Differences in Anthropometric, Sleep and Respiratory Characteristics between Hypercapnic and Normocapnic Patients...

Overlap syndrome (OS), the coexistence of chronic obstructive pulmonary disease and obstructive sleep apnea, is frequently characterized by the presence of daytime hypercapnia (pCO₂ ≥ 45 mmHg). The aim of this study was to investigate potential differences in anthropometric, sleep and respiratory characteristics between hypercapnic and normocapnic patients with OS.

Consecutive patients who underwent polysomnography, pulmonary function testing and arterial blood gases and had been diagnosed with OS were enrolled in the study.

According to pCO₂ levels in wakefulness, the patients were divided into group A, consisting of OS patients without hypercapnia (n = 108) or group B, consisting of OS patients with hypercapnia (n = 55). The majority of included patients in both groups were males (n = 92 in group A vs. n = 50 in group B). Group B had increased BMI (p = 0.001), neck (p = 0.017) and waist circumference (p = 0.013), higher scores in Epworth sleepiness scale (ESS) (p = 0.008), increased sleep efficiency (p = 0.033), oxygen desaturation index (p = 0.004) and time with oxyhemoglobin saturation <90% (p = 0.006) than group A. Also, Group B had decreased average and minimum oxyhemoglobin saturation during sleep (p < 0.001). Hypercapnic patients had lower FEV₁% (p = 0.003), FVC% (p = 0.004), pO₂ and pCO₂ (p < 0.001 for both) values compared with normocapnic patients. In binary regression analysis, which assessed various predictors on the likelihood of having hypercapnia, it was found that BMI (OR: 1.313, 95% CI: 1.048-1.646, p = 0.018) and FVC (OR: 0.913, 95% CI: 0.845-0.986, p = 0.020) were the major determinants of hypercapnia in OS patients.

Hypercapnic OS patients were more obese and sleepy and presented worse respiratory function in wakefulness and sleep hypoxia characteristics compared with normocapnic OS patients.