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EE: Diurnal Variation (2014)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the validity of extrapolating a single three- to five-minute measurement of resting metabolic rate (RMR) by indirect calorimetry (IC) to 24-hour resting energy production by measuring the within and between day variability in RMR.

Inclusion Criteria:
  • Adults
  • Volunteers
  • Healthy (definition not provided)
  • Able to consent.
Exclusion Criteria:

None specified

Description of Study Protocol:

Recruitment

Methods not described

Design

Time series

Blinding used

Not applicable

Intervention 

Not applicable

Statistical Analysis

  • Intraclass correlation coefficient (ICC) calculated using one-way analysis of variance to determine the within and between subject variances to estimate the reproducibility or reliability of the RMR measurement
    • One-way analysis of variance used to determine the within and between subject variances
    • The single-measure ICC was then calculated as the ratio of these variance components
      • An ICC of 1.0 indicates perfect reliability between measures (no within-subject variance)
      • An ICC of zero or less indicates no reliability
  • An ICC was also determined for the average of several measurements.
Data Collection Summary:

Timing of measurements

  • Volunteers admitted early in the morning on two separate days after an overnight fast
  • One-hour rest prior to initial measurement
  • Metabolic rate then measured hourly from 8:00 am (measurement 1) to 4:00 pm (measurement 8) on each day. 

Dependent variables

  • Within and between day variability in RMR
    • IC type: Two 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 one hour prior to initial measurement; after at least 30 minutes for each measurement thereafter. All patents were confined to bed for eight-hour measurement period, except for bathroom privileges
    • Measurement length: Specific length not specified but as measurement were made after at least 30 minutes 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 three consecutive cycles of the pneumotachograph
    • Fasting length: Overnight fast
    • Exercise restrictions prior to test: None mentioned
    • Room temp: Not mentioned
    • No. of measures within the measurement period: Eight 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 variability
    • Subject training of measuring process? Study and measurement techniques described to each subject prior to IC
    • Monitored heart rate? Yes
    • Body temperature? Yes
    • Medications administered? Not mentioned
    • Dietary: Not measured
    • Minute ventilation rate (VE) was measured using a digital pneumotachograph.
    • RMR measurements were recorded when the subject stabilized at a consistent VE  for three consecutive cycles of the pneumotachograph
    • Caloric expenditure was determined using the non-protein caloric equivalent for oxygen.

Independent variables

Day one and day two measurements

Other measures

  • Height and weight: Measured
  • Fat and fat-free body mass calculated according to the equations of Durin and Womersley from skinfold thickness measurements (biceps, triceps, ilac crest, subscapular).
Description of Actual Data Sample:
  • Initial N: Not given
  • Attrition (final N): N=14 healthy adults volunteered for the study:
    • Two males
    • 12 females
  • Age: (*mean age±std error mean) 26.8±1.7 years; range 22-47)
    • (*not broken down by gender)
  • Ethnicity: Not specified
  • Other relevant demographics: None specified
  • Anthropometrics: Mean±SE
    • Height: 167.4±2.0cm
    • Weight: 60.4±2.8kg
    • Fat-free body mass: 41.5±1.3kg
    • Fat mass: 18.9±2.3kg
  • Location: Atlanta, Georgia, USA.
Summary of Results:


Group Results

  • The average RMR for all measurements was 2% lower on day two than on day one. The greatest absolute difference between day one and day two in RMR was 5kcal per hour, and was much less for most measurements.
  • Trend for RQ to decrease throughout the day on both day one and day two 
    • The group mean average RQ range for day one was from 0.73 (taken at 8 a.m.) to 0.81 (taken at 2 p.m.). The group mean average taken on day two was from .81 (taken at 9 a.m.) to .73 (taken at 1 p.m.).
    • Declining RQ throughout the day is consistent with a progressive increase in lipoloysis with duration of fasting, such as the 12- to 20-hour fast in the current investigation
  • The average pulse rate for all subjects was 59.5 and 60.9 for days one and two, respectively 
  • Trend for oral body temperature to increase from an early morning minimum throughout the remainder of the day.

ICC for Day 1*

Measurement number      
1-8 8 a.m. to 4 p.m. sr=0.74 ar=0.96
1-3 8 a.m. to 10 a.m. sr=0.7 ar=0.87
4-6 11 a.m. to 1 p.m. sr=0.9 ar=0.96
7-9 2 p.m. to 4 p.m. sr=0.7 ar=0.87
2-4 9 a.m. to 11 a.m. sr=0.88 ar=0.96

Within the same day difference (Highest group mean RMR rate minus the lowest group mean RMR rate)

The greatest difference between an 0800 fasting measure (first measure) and 1200 fasting measure (5th measure) was approximately 4kcal per hour or 0.067kcal per minute.

ICC for Day 2

Measurement number      
1-8 8 a.m. to 4 p.m. sr=0.85 ar=0.98

1-3

8 a.m. to 10 a.m.

 sr=0.87 ar=0.95

4-6

11 a.m. to 1 p.m.

 sr=0.91 ar=0.97

7-9

2 p.m. to 4 p.m.

 sr=0.87 ar=0.95

2-4

9 a.m. to 11 a.m.

 sr=0.88 ar=0.96
  • *sr=single measure reliability (0.85 and above=good reliability, 0.76-0.84=questionable reliability, and 0.75 and below=poor reliability); ar=average reliability of three to eight measures (0.90 and above=good reliability, 0.81-0.89=questionable reliability, and 0.80 and below=poor reliability)
  • 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 one and two was 5kcal per hour and was much less for most measurements. Very similar RMR measurements were obtained in the middle part of both days.
  • During day one, 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 one, a good estimate of RMR was obtained by averaging measurements two to four (middle measurements)
  • RMR reliability was improved by averaging all measurements taken during the day, and maximum reliability was obtained by averaging the middle three RMR measurements
  • A similar trend was observed during day two, but the overall reliability was improved compared to day one
  • For day two, the best (most reliable) measure of RMR was found by averaging measurements four to six; however, the other groupings one to three and seven to nine provided very good estimates of RMR. These averages were more reliable than the comparable measurements on day one.

The magnitude of between-measurement variability was derived for the average of two or more within-subject measurements. Relevant 95% confidence intervals were:

Day 1

  • Measurements at one to two (i.e., 8:00 a.m. and 9 a.m.)
    ±11kcal per hour (264kcal per day)
  • Measurements one to three (i.e., 8:00 a.m., 9:00 a.m. and 10 a.m.)
    ±9.3kcal per hour (223kcal per day)
  • Measurements two to three(i.e., 9:00 a.m. and 10:00 a.m.)
    ±6.0kcal per hour (144kcal per day)
  • Measurements two to four (i.e., 9:00 a.m., 10:00 a.m. and 11:00 a.m.)
    ±4.0kcal per hour (96kcal per day).

Day 2

Measurements two to four ±4.0kcal per hour (96kcal per day).

Author Conclusion:

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 two 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 one and two 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.
Funding Source:
Government: NIH
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Limitations

  • Small sample size; especially males
  • ? generalizability; 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 eight hours on two days
  • Use of face mask rather than ventilated canopy system may not have been as reliable; need further testing.

Working Group Members

Had 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
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
  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
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? No
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? No
  2.2. Were criteria applied equally to all study groups? ???
  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? ???
3. Were study groups comparable? 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
  3.3. 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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  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? 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? ???
  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? 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
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  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
  8.1. 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
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  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? Yes
  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? Yes
  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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes