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950 Averaging
For pulse rates below 112 BPM the averaging calculation is based on
a 4-beat exponential average for SpO 2 (see below) and an 8-beat
sliding average for pulse rate. For pulse rates above 112 BPM the
averaging is doubled and then re-doubled above 225 BPM. The pulse
oximeter will not include questionable pulses in the average. Marginal
pulses may count less in the average than good pulses.
All averages are updated on a beat-by-beat basis. The display is
updated every 1 ½ seconds with the most recent value.
Also, if the pulse oximeter signal is "noisy" or missing, the display
will hold the last value for 10 seconds before showing dashes. With
the 4-beat exponential average, the effect of each measurement
gradually decreases beat by beat. Each measurement initially counts
for ¼ of the average. This weight is decreased by multiplying by ¾ on
each succeeding beat:
Beat
1
2
3
4
5
The SpO 2 4-beat exponential average is fast enough to follow
physiological changes.
For the pulse rate sliding 8-beat average, each beat counts 1/8 for 8
beats and thereafter has no affect on the average.
Effect (weighting in average)
¼
= 0.250
x ¾
= 0.1875
x ¾
= 0.1406
x ¾
= 0.1055
x ¾
= 0.0791
18
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