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Oxygen Saturation (SpO2)

The CardioMood utilizes the Photoplethysmography (PPG) sensor photodiodes to capture reflected light and calculate the patient’s oxygen saturation (SpO2). It uses the non-invasive technique of pulse oximetry to monitor the percentage of hemoglobin that is oxygen-saturated.

The working principle is spectrophotometry: the relative absorption of red light (absorbed by deoxygenated blood) and infrared light (absorbed by oxygenated blood) of the systolic component of the absorption waveform correlates to arterial blood oxygen saturations.

SpO2 system

Two light-emitting diodes, red with wavelength of 660 nm and infrared with a wavelength of 880 nm, are positioned so that they are opposite their respective photodiodes through 5-10 mm of tissue. The absorption of light at these wavelengths differs significantly between blood loaded with oxygen and blood lacking oxygen. Indeed, oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through, whereas deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light. 

The accelerometer (ACC) is utilized to compensate for movement artifacts. Measurements of relative light absorption and ACC are measured at 32Hz and data is processed by the algorithm to give a new reading of SpO2 every 28 seconds utilizing averaging to smooth SpO2 data and prevent inappropriate and transient artifacts from affecting stability of results.


The accuracy of the pulse oximetry function was measured by the Complementair Medisch Centrum (CMC) Europe, Belgium, in a controlled induced hypoxia study using 12 healthy adult volunteers in accordance with ISO 80601-2-61.

Graphic results on SpO2 measurements

Specification of SpO2

Sensing methodPulse Oximetry
Measurement range0% to 100%
Data update period28 seconds

Nominal wavelength525nm660nm880nm

Accuracy1.39 Arms1.34 Arms1.42 Arms1.45 Arms
Bias0.23 (0.07 – 0.39)0.01 (-0.23 – 0.25)E4FFF90.26 (-0.02 – 0.55)0.52 (0.22 – 0.82)
Upper LoA2.93 (2.77 – 3.08)2.64 (2.4 – 2.88)2.99 (2.71 – 3.28)3.16 (2.87 – 3.46)
Lower LoA-2.47 (-2.62 – -2.38)-2.62 (-2.86 – -2.38)-2.47 (-2.75 – -2.18)-2.12 (-2.42 – -1.83)

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