The purpose of the present study was to assess whether the variables associated with improvement in the ESS in patients with OSA on CPAP were different if the baseline ESS was high or normal and, in patients with a high baseline ESS, to assess which variables were associated with improvement of the ESS to a normal value. Perhaps the most striking finding was that when looking at improvement of the ESS from high to normal with CPAP (ie, normalization of the ESS), female sex was associated with lower rates of normalization. Furthermore, there was a significant interaction between ESS normalization, sex, and days of CPAP use. The longer that patients were on CPAP within the prespecified limits of this study (≤ 120 days), the greater this divergence in normalization rates between females and males. For example, if we compare the use of CPAP for 90 days vs 30 days (a difference of 60 days of use), the odds of normalization in females were only 3% of the odds in males. This finding has not previously been reported.
here are a number of possible explanations for the difference in normalization rates between males and females. It could be simply that females need more time than males to normalize the ESS. Indeed, in one very large study where ESS was assessed at baseline and 6 months later, female sex was associated with a higher, not lower, likelihood of ESS normalization.5 There were some differences in the variables assessed between that study and the present one: Depression in that study and diabetes and hypertension in the present study, and that the other study was a clinical trial (the APPLES trial) and the present study was done in a routine clinical setting. Given the fact that the proportion of females to males who normalized the ESS diverged over the limited time frame of the present study (30 to ≤ 120 days), it seems unlikely that in the study cohort there is an inflection point beyond 120 days where the rates of ESS normalization between females and males become similar.
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