System Processing Description 91
SpO
2
Processing
Pulse
oximetry
works
by
applying
a
sensor
to
a
pulsating
arteriolar
vascular
bed.
The
sensor
contains
a
dual
light
source
and
photodetector.
Bone,
tissue,
pigmentation,
and
venous
vessels
normally
absorb
a
constant
amount
of
light
over
time.
The
arteriolar
bed
normally
pulsates
and
absorbs
variable
amounts
of
light
during
systole
and
diastole,
as
blood
volume
increases
and
decreases.
The
ratio
of
light
absorbed
at
systole
and
diastole
is
translated
into
an
oxygen
saturation
measurement
(SpO
2
).
Because
a
measurement
of
SpO
2
is
dependent
upon
light
from
the
sensor,
excessive
ambient
light
can
interfere
with
this
measurement.
Pulse
oximetry
is
based
on
two
principles:
that
oxyhemoglobin
and
deoxyhemoglobin
differ
in
their
absorption
of
red
and
infrared
light
(spectrophotometry),
and
that
the
volume
of
arterial
blood
in
tissue
(and
hence,
light
absorption
by
that
blood)
changes
during
the
pulse
(plethysmography).
The
monitor
determines
SpO
2
by
passing
red
and
infrared
light
into
an
arteriolar
bed
and
measuring
changes
in
light
absorption
during
the
pulsatile
cycle.
Red
and
infrared
low
‐
voltage
light
‐
emitting
diodes
(LED)
in
the
oximetry
SpO
2
sensor
serve
as
light
sources;
a
photo
diode
serves
as
the
photo
detector.
Because
oxyhemoglobin
and
deoxyhemoglobin
differ
in
light
absorption,
the
amount
of
red
and
infrared
light
absorbed
by
blood
is
related
to
hemoglobin
oxygen
saturation.
To
identify
the
oxygen
saturation
of
arterial
hemoglobin,
the
monitor
uses
the
pulsatile
nature
of
arterial
flow.
During
systole,
a
new
pulse
of
arterial
blood
enters
the
vascular
bed,
and
blood
volume
and
light
absorption
increase.
During
diastole,
blood
volume
and
light
absorption
reach
their
lowest
point.
The
monitor
bases
its
SpO
2
measurements
on
the
difference
between
maximum
and
minimum
absorption
(measurements
at
systole
and
diastole).
By
doing
so,
it
focuses
on
light
absorption
by
pulsatile
arterial
blood,
eliminating
the
effects
of
nonpulsatile
absorbers
such
as
tissue,
bone,
and
venous
blood.
Содержание YM6000
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Страница 14: ...8 Introduction YM6000 Service Manual This page is intentionally left blank...
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