Research published in Sleep found that a no-contact sleep test held its own against polysomnography in the lab, but its application in the real world remains to be seen.

By Rose Rimler

Imagine a sleep study that can be performed without wires of any kind. That’s what the makers of Sonomat, a mattress topper that records a patient’s movement and breath sounds, envision. They published the results of their most recent trial, which compared the Sonomat with polysomnography (PSG) in children, in the journal Sleep this March.

The researchers tested the device in 76 children, six years old on average, in two sleep labs in Australia. They found no statistically significant difference in the Sonomat’s measurement of sleep time, respiratory events, or apnea-hypopnea index (AHI).

The Sonomat fits a single-person bed and is placed between the sheets and the mattress. The patient sleeps on it as normal without attachments to it or any other equipment. While the company is quick to tout the product’s wirelessness as a key selling point, Mark Norman, PhD, a researcher at the University of Sydney and first author on the Sleep paper, says the device is also a unique diagnostic tool.

“The Sonomat matches PSG in measuring the AHI metric, but also provides a quantitative measure of the presence and duration of partial obstruction, so better characterizes the type of SDB [sleep-disordered breathing] that is typical in the child,” he tells Sleep Review in an email.

Norman has studied the device for several years and receives funding and support from the company that makes Sonomat; his co-author, Colin Sullivan, is co-owner of the company and inventor of the CPAP.

Norman says that the majority of children suspected of having SDB do not present with the classic apnea indicators physicians expect from their adult patients, like complete obstructive events and high AHI. “[T]he majority of children presenting with signs and symptoms of SDB (that are now widely known in clinical practice) have very low apnea indices and are often labeled as merely ‘simple snorers’,” he writes. “This implies that the problem is innocuous. However, children typically have long periods of partially obstructed breathing during sleep, despite otherwise minimal or no significant falls in oxygen levels.”

Because the Sonomat picks up on subtler indications of obstructed breathing, the device can better suss out patients with nighttime breathing problems that are not apneas, he says.

Four sensors embedded in the mat act as stethoscopes detecting heart and lung sounds. They also measure body movements. Two microphones record room noise, which the investigators analyzed for higher frequency, hissing sounds coming from the child. Those sounds indicate stertor,  Norman says.

Home Sleep Testing Ahead?

Norman and colleagues end their paper with the suggestion that Sonomat is well on its way to being a type of home sleep test (HST).

“The device is portable, simple and does not require leads to be attached to the child, thus offering a convenient means of measuring and monitoring SDB in children in the laboratory and the home,” they write in the paper.

That remains to be seen, says David Gozal, MD, a professor at the University of Chicago who was not involved in the study.

“It’s a good result that should create some degree of optimism, but we need to be very careful,” he says. Taking the mat from the sleep lab to the home environment is a big leap, he says, and the study only shows what the device can do in the sleep lab when attended by experts and scored by highly trained individuals.

“To try and improve on a gold standard in the sleep lab obviously doesn’t make much sense,” he says. “Now, improving on certain elements that are already obtained anyhow in the sleep lab by adding information such as [what is] embedded in the sound signal could be a worthy effort.” But, he says, using the mat alone would miss some key parameters: oxygen levels, for one, which could indicate serious comorbidities; and EEG signals, for another. Norman acknowledges that the mat is not suitable for assessing sleep disorders that have a neurological basis.

Gozal would also like to see the mat tested in younger children and children with developmental disabilities, who often have a difficult time undergoing polysomnography.

“You have to show it retains its diagnostic ability even in the tough kids. So there’s a lot of work to be done.”

Norman, too, sees a potential use among such groups as well as the elderly and pregnant women; he hopes that further studies will use the mat to quantify the relationship between snoring and upper airway resistance.

Rose Rimler is associate editor of Sleep Review.