- To examine the validity of resting metabolic rate (RMR) obtained by indirect calorimetry (IC)-a single 3-5 minute measurement obtained after an overnight fast; this value is then extrapolated to 24 hr to provide a value for daily resting energy losses
- By measuring the within- and between-day variability in RMR.
To do so: the RMR was measured hourly in 14 healthy adults after an overnight fast on 2 separate days.
- Steady state: subject stabilized at a consistent VE for 3 consecutive cycles of the pneumotachograph.
- Healthy (definition not provided)
- Able to consent
- Refusal to consent
- Not meeting inclusion criteria
- Ht measured? yes (method not described)
- Wt measured? yes (method not described)
- Fat-free mass measured? Yes, using equations of Durin and Womersley
- Skinfold thicknesses measured? Yes—biceps, triceps, iliac crest, and subscapular skinfold thicknesses using standardized techniques
- Monitored heart rate? yes
- Body temperature? yes
- Medications administered? Not mentioned
Resting energy expenditure
Protocol the same for all volunteers.
Patients were admitted to research facility in morning on 2 separate days after overnight fast.
- IC type: 2 gas analyzers and a digital pneumotachograph with a face mask and meteorological balloon
- Equipment of Calibration: yes each morning and between each measurement
- Coefficient of variation using std gases: all gas volumes were corrected to standard temperature, pressure and density
- Rest before measure (state length of time rested if available): Rested in bed 1 hr prior to initial measurement; after at least 30 minutes for each measurement thereafter. All patents were confined to bed for 8 hour measurement period, except for bathroom privileges
- Measurement length: specific length not specified but as measurement were made after at least 30 min of bed rest and they were measured hourly they could not be longer than 30 minutes.
- Steady state: RMR measurements were recorded when the subject stabilized at a consistent VE for 3 consecutive cycles of the pneumotachograph.
- Fasting length: Overnight fast.
- Exercise restrictions prior to test? non mentioned
- Room temp: not mentioned
- No. of measures within the measurement period: 8 measurements were taken on each day (8 am:measurement 1—4 pm: measurement 8); measurements taken hourly each day
- Were some measures eliminated? no
- Were a set of measurements averaged? The hourly RMR were averaged as well as a set of hourly RMR to assess RMR reliability
- Training of measurer? Single trained measurer to limit interobserver measurement variabililty
- Subject training of measuring process? Study and measurement techniques described to each subject prior to IC.
Outcome(s) and other measures
- Measured RMR with IC
- Minute ventilation rate (VE) was measured using a digital pneumotachograph.
- RMR measurements were recorded when the subject stabilized at a consistent VE for 3 consecutive cycles of the pneumotachograph.
- Caloric expenditure was determined using the nonprotein caloric equivalent for oxygen.
- Fat and fat-free body mass calculated according to the equations of Durin and Womersley
- Independent variables of weight, height, age, fat-free mass, fat mass
- Hourly respiratory quotient (RQ, VCO2VO2 were compared for days 1 and 2.
- Hourly measured oral body temperature was compared for days 1 and 2.
- RMR measurements were compared within day and between days 1 and 2.
Blinding used: No
- N =14 healthy adults volunteered for the study
- N =2 males; 12 females
- (*mean age 26.8±1.7 y; range 22-47)
- (*not broken down by gender)
- Ht (cm): mean 167.4±2.0
- Wt (kg): mean 60.4±2.8
- Fat-free mass (kg): mean 41.5±1.3
- Fat mass (kg): mean 18.9±2.3
*not broken down by gender
- Medical tests/procedures: none other than IC and body composition measurements.
Number of Measurements
8 measurements were taken on each day (8 am:measurement 1-4 pm: measurement 8); measurements taken hourly each day
Length of Measurements
Specific length not specified but as measurement were made after at least 30 min of bed rest and they were measured hourly they could not be longer than 30 minutes.
[Analyst note: to recalculate to SD, 0.03 X v14 =0.112 SD. Then, 2 X 0.112 = 0.22; 98% of individuals would fall within 0.56-0.89 for 0800 measure on either day.]
- Group mean RQ on each day (Day 1 and Day 2) (after an overnight fast) at 16.00 (i.e., overnight fast plus 7 hrs was 0.75±.02 (SEM) and 0.74±0.01, respectively.
[Analyst note: to recalculate to SD, 0.02 X v14 = 0.07 SD and 0.01 X v14 = 0.04 SD. Then, 2 X 0.07 = 0.14 and 2 X 0.04 = 0.08 On Day 1, 98% of indivudals would fall within 0.64-0.89 and on Day 2, 98% of individuals would fall within 0.67-0.83.]
MEASUREMENT TIMING AND RELIABILITY
- Sleep or rest: complete bed rest; rested 1 hour prior to initial measurement and further measurements were done after at least 30 minutes of rest
- Various times in the day: Metabolic rate measured hourly by IC from 8 am (measurement 1) to 4 pm (measurement 8) on each day; repeated for 2 days.
- Analysis of variance of the individual data indicated that there was no significant between-day difference in measurements in RMR; overall the RMR measurements were the same on a daily basis.
- The greatest difference in average RMR between days 1 and 2 was 5 kcal/hr and was much less for most measurements. Very similar RMR measurements were obtained in the middle part of both days.
- During day 1, RMR remained virtually unchanged from early morning to late afternoon, and there was no significant difference between RMR measurements.
- In regard to average ICC results, for day 1, a good estimate of RMR was obtained by averaging measurements 2 to 4 (middle measurements)
- RMR reliability was improved by averaging all measurements taken during the day, and maximum reliability was obtained by averaging the middle 3 RMR measurements.
- A similar trend was observed during day 2, but the overall reliability was improved compared to day 1.
- For day 2, the best (most reliable) measure of RMR was found by averaging measurements 4 to 6; however, the other groupings 1 to 3 and 7 to 9 provided very good estimates of RMR. These averages were more reliable than the comparable measurements on day 1.
As stated by the author in body of report
The results suggest that RMR can be reproducibly measured in the same subject on different days. This was indicated by the very close agreement of the average of eight hourly measurements on the 2 days.
However, from examination of the individual RMR curves on both days and the ICC coefficients, it can be seen that the greatest chance of obtaining a large between-day and within-day difference (unreliability) in RMR is in the first few and last few measurements.
Thus, the results suggested that although the average RMRs on days 1 and 2 were not statistically significant, the current practice of establishing a patients’ RMR based upon a single measurement potentially can lead to large errors in determining energy needs.
Measurement reliability can be improved by serially measuring RMR, eliminating the initial measurement, and averaging the remaining two or three values.
The results suggest that new guidelines are recommended that minimize the errors due to measurement variability.Some workers suggest that collecting respiratory gases via a ventilated canopy system rather than a face mask system used in this study may be more reproducible. The expense and importance of these RMR values to the patient dictates that future studies address this issue.
|University/Hospital:||Emory University School|
- Small sample size; especially males.
- Convenience sample and relatively young age group
- (Self-selection bias)
- How the subjects were determined to be “healthy” was not discussed
- Not discussed whether heights and weights were self-reported or measured by study personnel
- Declining RQ during study indicated progressive lipolysis with duration of fasting; concern with ketonuria with the 12-to 20 hour fasting (medical complications)
- Length of study; participants confined to bed for 8 hours on 2 days
- Use of face mask rather than ventilated canopy system may not have been as reliable; need further testing.
Working Group MembersHad questions regarding the sample size since it was small and if it had the ability to detect difference between measurements (i.e., low power to detect differences and ability of an outlier effect). It was not clear whether variance reported in the article was due to inter-subject variability or intra-subject variability. The method may not be generalizable to the outpatient setting; potential generalizability in a research setting but not a treatment setting; Relevance to clinical setting questioned.
Quality Criteria Checklist: Primary Research
|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|
|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|
|1.||Was the research question clearly stated?||Yes|
|1.1.||Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?||N/A|
|1.2.||Was (were) the outcome(s) [dependent variable(s)] clearly indicated?||N/A|
|1.3.||Were the target population and setting specified?||N/A|
|2.||Was the selection of study subjects/patients free from bias?||No|
|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?||N/A|
|2.2.||Were criteria applied equally to all study groups?||N/A|
|2.3.||Were health, demographics, and other characteristics of subjects described?||N/A|
|2.4.||Were the subjects/patients a representative sample of the relevant population?||N/A|
|3.||Were study groups comparable?||No|
|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|
|3.3.||Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)||N/A|
|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?||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|
|4.||Was method of handling withdrawals described?||No|
|4.1.||Were follow-up methods described and the same for all groups?||N/A|
|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%.)||N/A|
|4.3.||Were all enrolled subjects/patients (in the original sample) accounted for?||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|
|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|
|5.2.||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|
|5.4.||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|
|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|
|6.2.||In observational study, were interventions, study settings, and clinicians/provider described?||N/A|
|6.3.||Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?||N/A|
|6.4.||Was the amount of exposure and, if relevant, subject/patient compliance measured?||N/A|
|6.5.||Were co-interventions (e.g., ancillary treatments, other therapies) 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|
|6.8.||In diagnostic study, were details of test administration and replication sufficient?||N/A|
|7.||Were outcomes clearly defined and the measurements valid and reliable?||No|
|7.1.||Were primary and secondary endpoints described and relevant to the question?||N/A|
|7.2.||Were nutrition measures appropriate to question and outcomes of concern?||N/A|
|7.3.||Was the period of follow-up long enough for important outcome(s) to occur?||N/A|
|7.4.||Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?||N/A|
|7.5.||Was the measurement of effect at an appropriate level of precision?||N/A|
|7.6.||Were other factors accounted for (measured) that could affect outcomes?||N/A|
|7.7.||Were the measurements conducted consistently across groups?||N/A|
|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?||N/A|
|8.2.||Were correct statistical tests used and assumptions of test not violated?||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|
|8.5.||Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?||N/A|
|8.6.||Was clinical significance as well as statistical significance reported?||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|
|9.1.||Is there a discussion of findings?||N/A|
|9.2.||Are biases and study limitations identified and discussed?||N/A|
|10.||Is bias due to study's funding or sponsorship unlikely?||Yes|
|10.1.||Were sources of funding and investigators' affiliations described?||N/A|
|10.2.||Was the study free from apparent conflict of interest?||N/A|