Development of Mobile Sleep Lab based on Fuel Cell Electric BusAssisting Access for All to the Best Sleep Medicine Regardless of Time and Place

Toyota Motor Corporation's Frontier Research Center and the International Institute for Integrative Sleep Medicine (IIIS)^*1 at the University of Tsukuba are collaborating research on association of mobility with sleep, which is one of the "big three" factors for a healthy life alongside diet and exercise. The collaboration is carried out by the R&D Center for Frontiers of MIRAI in Policy and Technology (F-MIRAI)^*2, a research center jointly established by Toyota and the University of Tsukuba on the university campus.

Here we introduce one Toyota/IIIS joint development project―the Mobile Sleep Lab, a fuel cell (FC) electric bus is remodeled to furnish equipment to conduct overnight polysomnography (PSG)^*3. PSG is a gold standard of diagnosis of sleep disorders.

The Effects of Lack of Sleep

Sleep deprivation is generally believed to not only cause a reduction of higher brain function, such as for memory or decision-making, but also increase the risk of a large number of illnesses, including depression, metabolic syndrome, and dementia^*4. In developed countries, the prevalence of sleep disorders^*5 is around 15%, and the lifetime prevalence is above 30%^*6. Among the 30 OECD nations, the average sleep time of the population in Japan is the shortest―442 minutes (7.3 hours) per day^*7―and the country's economic losses stemming from the lack of sleep are estimated at 138.6 billion dollars (16.6 trillion yen^*8), corresponding to 2.92% of GDP, the highest among OECD countries^*6. This shows that there is a real and urgent need for solutions to the sleep issues.

Current Sleep Studies

Around 700 sleep laboratories in Japan can perform PSG studies, but that is insufficient given the number of patients, who invariably have to wait three to four months for a test. The test also require a patient to stay one or two nights in a sleep laboratory or a hospital, and there may not even be a sleep laboratory nearby. This means that PSG studies are not readily accessible to people with limited time to spare or who cannot easily travel to a facility.

Remodeling an FC Electric Bus into a Mobile Sleep Lab

Predicting that many people with sleep disorders would benefit from PSG studies being more accessible, we set out to create the world's first^*9 mobile sleep laboratory that would deliver the PSG facility to the patients to help those who have been unable to undergo one so far. An FC electric bus was chosen as the best vehicle to house the sleep laboratory, given hydrogen use and hydrogen stations are expected to increase and advances in the fuel cell technology would improve the cruising range and the ability to climb slopes. It would also be able to provide a virtually silent, non-vibrating large power supply. This is expected to reduce the burden significantly on not only patients, but also the personnel performing PSG.

Problem-Solving and Development through Co-Creation

Our ambitious goal was to create a mobile sleep laboratory of advanced functionality^*10 with as many sleep study rooms as possible that would allow it to also be used as a human sleep research facility subject to even stricter conditions than a sleep laboratory conducting PSG studies.

For example, to satisfy the strict temperature and humidity conditions required for sleep study rooms in a human sleep research facility, we initially considered installation of a localized air conditioning system allowing high-precision temperature and humidity control. However, we realized the equipment alone would take up almost as much space as one sleep study room, therefore restricting the number of rooms overall, and that even with a fuel cell power supply we would run out of power in certain temperature, humidity and ventilation conditions. Instead, we adjusted the room temperature and humidity settings to the minimum requirement and switched to using household air conditioners and humidifier-dehumidifiers. As a result, we were able to fit two sleep study rooms inside the FC electric bus. Furthermore, because PSG electroencephalograph (EEG) equipment is easily affected by noises from the power supply and other things outside, we studied how it was affected by noises from the FC electric bus systems and the fuel cell power supply. Researchers and academic staffs repeatedly braved the noise tests in the FC electric bus under the blazing sun to put on EEG devices so we could evaluate noise components superimposed on the EEG data. The system we eventually proposed to avoid the effects of noises made use of independent special-purpose batteries and wireless communication.

Mobile Sleep Lab Performance Verification

Performance of the developed Mobile Sleep Lab was then verified to check that the PSG studies were in no way inferior to studies undertaken in a human sleep research facility.

First, participants were split into two groups and alternately underwent PSG studies in the Mobile Sleep Lab and the Human Sleep Lab in IIIS. (See Fig. 1)

EEG brain wave measurements in the Mobile Sleep Lab and Human Sleep Lab were analyzed by clinical laboratory technicians skilled in determining sleep stages. The waveforms unique to each sleep stage were observed, verifying that the PSG studies conducted in the Mobile Sleep Lab and the Human Sleep Lab were equivalent. (See Fig. 2)

Verification Testing Plans and Future Prospects

The idea is to have the Mobile Sleep Lab we developed quickly deployed in the field. We plan verification testing with patients from hospitals in Ibaraki Prefecture as test subjects and the results should be published in a paper next year.

Furthermore, it is our wish to have the Mobile Sleep Lab used for not only PSG studies of sleep disorder patients, but also other activities including sleep studies of top athletes who struggle with pre-competition insomnia due to excessive stress and sleep studies of people in other fields, such as long-distance drivers, who tend to sleep irregular hours. In this way, we hope to help addressing Japan's sleep deficiency problem.

To conclude, we feel that the development project has contributed in some way to the utilization and spread of fuel cell electric vehicles (FCEVs). Here is a comment on the development project from the department in charge of FCEV development: "Because vibration and noise levels of FCEVs are low compared to conventional vehicles, we expect they will help alleviate driver and passenger fatigue. Application of FCEVs to the Mobile Sleep Lab will allow us to evaluate those benefits and the value of FCEVs that we will then be able to wrap into services that will please drivers and passengers."

Authors

Hisamori Kurosu
Involved in industry-academia co-creative research at Toyota's Frontier Research Center since May 2021 after previous engagements in collaborative vehicle development and exploring improvements to driver maneuverability in limit handling of vehicle dynamics.

Masashi Obuchi
Currently involved in industry-academia co-creative research having previously engaged in development of wireless communication technology and driving safety support systems.

References

Contact Information (about this article)

Frontier Research Center

xr-probot@mail.toyota.co.jp