COPD: Determination of Energy Needs (2007)

Baarends EM, Schols AM, Akkermans MA, Wouters EF.  Decreased mechanical efficiency in clinically stable patients with COPD.  Thorax 1997;52(11):981-6. PubMed ID: 9487347
Study Design:
Cross-Sectional Study
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To measure the mechanical efficiency of submaximal leg exercise, and to characterize patients with a potentially low efficiency in terms of body composition, resting energy expenditure, lung function, and symptom limited exercise performance.
Inclusion Criteria:
  • Clinically stable patients with moderate to severe COPD according to criteria of American Thoracic Society 
Exclusion Criteria:
  • Patients exhibiting an increase in FEV1 > 10% after inhalation of beta-2 agonists or those requiring oxygen supplementation (PaO2 at rest <7.3 kPa)
  • None had respiratory tract infection or clinically visible signs of edema
  • None had any known cardiovascular, neurological, endocrine or locomotor disease
Description of Study Protocol:


All patients were admitted to a pulmonary rehab center in stable clinical condition.


Cross-Sectional Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Not applicable.

Statistical Analysis

Wilcoxon rank test used to test within group differences.  Group was split into those with low efficiency (17% or lower) and normal efficiency.  Mann-Whitney U test used to compare groups.  Bonferroni correction applied when necessary.

Data Collection Summary:

Timing of Measurements

Metabolic and ventilatory variables were measured breath by breath during submaximal cycle ergometry exercise performed at 50% of symptom limited achieved maximal load.

Dependent Variables

  • Pulmonary function tests:  FEV1, FVC, total lung capacity, intrathoracic gas volume, and airways resistance measured by body plethysmography, carbon monoxide transfer factor measured by single breath method, arterial oxygen and carbon dioxide tensions analyzed with blood gas analyzer
  • Body height, weight, BMI
  • Fat free mass assessed by bioelectrical resistance measurements
  • Resting energy expenditure and gas exchange measured with indirect calorimetry
  • Heart rate
  • Incremental cycle ergometry test
  • Blood samples analyzed for lactate
  • Submaximal leg exercise tests

Independent Variables

  • COPD

Control Variables


Description of Actual Data Sample:

Initial N: 33 clinically stable COPD patients, 23 men, 10 women

Attrition (final N):  33

Age:  median age 61 years, range 38 - 82 years

Ethnicity:  not mentioned

Other relevant demographics:


Location:  The Netherlands


Summary of Results:

Submaximal exercise response in patients with low and normal mechanical efficiency

  Low efficiency (<17%, n = 21) Normal efficiency (>17%, n = 12)

p value

VO2 (% peak)

85.1 (74.4 - 104.5) 73.6 (60.8 - 95.8) 0.002

RQ (% peak)

93.0 (60.9 - 120.2)

91.1 (86.8 - 101.9)


VE (% peak) 89.2 (72.9 - 110.0) 75.8 (64.5 - 100.6) 0.02
VO2/VE (ml/l) 25.6 (17.5 - 36.8) 20.9 (16.1 - 28.9) 0.005
Change in VO2/load (ml/watt) 20.6 (17.6 - 33.7) 14.6 (12.8 - 17.1) 0.000
VT (% peak) 102.3 (80.6 - 131.5) 89.6 (77.0 - 115.0) NS
BF (% peak) 90.0 (67.0 - 100.6) 86.1 (70.6 - 100.9) NS

HR (% peak)

88.7 (77.6 - 103.6)

87.4 (64.3 - 105.9)


StO2 (% peak) 101.1 (93.2 - 108.4) 101.5 (98.9 - 104.9) NS
VO2/HR (ml/x) 7.1 (4.6 - 12.4) 6.2 (5.0 - 11.8) NS

Other Findings

Median mechanical efficiency was 15.5% and ranged from 8.5% to 22.7%.

Patients with an extremely low mechanical efficiency (<17%, n = 21) demonstrated an increased VO2/VE compared with those with a normal efficiency (median difference 4.7 ml/l, p = 0.005) during submaximal exercise.

There was no difference between the groups differentiated by mechanical efficiency in blood gas tensions at rest, airflow obstruction, respiratory muscle strength, hyperinflation at rest, resting energy expenditure or body composition.

There was a significant difference in total airways resistance (92% predicted, p = 0.03) between the groups differentiated by mechanical efficiency. 

Author Conclusion:
In conclusion, the results of the present study suggest that many patients with COPD have decreased mechanical efficiency which is not related to body composition, REE, chronic hyperinflation, airflow obstruction, or respiratory muscle strength.  The findings suggest that the decreased efficiency is related to an increased oxygen cost of breathing during exercise.  Dynamic hyperinflation in patients with COPD is probably an important contributing factor to the increased oxygen cost of breathing during exercise, but this needs further investigation.
Funding Source:
Reviewer Comments:
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? 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.) 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? 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? 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? 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? 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