The Relationship of Energy Malnutrition, Skeletal Muscle and Physical Functional Performance in Patients with Stable Chronic Obstructive Pulmonary Disease

Abstract

Weight loss is a factor that affects prognosis in patients with chronic obstructive pulmonary disease (COPD) independent of lung function. One of the major factors for weight loss is energy malnutrition. There have been no reports on the factors related to energy malnutrition in COPD patients. This retrospective observational study aimed to investigate these factors. We included 163 male subjects with COPD. Respiratory quotient (RQ), an index of energy malnutrition, was calculated by expiratory gas analysis using an indirect calorimeter. RQ < 0.85 was defined as the energy-malnutrition group and RQ ≥ 0.85 as the no energy-malnutrition group. Factors related to energy malnutrition were examined by multivariate and decision-tree analysis. We finally analyzed data from 56 selected subjects (median age: 74 years, BMI: 22.5 kg/m2). Energy malnutrition was observed in 43%. The independent factors associated with energy malnutrition were tidal volume (VT) (OR 0.99; 95% CI 0.985−0.998; p = 0.015) and Th12 erector spinae muscle cross-sectional area SMI (Th12ESMSMI) (OR 0.71; 95% CI 0.535−0.946; p = 0.019). In decision-tree profiling of energy malnutrition, VT was extracted as the first distinguishable factor, and Th12ESMSMI as the second. In ROC analysis, VT < 647 mL (AUC, 0.72) or Th12ESMSMI < 10.1 (AUC, 0.70) was the cutoff value for energy malnutrition. Energy malnutrition may be an early warning sign of nutritional disorders.

Keywords: chronic obstructive pulmonary disease; energy malnutrition; erector spinae muscle; indirect calorimetry; physical functional performance; respiratory quotient; ventilation volume.

Figure 1

Flowchart of subject recruitment in this study. Abbreviation: COPD—chronic obstructive pulmonary disease.

Figure 2

A decision-tree analysis for energy malnutrition. The pie graphs indicate the proportion of subjects with RQ < 0.85 (white) and subjects with RQ ≥ 0.85 (black). Abbreviation: RQ—respiratory quotient; Th12 ESM_SMI—skeletal muscle index of Th12 Erector Spinae muscles; VT—tidal volume; BMI—body mass index; %FEV₁—FEV₁ predicted.

Figure 3

ROC analysis of Th12 ESM_SMI, VT for energy malnutrition. Abbreviation: ROC—receiver operating characteristic, Th12 ESM_SMI—skeletal muscle index of Th12 Erector Spinae muscles; VT—tidal volume.