Impulse Radio Ultra Wideband Pulse Doppler radar technology as a new tool for sleep assessment

Anyone who has ever had a bad nights sleep know how important it is for your health and well-being. All mammals need it. Birds and reptiles too. Even invertebrates and unicellular organisms exhibit daily 24-hour cycles of activity and rest. Research from the last century has revealed that far from being a passive state of unconsciousness, sleep has an active nature with a distinct cyclic architecture that manifests itself in the brain and body. Today there remains no doubt that sleep is an essential biological process that humans absolutely need in order to function (although the why of it remains mysterious!), and that sleep deprivation and sleep-related disorders have devastating personal and societal consequences. Subjective opinions of sleep are as ubiquitous as sleep itself yet the discovery and effective treatment of sleep related problems relies on also being able to measure how well you are actually sleeping objectively. And that remains surprisingly problematic! The gold standard for objective sleep monitoring and assessment is polysomnography (PSG). This is a complex method, requiring several sensors attached to the body and manual interpretation by an expert. The method is reliable and thorough, but also expensive and time consuming. The body-mounted sensors mean that it is also quite invasive for the patients, and less feasible for some patient groups (young children, mentally ill patients, etc). The only currently well-accepted alternative is actigraphy, a method based on small wrist-watch like devices that monitor movement for extended periods of time. Actigraphs are particularly well suited to monitoring activity-wake cycles of humans over time, but the information they give about sleep itself is usually limited to a sometimes-questionable estimate of sleep or wake. Inferences about sleep architecture or quality have not traditionally been made based on actigraphic recordings (although some more resent work has begun looking at exploiting more of the potential of this data ). This project aims to address the gap between PSG and actigraphy, to create an alternative that is easy to use and low-cost, as well as clinically and scientifically useful. The technology we use is the ultra-wideband radar developed by the Norwegian company Novelda. This radar can measure respiration and body movement with high precision, and our preliminary investigations indicate that these parameters carry significant information not only about sleep/wake state (like actigraphy), but also about the deeper sleep architecture. Furthermore, since the technology is completely contact free, it can be embedded in the ceiling of a hospital ward to monitor sleep and activity behaviour with absolutely no impact on the patient. We aim to compare the radar sensor to both prevalent clinical alternatives (PSG and actigraphy), as well as attempting to use the sensor in active research. To that end, we have been involved in several projects: We have a collaboration with researchers from Østmarka Psychiatric Hospital in Trondheim. Their main goal is to examine the effects of the special light conditions in the new emergency psychiatric ward. This building also has radar sensors embedded in all the ceilings. A study from last year resulted in continuous radar and actigraphic data from twelve healthy volunteers living in the ward for a two-week period, including four nights of PSG per participant. This data forms the core of a paper currently undergoing final revisions, where we have examined the ability of the radar to discriminate sleep from wake for this population, in particular in comparison to actigraphy. A continuation of this study has gathered data from patients in the ward over two six-month periods. The recording periods are now complete, and the analysis work will begin from early 2020. We have also collaborated with a St Olavs-based project to study the effect of CPAP treatment of patients with cluster headaches. 30 patients were included in this study, each getting a night of PSG and radar monitoring, and radar monitoring during their two-month periods of CPAP and placebo CPAP treatments. This project was featured on NRK Viten og Vilje, November 19th 2018. We have collaborated with The National Institute of Occupational Health (STAMI), in a comprehensive study on the effects of shift work. Sleep was recorded for 30 industrial workers over a period of five weeks autumn 2019. Actigraphy was used for two weeks, radar for five weeks, and the participants were asked to submit a sleep diary daily for five weeks. Spring 2020 we did another round of inclusion, this time with 40 industrial workers. The complete study is described in a protocol article, Cardiovascular health effects of shift work with long working hours and night shifts: study protocol for a 3-years prospective follow-up study on industrial workers.

De numeriske resultatene fra den preliminære proof-of-concept studien var akseptable, men som forventet fra et lite men heterogent datasett ble det observert høy interindividuell varians. Mangelen på uavhengig testing gjør at resultatene fra denne studien har begrenset overføringsverdi. De aktigrafi-inspirerte modellene for søvn/våkenhetsklassifisering brukt med radardata oppnådde resultater på nivå med, og noen ganger bedre enn, resultater fra aktigrafi. Sanntidsmodeller oppnådde litt svakere resultater enn ikke-sanntidsmodeller, men i en situasjon hvor sanntidsovervåkning er ønskelig vil tapet være lite. Aktigrafen oppnådde bedre resultater enn radaren over de heterogene søvnklinikkpasientene i DS2, men begge sensortypene oppnådde resultater sammenlignbare med tidligere rapporterte tall for aktigrafi sammenlignet med PSG over lignende grupper. Radar-utledet LIDS korrelerte sterkt med aktigraf-utledet LIDS, og begge korrelerte også sterkt med oppløsningsreduserte PSG-hypnogram. Når radar-LIDS, aktigrafi-LIDS, og hypnogram ble aggregert over datasettet kunne det observeres at nivåene av gjennomsnittssignalene sank omtrent like mye per syklus.

Selv om det i nyere år har skjedd en rask utvikling på markedet for konsumerprodukt for registrering og evaluering av søvn, har etterspørsel for, interesse i, og tilgjengelighet av kommersielle produkt hatt en tendens til å gå mye raskere enn den strenge valideringen nye teknologier trenger for å være brukbare alternativer i klinisk- og forskningsøyemed. Resultatet er at mens markedet oversvømmes av sensorer og teknologier for undersøkelse av søvn hos forbrukere, har det skjedd lite innovasjon i klinisk praksis. Gullstandarden for søvnundersøkelse i medisin og forskning er polysomnografi (PSG), en svært omfattende og resurskrevende metode for måling av et høyt antall elektrofysiologiske parametere i tillegg til kroppsposisjon, hjerterate, respirasjon, oksygenmetning, og beinbevegelser. Metoden har store fordeler for evaluering av søvn, men også vesentlige praktiske begrensninger – data må tolkes manuelt av kvalifisert personell (noe som ofte er tidkrevende), utstyret er dyrt, fungerer dårlig for gjentatte målinger over tid, og kan virke forstyrrende for pasienter. For flere pasientgrupper hvor evaluering av søvn er av særlig interesse, for eksempel demente, psykiatriske akuttpasienter, små barn, eller svært syke pasienter, er det særlig vanskelig og noen ganger umulig å benytte PSG. Det er derfor stort behov for et mindre krevende alternativ i klinisk praksis. Dette prosjektet ønsker å undersøke om, hvordan, og i hvilken grad XeThru Ultra-Wideband (UWB) radar, utviklet av Novelda AS, kan benyttes til registrering og evaluering av søvn i en klinisk- og forskningssetting. Prosjektet vil fokusere på å samle inn data, utvikle tolkningsalgoritmer, og sammenligne sensoren med de nevnte eksisterende alternativer.