en saturation; and body position. The PRRD was programmed to start 10 minutes after patients went to sleep. Sleep studies were performed at the patient's home using the unattended mode.
The AHI was calculated as the sum of the number of episodes of apnea and hypopnea per hour of recording. The analysis was performed manually using the criteria recommended by the American Academy of Sleep Medicine.12 Respiratory events were characterized as apnea when there was a cessation or reduction of more than 90% of airflow lasting 10 seconds and as hypopnea when any clearly discernible reduction in airflow (>30% and <90%) lasting 10 seconds was observed, associated with a dip of at least 3% in pulse oximeter oxygen saturation.
To assess OSAS severity, patients' AHI was classified as follows: an AHI value below 5.0/hour was considered normal; an AHI value of 5.0/hour to 14.0/hour, mild; an AHI value of 15.0/hour to 30.0/hour, moderate; and an AHI value higher than 30.0/hour, severe; in accordance with the guidelines of the American Academy of Sleep Medicine.11
Data are given as mean (SD). The bivariate relationships between AHI values and potential explanatory variables (sex; age; BMI; cervical perimeter; FL150; and FTP, TS, and uvula scores) were assessed using the Spearman correlation coefficient or the Wilcoxon rank sum test as appropriate. A multivariate regression analysis was conducted to investigate the predictive role of potential explanatory variables in more depth. To achieve normality and homoscedasticity, a logarithm transformation was used, so that the logarithm of the AHI (log AHI) was modeled rather than the AHI itself. Two different strategies were used to select the best-fitting model from a total of 511 alternatives. First, we looked for the model with lowest Mallows' Cp value. Second, we used a stepwise selection procedure with a 0.10 probability level of the F statistic entering or staying in the model. Once a model was selected, 2-way and 3-way interaction terms were also explored. The goodness of fit of the final model was assessed by inspecting residual plots. All statistical analyses were performed with SAS software (version 9.1; SAS Institute Inc, Cary, North Carolina).
The study protocol was approved by the hospital's institutional review board. Only patients' oral informed consent for the anonymous treatment of their data was required since the study protocol was the same as that used for the standard medical care of these patients in our institution.
We prospectively studied 301 consecutive patients from January 2006 to December 2009. Their ages ranged from 18 to 82 years (mean [SD], 51  years),12 71.1% were male, and 28.9% were female, the mean (SD) BMI was 29.8 (4.6), the cervical perimeter was 40.6 (3.7) cm, and the FL150 was 0.80 (0.26) cm3/s.
The distribution of FTP, TS, and uvula scores, along with other patients' characteristics, are displayed in Table 1. Note that for these 3 scores, the 2 middle categories accounted for about 80% of the sample. The AHI values ranged from 0.7/hour to 89.5/hour (mean [SD], 27.6/hour [19.4/hour]). Ninety-four percent had an AHI value higher than 5.0/hour.
The AHI values showed a statistically significant correlation with FTP scores, TS scores, uvula scores, BMI, cervical perimeter, and age. In all cases, the correlation was positive, but its intensity varied markedly: while a high correlation was found in the case of the FTP score (Spearman r = 0.88) (Table 2), the correlation was only moderate for the cervical perimeter (r = 0.40) and very low for the TS scores, uvula scores, and age (Table 2). We did not detect a significant correlation between AHI values and the FL150.
The AHI values were significantly higher in males than in females (Wilcoxon rank sum test; P = .02): the median AHI value was 24.3/hour for males and 18.0/hour for females.
Almost three-quarters of patients (74.1%) had FTP scores of 2 and 3 (Table 1). Findings from 18 of 301 patient studies (6%) were considered normal (AHI <5.0/hour): 16 were classified as FTP 1, and only 2 as FTP 2.
All patients w