Abstract
Patients with chronic obstructive pulmonary disease (COPD) have varying degrees of arterial oxyhaemoglobin desaturation during sleep, which have been shown to correlate with awake oxygen levels. We wished to ascertain if exercise desaturation was a better predictor of nocturnal oxygen desaturation than daytime blood gases. We studied 25 COPD patients with PaO 2 <10 kPa (mean=8·6 kPa), 12 of whom were normocapnic ( PaCO 2 ≤ 6 kPa, Group A), and 13 of whom were hypercapnic ( PaCO 2 >6 kPa, Group B), by means of overnight oximetry and maximum treadmill exercise testing. The overall group desaturated significantly more during sleep than exercise [12·9 ± 10·5 fall in nocturnal oxygen 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. 92·8 ± 2·9, P=n.s.). Awake SaO 2 correlated well with both mean values ( r=0·7, P<0·001), and minimum sleep SaO 2 ( r=0·44, P<0·05), but not with the fall in sleep SaO 2 ( r=0·21, P=n.s.). Minimum sleep and exercise 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 conclude that exercise studies add no extra information to awake blood gas analysis in predicting the likelihood of nocturnal oxygen desaturation in patients with COPD.
Published Version
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