COPD: Determination of Energy Needs (2007)


Carter R, Holiday DB, Stocks J, Grothues C, Tiep B.  Predicting oxygen uptake for men and women with moderate to severe chronic obstructive pulmonary disease.  Arch Phys Med Rehabil 2003;84(8):1158-64.

PubMed ID: 12917855
Study Design:
Cross-Sectional Study
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To develop regression equations for estimating peak oxygen consumption for men and women with moderate to severe COPD from the 6-minute walk test.
Inclusion Criteria:
  • Moderate to severe COPD based on indices of pulmonary function
  • All patients on a stable treatment program and had not been previously enrolled in a pulmonary rehab program
Exclusion Criteria:
  • Restrictive lung process, or heart, circulatory, renal, metabolic or neurologic processes that would contraindicate engagement in exercise training
Description of Study Protocol:


Methods not described.


Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Not applicable.

Statistical Analysis

Regression techniques were used to explore relationships among variables under study.  Backward elimination processes used for model building.

Data Collection Summary:

Timing of Measurements

Measurements completed and used to develop equations.

Dependent Variables

  • Pulmonary function testing:  maximal forced expiratory flow-volume loops performed using spirometry, lung volumes measured with body plethysmograph, diffusing capacity of lung for carbon monoxide measured by single-breath technique
  • Cycle ergometry with gas exchange using ramp protocol
  • 6-minute walk test 

Independent Variables

  • COPD

Control Variables


Description of Actual Data Sample:

Initial N: 124 patients (90 men, 34 women)

Attrition (final N):  124 patients

Age:  aged 45 - 81 years

Ethnicity:  not mentioned

Other relevant demographics:


Location: United States


Summary of Results:


Variable Men


P value

FEV1 (L)

1.44 +/- 0.44 1.08 +/- 0.26 0.0001


3.59 +/- 0.81

2.35 +/- 0.44


DLCO (ml/min/mmHg)

14.71 +/- 6.10

10.34 +/- 3.90


MIP (cmH2O) 68.26 +/- 22.44 52.17 +/- 18.24 0.0006
Exercise time (min) 9.77 +/- 2.64 7.66 +/- 2.10 0.0001
Work (W) 69.0 +/- 25.3 48.7 +/- 18.9 0.0001
VO2 (ml/min) 1183.8 +/- 302.1 860.3 +/- 256.4 0.0001
VCO2 (ml/min) 1153.3 +/- 349.8 830.5 +/- 281.2 0.0001
VE (L) 42.6 +/- 11.9 31.1 +/- 8.1 0.0001
RR (breaths/min) 30.7 +/- 5.7 33.4 +/- 7.0 0.0289
VT (ml) 1424.6 +/- 370.3 947.0 +/- 229.1 0.0001
VDS/VT (%) 0.29 +/- 0.05 0.31 +/- 0.05 0.0230
SaO2 (%) 95.6 +/- 3.6 95.8 +/- 3.3 NS
HR (bpm) 118.3 +/- 19.3 113.5 +/- 14.4 NS
SBP (mmHg) 164.4 +/- 22.2 156.2 +/- 19.4 NS
DBP (mmHg) 81.4 +/- 9.3 77.5 +/- 7.9 0.0284

Other Findings

Peak oxygen uptake averaged 1184 +/- 302 ml/min for men (58% of predicted) and 860 +/- 256 ml/min for women (68% of predicted).

Ventilatory reserve was limited at an achieved peak ventilation of 79.9% +/- 19.1% of predicted.

Borg scores for dyspnea and leg fatigue were equivalent for each test modality, with leg fatigue being slightly higher for each gender.

Work capacity based on the 6 minute walk test was the strongest independent predictor of peak VO2 (r = 0.81, P < 0.0001) whereas that for distance ambulated was correlated at r = 0.54, P < 0.0001.

Generalized regression modeling was used to develop equations for the estimation of peak VO2 for the 6 minute walk test.  Additional variables included in the model were diffusing capacity of lung for carbon dioxide, FVC, maximal inspiratory pressure, weight, and age, with their appropriate interactions.

Regression Model for Men:  VO2 = 299.76 + (0.013 x work) + (19.11 x DLCO) + (66.73 x FVC) + (-0.71 x MIP) + (2.55 x weight) + (-4.44 x age)

Regression Model for Women:  VO2 = 655.36 + (0.013 x work) + (7.8 x DLCO) + (-153.67 x FVC) + (4.59 x MIP) + (2.55 x weight) + (-4.44 x age)

This derived regression model accounted for 79% of the variance for estimation of peak VO2 in the patients studied. 

Author Conclusion:
No studies could be found that evaluated the relationship of the 6 minute walk test to peak VO2 for men and women with COPD.  This study showed that the work calculation is an improved index as an outcome for the 6 minute walk test.  Peak VO2 can be estimated for men and women using the generalized equations presented.
Funding Source:
Reviewer Comments:
Recruitment methods not described.  Regression equation for women only based on 34 women.  Authors note uncertainty about parts of the equation being negative/positive based on gender.
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) N/A
  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) N/A
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? ???
  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? ???
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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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? 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
  4.3. 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? 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.) Yes
  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? 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? 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? Yes
  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? 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
  7.3. 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? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? 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? ???
  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? ???
  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? 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