Acoustic analysis of vowel emission in obstructive sleep apnea

We studied vocalization in 18 men with obstructive sleep apnea syndrome (OSAS) (age, 49 [7.5] years; body mass index [BMI] 33.6 [7.6]) and 10 normal men as a control group (age, 46.7 [6.2] years; BMI 24.6 [2.2]). Polysomnographic data for patients with OSAS were as follows: total sleep time (TST), 387.5 [27.9] min; awake, 17.6 (12.6% TST); stage 1, 19.8 (18.7 percent TST); stage 2, 54.8 (23.2 percent TST); stage 3 and 4, 1.5 (0.3 percent TST); and stage REM, 4.2 (1.7 percent TST). Apnea hypopnea index (AHI) was 43.0 (18.2) and lowest O2 saturation was 73.6 (11.4). We recorded the following sounds in all subjects: /a/ as in "father"; /e/ as in "get"; /i/ as in "see"; /o/ as in "go"; /u/ as in "too." Three maneuvers for each vowel sound were taken for analysis. Signals were digitized at 10,000 Hz. Fast Fourier transformation was applied to segments of 512 points of each utterance corresponding to the vowel sound. The following parameters were obtained: maximum frequency of harmonics, mean frequency of harmonics, and the number of harmonics.

There were significant differences between both groups in the maximum frequency of harmonics of /i/ and /e/ vowels. (For /i/: 2,650 [672] Hz controls; 425 [71.2] Hz OSAS. For /e/: 2,605 [772.3] Hz controls; 1,250.0 [828.4] OSAS). The number of harmonics for /i/ vowel was 4.5 (1.2) for controls as compared with 2.7 (1) Hz for OSAS.

Vocalization in patients with OSAS is different from normal subjects. Vowel /i/ can distinguish these patients from normal subjects.