Indirect Calorimetry

1 Dr. Robert RobergsFall, 2010 Indirect Calorimetry1 Indirect CalorimetryIndirect CalorimetryCALORIMETRYThe science that quantifies the heat release from metabolism is termed CircuitOpen CircuitRespiration Chamber Expired gas analysis Carbon/nitrogen excretion Labeled water Respiration chamberDr. Robert RobergsFall, 2010 Indirect Calorimetry2 Bomb CalorimeterDr. Robert RobergsFall, 2010 Indirect Calorimetry3 Heat release & caloric equivalents macronutrientsThe heat release and caloric equivalents for oxygen for the main macronutrients of catabolism (simplified).Food Rubner s kcal/g Kcal/g (Bomb cal.) Kcal/g (body) RQ Kcal/L O2 CHO mix Fat mix Protein mix Alcohol Mixed Diet Dr. Robert RobergsFall, 2010 Indirect Calorimetry4 Applications of Indirect CalorimetryApplications of Indirect Calorimetry Metabolic IntensityAbsolute -VO2(mL/kg/min or L/min)Relative -% VO2max.

2 % LT Maximal Cardiorespiratory and Muscular Endurance (VO2max) Economy and Efficiency Accumulated O2 Deficit Metabolic Rate (BMR, RMR) EPOC energy expenditure VO2 KineticsLimitations Of Indirect CalorimetryLimitations Of Indirect body -the sum of all active tissue in body, not just contracting skeletal sophisticated and expensive sensitive to measurement only be accurately used for metabolic intensities, economy, efficiency, and energy expenditure during steady state subjects to wear apparatus on face or in Robert RobergsFall, 2010 Indirect Calorimetry5 Systems of MeasurementSystems of MeasurementInspired volume time-average systemExpired volume time-average systemCustom Built SystemMixing bagFlow turbineExpired gas analyzersFlow pumpDr. Robert RobergsFall, 2010 Indirect Calorimetry6 Non-Protein RER TableDefinitions & Abbreviations Used in CalorimetryVO2 Oxygen consumptionVCO2 Carbon dioxide productionRQRespiratory quotient = VCO2/ VO2for the cellRERR espiratory exchange ratio = VCO2/ VO2measuredfrom expired airKcal/LThe energy release from metabolism for each L of VO2 Bomb Calorimeter: instrument used to combust food and measure the VO2, VCO2, and heat : instrument that quantifies the body s Robert RobergsFall, 2010 Indirect Calorimetry7 QUESTIONS1.

3 Why are the Kcals/g values less for the body, especially for protein catabolism?2. Which type of molecule provides the greatest amount of energy per mass?3. If fat provides a greater store of energy , why does CHO provide more energy relative to VO2?(hint, think back to catabolism!!)4. What is the RQ, and why is it important to assess during rest and exercise?Open-circuit Indirect CalorimetryWhen concerned with exercise, the predominant application of Indirect Calorimetry is for the measurement of oxygen consumption(VO2). The measure is used to assess the metabolic intensityof the Gas Analysis CalorimetryFundamental Principles1. That the volume of oxygen consumed(VO2) by the body is equal to the difference between the volumes of inspired and expired That the volume of carbon dioxide produced(VCO2) by the body is equal to the difference between the volumes of expired and inspired carbon Robert RobergsFall, 2010 Indirect Calorimetry8 Measurements From Indirect Gas Analysis CalorimetryMixing bagFlow turbineExpired gas analyzersFlow pumpUnderstanding ATPS and STPDGas volumes vary with temperature and pressure, thus there needs to be a standard way to express gas volumes so that pressure and temperature variations are Atmospheric Temperature and Pressure, SaturatedSTPD= Standard Temperature and Pressure, DryActual air temperatureActual PressureRH=100%For a given RH, PH2 Ovaries with temperature~ mmHg at 18 C~ 47 mmHG at 37 C273 K = 0 CStandard pressure760 mmHgRH = 0%PH2O= 0 mmHgVESTPD= VEATPS* (273 / (273 + Troom))

4 * ((PB PH2O) / 760)= 273 + Troom in CDr. Robert RobergsFall, 2010 Indirect Calorimetry9 Calculating VO21VO2= VIO2-VEO2as a gas volume = the volume of air multiplied by the gas fraction;2VO2= ( VIFIO2 ) -( VEFEO2 )where FIO2 = fraction of oxygen in inspired air = = fraction of oxygen in expired air = variableTo prevent the need to measure both inspiredand expiredvolumes, and introduce the measure of carbon dioxide, the Haldane transformation is Robert RobergsFall, 2010 Indirect Calorimetry10 Haldane TransformationThis tranformation assumes that nitrogen is physiologically inert. Therefore, the volume of inspired nitrogen must equal the volume of expired ( VI FIN2) = ( VE FEN2)4VI= ( VE FEN2) / FI N25VI= VE (FEN2/ FI N2)where FIN2= fraction of inspired nitrogen = ,FEN2= [ (FEO2+ FEO2)]Thus,6VI= VE ([ (FEO2+ FEO2)] / )Incorporating equation 6into 2provides the final equation to calculate ( VE ([ (FEO2+ FEO2)] / ) x FIO2) -( VEFEO2 )Calculating VCO2 VCO2= VECO2-VICO2where FICO2= fraction of carbon dioxide in inspired air = ( VEFECO2 ) -( VIx )Calculating RERRER= VCO2/ VO2 VIDr.

5 Robert RobergsFall, 2010 Indirect Calorimetry11RQ vs RERThe RQ and RER are the same measurement, yet as the components of the measure are obtained differently(cell respiration vs exhaled air from the lung), under certain circumstances the values can maximal range of RQ is from to range of RER may vary from < to > Why can RER vary so much more than RQ?2. How do these differences alter test requirements and data interpretations?1. Metabolic acidosis-inflates VCO2causing RER> Non-steady state exercise-lower than expected VO2and a likelihood for an inflated VCO2and Hyperventilation-causes a higher VCO2and inflates the Excess post-exercise VO2-sustained elevated VO2can cause RER to be lower than Prolonged exercise-if CHO nutrition was poor and muscle and liver glycogen are low, the longer the exercise session that greater the amino acid assumption of equality between RQ and RER cannot be made during the following;Dr.

6 Robert RobergsFall, 2010 Indirect Calorimetry12 Calculating energy ExpenditureTo calculate energy expenditure most accurately, you need to know the following;1. VO22. RER3. RER caloric equivalent4. Exercise durationKcal = VO2(L/min)x RER caloric equivalentx time(min)For example,when exercising at a VO2= L/min and RER = for 30 min;Kcal = (L/min) x 30(min)= Where does the value of come from?2. Assuming all assumptions are met for calculating fat and carbohydrate contributions to energy expenditure , how much energy (kcals) came from these fuels?3. Assuming 4 kcal/g and 9 kcal/g as the caloric densities for fat and carbohydrate, respectively, how much fat and carbohydrate were used during this exercise condition?Dr. Robert RobergsFall, 2010 Indirect Calorimetry13 Economy vs. EfficiencyEconomy-refers to the energy cost of an exercise mechanical energy produced relative to the metabolic energy expenditureFor example;The VO2during running is often termed running economy or submaximal VO2.

7 A person with a lower running VO2for a given pace has better , if a person requires a smaller increase in VO2during a change in running pace, then that person has better efficiencycan be related, but the terms should not be used Robert RobergsFall, 2010 Indirect Calorimetry14 Computation Examples in Computation Examples in Indirect Indirect CalorimetryCalorimetryTimeVE (ATPS) the following environmental gas volumes to STPD based on the conditions of : Tr= C; PB=635 mmHg; RH=100%; PH2O= mmHg12 L/min ; 59 L/min ; 130 L/min ; 180 L/minCompute VO2, VCO2, & RER for the following tabled values and environmental conditions volume correct to STPD:12 = L/min ; 59 = L/min ; 130 = L/min ; 180 = L/minVO2, VCO2and RER Questions:TimeVE (STPD)FEO2 FECO2