OXYGEN DESATURATION DURING SLEEP AND EXERCISE IN PATIENTS WITH SEVERECHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Patients with chronic obstructive pulmonary disease (COPD) have varyin g degrees of arterial oxyhaemoglobin desaturation during sleep, which have been shown to correlate with awake oxygen levels. We wished to as certain if exercise desaturation was a better predictor of nocturnal o xygen desaturation than daytime blood gases. We studied 25 COPD patien ts with PaO2 <10 kPa (mean=8.6 kPa), 12 of whom were normocapnic(PaCO2 less than or equal to 6 kPa, Group A), and 13 of whom were hypercapni c (PaCO2 > 6kPa, Group B), by means of overnight oximetry and maximum treadmill exercise testing. The overall group desaturated significantl y more during sleep than exercise [12.9 +/- 10.5 fall in nocturnal oxy gen saturation (SaO(2)) vs. 4.5 +/- 3.7, P<0.01]. Group B had a lower minimum SaO(2) during sleep than Group A (74.3 +/- 13.4 vs. 84.6 +/- 5 .8, P<0.05), despite very similar pre-sleep SaO(2) (91.9 +/- 3.2 vs. 9 2.8 +/- 2.9, P=n.s.). Awake SaO(2) correlated well with both mean valu es (r=0.7, P<O.001), and minimum sleep SaO(2) (r=0.44, P<0.05), but no t with the fall in sleep SaO(2) (r=0.21, P=n.s.). Minimum sleep and ex ercise SaO(2) were also significantly correlated (r=0.44, P<0.05), but the fall in SaO(2) during sleep and exercise was not (P=n.s.). We con clude that exercise studies add no extra information to awake blood ga s analysis in predicting the likelihood of nocturnal oxygen desaturati on in patients with COPD.