Predictors of nocturnal oxyhemoglobin desaturation in COPD.

It would be useful to detect predictors of marked nocturnal oxyhemoglobin desaturation (NOD) among COPD patients, who do not have respiratory failure when awake and sleep apnea (SA). Stable COPD patients with awake PaO2 ≥ 60 mmHg and PaCO2 ≤ 45 mmHg underwent cardio-respiratorypolysomnography to exclude SA and to assess NOD. The patients that spent more than 30% of nighttime with SpO2 < 90%, were defined desaturators (D), and the others non desaturators (ND). Pulmonaryfunction testing was performed to determine lung volumes, maximal flow rates, lung diffusion capacity for carbon monoxide and maximal inspiratory and expiratory pressure (PImax and PEmax). Negative expiratory pressure test was performed to assess tidal expiratory flow limitation. Supine pharyngometry was performed to determine upper airway size, shuttle walking test to assess exercise desaturation. Twenty-one patients were included in the study (18 male, age 66.0 ± 7.2 years, Body Mass Index 25.9 ± 4.4 kg/m2, FEV1 47.2 ± 16.4% pred., PaO274.7 ± 6.9 mmHg, PaCO240.3 ± 3.4 mmHg): 10 were D and 11 ND. Significant differences between the two groups were found in diurnal PaCO2 (D: 42.4 ± 3.0 vs. ND: 38.3 ± 2.6 mmHg; p < 0.01), diurnal SpO2 (D: 94.0 ± 1.5 vs. ND: 95.9 ± 0.9%; p < 0.01), inspiratory capacity (IC) (D: 69.6 ± 11.9 vs. ND: 87.0 ± 17.7% pred.; p < 0.05), and oro-pharyngeal junction area (OPJ) (D: 0.8 ± 0.2 vs. ND: 1.2 ± 0.3 cm2; p < 0.01). Among parameters related to marked NOD at the univariate analysis, SpO2 and OPJ remained as independent predictors after stepwise multiple regression analysis. These findings indicate that previously unrecognized factors such as smaller upper airway caliber and lung dynamic hyperinflation are associated with marked NOD in stable COPD patients without daytime respiratory failure and SA.