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Comparison of Two Systems of Measuring Energy Expenditure

From the University of Cincinnati Medical Center, Cincinnati, OH

Correspondence: Cynthia M. Goody, PhD, Department of Nutritional Sciences, University of Cincinnati, 3202 Eden Avenue, PO Box 039467, Cincinnati, OH 45267. Electronic mail may be sent to cynthia.goody{at}uc.edu.

Background: Health care professionals typically use resting metabolic rate (RMR) via indirect calorimetry to determine a person's energy expenditure. Traditional indirect calorimetry measurements involve an expensive, cumbersome piece of equipment that requires careful calibration. The recent development of a handheld indirect calorimeter makes it easier to measure RMR. The purpose of this study was to compare simultaneous measurements of RMR with handheld and traditional indirect calorimeters. Methods: Healthy, free-living subjects (n = 50) age 18 years and older were tested simultaneously with both indirect calorimeters. All subjects breathed through the handheld device using a mouthpiece while wearing noseclips to prevent leaks. The handheld indirect calorimetry device was placed inside a canopy. The exhaled gas from the handheld was positioned directly over the inlet to the port delivering gases to the traditional device's mixing chamber. The canopy facilitated the simultaneous collection of all expired gases into the traditional device. During the measurement, oxygen consumption and RMR were continuously recorded on a personal computer.Results: Mean oxygen consumption and RMR did not significantly differ between the two devices, with a mean difference of 0.58 ± 15.33 mL/min (p = .790) and 4.66 ± 113.39 kcal/day (p = .773) and an absolute difference of 12.3 ± 8.99 mL/min and 86.58 ± 72.32 kcal/day, respectively. Correlation coefficients for oxygen consumption and RMR were 0.945 and 0.941, respectively. Conclusions: No significant difference was found between the measurements of indirect calorimetry with the MedGem (HealtheTech, Golden, CO) device compared with the DeltaTrac device (Datex-Ohmeda, Madison, WI). These findings suggest that the handheld indirect calorimeter may provide an accurate measure of oxygen consumption and RMR measurements for spontaneously breathing subjects.

Accurate nutrition assessment is essential for proper nutrition counseling and support. Health professionals typically use the Harris-Benedict equation to estimate a patient's predicted resting metabolic rate (RMR).¹ This equation considers the patient's weight, height, age, and sex to determine energy needs. Predictive equations have been shown to be unsystematically incorrect and may vary by 70%–140% when compared with measurement of energy consumption. Body composition, physical activity habits, race/ethnicity, and condition-related metabolic disturbances affect RMR and cannot be factored in as a part of the predicted value.^2–5

RMR may be accurately assessed via indirect calorimetry by oxygen consumption (VO₂) with or without the measurement of carbon dioxide production (VCO₂). The traditional indirect calorimeter is an expensive ($25,000), heavy piece of equipment that requires careful calibration, making routine RMR measurement difficult and impractical.⁶ These limitations suggest a need for an inexpensive, portable device to measure RMR in healthcare settings. The recent development of a handheld device now makes it possible for health care professionals to easily measure RMR.⁷ The MedGem RMR analyzer costs $2500 and weighs <1 pound (HealtheTech, Golden, CO). However, few investigators have compared the effectiveness and efficacy of this new device to traditional indirect calorimetry equipment.^8,9 The purpose of this study was to compare simultaneous measurements of RMR with a handheld and a traditional indirect calorimeter. Specifically, this is the first study that simultaneously compares the measurement of VO₂ and RMR with the MedGem and the DeltaTrac (Datex-Ohmeda, Madison, WI), a well-studied and validated traditional open circuit indirect calorimeter that uses the dilution principle.^10,11

	MATERIALS AND METHODS

Top MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION

 
Subjects
Free-living, healthy subjects 18 years and older were recruited by posting an advertisement about this study throughout the University of Cincinnati Medical Center. Before study initiation, the investigators tested the simultaneous measurement procedure to assure proper function and comfort. Each of the investigators performed the simultaneous measurements to determine the optimum level of the MedGem inside the canopy to allow the mouthpiece to rest comfortably in the mouth and maintain the expired gas outlet of the MedGem directly over the canopy outlet. The University of Cincinnati Medical Center Institutional Review Board approved the study and informed consent was obtained from subjects after the nature of the procedure had been explained.

More subjects were included due to a high level of interest during recruitment and the noninvasive nature of the procedures. In all, 52 people volunteered to participate in the study. Two subjects did not attend their study appointment and were dropped from the study. Fifty subjects, on an individual basis, were tested simultaneously with both the MedGem and DeltaTrac indirect calorimeters. Demographic information including age, gender, and race/ethnicity was collected from each subject. Testing occurred during a single visit between 6:30 AM and 10:00 AM. Morning hours were selected to allow subjects greater ease for fasting. The subjects refrained from exercise for 24 hours before the testing and fasted 12 hours before the testing. Exercising and consuming food and beverages before testing can falsely elevate the measurement.

Statistics
A power analysis was performed with previous results for differences in RMR between the MedGem and traditional calorimeter, using an alternative hypothesis of 150 kcal difference between measurements with p = .05 and power of 0.80. Results indicated that 33 patients were required for study. Mean ± standard deviations were determined for the simultaneous measurements of VO₂ and RMR and compared using a standard t test for paired measurements. Pearson product moment coefficients (r) were used to determine the relationship between the individual VO₂ and RMR measurements. Bland-Altman plots comparing the mean of the simultaneous measurements against the difference in the simultaneous measurements were used to evaluate the individual difference scores.

Procedure
Each subject's height and weight were measured using a stadiometer and beam balance scale (Detecto-Medic, Brooklyn, NY). Before the testing, subjects reclined quietly in a chair for 5–10 minutes to stabilize their breathing and heart rate. The MedGem was placed inside the canopy with the exhaled gas from the MedGem positioned directly over the inlet to the port delivering gases to the DeltaTrac's mixing chamber (Fig. 1). All subjects breathed through the MedGem using a disposable, scuba-type mouthpiece. Noseclips were applied to prevent leaks. The MedGem was held in place with a clamp at the end of an extension rod. Subjects were instructed to keep their arms at their sides. All expired gases were simultaneously collected into the DeltaTrac monitor via a canopy. The measurement time was 10 minutes because the MedGem is designed to stop testing after a 10-minute period or when a steady state of breathing has been achieved. The subjects were instructed to remain relaxed and to breathe normally during the testing. During the measurement, VO₂ and RMR were continuously and electronically recorded to a personal computer. To ensure subject comfort, heart rate and oxygen saturation were continuously monitored via pulse oximetry.

View larger version (145K): [in this window] [in a new window]   FIG. 1. Photograph of a subject during simultaneous measurement with the DeltaTrac (right) and MedGem (held by a C-clamp under the canopy). Data were directly stored to a laptop personal computer for later review and analysis. Note position of the MedGem directly above gas outlet of the canopy.

MedGem
Before each test, the MedGem performs an automatic calibration (a 5-second time period which the ultrasonic flow sensors are set). The device eliminates the first 2 minutes of breathing before beginning a minute-to-minute measurement of RMR. At the conclusion of the test, the device displays the RMR and the oxygen consumption. Internal sensors measured humidity, temperature, and barometric pressure to allow accurate determination of minute volume. A proprietary dual-channeled fluorescent quenching sensor measured oxygen concentration in the inspired and expired airflow. The primary principle of operation uses deactivation of ruthenium in the presence of oxygen. A ruthenium cell is excited by an internal light source and fluoresces. This reaction is repressed by the presence of oxygen. The magnitude of the repression is proportional to the concentration of oxygen. The response time of the sensor is 50 ms and the oxygen concentration is sampled at 10 Hz. Ultrasonic sensing technology measures the volume of inspired and expired air. A transducer at both ends of the flow tube emits a sound pulse. The time it takes the signal to travel from the sending transducer to the receiving transducer is increased or decreased in proportion to the rate and direction of airflow. The sensors operate at a rate of 100 Hz. RMR is calculated from oxygen consumption, a fixed respiratory quotient (RQ) of 0.85, and grams of urinary nitrogen calculated from the average energy and protein intake of the United States population using a modified Weir equation:

VO₂ is measured in L/day. Grams of urinary nitrogen are calculated by [(kcal/day x 1.16) / 4] / 6.25.

MedGem sensor specifications are as follows: barometric pressure (mmHg), ± 4 mmHg with a resolution of 0.05 mmHg; temperature (°C), ±1°C with a resolution of 0.01°C; humidity (mg H₂O/L), ±4.2% with a resolution of 0.01% relative humidity; oxygen (%), ±0.4%–0.8% O₂ with a resolution of 0.03% O₂; and volume (L), ±0.5%, with a resolution of 0.001 L/s.

DeltaTrac
Before each measurement the DeltaTrac was calibrated for pressure against the local barometric pressure measured by a mercury barometer and the gas analyzers were calibrated against a known standard gas consisting of 96% oxygen and 4% carbon dioxide. The DeltaTrac collected expired gases in a canopy for 10 minutes, but used only the last 8 minutes in calculation. The device consists of a 4-L mixing chamber, a paramagnetic oxygen analyzer, infrared CO₂ analyzer, microprocessor, and CRT display. The expired gases travel from the canopy to the mixing chamber where the gases are measured. The gases are then diluted with room air by the flow generator making the total flow (Q) through the system equal to the flow generator's output. VCO₂, VO_2, and RQ are then calculated using the following equations, where FCO is the fractional concentration of carbon dioxide, FO₂ is the fractional concentration of oxygen, and FI_O2 is the fractional inspired concentration of oxygen:

	RESULTS

Top MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION

 
Fifty subjects, 12 men and 38 women, completed the study. Subject characteristics are shown in Table I, with data summarized for age, height, and weight. Oxygen consumption and RMR data are summarized in Figure 2. Bland-Altman plots in Figure 3 demonstrate the difference score between the 2 methods (DeltaTrac and MedGem).

View larger version (21K): [in this window] [in a new window]   FIG. 2. Comparison of resting metabolic rate (RMR) values between the MedGem and DeltaTrac methods (n = 50, all subjects combined).

View larger version (18K): [in this window] [in a new window]   FIG. 3. Bland-Altman plot depicting the absolute differences in resting metabolic rate values between the DeltaTrac and the MedGem methods vs mean values (n = 50). Solid line depicts the mean difference between the methods, and dotted lines depict 2 standard deviations from this mean. Sloped line represents the linear trend of the data.

Mean oxygen consumption and RMR did not significantly differ between methods. The mean difference for oxygen consumption was 0.58 ± 15.33 mL/min (p = .790) with an absolute difference of 12.3 ± 8.99 mL/min. The correlation coefficient for the oxygen consumption measurements was r = 0.945 (p < .01). The mean difference for RMR was 4.66 ± 113.39 kcal/day (p = .773) and with an absolute difference of 86.58 ± 72.32 kcal/day. The correlation coefficient for RMR was r = .941 (p < .01).

	DISCUSSION

Top MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION

 
The purpose of this study was to simultaneously compare the VO₂ and RMR measurements of the DeltaTrac indirect calorimeter with the MedGem. No significant difference was found between devices. Our data suggest that the MedGem can accurately measure VO₂ and RMR in healthy, spontaneously breathing subjects who do not require supplemental oxygen. This study advances the research of Nieman and colleagues in that we used simultaneous measurements to compare the accuracy of the MedGem and DeltaTrac.⁸

Confounding variables seen in other studies that could potentially alter the measurements, such as changes in positioning or breathing between tests, were reduced or eliminated by simultaneous testing. Minimal activity, such as subjects using their hand to hold the device in their mouth, could increase oxygen consumption. Any variation in the subjects' breathing patterns between tests could also cause the test results to vary. For example, if the subject was more relaxed during the testing of the MedGem device, the measurements taken from it would reflect lower oxygen consumption and RMR. Other conditions that may alter RMR and result in error also include fasting with ketosis and overfeeding. Nieman et al compared the measurements from the MedGem with the measurements made by the Douglas bag technique.⁸ Mean oxygen consumption and RMR were not significantly different between methods, with a mean difference of 0.9 ± 19.0 mL/min and 7 ± 134 kcal/day. Correlation coefficients for oxygen consumption ranged from 0.81 to 0.87 when comparing data from the MedGem to the Douglas bag method. The results indicated strong agreement in RMR measured by the MedGem and the Sensormedics 2900 cart. The trial-to-trial intraclass reliability coefficients were >0.90 for both MedGem and the Sensormedics 2900 cart. Additionally, the RMR measured with the MedGem and the Sensormedics 2900 were highly correlated. Table II compares characteristics of the MedGem and the DeltaTrac.

This study has several limitations. First, each device uses different equations to calculate the RMR. The DeltaTrac uses VO₂ and VCO₂, whereas the MedGem uses only VO₂. For this reason, the RQ cannot be obtained using the MedGem. In cases of hyperventilation, VCO₂ may be elevated and result in an increase in RMR calculated by the DeltaTrac. Because the MedGem does not consider VCO₂, this could account for differences in RMR between the devices. Second, the devices' mechanical differences limit the study. The DeltaTrac consistently measures the subjects' breathing for 10 minutes. The MedGem runs the test for 10 minutes or until a steady breathing state is achieved. In this study, 20 subjects reached a steady breathing state before 10 minutes of testing were completed. The remaining 30 subjects were tested with both devices for 10 minutes. Third, the physical comfort of the subjects may also have limited the study. The mouthpiece and noseclips may have caused mild discomfort. During the testing procedures, the researchers encouraged subjects to communicate any discomfort. Fourth, rigorous attention was given to the performing the measurements; however, this approach may be difficult to replicate in nonresearch-based settings among people who are not in a resting state. Future research could include an investigation varying activity states. Lastly, this study only included healthy subjects. Persons with compromised health status may have a higher RMR and may not have the ability to use a mouthpiece or noseclips to maintain the 10-minute testing period required for accurate measurements. Additionally, inflammation increases energy consumption above resting state and is likely to be encountered in other settings.

From all statistical standpoints, the 2 devices provide closely related results. However, we noted differences in a number of subjects >100 kcal. We believe that an error of >150 kcal would result in a significant difference in the recommended caloric intake for an individual subject. From the Bland-Altman plot, this was identified in 6 instances. These differences were most often seen in men and in patients with difficulty adjusting their breathing pattern. In all 6 cases, the individual mean minute ventilation was >9 L/min (range 9.5–13 L/min). These differences may be explained by hyperventilation or discomfort with the mouthpiece. Determining the source of the error in the current trial is difficult. If hyperventilation was the issue, measurement by the DeltaTrac (which includes VCO₂ in the equation) would result in greater RMR than the MedGem (which does not include VCO₂). We believe the practical answer is to assure steady state measurements by assessing respiratory rate and depth. If normal breathing cannot be obtained with use of a mouthpiece and nose clips, a canopy system may prove superior in those subjects.

	CONCLUSION

Top MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION

 
These findings suggest that the MedGem provides an accurate measure of oxygen consumption and RMR measurements for spontaneously breathing subjects. A statistically significant difference did not exist between the measurements from the two devices.

Further research is needed to compare the RMR measurements of the MedGem and the Harris-Benedict equation. Future research comparing the measurements from the MedGem and a standard metabolic cart in persons with compromised health status should also be considered.

Implications of the findings from this research for practitioners and researchers include the validation of a handheld device which is easy to operate and available at a relatively low cost. The results of this study suggest the MedGem can be used to accurately measure oxygen consumption and RMR in capacities where a traditional metabolic cart would not be practical or cost-effective, including long-term health care facilities, low-capacity hospitals, athletic training centers, health clubs, and weight loss clinics. Nutrition professionals in these settings could use the MedGem as part of their assessment and counseling.

The authors thank Zung Vu Tran, PhD, from the University of Colorado Health Sciences Center, for statistical review.

Received for publication September 20, 2004. Accepted for publication February 14, 2005.

1. Zeman F, Ney D. Applications in medical nutrition therapy. In: Davis K, ed. Applications in medical nutrition therapy. Columbus, OH: Prentice Hall, 1996.
2. Gilliat-Wimberly M, Manore M, Woolf K, Swan P, Carroll S. Effects of habitual physical activity on the resting metabolic rates and body composition of women aged 35 to 50 years. J Am Diet Assoc.2001; 101:1181 –1188.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
3. Müller M, Illner K, Bosy-Westphal A, Brinkmann G, Heller M. Regional lean body mass and resting energy expenditure in non-obese adults.Eur J Nutr. 2001;40:93 –97.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
4. Bandini L, Must A, Spadano J, Dietz W. Relation of body composition, parental overweight, pubertal stage, and race-ethnicity to energy expenditure among premenarcheal girls. Am J Clin Nutr.2002; 76:1040 –1047.[Abstract/Free Full Text]
5. Buchholz A, McGillivray C, Pencharz P. Differences in resting metabolic rate between paraplegic and able-bodied subjects are explained by differences in body composition. Am J Clin Nutr.2003; 77:371 –378.[Abstract/Free Full Text]
6. Kacmarek R, Hess D, Stoller J. Monitoring in respiratory care. In: Marshall D, ed. St. Louis, MO: Mosby,1993 .
7. Kearney J, Murphy O. The MedGem is a valid and reliable indirect calorimeter. White Paper. Golden, CO: HealtheTech,2003 .
8. Nieman D, Trone G, Austin M. A new device for measuring resting metabolic rate and oxygen consumption. J Am Diet Assoc.2003; 103:588 –593.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
9. St-Onge M, Rubiano F, Jones A, Heymsfield S. A new hand-held indirect calorimeter to measure postprandial energy expenditure.Obesity Res. 2004;12:704 –709.[Web of Science][Medline] [Order article via Infotrieve]
10. Takala J, Keinanen O, Vaisanen P. Measurement of gas exchange in intensive care: laboratory and clinical validation of a new device.Crit Care Med. 1989;17:1041 –1047.[Web of Science][Medline] [Order article via Infotrieve]
11. Weissman C, Sardar A, Kemper M. In vitro evaluation of a compact metabolic measurement instrument. JPEN J Parenter Enteral Nutr.1990; 14:216 –221.[Abstract]

Journal of Parenteral and Enteral Nutrition, Vol. 29, No. 3, 212-217 (2005)
DOI: 10.1177/0148607105029003212


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