 uptake

5 kcal/L of O2 consumed is liberated

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

Open-Circuit Spirometry

Inhale ambient air w/ constant composition (20.93% O2, 0.03% CO2, 79.04% N2)

O2 consumption = inspired O2 - expired O2

Open-Circuit Spirometry

Portable

Bag Technique

Computerized Instrumentation

Open-Circuit Spirometry

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

Respiratory Quotient (RQ)

Determine magnitude & type of food metabolized

% contribution of lipids and CHO

Chemical composition of various CHO, fats, and proteins varies

Respiratory Quotient (RQ)

Quantity of CO2 produced / O2 consumed

RQ = VCO2 / VO2

Varies depending on the composition

Respiratory Quotient (RQ)

RQ = CO2 produced / O2 consumed

CHO C6H12O6 + 6 O2 6 CO2 + 6 H2O

RQ = 6 CO2 / 6 O2 = 1.0

Respiratory Quotient (RQ)

Lipid- C16H32O2 + 23 O2 16 CO2 + 16 H2O

RQ = 16 CO2 / 23 O2 = 0.696

RQ 0.70

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

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

Respiratory Quotient (RQ)

However, impossible to determine proteins contribution to RQ. Why?

Not completely oxidized

As a result ...

Calulate the Nonprotein RQ

Ignore protein oxidation

Calculate only CHO and Fat oxidation

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

Respiratory Exchange Ratio (RER)

RQ assumption holds true only in steady-rate conditions

Identical calculation to RQ

reflects gas exchange only

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

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

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)

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

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

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)