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

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To determine if REE measurements are reproducible in stable COPD patients
  • To determine the influence of physical activity on the REE measurement
  • To determine if there is a difference in REE measurements using a ventilated hood or a mouthpiece.
Inclusion Criteria:
  • COPD patients in stable condition admitted to a pulmonary rehabilitation center
  • Maintenance medications were allowed
  • Healthy volunteers.
Exclusion Criteria:

None specified.


Description of Study Protocol:

Recruitment

  • COPD patients in stable clinical condition admitted to a pulmonary rehabilitation center were included as subjects
  • Healthy volunteers consisted of hospital staff members.

Design

Five different sub-studies were reported:

  • Study 1: Cross-sectional
  • Study 2: Time series
  • Study 3: Cross-sectional
  • Study 4: Time series
  • Study 5: Randomized controlled crossover trial.

Statistical Analysis

  • Comparisons between measurements under different circumstances were made using the statistical analysis of Bland and Altman
  • The differences in REE under different circumstances were plotted against the means of the two methods, which was then used to calculate
    • The overall mean bias (mean difference) between the two methods
    • The associated limits of agreement (+2 standard deviations of the differences between methods)
    • The extent to which the mean bias changes with an increase in the mean of two measurements.
Data Collection Summary:

Timing of Measurements

  • Measurements were performed in the early morning after a 10-plus-hour fast, approximately two hours after patients had received maintenance medication
  • Study 2: Effect of light activities of daily living before the measurement was tested on two consecutive days
  • Study 3: REE calculated after five, 10, 15, 20 and 25 minutes
  • Study 4: Reproducibility of REE measurements during two-month interval was established.

Dependent Variables

  • Measured REE [(VO2, L per minute), VCO2 (L per minute; ml per kg per minute), RQ, ventilation (L per minute)]:
    • IC type: Computerized open circuit ventilated hood
    • Equipment of calibration: Extensive description; completed at the beginning and at the end of each test
    • Coefficient of variation using std gases: Yes
    • Rest before measure (state length of time rested if available): Lying in semi-recumbent position; taken at 8:30 to 9:30 A.M.
    • Measurement length: Measurements of different duration were compared: five, 10, 15, 20, 25 and 30 minutes
    • Steady state: Investigators ensured that the subjects did not move or sleep; after initiating the measurements, time was allowed (±7 minutes) to adjust to the hood and to stabilize energy expenditure
    • Fasting length: Yes, 10 hours; two hours after maintenance medications
    • Exercise restrictions XX hours prior to test? As part of study question, activities of daily living were evaluated in Study 2.
    • Room temperature: Not specified
    • Number of measures within the measurement period: Was part of Study 4
    • Were some measures eliminated?
    • Were sets of measurements averaged? No
    • If average, identify length of each measure and number of measurements?
    • Coefficient of variation in subjects’ measures? Not specified
    • Training of measurer? Given the equipment specifications, yes
    • Subject training of measuring process? Subjects allowed initial time to acclimatize to IC
    • Monitored heart rate? Unknown
    • Body temperature? Unknown
    • Medications administered? Mention of broncho-dilators and theophylline
    • Inspiratory vital capacity; forced expiratory volume in one second (FEV1); arterial oxygen (carbon dioxide) tension (i.e., PaO2 (kPa) and PaCO2 (kPa)
  • Study outcomes: 
    • Study 1 outcome: Variability and accuracy of measurement
    • Study 2 outcome: Differences in measurements after no activity and light activity
    • Study 3 outcome: Calculated REE
    • Study 4 outcome: Reproducibility of the measurement
    • Study 5 outcome: Difference between measurements with mouthpiece vs. hood.

Independent Variables

  • Study 1: Ethanol combustion
  • Study 2: Activities of daily living vs. rest:
    • One day one, patients were allowed to dress, wash and walk to the metabolic ward. After lying down for 20 minutes, energy expenditure was measured over a 30-minute period.
    • On the next day, the patients stayed in their beds until the investigator took them in a wheelchair to the metabolic ward. Both measurements completed in the same position.
  • Study 3: Length of measurement
  • Study 4: Measurement one vs. measurement two (two months later)
  • Study 5: Ventilated hood vs. mouthpiece.

 

Description of Actual Data Sample:
  • Final N: See below  (gender not specified)
  • Age: See below
  • Ethnicity: Unknown; probably Dutch as study was done in the Netherlands.

Anthropometrics

  • Study 1: Variability and accuracy of the method (12 stable COPD patients)
  • Study 2: Effect of activities of daily living
  • Study 3: Length of measurement
    • N=12 patients aged mean 66±6 years
    • Gender unknown.

Patients Controls

  N=12
Mean±
SD
N=14
Mean±SD

Age

66±6 31±8

Weight

65.7±11.0 65.5±10
Height 170.0±7.0 172.0±8.1

IVC, percent

61±16  
FEV1, percent 29±10  

PaO2 (kPa), percent

8.2±1.5  

PaCO2 (kPa), percent

5.5±0.6  

 

  • Study 4: Reproducibility of the method
    • N=12 patients aged mean 66±6 years
    • Gender unknown.

Patients

N=12 Mean±SD

Age

65±9

Weight

64.7±14.3
Height 168.0±7.8
IVC, percent 70±20

FEV1, percent

34±16

PaO2 (kPa), percent

8.1±1.4

PaCO2 (kPa), percent

5.8±0.9

  • Study 5: Ventilated hood or mouthpiece
    • N=12 patients aged mean 66±6 years
    • Gender unknown.

Patients Controls

 

N=12
Mean±
SD
N=6
Mean±SD

Age

63±7 31±16

Weight

61.7±8.8 73.0±10.4

Height

170.0±7.0 177.3±8.2

IVC, percent

61±16  
FEV1, percent 29±10  
PaO2 (kPa), percent 8.2±1.5  

PaCO2 (kPa), percent

5.5±0.6  

 

Location

Netherlands.


 

Summary of Results:

Study 1: Variability and Accuracy of the Method

  • Variability and Method Accuracy: Ethanol combustion tests revealed that the gain during the calibration was slight to high (2.2%) and that the deviation of measurements was 2.7% for O2, 2.1% for CO2, and 1.7% for RQ
  • Study 1, after 12 patients (mean age 66±6 years) were awakened and lying in a semi-recumbent position, a 7-minute acclimatization period to the hood was allowed to stabilize energy expenditure
  • [Analyst note: Measurement length was not stated but due to association with Study 2, most likely 30 minutes; one dropout due to claustrophobia.]

Study 2: Effect of Activities of Daily Living

  • The same 11 patients from Study 1 were allowed to awaken, dress, wash and walk to the metabolic ward. Once they arrived, they were asked to lie down and for a 20-minute rest period; then, a 30-minute RMR was taken. On a separate day, the patients did not get out of bed and were wheeled down to the metabolic ward for a RMR measure. No significant group mean RMR differences were established between measurements performed after awakening, being wheeled down to the measurement lab and allowing a seven-minute acclimatization period compared to a RMR measure taken after light physical activities and allowing a 20-minute rest (1,406±238kcal vs. 1,431±259kcal per day).
  • [Analyst note: Results section for this study reference Figure 2 that reports data for 11 individuals and discussed in text as one patient being claustrophobic in Study 1. In Figure 2, individual RMR kcal per day difference expressed relative to the mean RMR (RMR rest plus RMR activity for Group 2) ranges from resting RMR being approximately 30 to 70kcal greater to activity RMR (after a 20-minute rest) being 5 to 70kcals greater.]

Study 3: Length of Measurement

  • N=12 patients aged mean 66±6 years
  • Gender unknown.

  Patients         Controls
  N=12 N=14
  Mean±SD Mean±SD
Age 66±6 31±8
Weight 65.7±11.0

65.5±10

Height                  170.0±7.

172.0±8.1

IVC, percent                

61±16

 
FEV1, percent              

29±10

 
PaO2 (kPa), percent       

8.2±1.5

 
PaCO2 (kPa), percent  

5.5±0.6

 

Measured REE did not differ significantly between measurements of five, 10, 15, 20, 25 and 30 minutes’ duration. (no P-value given). 

Time, Minutes Patients Control

Five

1,420±242 1,510±227

10

1,410±226 1,505±224

15

1,410±237 1,514±225

20

1,414±239 1,521±229
25 1,428±243 1,531±229

30

1,436±245 1,535±231
  • In Study 3, the same group of patients and an additional 14 healthy controls (mean age 31±8 years), group mean RMR not differ between a five-, 10-, 15-, 20-, 25- and 30-minute measurement duration
  • [Analyst note: There is no rest time described for Study 3; therefore, healthy adults either slept overnight in facility and were wheeled down and given a seven-minute acclimatization period after awakening or allowed to complete daily living activities and given a 20-minute rest period]
  • Group mean RMR in healthy adults ranged from the lowest at 1,505±224kcal per day after a 10-minute measurement interval (plus rest time) to 1,535±231kcal per day at a 30-minute measurement interval (plus rest time)
  • Group mean RMR in patients ranged from the lowest at 140±267kcal per day after a 10-minute measurement interval (plus rest time) to 1,436±245kcal per day at a 30-minute measurement interval (plus rest time).

Study 4: Reproducibility of the Method

  • N=12 patients aged mean 66±6 years
  • Gender unknown.

  Patients
  N=12
  Mean±SD
Age 65±9
Weight 64.7±14.3
Height 168.0±7.8
IVC, percent 70±20

FEV1, percent

34±16
PaO2 (kPa), percent

8.1±1.4

PaCO2 (kPa), percent 5.8±0.9

Average REE in the 12 weight-stable patients after two months was not significantly different from the baseline value at admission to the center (198±138kcal per day).

Study 5: Ventilated Hood or Mouthpiece

  • N= 12 patients aged mean 66±6 years
  • Gender unknown.

  Patients Controls
  N=12 N=6
  Mean±SD Mean±SD

Age

63±7                31±16

Weight

61.7±8.8          73.0±10.4

Height 

170.0±7.0        177.3±8.2

IVC, percent

61±16  
FEV1, percent 29±10  
PaO2 (kPa), percent 8.2±1.5  

PaCO2 (kPa), percent

5.5±0.6  

The difference between measurements with mouthpiece and ventilated hood was larger in patients than in control subjects, but no systematic difference could be established between both devices in either group. The difference between measured REE (using only O2) or VO2 and VCO2 measurements amounted to 16kcal per day, or -1.9% (range, -3% to 0.3%).

 

Author Conclusion:

As stated by the author in body of report:

  • The ethanol combustion tests revealed that when properly maintained, calibrated and interfaced to the patient, the device is very accurate
  • A considerable number of patients were dyspneic at rest or suffered from severe exercise impairment... in agreement with finding in patients not suffering from COPD, we found that limited physical activity had no measurable effect on REE when a short rest was taken before the assessment
  • Based on the experiments and to obtain an optimum between sample frequency and acceptability of the measurements, we changed the duration of our standard REE experiments from 30 minutes to 15 minutes. Reproducibility of two measurements with the ventilated hood performed under the same standard conditions with an interval of two months was excellent and comparable with findings in healthy subjects…
  • Although in some patients measurements with a mouthpiece and a ventilated hood indeed varied substantially, no systematic difference was established in patients or control subjects
  • The following implications for the clinical measurement of REE can be drawn from these results: REE measurements using a ventilated hood are highly reproducible, suggesting that one measurement will suffice to characterize resting metabolic rate at a certain time point in patients with stable COPD.... REE in patients with severe COPD can be measured on an outpatient basis providing a rest is taken before the measurement.
Funding Source:
University/Hospital: University of Limbourg
Reviewer Comments:

Strengths

  • Comprehensive, and detailed description of the indirect calorimeter used, with attention to gas pressure and flow, humidity and calibration
  • Use of the Bland-Altman technique to establish limits of agreement between two measurements two months apart and in comparing differences between measurement type
  • Did a nice job describing the medication intervening possibilities of increasing or decreasing REE.

Generalizability/Weaknesses

  • Generalizability to pulmonary rehab settings and due to small sample size, unable to apply to general outpatient clinic settings
  • Very small convenience patient samples; not many specifics about inclusion and exclusion criteria
  • Healthy ‘control’ sample is also open to bias as it is a convenience sample of hospital staff members. Since no blinding is possible, staff members more trained than patients. Also, control sample is younger and heavier than patient sample, weakening statements of comparison based on tolerance to machine type tolerance and age.
  • Intervening factors: As discussed by the researchers, the precise influence of B2 agonists and theophylline was not measured because withdrawing treatment might exacerbate the condition. [In contrast], bronchodilating treatment itself may reduce the work of breathing.

Analyst Note

Little information was available about the statistical analysis and which sample was used for each of the five studies included.

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? Yes
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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  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
  3.4. 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? ???
  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? Yes
  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? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? No
  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? ???
  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? ???
  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? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? ???
  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)? ???
  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? No
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes