An acoustical analysis of the respiratory sounds of sleep : a foundation for the origin of snoring and its relationship to sleep disorders

This research is an attempt to lay a scientific foundation for the origin of snoring and its relationship to sleep disorders. Acoustical analysis of the sounds of sleep provides the basis for the following results.

Frequency analysis of the sounds of snoring substantiates the theory that snoring originates from flow over an obstruction, causing vortex shedding. This flow phenomenon results in sounds that can be characterized as tones. These tonal sounds are then amplified by the elastic structure of the nasal and/or oral cavities. The characteristic length of the obstruction is on the order of 1 cm. It is shown that the tonal characteristics of snoring sounds for patients with obstructive sleep apnea is considerably more complicated than for "healthy" patients.

The relationship between the sounds of sleep and sleep disorders is based on pattern recognition. Hypopnea and obstructive sleep apnea are characterized by a decrease or cessation of breathing respectively. Through the use of a strip chart recorder, overall-sound-pressure-level (OASPL) data of the respiratory sounds of sleep are recorded and directly correlated with the respiration airflow. When cessation of breathing occurs, the OASPL time record also shows a break in activity. When a patient is breathing, the OASPL curve shows a repeating pattern of snoring/breathing sounds. The recordings also directly relate to chest effort, heart rate, chin electromyogram (EMG), and other physiologic sleep parameters.