T<90% (Time Below 90% SpO2)
The percentage of recording time with blood oxygen below 90%. Indicates sustained hypoxemia that may affect organ function.
What Is T<90% (Time Below 90% SpO2)?
T<90% (also written as Time Below 90%) measures the percentage of the recording period during which blood oxygen saturation (SpO2) falls below 90%. This metric captures sustained hypoxemia, which is clinically significant because prolonged low oxygen levels can affect organ function, particularly the brain and cardiovascular system.
While ODI measures the frequency of oxygen drops, T<90% measures their cumulative duration. A person might have a low ODI (few events per hour) but high T<90% if each event causes a prolonged desaturation. Conversely, frequent brief desaturations can produce a high ODI with low T<90%.
On well-controlled PAP therapy, T<90% should be below 5%. Values above 15% indicate significant time with low oxygen during sleep and warrant clinical attention. AirwayLab also reports T<94% as a more sensitive threshold that captures milder but still potentially relevant hypoxemia.
Normal Ranges
How AirwayLab Measures This
The Oximetry Pipeline calculates T<90% from Viatom/Checkme O2 Max data by counting the number of valid SpO2 samples below 90% and dividing by total valid samples. Also computes T<94% using the same method with a higher threshold. Reported on the Oximetry tab.
Try it with your dataFrequently Asked Questions
How much time below 90% SpO2 is concerning?
On PAP therapy, less than 5% of time below 90% is considered good. Between 5-15% is borderline. Above 15% indicates significant nocturnal hypoxemia that warrants clinical discussion about therapy adjustments.
Related Terms
Medical Disclaimer
AirwayLab is not a medical device and is not FDA-cleared or CE-marked. It is provided for educational and informational purposes only. The analysis results should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult qualified healthcare providers regarding your sleep therapy and any changes to PAP settings.