- Click here for explanation of classification scheme.

1. Evaluate the consistency of measurements in adult, healthy volunteers taken over a three-day period using a mouthpiece or nose clips, face mask and ventilated canopy
2. To systematically evaluate the reactivity of the testing procedure and whether this reactivity varies as a function of the collection system used
3. To determine the degree of reliability of a single measurement of varying duration using a mouthpiece, face mask and canopy data collection system.

1. Understand and give written consent
2. Healthy (screened for respiratory disorders, medication usage known to affect metabolic rates and any medical condition thought to be associated with metallic rate—diabetes, eating disorders
3. Adult volunteers
4. Females
5. Non-smoking
6. Weight falling between the 25^th and 75^th percentile norms.

1. Refusal to consent
2. Not meeting inclusion criteria
3. Diseases in subjects that were excluded: Diabetes, eating disorders
4. Medications excluded: those known to affect metabolic rates
5. Smokers
6. Overweight or underweight.

Recruitment

Subjects recruited through newspaper advertisements

Design

Time series

Blinding used

Not applicable

Intervention

Not applicable

Statistical Analysis

• 3 (system) X 3 (time) X 2 (first five minutes vs. 40 subsequent minutes) repeated measures analysis of variance to evaluate possible reactivity and differences between systems and across time
• Intraclass correlation coefficients (ICC) calculated to determine reliability
  
  • One-way analysis of variance to calculate both the within-subject and between-subject variances
  • ICC then computed as the ratio of these variance components
  • ICCs were computed for each collection method on 10-, 20- and 40-minute blocks following the five-minute adaptation period
  • An ICC of 0.70 is considered an acceptable level of reliability.

Timing of Measurements

Data were collected on each subject for 50 consecutive minutes a day over three consecutive days at the same time of day. 

Dependent variables/outcomes

• Reactivity of testing procedures
• Differences between collection systems
• Reliability of a single metabolic measurement of varying duration using different collection systems.

Independent variables/measures

Indirect calorimetry using three different collection systems:

• IC type: Subjects stratified randomly and assigned (based on baseline predicted resting energy expenditures) to one of three collection methods:
  • Mouthpiece or nose clips
  • Face mask
  • Ventilated canopy
• Equipment of calibration: Yes prior to each test; in addition leakage carefully controlled in all three collection systems; throughout testing subjects were monitored to insure leakage had not occurred
• Coefficient of variation using std gases: Yes
• Rest before measure: Five minutes prior to testing
• Measurement length: 50 consecutive minutes a day for three consecutive days at the same time of day with the same collection system assigned to
• Steady state: Not discussed
• Fasting length: Abstain from food and caffeinated beverages for five hours prior to testing
• Exercise restrictions: Instructed to avoid any strenuous, aerobic-type physical activity for at least five hours prior to testing
• Room temp: Thermally neutral
• Number of measures within the measurement period: Intraclass correlation coefficients (ICCs) were computed for each collection method on 10-, 20- and 40-minute blocks following the five-minute adaptation period (not eliminated)
• Were some measures eliminated? No
• Were a set of measurements averaged? REE across the three days were averaged to evaluate whether REE measurements in the first five minutes were different than in the subsequent 40-minute period
• Training of measurer? Not mentioned
• Subject training of measuring process? Yes; while resting before testing (five minutes)
• Monitored heart rate? Not discussed
• Body temperature? Not discussed
• Medications administered? Not discussed.

 

• Initial N: N=30
• Attrition (final N):  N=30 non-smoking adult females
• Age:  Not reported
• Ethnicity:  Not reported
• Other relevant demographics: Not reported
• Anthropometrics:  Not reported (inclusion criteria: Between 25th and 75th percentile for weight)
• Location: Memphis State University and University of Tennessee, Memphis, TN.

• Results indicated no significant effects for collection procedure, day or interactions between method and day
• There were no significant differences between methods on the first five minutes or between methods on the last 40 minutes
• However, all three methods had significantly elevated REE measurements (reactivity) in the first five minutes of testing compared with the subsequent 40 minutes (see below)
  • There was a significant two-way interaction between method and reactivity (P=0.023).

Collection Method* Mean REE(kcal per day) ±SD

1. Mouthpiece
   • First five minutes=1,521.71±270.86
   • 40 minutes=1,250.86±135.68
   • P<0.001                                                                                                  
   • Reduction=270.86kcal per day
2. Face mask       
   • First five minutes=1,509.67±171.85
   • 40 minutes=1,337.82±182.85
   • P<0.05
   • Reduction=171.85kcal per day
3. Canopy           
   • First five minutes=1,674.97±379.01
   • 40 minutes=1,295.96±162.97
   • P<0.000
   • Reduction=379.01kcal per day.

*mean REE=average REE over three-day measurement period

The face mask had the least drop in resting energy expenditure.

ICCs For Collection Method

1. Mouthpiece/nose clips
   • 10-minutes=0.75
   • 20-minutes=0.62
   • 40-minutes=0.40
2. Face mask
   • 10-minutes=0.43
   • 20-minutes=0.60
   • 40-minutes=0.79
3. Canopy
   • 10-minutes=0.44
   • 20-minutes=0.75
   • 40-minutes=0.79.

• As indicated above, the mouthpiece shows acceptable reliability (>0.7) for the 10-minute period, but the reliability progressively decreased as the measurement duration increased
• The face mask show poor reliability for the 10-minutes, an increase in reliability with a 20-minute measurement and strong reliability with a 40-minute measurement length
• For the canopy, the 10-minute period showed poor reliability, but both the 20- and 40-minute measurement periods were strongly reliable.

 

• The results of the current study indicate that there are no significant REE differences between data collected with mouthpiece or nose clips, a face mask or a canopy collection system. Additionally, there were no differences between systems over time.
• However, across all three days of measurement, the first five minutes of data collection on all three systems were more reactive (i.e., significantly higher) than the subsequent 40 minutes of assessment. Reliability analyses indicated that following a five-minute adjustment period, acceptable reliability coefficients were obtained after 20 minutes of continuous data collection in the ventilated canopy and after 40 minutes with the face mask. Reliability coefficients with the mouthpiece and nose clips steadily decreased as the length of the testing session increased.
• The finding that the first five minutes of data collection were significantly higher than the subsequent 40 minutes despite the fact that the subjects rested prior to assessment and the procedure was explained to them prior to initiation, confirms earlier observations which indicated a need to acclimate to the testing procedure once the collection system was attached and also indicated that values obtained during the first five minutes were likely to be unstable and unrepresentative regardless of the method used. Thus, it is recommended that a five-minute acclimation period following attachment of the collection system be conducted in all clinical and research studies.
• Results also indicated that reliability of both the face mask and the canopy increased as test length increased. In contrast, the data collected with the mouthpiece or nose clips method indicated that as test duration increased, reliability decreased. This is likely due to increasing discomfort on the part of the subject with the mouthpiece and nose clips as test length increased (acceptable reliability obtained after 10-minutes). Given that most clinical and research metabolic evaluations require relatively longer test durations, it is recommended that either a face mask or canopy be used for testing sessions lasting longer than 10 minutes.
• Whereas the canopy system achieved acceptable levels of reproducibility following a 20-minute test, it appears that both the face mask and canopy are reliable collection methods during longer tests (40 minutes)
• On balance, the feature of reliability, comfort and non-obtrusiveness my make the canopy system a more advantageous method for measuring REE in research and clinical applications
• In summary, it appears that both the face mask and canopy data collection systems yield reproducible metabolic data, provided that acclimation to the procedure be conducted.

Government:

NHLBI, State of Tennessee

Strengths

Good description of three metabolic collection systems; the calibration and evaluation of leakage throughout the testing sessions.

 

Limitations

• Limited generalizability; sample consisted of healthy females and generalizability to males and other populations is not known
• Sample was restricted to non-obese and nonsmokers
• Role of factors such as smoking, obesity (?)
• Data on age, height, weight, ethnicity not reported (potential confounders?)
• Measurements made after five-hour fast rather than more standard 12-hour fast, and had not participated in physical activity for only five hours; number of hours may not have been consistent across groups (accounted for by testing conducted at same time each day?)