Nocturnal saturation and respiratory muscle function in patients with chronic obstructive pulmonary disease

Background N octurnal desaturations , m ainly caused by hypoventilation, occur frequently in patients w ith chronic ob­ structive pulm onary disease (C O PD ). D aytim e arterial oxygen and carbon di­ oxide tensions (P a 0 2 and PaC02) appear to predict w hich patients w ill desaturate at night. It is unknown if respiratory m uscle strength, w hich m ay be decreased in these patients, plays an additional part. Methods Polysom nography, m axim al respiratory pressures, lung function, and arterial blood gas tensions were m easured in 34 patients w ith C O PD (m ean (SD) forced expiratory volum e in one second (FEVj) 41-7 (19*9)% pred). Results S ignificant correlations were found betw een the m ean nocturnal arterial oxygen saturation and m axim al in ­ spiratory m outh pressure (r = 0*65), m ax­ im al inspiratory trans diaphragm atic pressure (r = 0*53), FEVi (r = 0-61), trans­ fer coefficient (KCO) (r = 0*38), arterial oxygen saturation (S a02) (r — 0-75), and PaC02 (r = —0*44). M ultiple regression analysis show ed that 75% of the variance in nocturnal S a o 2 was explained by a com ­ bination o f S a 0 2 (70%) and FEVX (5%). Conclusion Inspiratory m uscle strength and nocturnal saturation data are cor­ related, but daytim e S a o 2 and FEVj re­ m ain the m ost im portant predictors o f nocturnal saturation. ( Thorax 1995;50:610-612)