NOCTURNAL SATURATION AND RESPIRATORY MUSCLE FUNCTION IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Background - Nocturnal desaturations, mainly caused by hypoventilation, occur frequently in patients with chronic obstructive pulmonary disease (COPD). Daytime arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) appear to predict which patients will desaturate at night. It is unknown if respiratory muscle strength, which may be decreased in these patients, plays an additional part. Methods - Polysomnography, maximal respiratory pressures, lung function, and arterial blood gas tensions were measured in 34 patients with COPD (mean (SD) forced expiratory volume in one second (FEV(1)) 41.7 (19.9)% pred). Results - Significant correlations were found between the mean nocturnal arterial oxygen saturation and maximal inspiratory mouth pressure (r = 0.65), maximal inspiratory transdiaphragmatic pressure (r = 0.53), FEV(1) (r = 0.61), transfer coefficient (KCO) (r = 0.38), arterial oxygen saturation (SaO(2)) (r = 0.75), and PaCO2 (r = -0.44). Multiple regression analysis showed that 75% of the variance in nocturnal SaO(2) was explained by a combination of SaO(2) (70%) and FEV(1) (5%). Conclusion - Inspiratory muscle strength and nocturnal saturation data are correlated, but daytime SaO(2) and FEV(1) remain the most important predictors of nocturnal saturation.