¹Vanderbilt Institute for Clinical and Translational Research, Vanderbilt University Medical Center, Nashville, TN; ²MEI Research, Ltd, St Louis Park, MN;. ³NIDDK ...
Detecting Fractional Changes in Metabolism with a Room Respiration Calorimeter Lauren Whitaker¹, Erica Wohlers², Jon Moon², Kong Y. Chen³, and Maciej S. Buchowski¹ ¹Vanderbilt Institute for Clinical and Translational Research, Vanderbilt University Medical Center, Nashville, TN; ²MEI Research, Ltd, St Louis Park, MN; ³NIDDK, National Institutes of Health, Bethesda, MD
BACKGROUND:
Room indirect calorimeters (IC) are well-suited to measure energy expenditure (EE) and its components and respiratory quotient (RQ) from 2 to 24 hours or longer. It may be used to assess dynamic changes in metabolic rate (MR) and RQ above resting levels, resulting from thermic effect of food (TEF), physical activity (PA), thermoregulation, and drug effort. The challenge is to detect small changes, 5-15% over baseline, in a large volume calorimeter (18 m3) without compromising static stability. The aim of this study is to test the dynamic response and sensitivity of the Vanderbilt University IC after a recent renovation.
MR (kcal/min) Averages ± SD During 2 Hour Step Test MR
Expected
Measured
RMRhigh -10%
1.59
1.56 ±0.05**
RMRhigh
1.72
RMRhigh +10%
2 1.5
1.94
During 30 minute step test intervals, average expected and measured change for RMRlow and RMRhigh were 10.04 ±0.2% and 10.00 ±2.75%** (difference 0.04%; CI -0.6 to 0.68%). Corresponding values for O2 consumption (VO2) were 10.03 ±0.25% and 9.94 ±3.07%** (0.1%; CI -0.6 to 0.8%), for CO2 production were 10.07 ±0.37% and 10.3 ±1.89%** (-0.24%; CI -0.7 to 0.2%). Average expected and measured change for MR during 2 hour step test intervals were 12.7 ±1.4% and 12 ±1.1%** (difference 0.6%; CI -0.2 to 1.5%). Corresponding values for O2 consumption (VO2) were 9.3 ±1.1% and 8.6±1.1% (0.7%; CI 0.1 to 1.4%), and for CO2 production were 20.6 ±2.2% and 21.2±3.1%** (-0.7%; CI -1.8 to 0.5%). *p>0.05, **p>0.1.
Schematic of room indirect calorimeter.
METHODS:
Two resting metabolic rates, RMRlow and RMRhigh, were generated by simulating O2 consumption (VO2) and CO2 production (VCO2) with a blended gas infusion into the IC. Step tests were performed by alternating between RMRlow at 0.72 kcal/min +/-10% RMRlow and RMRhigh at 1.68 kcal/min +/-10% RMRhigh in 30 minute increments to simulate TEF or light physical activity. RQ was set at 0.8. Following the step tests, RMRhigh levels were infused for 2 hours. Before each test, the calibration on inflow and outflow analyzers was verified. Gas from the chamber was sent to the inflow and outflow analyzers. The difference between the analyzers was recorded and a correction applied during data analysis. This process was repeated after the infusion was finished to confirm there was no drift in the analyzers. Data were analyzed after the study was complete to allow for calculations that could not be performed during real time. An eight minute centered derivative was used to calculate VO2 and VCO2. An infinite impulse response (IIR) filter was used to smooth the outflow O2 and CO2 data.
1.88 ±0.03*
Measured MR
0
100
200 300 Time (min)
400
500
*p>0.05, **p>0.1
Components of daily energy expenditure showing TEF around 5-15%.
MR (kcal/min) Averages ± SD During 30 Minute Step Test MR Expected Measured RMRlow -10% 0.65 0.64 ±0.04** RMRlow 0.72 0.71 ±0.05 * RMRlow +10% 0.80 0.79 ±0.05** RMRhigh -10% 1.52 1.55 ±0.11** RMRhigh 1.68 1.67 ±0.12** RMRhigh +10% 1.85 1.84 ±0.13**
Expected MR
1.68 ±0.03* 1
RESULTS:
MR(kcal / min) = (3.941 ×V&O2 + 1.104 ×V&CO2 )
Simulated MR During 2 Hour Step Test 2.5
24 Hour Indirect Calorimetry Data
8
3
Δ MR = RMR - SMR
2
6
1 0
4
100
Resting
200
300
400
Sleep
2 0 0
200
400
600 800 Time (min)
1000
1200
24 hour study to measure the MR of heart failure patients (56 yo male, 105 kg).
Simulated MR During 30 Minute Step Test 2.5 2 1.5 1 Expected MR
0.5
Measured MR
0 0
50
100
150
200
250
Time (min)
*p>0.05, **p>0.1
Indirect calorimeter room and equipment at Vanderbilt Institute for Clinical and Translational Research.
Indirect Calorimetry Data Showing Metabolic Rate Change Caused by TEF 1.5 1.4
Meal Finished
1.3
30 Minutes Postprandial
Meal Given
1.2 1.1
changes in metabolic rate to 2.7% over 30 minute time interval and 0.6% over 2 hour measurement period.
80
ACKNOWLEDGEMENTS: This work was supported in part by
Fasting RMR
1 0
20
40
60
CONCLUSIONS: Indirect calorimeters reliably detect short-term
Δ MR = TEF = +9.4% 100
Time (min)
Metabolic rate during study measuring the thermic effect of food on obese children (10 yo male, 55 kg).
funding through the Vanderbilt Institute for Clinical and Translational Research (UL1 RR024975-1 from NCRR/NIH).
