System Processing Description 93
Respiration
Processing
The
respiration
monitoring
is
designed
to
use
the
variation
of
this
thoracic
impedance.
The
chest
contains
various
materials,
ranging
from
bone
to
air.
Each
of
these
materials
has
different
electrical
properties
and
is
located
in
a
different
portion
of
the
chest.
The
materials
of
the
chest
vary
in
electrical
resistivity
(the
amount
of
electrical
resistance
between
opposite
faces
of
a
cube
of
that
material),
which
is
an
important
determinant
of
electrical
impedance
in
the
body.
Two
of
the
major
components
of
the
chest,
blood
and
air,
are
at
opposite
ends
of
the
scale.
Furthermore,
the
volume
of
each
of
these
materials
varies
with
time
over
the
cardiac
and
breathing
cycles.
The
variation
of
the
thoracic
impedance
is
caused
by
the
difference
between
air
and
blood
in
the
thoracic
impedance.
Blood
has
relatively
low
resistivity,
which
varies
over
the
cardiac
cycle
owing
to
changing
blood
volumes
in
the
heart
and
in
the
vascular
compartment.
Air,
on
the
other
hand,
has
high
electrical
resistivity
and
hence
impedance,
and
it
undergoes
wide
volume
changes
in
the
lungs
during
normal
breathing.
i.e.
the
impedance
of
blood
is
150
ohm/cm
and
the
one
of
air
is
5000
ohm/cm.
The
patient’s
respiration
is
detected
by
using
two
of
the
three
leads
of
the
ECG
electrodes
(RA
and
LA,
or
RA
and
LL)
and
cable.
The
electrical
impedance
between
a
pair
of
electrodes
is
determined
by
dividing
the
voltage
difference
between
the
two
electrodes
by
the
current
that
passes
between
them.
When
the
electrodes
are
placed
on
the
actual
structure,
respective
structures
change.
A
low
‐
level
excitation
signal
is
applied
to
these
leads,
and
the
variation
of
the
thoracic
impedance
caused
by
the
breathing
is
sensed
and
processed
for
display
and
measurement.
This
variation
is
processed
to
the
voltage
value
for
the
measurement.
In
order
to
transfer
the
thoracic
impedance
by
a
transformer,
it
is
used
a
minimum
constant
current
of
the
sine
wave
carrier
signal.
The
transferred
thoracic
impedance
is
changed
to
the
voltage
signal
by
using
bridge
circuit
and
differential
amplifier.
Then,
ECG
signal
is
removed
by
filter,
and
carrier
frequency
is
removed
by
full
wave
rectifier
and
filter
in
order
to
extract
only
thoracic
impedance
in
amplifying
at
the
definite
level
of
signal.
This
extracted
thoracic
impedance
signal
is
used
to
measure
the
respiration
by
digital
signal
processing.
Temperature
Processing
Measurement
of
patient
temperature
is
accomplished
by
processing
the
signal
from
a
probe
containing
a
resistor
whose
resistance
is
temperature
dependent.
The
class
of
such
components
is
called
thermistor.
Temperature
measurement
used
by
the
YM6000
monitor
based
on
a
thermistor
whose
resistance
is
inversely
proportional
to
its
temperature.
By
measuring
the
thermistor’s
resistance,
its
temperature
can
be
calculated.
The
resistance
of
the
thermistor
is
measured
by
passing
a
current
through
it
and
measuring
the
voltage
developed
across
it.
The
YM6000
monitor
is
designed
to
accept
the
signals
from
electrically
isolated
a
range
of
temperature
probes
from
YSI
‐
400
series.
The
probes
may
be
used
for
skin
or
rectal
temperature
measurement.
Probes
are
furnished
with
a
standard
10
‐
feet
lead;
extension
leads
are
available.
The
signal
from
the
probe
is
conditioned
by
the
monitor
input
circuitry,
processed,
and
used
to
drive
the
numeric
display.
Содержание YM6000
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