PRINCIPLES
OF
OPERATION
vgs/
Oximetry
Operating Principles
w OXIMETRY OPERATING PRINCIPLES
^
Many
times
each
second,
the
N-20/N-20P
passes
red
and
^ infrared light into the sensor site and determines absorption.
Measurements
that
are
taken
during
the
arterial
pulse
reflect
^
absorption
by
arterial
blood,
nonpulsatile
blood,
and
tissue.
w Measurementsthat are obtainedbetweenpulses reflect
absorption
by
nonpulsatile
blood
and
tissue.
By correcting
**"
"during-pulse''
absorption
for "between-pulse"
absorption,
the
^ N-20/N-20P determines red and infrared absorptionby
pulsatile
arterial
blood.
Because
oxyhemoglobin
and
^ deoxyhemoglobin differ
in
red
and
infrared
absorption,
this
^ corrected measurement can be used to determine the
percentage
of oxyhemoglobin
in
arterial
blood:
Sp02
is
the
ratio
***
of
corrected
absorption
at
each
wavelength.
Automatic
Calibration
The
N-20/N-20P
is
automatically
calibrated
each
time
it
is
turned
on
and
whenever
a
new
sensor
is
connected:
it
sets
\ws
sensor-specific
calibration
coefficients
by
reading
a
calibration
resistor
in
the
sensor.
Also,
the
intensity
of
the
sensor's
light
sources
are
adjusted
automatically
to
compensate
for
differences
in
tissue
thickness
and
darkness.
Vgjj^
*igii>>
Functional
and
Fractional
Saturation
The
N-207N-20P
measures
functional
saturation,
i.e.,
***
oxygenated hemoglobin expressed as a percentage of
the
vgpz
hemoglobin
that
is capable of transporting oxygen.
It
does not
detect
significant levels of dyshemoglobins.
In
contrast,
^
instruments
such
as
the
IL282
CO-Oximeter
measure
^ fractional saturation, i.e., oxygenated hemoglobin expressed as
a
percentage
of
all
measured
hemoglobin,
including
^ dyshemoglobins.
25
^iiai/
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