Nocturnal Hypoxemia Is Associated with Sarcopenia in COPD Patients.

ABSTRACT

OBJECTIVE: Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide. Our previous studies have identified that nocturnal hypoxemia causes skeletal muscle loss (i.e. sarcopenia) in in vitro models of COPD. RATIONALE We aimed to extend our preclinical mechanistic findings by analyzing a large sleep registry to determine whether nocturnal hypoxemia is associated with sarcopenia in COPD patients. METHODS: Sleep studies from COPD patients (n=479) and control subjects without COPD (n=275) were analyzed. Patients with obstructive sleep apnea (OSA), as defined by apnea hypopnea index >5, were excluded. Pectoralis muscle cross sectional area (PMcsa) was quantified using CT scans performed within one year of the sleep study. We defined sarcopenia as less than the lowest 20% residuals for PMcsa of controls, which was adjusted for age, BMI, and stratified by sex. Youden's optimal cutpoint criteria was used to predict sarcopenia based on mean oxygen saturation (mean SaO2) during sleep. Additional measures of nocturnal hypoxemia were analyzed. Pectoralis muscle index (PMI) was defined as PMcsa normalized to BMI. RESULTS: On average, COPD males had 16.6% lower PMI than control males (1.41+0.44 vs 1.69+0.56 cm2/BMI, p<0.001), while COPD females had 9.4% lower PMI than control females (0.96+0.27 vs 1.06+0.33 cm2/BMI, p<0.001). COPD males with nocturnal hypoxemia had a 9.5% decrease in PMI versus COPD with normal O2 (1.33+0.39 vs 1.47+0.46 cm2/BMI, p<0.05), and 23.6% decrease compared to controls (1.33+0.39 vs 1.74+0.56 cm2/BMI, p<0.001). COPD females with nocturnal hypoxemia had a 11.2% decrease versus COPD with normal O2 (0.87+0.26 vs 0.98+0.28 cm2/BMI, p<0.05), and 17.9% decrease compared to controls (0.87+0.26 vs 1.06+0.33 cm2/BMI, p<0.001). These findings were largely replicated using multiple measures of nocturnal hypoxemia. CONCLUSIONS: We defined sarcopenia in the pectoralis muscle using residuals that take into account age, BMI, and sex. We found that COPD patients have lower PMI than non-COPD patients, and that nocturnal hypoxemia was associated with an additional decrease in the PMI of COPD patients. Additional prospective analyses are needed to determine a protective threshold of oxygen saturation to prevent or reverse sarcopenia due to nocturnal hypoxemia in COPD.