The population prevalence of insomnia has been surveyed numerous times and is among the most common medical complaints. This common problem has wide ranging psychological and physiological health consequences.
Ample anecdotal evidence exists that motion promotes sleep: automobile and train passengers are routinely observed becoming drowsy and falling asleep [1]. The sleep-inducing effect of motion has long been appreciated in the scientific community as well. For example, rocking effectively produces sleep in infants [2]. Sleepiness is also a primary symptom of motion sickness and in some cases may be its sole manifestation [3]. To date, three studies have attempted to determine whether vestibular stimulation promotes sleepiness in adults. Two of these studies involved rocking beds. In one study, investigators found that regular, periodic motion achieved using a rocking bed reduced sleep onset latency (SOL) and increased REM in normal sleepers [4]. In another study, normal sleepers napped in a swinging bed of the same design. The study showed that rocking motion promotes sleep onset and transition to deeper, more restful stages of sleep [5]. In another study, investigators employed electrical stimulation of the inner ear in an attempt to decrease SOL, finding a significant reduction in a subset of participants whose SOL was elevated at baseline [6]. This illustrates that insomniacs may be particularly responsive to vestibular stimulation.
The non-pharmacological promotion of sleep is an active commercial pursuit with numerous related patents filed and commercial products introduced in recent years; however, existing devices suffer serious shortcomings. Previous experimental and current commercial designs intended for adults function(ed) as a pendulum, requiring a custom bed (and associated custom linens) along with a special overarching scaffolding installation to suspend the bed [7]. An advanced robotic infant seat [8], while elegantly designed, utilizes active load support, severely limiting the maximum weight capacity and excluding the possibility that a similar implementation could be used for adults. Phillips Respironics developed the SleepWave, a non-invasive (clip-on) device to electrically stimulate the vestibular nerve to generate the sensation of motion, which has undergone promising clinical trials but is not yet commercially available [9].
The motivation for a mechatronic bed as a treatment for insomnia is based on the demonstrated link between motion-induced vestibular stimulation and sleep induction. To date, no design has been proposed that is practical to implement or capable of being incorporated into existing beds: cost, necessary dedicated physical space, and convenience represent substantial barriers to acceptance.
