- sleeping - replaces the RMR for infants

Caloric and Isotopic methods Flashcards by Alisa Jan Chin

What is the energy balance equation?

Energy intake = Energy expenditure ± ∆ stores

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What has to be measured when we want to involve the energy balance equation?

energy intake and expenditure

and body composition

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what are the major difficulties in measuring energy intake?

qualitative/quantitative description of intake
reliability of reference data
deliberate and unconscious bias
indirect recording for infants/toddlers

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What are the fundamental energetics of any biological system?

Energy in = Energy out ± Δ Energy content

Total work done is INDEPENDENT of pathways

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What are the possible types of energy in the body?

chemical
urinal/faecal
mechanical
electrical
thermal

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As an outcome of metabolism to result in ‘work’… what is produced?

heat

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What did Boyle investigate regarding calorimetry methods?

fire and life are combustion processes

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What did Lavoiser and Laplace investigate regarding calorimetry methods?

CO2 and heat production

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What did Magnus investigate regarding calorimetry methods?

arteries have increased O2 and decreased CO2

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What did Helmholtz investigate regarding calorimetry methods?

heat produced by isolated muscle

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What did Lavoisier (on his own) investigate regarding calorimetry methods?

digestion, PA and cold increase VO2

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What did Regnault and Reiset investigate regarding calorimetry methods?

Ratio of CO2 and O2 in gas exchange related to dietary composition

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What also defines Joule?

watts per second

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what is the SI unit of Joules?

kg/m2/s2

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What defines calorie?

the heat required to raise 1g water by 1^C

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How much is 1 kcal in J?

4.184

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What are the current 4 modern approaches to total energy expenditure?

Douglas bag - fast, but unrepresentative
Indirect calorimetry - accurate, fast, but constrained
Direct calorimetry - accurate, fast, but constrained
Doubly labelled water - accurate, free-living but slow response

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What is SMR?

sleeping

- replaces the RMR for infants

What does the classical indirect calorimetry involve?

standardised conditions
assumes steady state
BMR, RMR, SMR
studies of physiology

What are the output results from indirect calorimetry method?

oxygen uptake
carbon dioxide production
resting energy expenditure
fuel utilisation (RQ)

What is the EE formula for indirect calorimetry?

EE = 3.941 VO2 + 1.106 VCO2 - 2.17 Un

Un = urea nitrogen production

How much % is the effect of neglecting nitrogen in EE?

Give the general understanding of doubly labelled water:

uses isotopes 2^H and 18^H
traces the kinetics of H2O and CO2
estimates CO2 elimination rate

What is the key principle in doubly labelled water?

O2 in respiratory CO2 is in isotopic equilibrium with O2 in body water

What is collected in doubly labelled water method, to analyse?

blood, saliva, urine samples

What is the formula for the expression of isotopic enrichment, the mass spectrometer analysis?

δ = [R(sample) - R(reference) x 1000] DIVIDED BY R(reference)

What is the fundamental calculation for rCO2, in DLW?

rCO2 = N [k(o) - k(d)]/2 ``` N = dilution space k = rate constant ```

What is the fundamental calculation for VO2, in DLW?

VO2 = VCO2/RQ

What is the fundamental calculation for TEE, in DLW?

TEE = k(1)VO2 + K(2)VCO2

What are the assumptions of DLW?

- TBW is constant - isotopes only equilibrate with TBW - Isotopes only leave as water or CO2 - rates of influx and efflux constant during measurement - no isotopic fractionation - no tracer re-enters TBW once lost - natural isotopic levels unchanged

What are the two approaches in calculating dilution spaces (N) in DLW?

- plateau method | - back extrapolation method

What is the plateau result when isotope turnover is slow?

plateau is relatively stable

What is the plateau result when isotope turnover is fast?

- plateau occurs at specific time | - tracee intake during equilibration period is high

Which named approach reduces error in the rCO2 calculation in DLW?

Bayesian approach

Is there fractionation in DLW?

only possible in reaction not going to completion

what is the calculation for fractionation factor (f)?

(f) = [Ratio of heavy : light isotopes in product] DIVIDE BY [Ratio of heavy : light isotopes in reactant]

Explain why isotopic intake is not constant

- 2^H and 18^O occur at natural abundance levels - levels vary by diet, geographic location - Pre-dose sample provides this information

What is the random variability in DLW?

50% internal imprecision

what is the systemic variability in DLW?

- weaning in infants - expedition in adults - marked dietary interventions

How do we address the precision of EE internally, in DLW?

- calculate in relation to slopes and intercepts | - address sample times and mass spec

How do we address the precision of EE externally, in DLW?

address consistency of behaviour

What is the formula for lean mass, in regards to body composition from isotopes?

Lean mass = Total body water/lean tissue hydration

What is the formula for fat mass, in regards to body composition from isotopes?

= weight - lean mass

What is the measuring metabolisable energy intake (MEi) formula?

MEi = Total energy expenditure + energy stored