Blood Oxygen (SpO2)
How Pulsyn tracks overnight SpO2, what the numbers mean, and how to read trends responsibly.
Last updated: July 13, 2026
SpO2 is an estimate of the percentage of oxygen-carrying haemoglobin in your blood. Pulsyn reports it as a percentage (%), typically averaged overnight.
What the number means
SpO2 is presented as an average value and as a trend relative to your baseline. A value close to your personal average is unremarkable. A noticeable drop, especially when paired with elevated heart rate or temperature, can flag a context such as heat stress or altitude adaptation.
How Pulsyn measures SpO2
Rune 1 uses red and infrared LEDs to estimate blood oxygen while you sleep. The strongest readings come from overnight sessions because the measurement depends on good sensor contact and stillness.
SpO2 in other scores
SpO2 is one of the contributors to Readiness Score. A sustained dip can contribute to heat or altitude adjustments, so the score reflects your current physiological context.
Important limitations
SpO2 from a smart ring is a wellness and fitness metric, not a medical pulse oximeter reading. It is not intended to diagnose, monitor, or treat any medical condition. If you have concerns about blood oxygen, consult a healthcare professional and use a clinical-grade device.
Reading the trend
- Look at multi-night averages rather than single readings.
- Pair SpO2 with resting heart rate, temperature, and how you feel.
- See the FAQ for details on the sensors Rune 1 uses.