Patients with sleep disorders are often evaluated by polysomnography (PSG), which measures an assortment of the body's activity during sleep, including brain activity, eye movement, and heart rhythms. Osaka University Associate Professor Ken-ichi Fukui calls PSGs ineffective because they take the patient out of his natural sleeping environment.
"Our environment influences how we sleep. We should not expect the same patterns sleeping at a hospital or sleeping at home."
Ken-ichi Fukui and other researchers at the Institute of Scientific and Industrial Research, Osaka University, collaborated with researchers at the Dental School. The sounds of sleeping dental students were recorded using smartphones placed bedside. Ken-ichi Fukui then used a novel machine learning algorithm prepared by his group to analyze the sounds and compare them with PSG data taken from the same sleeping students.
"We modified self-organizing map (SOM) algorithms to visualize the dynamics of sleep", he stated.
The SOMs extracted very obvious sleeping patterns, as subjects showed clear changes in their sounds with their sleep stage. Snoring was evident during deep sleep periods, whereas some of the sleepers tended to grind their teeth during light sleep periods.
"Visualization by SOM makes it very easy to detect abnormal patterns in sleeping", stated Ken-ichi Fukui.
Associating sleep sounds with sleep patterns provides a whole new prospect of sleep diagnostics.
"There are lots of devices that assess sleep", Ken-ichi Fukui noted, "but none are scientifically proven, and they usually require you wear the device", which, he added, discourages their use.
Ken-ichi Fukui expects that apps for smartphones and tablets can be used to record sleep sounds and convert the information into recommended adjustments to the home, such as lighting or room temperature, for better sleep.
This research is supported by the Center of Innovation Program from Japan Science and Technology Agency, JST. The sleep experiments with PSG were conducted by Prof. Takafumi Kato, Graduate School of Dentistry, Osaka University.