EE: Duration of Measurement (Steady State) (2014)

Citation:

Horner NK, Lampe JW, Patterson RE, Neuhouser ML, Beresford SA, Prentice RL. Indirect calorimetry protocol development for measuring resting metabolic rate as a component of total energy expenditure in free-living postmenopausal women. J Nutr. 2001; 131 (8): 2,215-2,218.

PubMed ID: 11481420
 
Study Design:
Time Study
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To develop IC protocol that is practical for use in large-scale studies and produce reliable estimates of RMR in free-living, post-menopausal women. Specifically addressed the length of the data collection period, the value of duplicate measures and the pros and cons of conducting IC until achievement of specific steady state criteria.

Inclusion Criteria:
  • Understand and give written consent
  • Free-living, post-menopausal women (post-menopausal: At least 55 years of age or at least 12 months since last menses).
Exclusion Criteria:
  • Refusal to consent
  • Not meeting inclusion criteria
  • Subjects that were excluded: Bowel disease, diabetes, hypoglycemia, renal disease, liver disease, claustrophobia, weight change in excess of 4.5kg in the two months before enrollment and alcohol intake more than two servings per day.

 

Description of Study Protocol:
  • Recruitment: Women were recruited through direct mailings using the Washington State Department of Licensure list, flyers and newspaper advertisements. Those interested in participating contacted the researchers by phone and were screened.
  • Design: Time series
  • Blinding used: Not applicable
  • Intervention: Not applicable.

Statistical Analysis

  • Analytical goal: Determining whether there is any advantage to conducting IC for a specified length of time or until achievement of defined stability criteria
  • Natural logarithmic transformation of all RMR was used to improve the normal distribution approximations, followed by paired T-test comparisons
  • Pearson correlation coefficients comparing mean RMR and body composition indices were calculated using the five to 10-minute and five to 30-minute IC segments 
  • Various lengths of the IC testing period during any one clinic visit period were compared to determine whether longer data collection produced significantly different RMR
    • Visit One time segments were compared with those of Visit Two to ascertain whether significant differences could be detected
    • To determine whether more stringent stability definitions would produce different RMR estimates, RMR conforming to each of the definitions by visit and a two-visit mean were compared.
  • To assess bias, mean differences between measured (time segments and segments meeting each stability definition) were compared and predicted RMR from four published equations were compared
  • Pearson correlation coefficients were calculated between predictive equation RMR and measured RMR for Visit One, Visit Two and a two-day mean.
Data Collection Summary:

Timing of Measurements

  • Two fasting visits one week apart
  • 24-hour urine collection prior to each visit
  • RMR compared for zero to five, five to 10, five to 15, five to 20, five to 25, five to 30 and zero to 30-minutes IC segments and segments meeting stability criteria.

Dependent Variables and Outcomes

  • Effect of using different IC data collection periods and a second IC measure:
    • Differences in RMR at different time segments compared
    • Correlation between time segments for RMR measurement at Visit One and Visit Two
  • Mean differences between measured RMR and predicted RMR
  • Correlation between RMR and body composition.

Independent Variables

  • Measured RMR
    • IC type: VMAX2900
    • Equipment of calibration: Sensormedics
    • Coefficient of variation using standard gases: Yes or no
    • Rest before measure (state length of time rested if available): 30 minutes
    • Measurement length
      • Steady state: 10 minutes during which the volume of oxygen consumed, variation in minute ventilation (VE) and RQ did not vary more than 10%. If 10 minutes of steady state was not achieved by 30-minute data collection, the test was continued until 10 minutes of ‘steady state’ vs. achieved or at 45 minutes of data collection, whichever occurred first.
      • Fasting length: Eight hours prior to measurements
      • Exercise restrictions XX hours prior to test? 48 hours.
    • Room temperature: Thermally neutral
    • Number of measures within the measurement period: Data points were collected every 30 seconds
    • Were some measures eliminated? Not specified
    • Coefficient of variation in subjects measures? No
    • Training of measurer? Yes
    • Subject training of measuring process? One trained technician conducted all IC measurements.
  • Predicted RMR: Equations of Harris-Benedict, Mifflin, WHO, Arciero
  • Body composition: Estimated using urinary creatinine from duplicate 24-hour urine collections
    • Fat-free mass (FFM): Welle's formula for older adults
    • Kg fat=weight-FFM
    • Percent body fat=kg fat/weight x100.
Description of Actual Data Sample:
  • Initial N: Not given
  • Final N: 102 females
  • Age: 62.5±8.2 years
  • Ethnicity: Not specified
  • Other relevant demographics
    • 94% Caucasian
    • 62% had a college education.
  • Anthropometrics
    • 31% with BMI under 23.1
    • 34% with BMI between 23.1 and 27.3
    • 20% overweight, BMI between 27.3-32.2
    • 15% obese (BMI over 32.2)
    • FFM: 47.3±4.7kg
    • Percentage body fat: 32.4±10%.
  • Location: Seattle, Washington.
Summary of Results:
  • RMR from five to 10 minutes was positively correlated with FFM (R=0.62, P<0.0001), BMI (R=0.83, P<0.0001) and percentage body fat (R=0.36, P<0.0002). Relationships between these measures and the mean RMR recorded from five to 30 minutes were almost identical.
  • The mean RMR for the first five minutes was significantly higher than other time segments (P=0.001). Correlation coefficients between duplicate measures were high (R=0.90).

Cumulative Percentage of Subjects Achieving Criteria
Minus the first five minutes

Minutes 15 30 45
Visit One Less than 5% variation for 5 minutes
23
34
39
Less than 5% variation for 10 minutes
2
2
2
Less than 10% variation for 5 minutes
82
93
94
Less than 10% variation for 10 minutes
32
47
58
  • Stringent steady-state criteria (10 minutes with VO2, VE and RQ varying less than 5%) were too difficult for most women to achieve even after 45 minutes of data collection. Conversely, nearly all women (94%) achieved five minutes with less than 10% variability in VO2, VE and RQ.
  • In general, more subjects achieved steady state criteria more quickly and more often at Visit Two than at Visit One. 84% of women achieved five minutes with less than percentage variability in VO2, VE and RQ in 15 minutes; 65% achieved less than 10% variation for 10 minutes variability in VO2, VE and RQ in 45 minutes; slightly less than half (43%) achieved less than 5% variation for five minutes within the first 45 minutes; only 4% achieved this variation for 10 minutes in the first 45 minutes.
  • For subjects not achieving 10 minutes with less than 10% variability in VO2, VE and RQ by 30 minutes, there was a mean increase of three to six kcal in RMR when we continued IC until either this criteria was achieved or 45 minutes elapse (P=0.005)
  • Compared with Visit One, RMR were lower at Visit Two for the zero to five minutes (P=0.001), five to 15 (P=0.04) and zero to 30-minute (P=0.05) segments
  • RMR calculated from the full-length of IC were lower for Visit Two (P=0.06)
  • RMR correlations between visits ranged from 0.86 to 0.92 by time segment.

Comparison to Prediction Formulas 

Predicted RMR were 100kcal to 200kcal higher than measured values using the five- to 10-minute segment of IC from each visit and a two-visit mean (P=0.001) RMR measured from segments that met the three achievable definitions of steady-state were 10kcal to 30kcal closer to predicted values. However, differences between measured and predicted RMR remained (P<0.02).

  Measured
kcal
Range
kcal
Visit One HB
177±108
-167 to -477
Mifflin
102±114 
-218 to -382 
WHO
236±112 
-89 to -491 
Arciero
183±109 
-140 to -451 
Visit Two HB
187±102 
-92 to -434 
Mifflin
112±106 
-145 to -419 
WHO
246±102 
-46 to -493 
Arciero
193±102 
-96 to -380 
Two-Visit Mean HB
179±99 
-143 to -435 
Mifflin
104±102
-180 to -340 
WHO
238±101 
-98 to -449 
Arciero
184±102 
-220 to -409 

RMR measures from segments that met the three achievable definitions of steady state were 10kcal to 30kcal closer to predicted values; differences between measured and predicted RMR remained (P<0.02).

Author Conclusion:
  • Data suggested that IC measurements longer than 10 minutes offer little improvement in RMR estimates
  • Conducting IC to achieve predetermined steady-state criteria offered few improvements in RMR accuracy, increased subject burden and would reduce sample size because some subjects were unable to meet the criteria
  • Small differences in mean RMR seen when IC is conducted for various lengths of time, although statistically significant, are likely to be inconsequential in the overall TE calculation that includes the highly variable activity-related energy expenditure component
  • More reactive RMR data during the first five minutes of measurement, suggesting it may not reflect RMR and should be discarded
  • At the second visit, more subjects were able to achieve stability criteria by 20 minutes and there was a 10kcal to 20kcal reduction in mean RMR compared with the first visit. Nonetheless, the average difference in RMR between the two visit measures was less than 20kcal and correlating coefficients between the two visits were approximately 0.90, which suggest that doing a second measure is of limited value.
  • Limitations include comparing time segments of continuous IC studies instead of conducting studies of various lengths on each subject, which may underestimate differences that occur when the shorter measures are taken; only assessed RMR using IC study lengths, duplicate measures and three steady-state criteria definitions; did not explore various lengths of relaxation before measurements
  • For public health protocol including IC to assess RMR as a component of TEE in post-menopausal women, a 10-minute canopy study (excluding the first five minutes of data collection) produced reliable results with minimal subject burden
  • Use of steady state criteria (i.e., achieve five minutes of less than 10% criteria variation by 45 minutes) offered no additional precision and clinically unimportant differences in mean RMR measures.
Funding Source:
Government: National Cancer Institute
Not-for-profit
Reviewer Comments:

Strongly agree with author’s conclusion.  

Strengths  

  • Well-defined population and well-set inclusion and exclusion criteria
  • Controlled for diet and physical activity before each measurement
  • One trained technician performed the IC measurement, which increased the reliability and consistency of the measurements
  • Limitations were fully discussed.

Generalizability/Weaknesses

  • Generalizability may be limited to free-living, post-menopausal women
  • Questionable validity of indirect calorimeter.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  4. Was method of handling withdrawals described? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  5. Was blinding used to prevent introduction of bias? No
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  7. Were outcomes clearly defined and the measurements valid and reliable? ???
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? N/A
  8.3. Were statistics reported with levels of significance and/or confidence intervals? N/A
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  10. Is bias due to study's funding or sponsorship unlikely? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes