COPD: Determination of Energy Needs (2007)

Citation:

Vestbo J, Prescott E, Almdal T, Dahl M, Nordestgaard BG, Andersen T, Sorensen TIA, Lange P.  Body mass, fat-free body mass, and prognosis in patients with chronic obstructive pulmonary disease from a random population sample.  Am J Respir Crit Care Med 2006;173:79-83.

PubMed ID: 16368793
 
Study Design:
Cohort
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To study the distribution and prognostic importance of body mass and fat free mass in patients with COPD identified from an ongoing population study, the Copenhagen City Heart Study.
Inclusion Criteria:
  • Age 20 years or more
  • Subjects with COPD identified on the basis of a ratio of FEV1 to FVC of less than 0.7 or presence of chronic mucus secretion
Exclusion Criteria:
  • Self-reported asthma
  • Missing data
Description of Study Protocol:

Recruitment

Data from the Copenhagen City Heart Study.  Population derived from a random, age-stratified sample of 19,329 individuals recruited in 1976.

Design

Population-based cohort.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Fat free mass was measured using bioelectrical impedance analysis and patients were followed for a mean of 7 years.

Statistical Analysis

To assess the independent contribution of BMI and fat free mass index to mortality in COPD, the Cox proportional hazards model was used, but both were not used in the same model.  The results of the regression analyses are given in terms of estimated relative risks (hazard ratios) with corresponding 95% confidence intervals.

Data Collection Summary:

Timing of Measurements

Subjects measured and monitored until December 2002 for all cause mortality and until January 1, 2000 for COPD related mortality.

Dependent Variables

  • Mortality measured through Notification of Death and causes of death from National Board of Health 
  • Systemic inflammation measured through plasma fibrinogen using a standard colorimetric assay

Independent Variables

  • Body mass index calculated and categorized into 4 groups using WHO guidelines
  • Fat free mass index measured with bioelectrical impedance in non-fasting state

Control Variables

  • Age
  • Sex
  • Smoking
  • Lung function measured through dry wedge spirometry and classified according to GOLD (Global Initiative for Chronic Obstructive Lung Disease) guidelines 
Description of Actual Data Sample:

Initial N: 2,404 patients with COPD identified.  After application of exclusion criteria, 1,898 patients with COPD available for analysis.

Attrition (final N):  1,898 subjects

Age: mean age GOLD stage 0 = 57.6 years, stage 1 = 64.7 years, stage 2 = 66.0 years, stage 3 = 67.9 years, stage 4 = 64.1 years

Ethnicity:  not mentioned 

Other relevant demographics:

Anthropometrics:

Location:  Denmark

 

Summary of Results:

 Mortality Risk Associated with Low Fat Free Mass Index and Low BMI

  Low Fat Free Mass Index Low BMI

All COPD Subjects:  Overall mortality

1.5 (1.2 - 1.8) 1.8 (1.3 - 2.7)

All COPD Subjects: COPD mortality

2.4 (1.4 - 4.1)

3.2 (1.5 - 7.0)

Subjects with normal BMI:  Overall mortality

1.3 (1.1 - 1.7)

 --

Subjects with normal BMI:  COPD mortality 2.0 (0.9 - 4.5)  --

Other Findings

The mean fat free mass index was 16.0 kg/m2 for women and 18.7 kg/m2 for men.

Among subjects with normal BMI, 26.1% had a fat free mass index lower than the 10th percentile of the general population.

BMI and fat free mass index were significant predictors of mortality, independent of relevant covariates.

Being in the lowest 10th percentile of the general population for fat free mass index was associated with a hazard ratio of 1.5 (95% confidence interval, 1.2 - 1.8) for overall mortality and 2.4 (95% confidence interval, 1.4 - 4.0) for COPD-related mortality.

Fat free mass index was also a predictor of overall mortality when analyses were restricted to subjects with normal BMI. 

Author Conclusion:
In conclusion, our study indicates that patients with COPD are at risk of a low FFM and that a low FFM is prevalent even among subjects with normal BMI.  Because fat free mass index is associated with prognosis, it seems that assessment of fat free mass provides important information in COPD and should be considered in the routine evaluation of patients with this condition.
Funding Source:
Reviewer Comments:
Authors note that fat free mass index measures may not be precise since they were completed in a nonfasting state.
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? 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
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
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
  3.2. 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? 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
  3.6. 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? N/A
  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? Yes
  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? Yes
  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? N/A
  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? 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? Yes
  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? ???
  7.1. 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? N/A
  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? 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)? 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
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? 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