Cuffless blood pressure (BP) has become table stakes for wearables. Apple and Samsung are building toward blood pressure features, smart rings are piling up preorders, and Omron keeps pushing at-home monitors that promise fewer squeezes and more data. The open question is clinical: will any of it change who gets treated, when, and for what? 

Korea University Guro Hospital is putting that to the test. The hospital has begun a prospective study, approved by its institutional review board, that will put a finger-worn blood-pressure ring on every overnight sleep-lab patient and test a practical idea: can five-minute nighttime systolic patterns identify which obstructive sleep apnea patients should be fast-tracked for a full study and treatment?

The device is Sky Labs’ Cart BP Pro, currently the only medically certified blood-pressure ring in use in Korea.

In an interview with Korea Biomedical Review, lead investigator Na Jin-oh of cardiology at Guro Hospital, said sleep laboratories capture many signals at night but rarely blood pressure because inflating a cuff disturbs sleep and can alter the physiology under observation. 

In his phrasing, blood pressure “should be there.” He added that the ring, which measures without squeezing after a quick cuff calibration, is “about 90 percent” of the way to routine use if its patterns track apnea events and the loss of the normal nighttime dip. 

(Polysomnography typically records brain waves, eye movements, muscle tone, heart rhythm, airflow, respiratory effort, oxygen saturation, body position and leg movements. Blood pressure is not standard in that set, in part because cuffs can wake patients.)

What the study will test

The team plans to enroll about 200 sequential patients over roughly a year from cardiology, neurology, and ear-nose-throat clinics, according to Professor Na. Each patient will wear the ring during a standard hospital sleep study. Analysts will align the ring’s readings with apneas, oxygen drops, and arousals to see whether variation in nighttime systolic pressure maps to apnea severity and signals near-term cardiovascular risk better than daytime snapshots.

Sampling cadence is central. In current hospital deployments, the Cart BP Pro defaults to 20-minute intervals, according to Sky Labs. Na said he asked the company to tighten the interval to five minutes so short apnea clusters are not missed. He said clinicians will annotate and compare the traces against the sleep-lab timeline, then bring in software to automatically time-match the streams and flag segments for clinician review if volume grows.

The question is narrow and testable: do five-minute nocturnal systolic curves separate moderate to severe apnea from mild or none in routine workflow? If so, Na said, the ring becomes a pre-polysomnography screen that improves referral yield and moves treatment earlier for those most likely to benefit. He described success as “a queue that moves.”

Why this matters now

Na estimates only about 20 percent of people in Korea who need therapy for sleep apnea are diagnosed, and “maybe three or four in a hundred” receive effective nighttime treatment. Capacity is tight. Guro can run two overnight polysomnography slots per night, he said, while a larger regional site in Seoul manages roughly eight. Patients often resist the exam itself because it requires arriving at night, sleeping in an unfamiliar room with multiple sensors, and being observed.

That is the use case the ring is meant to address. Rather than replace cuffs in the clinic, the study focuses on nighttime physiology that labs typically miss. During severe apnea, Na said, it can feel “like being pushed underwater,” a sympathetic surge he expects to see as lost dipping and sharp variability in the blood-pressure curve.

The device maker’s position

Sky Labs says Cart BP Pro has been used about 120,000 times in Korean clinics. A European CE mark is in process. The company plans U.S. clinical trials for FDA review in 2026 to 2027, which it acknowledges will be costly. The Seoul study is intended to give clinicians and payers near-term utility data while longer, outcomes-oriented programs are built.

The study protocol was approved by the hospital’s institutional review board, and data will remain within the hospital’s clinical systems. Na said participants give informed consent and that privacy safeguards are in place.

The trial is not designed to measure hard outcomes such as stroke, heart failure, or death. Those would require larger, multicenter studies over three to five years. The near-term goal, according to Na, is narrower: show that five-minute nighttime systolic variability helps triage patients by improving referral yield (a higher share of polysomnography referrals confirming moderate to severe apnea) and shortening time to treatment.

If the association is weak or inconsistent, the result will indicate limited clinical value for cuffless nighttime pressure in this setting. If it is strong, the hospital could adopt a ring-first screen to prioritize sleep-lab slots and start therapy sooner for higher-risk patients.