Sleep duration and sleep timing are well-accepted aspects of a healthy sleep, but “less attention has been paid to another dimension of sleep—sleep depth or quality—largely because until now, there’s been no practical or reliable way to objectively measure this,” says Earl Gardiner, CEO of digital health and virtual care company Cerebra Health Inc, in a release.
The Winnipeg, Canada-based company has patented an algorithm that micro-analyzes the EEG signal to provide such an objective measurement. “Odd Ratio Product” or ORP provides a continuous measure of sleep depth over the entire night’s sleep.
Two newly published research studies show what ORP may be useful for. One compares ORP’s accuracy compared to measuring delta power and the other uses ORP to predict driving safety in patients with obstructive sleep apnea (OSA).
Compared to Delta Power
Data from 41 healthy subjects who underwent a series of controlled sleep studies compared how delta power and ORP responded to conditions where sleep depth was a factor—including correlation with sleep staging, response to sleep restriction, and relation to an individual’s arousability.
The study was conducted by Magdy Younes, MD, PhD, who developed ORP, with James Walsh, PhD, and colleagues from St. Luke’s Hospital in Missouri and published in SLEEP. Delta power is a traditional measure used in research. The study concluded ORP is more sensitive to sleep restriction and more closely associated with patient arousability compared to delta power.
Predicting Driving Safety in Patients with OSA
Sleep apnea is associated with a higher risk of car accidents due to neurocognitive impairment. However, the common diagnostic metric for sleep apnea, the apnea hypopnea index (AHI), is unable to provide insight into the level of risk for a given severity of OSA.
Research supports the idea that humans, when sleep deprived, begin to sleep more deeply in one half of the brain than the other. This paper hypothesizes that poor synchrony in sleep depth across the brain is a result of sleep deprivation due to frequent respiratory events.
Ali Azarabarzin, PhD, and his fellow researchers at Harvard Medical School, were able to use Cerebra’s ORP metric to determine whether differences in sleep depth across the right and left hemisphere of the brain identified sleep apnea patients at increased risk of motor vehicle accidents.
Published in the Journal of Sleep Research, they found, in the study of 1,378 sleep apnea patients, individuals with a higher degree of synchronization in sleep across the right and left halves of the brain had a significantly lower (62%) risk of motor vehicle crashes, than those with the lowest synchronization in sleep across the brain.
“We are seeing the growing impact ORP is having on the field of sleep medicine,” says Gardiner, “not just in research but increasingly in clinical practice as physicians use ORP to better understand their patients’ sleep quality to better guide diagnosis and treatment.”