Sleep disordered breathing in chronic obstructive pulmonary disease

We prospectively studied sleep disordered breathing in 50 consecutive patients (39 males) with chronic obstructive pulmonary disease (COPD) with chronic respiratory failure (CRF) (n=33) and without CRF (n=17) by performing polysomnography. Patients with CRF had a lower mean nocturnal oxygen saturation (SaO2 %) (88.6+/-6.7 vs. 96.3+/-0.8; p=0.0001) and a lower minimal nocturnal SaO2 (73.6+/-12.0 vs. 84.3+/-7.3; p=0.002) compared to those without CRF, suggesting that patients with CRF tend to have more severe drops in nocturnal SaO2. Patients with CRF also had a lower FEV1 (% predicted) (p=0.01) and PEFR (% predicted) (p=0.031) compared to those without CRF suggesting an indirect relation to the oxygen saturation. Other pulmonary functions were comparable between both the groups. Among patients with and without CRF, the total sleep time (minutes); the rapid eye movement (REM) stage (% of total sleep time); the non-rapid eye movement (NREM) stage (% of total sleep time) were comparable (p=NS). Only three of the 50 patients with COPD had a significant (>5) apnea-hypopnea index (AHI) (total no. of apneas + total no. of hypopneas/ total sleep time [(hours) = AHI] and these three patients had a mean BMI = 27.7 which was higher than the mean BMI of the whole group (21.1). The AHI was comparable in patients with and without respiratory failure. Multiple regression analysis revealed a positive correlation between AHI and the neck circumference (r=0.41; p=0.005) and BMI (r=0.31; p=NS). There was a small but statistically insignificant negative correlation between AHI and neck length (r= -0.28; p=NS). We conclude that, BMI per se contributes to the AHI and nocturnal desaturation in patients with COPD.