In a physician's evaluation of a patient's snoring, listening to a tape recording of the sounds, in addition to a routine examination, is important. By listening to snoring sounds we can detect apneic episodes and analyze snoring sound frequencies to determine whether the patient can be treated by operation. However, it is not always possible to get stable data from recorded snoring sounds. To show the relation between different kinds of snoring and sleep stages,7 simple snorers and 7 patients with obstructive sleep apnea syndrome (OSAS) were polysomnographically studied.
Snores can generally be classified two by acoustic analysis as either vibratory or stenotic. Vibratory snoring is a regular sound, the fundamental frequency of which is under 200 Hz; the sound is thought to be due to a relaxed velum. Patients with this type of snoring can be treated by an operation. Stenotic snoring is an irregular sound with a fundamental frequency over 500 Hz; the sound is thought to be due to either a dependent tongue base or tonsillar hypertrophy, or both conditions. The former condition is inoperable, while the latter is operable.
The sites of sound origin have never been observed visually. To determine the conditions and sites of sound origin, we performed a fiber-optic study of the mesopharynx and larynx in a group of 40 patients, which included 28 simple snorers and 12 patients with OSAS, all of whom had been sedated with diazepam.
The results are as follows:
I. Sleep study
1. Inspiratory snoring appeared upon falling asleep (Non-REM I) and occured progressively more often through deeper sleep stages (Non-REM III and IV). The frequency of REM-stage inspiratory snoring was comparable to that of Non-REM I inspiratory snoring. However, expiratory snoring frequency did not vary through sleep stages.
2. Inspiratory snoring during Non-REM I occured more often when the subject was supine than when the subject was lying in the lateral position. There was no significant difference in the frequency of snoring between these two sleep positions during all sleep stages.
3. Snoring was more common during the inspiratory phase than during the expiratory phase.
4. Apneas were observed only in Non-REM I and II, and REM stages.
5. Respiration was not greatly distubed by the vibratory snoring caused by a relaxed velum. II. Study of Sleep induced by diazepam.
1. Sound sources in the mesopharynx included a relaxed velum, a dependent tongue base, and tonsillar hypertrophy, and those in the larynx included the mucosa of the arytenoid cartilage, the epiglottis, and the vocal folds.
2. Obstructed points in patients with OSAS were mainly in the mesopharynx and were rarely in the tongue base.

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