Ohmeda Biox 3700 - Digital Processing

1118-301
DIGITAL PROCESSING
A. From theory, oxygen saturation calculates as:
Sa02 = KIR2 + K2R + K3
where R- A red and K1 f K2, K3 are
A *R constants
where oxygen saturation at any point in time is a function of the
change in the red channel divided by the change in the infrared
S?iK«M °P«?aJ characteristics of hemoglobin are the basis of the
in«™? COefficlents: K1> K2» ™* K3. The oximeter processes the
" t;na2?J 0Xyfn ^turation values to produce the "average saturation
vaiues. This value appears on the oximeter's digital display.
One key digital processing function is to properly average the instan
taneous oxygen saturation values. A running average gives a reasonable,
but not excellent result. A weighted average of instantaneous values pro
vides for a much more acceptable result. Perfusion at the test site and
the current average saturation are the basis for the weight assigned to
each instantaneous calculation. For example, movement at the probe site
can create signal distortion, thus creating some erroneous instantaneous
oxygen saturation values.
Since there are many saturation measurements per second, it is possible to
discard bad values away and the displayed saturation remains stable. The
weighting function provides a stable reading, with low sensitivity to
11 ie/etain!ng the caPabilitv ot responding quickly to saturation
£«£/? \ V1/^ ,ngt wei*hted average uses data over a six/three (Slow
Mode/Fast Mode) of data and is updated every 0.67/0.33 (Slow Mode/Fast
Mode) seconds.
~ 12 - 01/27/86