Wellue O2Ring Case Study from Dr. Frederico Ribeiro

by Mar 13, 2023Respiratory0 comments

A 75-year-old male patient with Hypertension, Dyslipidemia, Coronary Artery Disease and overweight. He has complaints of Snoring, non-restorative sleep, daytime sleepiness and 2 episodes of lacunar stroke, confirmed with Magnetic Resonance Image.

Initially, while waiting for the polysomnography examination, we decided to monitored the patient’s sleep using the Wellue O2 Ring, a continuous blood oxygenation and heart rate monitor.

Figure 1. Sleep report, generated by the O2 Ring Wellue application, showing 7 hours and 52 minutes of monitoring, 15 oxygen drops in more than 4%, higher oxygen level at 98%, lower at 88% and an average of 94%, getting 1 minute and 24 seconds of oxygen levels below 90%, giving an O2 Score of 8.4. Little heart rate variability, since the patient is on beta-blocker medication.

Figure 2 – Sleep report, generated by the O2 Ring Wellue application, showing 8 hours and 28 minutes of monitoring, 28 oxygen drops in more than 4%, higher oxygen level at 98%, lower at 88% and average of 92%,, getting 26 minutes and 56 seconds with oxygen levels below 90%, giving an O2 Score of 8.3. Little heart rate variability, since the patient is on beta-blocker medication.

Figure 3 – Performed Ambulatory Blood Pressure Monitoring, which showed increased blood pressure loads during sleep, in addition to inversion of nocturnal descent, i.e., blood pressure was higher during sleep. Together with the clinical data with the monitoring of Oxygen and Blood Pressure, we have as diagnostic hypothesis, Obstructive Sleep Apnea Syndrome.

Figures 4 and 5 – Show Polysomnography that confirms the Diagnosis of Moderate Sleep
Apnea, associated with important hemoglobin desaturation with a maximum oxygen
level of 94%, minimum of 77% and an average of 91%, keeping 17% of the time monitored
with oxygen levels below 90%.






Sleep Apnea is the most common type of sleep disorder, affecting about 23.4% of women and 49.7% of men in the general population. American Association of Sleep Medicine guidelines recommend the diagnosis of Sleep Apnea in patients with single-night sleep study with polysomnography in adult patients with suspected disease.

Polysomnography is a technique that makes the graphic recording of multiple physiological variables over sleep time.

Polysomnographic examinations are usually done in specialized laboratories, as the exams are monitored at all times by a trained technician.

Polysomnography, and home sleep apnea test devices provide the apnea-hypopnea index (AHI) and oxygen desaturation index (ODI), both values that present the number of respiratory events per hour used to diagnose sleep apnea and disease severity.

Diagnosing disease with a single test requires high precision of the test method, as well as a stable disease to reduce false-negative and false-positive test results.

However, there is strong evidence of high nocturnal variability of respiratory events in patients with sleep apnea, leading to misdiagnoses and classifications resulting from one-night sleep tests. Undiagnosed and untreated sleep apnea is associated with daytime sleepiness, decreased quality of life, increased risk of accidents, hypertension, cardiovascular events, particularly stroke.


An observational study conducted in the Department of Pulmonology of the University Hospital of Zurich submitted 108 patients with suspected sleep apnea to 14 nights of nocturnal oximetry at home and 1 night of hospital respiratory polysomnography, with the objective of analyzing the variability of clinically relevant nocturnal respiratory events in these patients.

It was found that compared to the results of hospital polysomnography, 1/5 ofthe patients would have been misdiagnosed compared to the test using the pulseoximeter, with a variability of about 3% in the oxygen denaturation index. About 31patients would be misdiagnosed as to the severity of the disease on the first night of theexamination, and by the end of the 13 nights, 83 patients would have been incorrectlyclassified with severe sleep apnea.

The first night of sleep has already demonstrated high sensitivity and specificityof the analyses using the pulse oximeter. Increasing further on a second night of testing.


About 71% of patients would have been diagnosed with sleep apnea on the firstnight, increasing to 88% with an additional night of study, this demonstrates theimportance of performing monitoring for more than 1 night.

Looking at the raw data, it becomes obvious that some of the patients who hadnegative results for sleep apnea during monitoring on the first night, but actuallyshowed positive results during sleep monitoring in hospital polysomnography.

Patients who presented negative results on hospital polysomnography showedvery low oxygen desaturation index values so not even the variability of theseveral-night examination led to a diagnosis of moderate sleep apnea.

Although theaddition of a second night of study significantly increased sensitivity, the negativepredictive value of a recording night was already high. However, it remains debatablewhether a single study showing negative results is sufficient to exclude moderate sleepapnea.

Although the American Association of Sleep Medicine still indicates a single-nightsleep test for patients with suspected sleep apnea, there is an increased risk of false-positive tests. However, the study contradicts showing high specificity, therefore lowfalse-positive rates on several nights of sleep.

Another counterargument againstmultiple night tests is the growing discomfort of this approach, because not all patientsmay be willing to perform repeated night tests in a hospital environment. Alreadyrepeating several nights of examination at home seems reasonable for most patientswith suspected sleep apnea.

In addition to the high cost for the health system to repeatthe examination in a hospital environment, it results in the direct or indirect costs ofuntreated sleep apnea. Studies show that sleep apnea when diagnosed and treated has a positive impact on the economy.

Therefore, as an alternative to expensive and technically complex polysomnography, patients with high probability and lack of relevant comorbidity can be evaluated through portable home sleep apnea tests such as pulse oximetry.

This study revealed considerable nocturnal variability of respiratory events, leading to an identification of a relevant number of patients with sleep apnea who would have been diagnosed or would have the severity of the disease misclassified with the sleep examination performed in a single night.

Especially, patients with lower respiratory event rates were at higher risk of the high variability of respiratory events overnight. Several study nights significantly increased the accuracy of the diagnosis for moderate sleep apnea.

Dr. Frederico de Morais Ribeiro


Medical Registration 9944 Goiás




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