Determining the Accuracy and Reliability of Indirect Calorimeters Utilizing the Methanol Combustion Technique
Authors: Kaviani Sepideh , Schoeller Dale A , Ravussin Eric , Melanson Edward L , Henes Sarah T , Dugas Lara R , Dechert Ronald E , Mitri George E , Schoffelen Paul F.M. , Gubbels Pim , Tornberg Asa , Fritzdorf Stephen , Akkermans Marco , Cooper Jamie A. 
Published: November 2023

Objective

There are several indirect calorimetry (IC) instruments commercially available but validity and reliability data is lacking. Site‐to‐site inconsistencies in protocols and subject characteristics, and comparisons to a “gold standard” instrument or method which may no longer be accurate enough, have put restraints on drawing conclusions about instruments' performance.

Purpose

To compare the accuracy and reliability of different metabolic carts using the methanol combustion technique as the criterion measure.

Methods

A total of eight, 20‐minute methanol burn trials were completed on 12 metabolic carts (2 Cosmed Quark CPET, 2 DeltaTrac II, 2 Parvo Medics TrueOne 2400, 2 Iaeger Oxycon Pros, 2 Omnicals, a Vmax Encore, and a Max‐II Metabolic System) at 11 international study sites. Methanol tests were performed at 0700, 1000, 1300, and 1600 hours on 2 consecutive days. Respiratory Exchange Ratio (RER) and percent (%) recovery of O2 and CO2 were calculated after each test.

Results

Accuracy – 1 Omnical, Cosmed, and Parvo were accurate in measuring RER and % recovery O2, while 1 DeltaTrac was also accurate for % recovery O2. The same Cosmed and Parvo, and the other DeltaTrac were accurate in measuring % recovery CO2. Reliability – 8 instruments were shown to be reliable with the two Omnicals ranking best based on the smallest coefficient of variation (CV) (all CV(s) 1.26%). Both Cosmeds, Parvos, DeltaTracs and 1 Vmax were the reliable instruments for at least one variable (CV(s) 3%). Multiple Regression– Humidity, amount of methanol combusted, and temperature were tested as predictors of IC outcomes. Humidity and amount of combusted methanol were significant predictors of RER (F (2, 60) =10.91, p<0.001, R2=0.33). Temperature and amount of burned methanol were significant predictors of % recovery O2 (F (2, 60) =8.32, p<0.001, R2=0.18) while only humidity was a predictor for % recovery CO2 (F (1, 61) =21.10, p<0.001, R2=0.15).

Conclusion

Omnical, Cosmed, and Parvo showed superior accuracy and reliability; however, accuracy was only found at one of two study sites. Exogenous factors such as humidity and temperature may be influencing instrument performance and could be modified in the lab to optimize IC conditions.

Support or Funding Information

There were no sources of funding for this manuscript, nor were there any sponsors.

Instument Accuracy

Instruments
RER
Instruments
O2 Recovery (%)
Instruments
CO2 Recovery (%)

X̄±SD
%RE
Rank
X̄±SD
%RE
Rank
X̄±SD
%RE
Rank

Omnical2
0.667±0.002
0.001*
1
Omnical 1
100.1±0.8
0.094*
1
Parvo2
100.1±3.2
0.144*
1

Cosmed2
0.673±0.005
0.927*
2
Cosmed2
99.8±2.1
−0.250*
2
Cosmed2
100.7±1.7
0.666*
2

Parvo2
0.660±0.005
−1.034*‡
3
Delta Trac2
100.8±2.4
0.794*
3
Delta Trac1
100.7±1.5
0.702*
3

Omnical1
0.677±0.003
1.546
4
Parvo2
101.2±2.9
1.185*
4
Vmax Encore
98.4±2.1
−1.615
4

Parvol
0.678±0.006
1.685
5
Vmax Encore
101.8±5.1
1.804
5
Omnical1
101.6±0.8
1.640
5

Max‐II
0.652±0.022
−2.226
6
Parvol
102.0±13.9
2.026
6
Delta Trac2
98.1±3.8
−1.874
6

Delta Trac2
0.649±0.020
−2.649
7
Oxycon2
97.9±7.2
−2.051
7
Omnical2
103.6±1.3
3.647
7

Oxycon1
0.649±0.007
−2.705
8
Cosmed1
102.5±2.2
2.469
8
Parvo1
104.0±14.4
3.976
8

Vmax Encore
0.645±0.023
−3.221
9
Delta Trac1
97.4±1.7
−2.619
9
Cosmed1
95.7±1.2
−4.293
9

Delta Trac1
0.689±0.008
3.420
10
Omnical2
103.6±1.3
3.647
10
Oxycon2
104.4±6.7
4.368
10

Cosmed1
0.626±0.014
−6.089
11
Max‐II
107.0±3.9
6.970
11
Max‐II
104.5±2.2
4.493
11

Oxycon2
0.712±0.040
6.755
12
Oxycon1
91.4±3.1
−8.615
12
Oxycon1
88.9±2.6
−11.103
12

X̄ Average of measured values by the instruments throughout the 8 burns, SD: Standard Deviation, %RE: Percent of Relative Error, RER: Respiratory Exchange Ratio.

Negative %RE values on this table indicate that the calculated averages for the corresponding instruments were less than the theoretical value. Instruments rankings (best to worst) are based on ; which explains the difference of the average values measured by the instruments from theoretical. Theoretical values are 0.667 (for RER), and 100% (1.00 for O2 and CO2 recoveries).

denotes accurate instrument based on a %RE≤1.5%.

Instument Reliability

Instruments
RER
Instruments
% Recovery O2
Instruments
% Recovery CO2

CV (%)
Rank
CV (%)
Rank
CV (%)
Rank

Omnical2
0.23*
1
Omnical1
0.75*
1
Omnical1
0.76*
1

Omnical1
0.49*
2
Omnical2
1.26*
2
Omnical2
1.21*
2

Cosmed2
0.68*
3
Delta Trac1
1.76*
3
Cosmed1
1.22*
3

Parvo2
0.75*
4
Cosmed2
2.10*
4
Delta Trac1
1.47*
4

Parvo1
0.85*
5
Cosmed1
2.18*
5
Cosmcd2
1.65*
5

Oxycon1
1.05*
6
Delta Trac2
2.35*
6
Vmax Encore
2.09*
6

Delta Trac1
1.13*
7
Parvo2
2.89*
7
Max‐II
2.14*
7

Cosmed1
2.28*
8
Oxycon1
3.42
8
Oxycon1
2.97*
8

DeltaTrac2
3.01
9
Max‐II
3.69
9
Parvo2
3.18
9

Max‐II
3.42
10
Vmax Encore
4.97
10
Delta Trac2
3.84
10

Vmax Encore
3.50
11
Oxycon2
7.31
11
Oxycon2
6.46
11

Oxycon2
5.49
12
Parvo1
13.46
12
Parvo1
13.86
12

CV: Coefficient of Variation, RER: Respiratory Exchange Ratio.

Instruments rankings (best to worst) are based on CV which was used to assess reliability of measurements by each instruments.

denotes reliable instrument based on a CV ≤ 3%.