COPD assessment test and FEV₁: do they predict oxygen uptake in COPD?

Abstract

Background

Chronic obstructive pulmonary disease (COPD) manifests itself in complex ways, with local and systemic effects; because of this, a multifactorial approach is needed for disease evaluation, in order to understand its severity and impact on each individual. Thus, our objective was to study the correlation between easily accessible variables, usually available in clinical practice, and maximum aerobic capacity, and to determine models for peak oxygen uptake (VO₂peak) estimation in COPD patients.

Subjects and methods

Individuals with COPD were selected for the study. At the first visit, clinical evaluation was performed. During the second visit, the volunteers were subjected to the cardiopulmonary exercise test. To determine the correlation coefficient of VO₂peak with forced expiratory volume in 1 second (FEV₁) (% pred.) and the COPD Assessment Test score (CATs), Pearson or Spearman tests were performed. VO₂ at the peak of the exercise was estimated from the clinical variables by simple and multiple linear regression analyses.

Results

A total of 249 subjects were selected, 27 of whom were included after screening (gender: 21M/5F; age: 65.0±7.3 years; body mass index: 26.6±5.0 kg/m²; FEV₁ (% pred.): 56.4±15.7, CAT: 12.4±7.4). Mean VO₂ peak was 12.8±3.0 mL⋅kg⁻¹⋅min⁻¹ and VO₂peak (% pred.) was 62.1%±14.9%. VO₂peak presented a strong positive correlation with FEV₁ (% pred.), r: 0.70, and a moderate negative correlation with the CATs, r: -0.54. In the VO₂peak estimation model based on the CAT (estimated VO₂peak =15.148− [0.185× CATs]), the index explained 20% of the variance, with estimated error of 2.826 mL⋅kg⁻¹⋅min⁻¹. In the VO₂peak estimation model based on FEV₁ (estimated VO₂peak =6.490+ [0.113× FEV₁]), the variable explained 50% of the variance, with an estimated error of 2.231 mL⋅kg⁻¹⋅min⁻¹. In the VO₂peak estimation model based on CATs and FEV₁ (estimated VO₂peak =8.441− [0.0999× CAT] + [0.1000× FEV₁]), the variables explained 55% of the variance, with an estimated error of 2.156 mL⋅kg⁻¹⋅min⁻¹.

Conclusion

COPD patients’ maximum aerobic capacity has a significant correlation with easily accessible and widely used clinical variables, such as the CATs and FEV₁, which can be used to estimate peak VO₂.

Keywords:

• chronic obstructive pulmonary disease
• exercise
• oxygen uptake
• symptoms

Acknowledgments

The authors would like to thank all the volunteers who participated in this study and all researchers of the Cardiopulmonary Physiotherapy Laboratory of Federal University of Sao Carlos (LACAP – UFSCar) for their support. This study was funded by CNPq (protocol no 163789/2015–0) and FAPESP (protocol no 2015/26501–1).

Author contributions

All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; gave final approval of the version to be published; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.