## 3 Results  
All the patients of the sample had a first diagnostic PSG (T0) with obstructive respiratory events per hour of sleep, AHI, >5 all of which reduced in the second PSG after three months (T1).  
The examination of the boxplots and Q-Q plots revealed that, concerning the CSA values, three cases were outliers. Because those cases showed a number of central apnea events very high at T1 of 125, 62, and 176, well above the mean of the whole samples that was equal to 10.94 (Table 1). It is clear that the presence of those subjects clearly influenced the significance of the results. Those three outliers were removed from the analysis, but this allowed the authors to guess that these subjects defined as \"outliers\" would be critical to the purpose of the study.  
Figure 2 describes the statistical results for OSA, CSA, MIXED apnea, AHI and ODI data from T0 to T1 without the three outliers and shows the mean values of the variables OSA, CSA, MIXED apnea, AHI and ODI at T0 and at T1. Statistical comparison of mean values for the parameters considered was significant for all values, with a \(p\) value < 0.001 for OSA, MIXED apnea, AHI and ODI and a \(p\) value < 0.05 for CSA.  
The number of OSA events was markedly reduced from T0 to T1. Central and mixed apnea values showed an important reduction from T0 to T1. MAD therapy showed also an important effectiveness in reducing AHI and ODI. All these changes were statistically significant.  
The Authors divided the sample in two different groups: those who neither developed nor increased the number of central apneas during treatment (40 patients) (Figure 3) and those who as a result of the use of MAD developed or increased the number of central apneas (16 patients including 3 outliers) (Figure 4). Figure 3 describes variables at T0 in patients without developing o increasing CSA. Mean value in OSA is 113.05 while SD is 77.16, mean advancement is 79.74 while SD is 15.28. Mean AHI value is 24.48 while SD is 12.17, mean ODI value is 18.04 and SD is 9.41. Mean age and mean BMI are, respectively, 56.62 and 27.27 while SD are, respectively, 12.71 and 2.74. Figure 4 describes variables in patients who developed or increased the number of CSA at T0. In this case mean OSA is 106.27 and SD is 97.27. Mean mandibular advancement is 50.67 while SD is 16.78. Mean AHI and mean ODI are, respectively, 25.22 and 20.39 and SD are, respectively, 13,09 and 16.23. Mean age and mean BMI are, respectively, 54.07 and 26.72 and SD are, respectively, 11.56 and 2.76.  
\begin{table}
\begin{tabular}{l c c c} \hline
**PSG** & **CASE n.12** & **CASE n.25** & **CASE n.41** \\
**DATA** & & & \\ \hline OSA T0 & 84 & 81 & 42 \\ OSA T1 & 5 & 23 & 6 \\ CSA T0 & **23** & **63** & **42** \\ CSAT1 & **125** & **176** & **62** \\ MIXED T0 & 135 & 64 & 11 \\ MIXED T1 & 9 & 12 & 2 \\ AHI T0 & 40.8 & 32.4 & 15.3 \\ AHI T1 & 23.5 & 31.3 & 10.6 \\ ODI T0 & 41.9 & 23.1 & 8.5 \\ ODI T1 & 20.2 & 22.3 & 2.8 \\ \hline \end{tabular}
\end{table}
Table 1: PSG parameters of outliers before and after treatment. CSA parameters at T0 and T1 are written in bold.  
When comparing the two groups there were no statistically significant difference for the studied variables. According to data distribution were used for two different statistical tests to analyze variables at T0: the \(t\)-test has been used for AGE and BMI variables while the Mann-Whitney U test has been used for OSA, Mandibular advancement, AHI and ODI variables.  
Analyzing and evaluating the medical records of the outlier patients a mild hypertension was found in 2 of the 3 patients and only one of them had a history of opioid drugs use not taken at the time of diagnosis.  
Figure 3: Descriptive variables table in patients who neither developed nor increased the number of CSA.  
Figure 2: Descriptive statistics and statistical comparison of PSG parameters before (TO) and after (T1) treatment, standard deviation (SD) of the mean value of the difference between T1 and T0 for all the parameters (* \(p<0.05\); ** \(p<0.01\)).