Oxygen Uptake and Energy Expenditure

M.Prasad NaiduMSc Medical Biochemistry, Ph.D,.

ObjectivesUnderstand the meaning and derivation of

the oxygen uptake measurement and measurement of energy expenditure.

Perform techniques to measure oxygen uptake (O2), carbon dioxide production (CO2), and RER.

Calculate energy expenditure during exercise.

Aerobic Metabolism

O2 CO2 AIR

LUNGS

O2CO2 V/Q Lungs

Pulmonary Circulation

Heart

Muscle/Tissues

Use O2, produce CO2

ATP from CHO, Fats

VO2 Fick RelationshipVO2 (ml/min) = Q(L/min) * AVDO2

Expanded: [HR * SV] * [1.34 * [Hb] * (SaO2 - SvO2)]

SV = L blood/bt [Hb] = g Hb/100 ml blood1.34 = ml O2/gm Hb Saturations in decimal

equivalent of %

Affects of: Heart Disease? Altitude? Lung Disease? Training?

Uses:Energy expenditure, efficiency, VO2max index

of fitness, Time course of VO2 in response to work

Steady state concept

Important variables for measurement of VO2

VE or VI, FeO2, FIO2, FI CO 2, FeCO2

Assumption: N2 not produced or used by body during exercise

Convert gas volumes to STPD from ATPS(CCJ Lab Manual p. 60)

Standard Temperature Pressure DryTemperature = 0 degrees CelsiusPressure = 760 mmHg (sea level)Dry = 0% humidityEquation 1: 

VSTPD = VATPS * [(Pb - PH2O) /760] * [273/(oC + 273)]

  Note: PH2O under saturated conditions is temperature dependent (CCJ, p. 60).

  Ambient PH2O is obtained as:

 Equation 2:  Ambient PH2O = Saturated PH2O * % Relative

Humidity/100

VO2 Consumption is: volume O2 inhaled - volume O2 exhaled

Equation 3:VO2 = (VI * FIO2) - (VE * FeO2)

NOTE: VI … VE unless 100% Carbohydrate oxidized

Remember: C6H12O6 + 6O2 = 6H2O + 6CO2

Therefore: CO2 / O2 = 1

Haldane Transformation: Allows us to calculate either VI or VE if only one is known. Based on fact N2 is not used or given off by body.

ˆ N2 in = N2 out or

Equation 4:VI * FI N2 = VE * FeN2

  Assume: FIN2 = 1 - FIO2 - FICO2

FEN2 = 1 - FEO2 - FECO2

 Standard air values:FIO2 = .2093

FICO2 = .0003FIN2 = .7904

Hadane Transformation (con’t)Rearrange and combine: Equation 5:

VI =VE * (FeN2 / FI N2) or VE = VI * (FI N2 / FeN2)  

Substitute into VO2 equation if we measure VE gives:Equation 6:

VO2 = [VE * (FeN2 / FI N2) * FIO2 ] - (VE * FEO2)

|_________VI __________| - |__VE ___|

VCO2 Production is: volume CO 2 exhaled - volume CO 2 inhaled

Equation 7:VCO2 = (VE * FECO2) - (VI * FICO2)

 Applying Haldane Transformation:

Equation 8:VCO2 = VE * FECO2 - [VE * (FeN2 / FI N2)] * FICO2

|___ VE __| -|__________ VI __________| 

Respiratory Exchange RatioCaloric equivalents as function of fuels

consumed (CCJ, Table 6.1, p 62)

Equation 9: RER = VCO2 /VO2

Examples of caloric equivalents and % fuels consumed

RER kcal/L oxygen % CHO % Fat

0.78 4.776 26 74

0.9 4.924 68 32

1.0 5.047 100 0