Clinical characteristics and lung function in chronic obstructive pulmonary disease complicated with impaired peripheral oxygenation

Abstract

During exercise testing, patients with chronic obstructive pulmonary disease (COPD) often present with ventilatory limitations and various combinations of impaired peripheral oxygenation (IPO) to the exercising muscles. The entities of IPO include anemia, circulation impairment and deconditioning. COPD-IPO is not widely accepted as being a subgroup of COPD. Therefore, the aim of this study was to evaluate the clinical features of COPD-IPO patients. Forty-seven COPD patients underwent cardiopulmonary exercise testing. COPD-IPO was identified when all IPO variables had abnormal values. The patients who did not meet the COPD-IPO criteria were defined as the NIPO group. The variables with abnormal values included peak oxygen uptake (${\dot{\text{V}}\text{O}}_{ 2}$) <85 % predicated, anaerobic threshold <40 %${\dot{\text{V}}\text{O}}_{{ 2 {\text{max}}}}$ pred, ${\dot{\text{V}}\text{O}}_{ 2}$-work rate slope <8.6 ml/watt, oxygen pulse <80 %pred, and ventilatory equivalents for O₂ and CO₂ at nadir (>31 and >34, respectively). Anthropometrics, biochemistry, and lung function were compared between the groups. Forty-six COPD patients were enrolled after excluding one patient who had technical difficulties in performing the exercise tests. Despite FEV₁ and FVC being similarly reduced (p = NS) between the groups, the COPD-IPO (n = 13, 28 %) patients had lower body mass index and were taller, and had impaired diffusing capacity and larger total lung capacity and air-trapping (all p < 0.05). We concluded that COPD patients with all six variables having abnormal values are a unique subgroup and that identification of these patients is worthwhile for further investigations and management such as exercise training and nutritional supplements.