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MS board decomposes S (660) and S (905) into an arterial signal, plus a noise component and calculates the
arterial signal ratio without noise:
S(660) = S1+N1
S(905) = S2+N2
R = S1 / S2
Again, R is the ratio of two pulsed arterial absorption signals and its value is used to find SpO
2
saturation in an empirical derived equation in the oximeter software. The values in the empirical derived
equation were obtained based on studies on human blood, performed with healthy adult volunteers, in
situations of induced hypoxia.
The above equations are combined and a reference noise (N') is determined:
N’ = S(660) - S(950) x R
If there is no noise N'= 0: then S (660) = S (905) x R which is the same ratio as the traditional pulse
oximeter.
The equation for reference noise is based on the value of R, at the value sought to determine SpO
2
.
The MS board software scans all possible R values that correspond to the SpO
2
values between 1% and 100%
and generates a value N 'for each of these R values. Signals S (660) and S (905) are (ACC) that produces a
power output versus a possible SpO
2
value as shown in the following figure where R corresponds to SpO
2
=
97%:
The DST curve has two peaks: a peak corresponding to the highest saturation is selected as the SpO
2
value. The entire sequence is repeated every two seconds in the most recent four seconds of the received
data. Concluding the SpO
2
of the MS board, corresponds to the running evaluation of arterial saturation of the
hemoglobin updated every two seconds.