The aim of the study was to determine which factors are important for desaturation depth during sleep in obstructive sleep apnea (OSA) and to establish impact of nocturnal oxygen desaturation on the daytime sleepiness. 190 consecutive patients were included in the study (135 men and 55 women, mean age 52.59+/-11.31 and 58.93+/-8.85 years, respectively). Desaturation level depended on body-mass index and correlation with Epworth sleepiness scale (ESS) was statistically significant but not high (p<0.5). In the univariate analysis assessing factors important for severe daytime sleepiness (ESS more than 10), age and obesity were not statistically significant. A probability of severe sleepiness increased in male patients (odds ratio 3.52), and when microarousal index was more than 30 (odds ratio 6.12), apnea-hypopnea index more than 35 (odds ratio 4.25), mean desaturation less than 90% (odds ratio 4.09), maximum desaturation less 80% (odds ratio 3.06), general desaturation index more than 36 per hour (odds ratio 2.86), desaturation index during non-REM sleep more than 38 per hour (odds ratio 3.2). In the multivariate analysis only arousal index more than 30 per hour increased a probability of severe sleepiness in patients with OSA (odds ratio 4.97).
Conclusions: Hypoxemia depth at night is an important factor for daytime sleepiness having obstructive sleep apnea, but the most important is microarousal index. Hypoxemia depth depends on initial saturation and patients' body-mass index.