An Interrupter
Technique for Measuring
Respiratory
Mechanics and the Pressure
Generated
by Respiratory
Muscles during
Partial Ventilatory Support*
Antonio
Pesenti,
Lsca
D’Andrea,
M.D.;
M.D.;
Paolo Pelosi,
M.D.;
Giuseppe
and Nicola
Rossi,
M.D.
We evaluated
the airway
to estimate
respiratory
and
the pressure
generated
occlusion
maneuver
as
Foti,
a method
respiratory
elastance
by respiratory
muscles
in ICU
patients
breathing
in the
PSV mode.
The airflow
was
interrupted
at selected
flows or volumes
during inspiration
by a computer-driven
rapid occlusion
pneumatic
valve. The
airway
occlusion
was
resistance,
maintained
for
2
to
3
s.
From
the
pressure
tracing we obtained
various
of pressure.
We then computed
the pressure
measurements
generated
by
method
was validated
groups
of patients:
the
airway
the patient’s
inspiratory
muscles.
The
by two different
approaches
in two
Pes and the CMV
protocols.
We conclude
that
the airflow
interruption
method
can
be used
to measure
basic respiratory mechanical
parameters
in PSV patients.
The
method
also
offers an opportunity
to evaluate
Pmusc,aw
and the
respiratory work performed by the patient.
(Chest
1992; 102:918-23)
T
he
importance
of
in patients
assessing
requiring
respiratory
ventilatory
has
CMV=
controlled
mechanical
ventilation;
DP,int=occlusion
pressure
drop;
El,rs = respiratory
system
elastance
(reciprocal
of compliance);
ESTDP=estimated
resistive
pressure drop;
ESTPA = estimated
alveolar
pressure; ESTPeI,rs
= estimated
elastic
recoil
pressure
of the respiratory
system;
PA = alveolar
pressure;
Paw
(i) = airway
pressure
at occlusion;
PEEPi
=
intrinsic
positive end-expiratory
pressure;
Pel,cw=elas
tic
recoil
pressure
of the chest
wall;
Pel,lung=
elsa
tic recoil
pressure
of the lung;
Pel,rs
= elastic
recoil
pressure
of the
respiratory
system;
Pes = esophageal
pressure; Pes(i) = esophageal pressure
at occlusion;
Pmax = peak inspiratory
pressure;
Pmusc
= pressure
generated
by respiratory
muscles
during
inspiration;
Pmusc,aw
= pressure
generated
by respiratory
muscles
during
inspiration,
measured
at the airway
opening;
Pmusc,
es = pressure
generated
by respiratory muscles
during
inspiration,
measured
by an esophageal
balloon;
PSV = pressure
support
ventilation;
Rint = total
inspiratory
resistance
(including
the artificial
airway)
during
pressure
support ventilation) (DP,int/flow);
Rlung = pulmonary
resistance
during
pressure
support
ventilation
(including
the artificial
airway);
Rrs,cmv
= total
inspiratory
resistance
(including
the artificial
airway)
during
controlled
mechanical
ventilation
very
mechanics
support
M.D.;
been
selected
recognized
increasingly
in recent
years.
Respiratory
system compliance
has indeed proved to be one of the
noninvasive
breathing
most important
parameters
for diagnostic,
and even
therapeutic
purposes.
Moreover,
airway
prognostic
tory
resistance
recently
regained
ting.4
Most
of the
assess
methods
to
paralyzed
management
the
popularity
respiratory
developed
be
and
is
shifting
own
intermittent
mandatory
the
almost
invariably
care
modes
requires
of
an
to
been
in a
preserving
as
Under
efficient
of
breathing,
therapy.
Institute
line,8
The
a
entirely
devoid
of problems.9
Classic
methods
are obviously confined to
of Anesthesia
and
Intensive
Care,
interrupter
flow
through
method
by the
it allows
the
respiratory
determinant
AND
the
I,
technique
the
to the point
pressure
is
within
after
the
the
the
com-
work
of
of respiratory
METHODS
involves
while
The
ascribed
pressure
change
the
disappearance
system.
should
following
an interruption
the
sudden
respiratory
difference
just
nsaking
measuring
to
occlusion
pressure
and
resistive
airways
of occlusion.
occlusion
before
University
of Milan,
and the Department
of Anesthesia and Intensive
Care
Ospedale
S. Cerardo
Monza,
Milan,
Italy
Supported
in part by MURST
(Rome)
and CNR (Rome).
Manuscript
received
November
26; revision
accepted
March
6.
Reprint
requests:
Dr. Pesenti, Institute
of Anesthesia,
Via Donizetti,
Monza (MI)
1-20052
Italy
918
an
Principle
con-
and
the
total
MATERIALS
right
*From
require
Since the
developed
muscles,
patients’
important
or
mechanics
Pes
an
on a rapid
not
of compliance).
of the pressure
respiratory
the
based
does
the
PSV
these
respiratory
own
for practical
pressure
line, and should
provide
of respiratory
resistance
and elas-
(the reciprocal
an estimate
putation
that, being
maneuver,’0
balloon
estimate
patient’s
emerged
applicable
to the spontaneously
patients.
We present
here a rela-
method
occlusion
tance
offers
situations.
has therefore
methods
intubated
esophageal
a useful
ventilatory
evolution
and
such
ventilation.7
have
set-
available
contemporary
a very rapid
activity,
measurement
technique
not
plethysmographic
critical
technology
toward
respiratory
ditions
monitoring
mechanics
in the ICU have
applied
during
CMV,
usually
patient.
However,
is undergoing
focus
patient’s
and
in the
measurements
need
tively simple
respira-
‘
experimental
A new
be
of
the
to the
the
occlusion,
two
of gas
just
in pressure
Ideally,
equal
between
the
pressure
the
values,
should
by
resistive
airway
alveolar
distal
caused
pressure
pressure,
taken
just
represent
the
drop.’
Technique
The
technique,
originally
patients, has been
Interrupter
accepted
Technique
developed
in spontaneously
as a standard
for Measuring
Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21654/ on 06/16/2017
Respiratory
method
Mechanics
breathing
in respiratory
(Pesenti
eta!)
.5
occlusion.
The
relaxed
.25
difference
>
inspiration,
tory
effort.
occlusion
should
The
quantify
the
as
the
PA
the preced-
patient’s
not
discarded
and
during
maneuvers
be
the
system.
plateau
muscles
therefore
occlusion
approximate
respiratory
respiratory
should
plateau
should
the
relaxed
of the
and
of
inspira-
showing
a
unsuccessful
clear
measure-
ments.’5
10
-.
the
Airway
relaxation
pressure
pressure
between
ing
plateau
recoil
the activity
measures
0
occlusion
elastic
x
Subjects
a,
a,
We studied
diagnoses
-10
900
a total
(Table
C (Siemens
cheal tube
AB,
or
of
admitted
were
Berlin,
Germany),
airway
10
The
investigation
committee,
a,
or
In all patients,
and
.5
in the therapeutic
the
beside
by the
families
the
positioning
of
protocol
group,
or semirecumbent
approved
or their
Servo
institutional
gave
an
Table
1).
position.
ethics
informed
consent.
and Flow Measurements
Pressure
a)
was
all subjects
various
an endotra-
introduced,
occlusion
protocol
and
with
either
No changes
were
esophageal
balloon
catheter
(esophageal
All patients were studied in the supine
I
ICU
by a Siemens
through
treatment
the
to the
ventilated
cannula.
ventilatory
performance
0Cl
2) who
or a tracheostomy
regimen
20
of 13 patients
1 and
the
Paw
was
artificial
airway
six patients
(Table
measured
between
connector
by
the
a Bentley
airway
occluder
Trantec
pressure
transducer.
In
0
intrathoracic
2
FIGURE 1. Tracing
PA is determined
linear
regression
0.080
s (arrow
A)
of V, Pes, Paw and ‘ of an occluded
as the intercept
to time 0 (occlusion
computed
on airway
pressure
data
to 0.250
s (arrow
B)
over time.
S
PSV breath.
time) of the
points
from
Bentley
and
and
tients.’2’3
We
ventilation,
has
been
have
applied
according
occlusion
1), the
drops
continues
position
the
(usually
less
appears
to relax
rapidly
as long
occluded
airway.
corresponding
the
patient
airway
pressure
occlusion.
often
It
his inspiratory
reaches
(an
is higher
effort
next
a new
1-Relevant
indication
the
Paw
Parameters
Weight
(kg)
!ressure
support
V (IJmin)
RR (breaths
per
level
(cm
H,O)
mm)
El,rs (cm H,OIL)
PEEP
(cm
H20)
Flo,
PaO,(mmHg)
=
postoperative
polytrauma.
Respiratory
(abdominal
parameters
surgery);
are
the
recorded
a test
endotracheal
No.
gas
Bologna,
tube
2) connected
to a
MP45,
Valydine
mixture
in use.
by
Italy)
Co,
a four-channel
and
pen
processed
(75 samples per second)
calculations. Volume
was
flow
was
valve,
via
an
by a portable
computed
by
signal.
obtained
airway
by the
operated
In vitro tests
from
in turn
showed
that
in 10 to 20 ms.
the
Pressure
portable
Protocol
sudden
inflation
of a latex
by a solenoid-driven
the
valve
The
solenoid
computer.
The
assembly
valve
pneucompletely
was
computer
driven
by
could
be
Patients5
4
3
M
M
6
5
M
M
M
77
18
16
68
65
69
60
68
85
75
1.85
1.73
ARF-BP
P0
1.70
1.85
ARF-PT
ARF-PT
12
1.72
P0
5
10
10
5
15
12.8
10.5
10.4
12.1
22
21
13
20
15
13
23.8
16.1
20.8
34.5
31.3
19.2
8.9
11.3
8
8
2
8
4
2
0.5
0.5
0.4
0.5
0.4
0.21
102
41
PaCO2(mmllg)
the
of the
differences
during
58
ARF-BP
Diagnosis
were
the
the
swings
a
volume
53
1.76
Height(m)
closed
2
M
Sex
Age(yr)
valve.
of the Esophageal
1
No.
airway
matic
with
of
to
Technique
interruption
a signal
before
of the
Interrupter
balloon
value,
signals
end
estimate
inflation
to minimize
pressure
(Valydine
calibrated
(an
connected
balloon
(Fleish
Bangoni,
integration
Flow
and
inspiratory
indirect
than
The
of time
airway
transducer
analog-to-digital
coisverter
computer
for storage and
digital
effort
amount
then
the
then
pressure
(Battaglia
Pes
balloon
selected
and
at the proximal
Ca) and
and
measured
The
pneumotachograph
Northflidge,
Fig
also
esophageal
empirically
differential pressure
Flow
an
transducer.
esophageal
a heated
recorder
reflect
an inspiratory
the
were
of airway
the
PSV,
occlusion.
Before
pressure
the
with
If
during
should
of
plateau,”’
which
pa-
support
follow.
a variable
ceases
Table
Patient
which
sustains
muscles.
relaxed
in a patient
(eg,
time
Following
to an “occlusion
relaxation),
the
patient
his inspiratory
effort,
that
to a value
as the
or
inspiration
activity
at
than 0.5 s) the
(or expiratory)
of muscle
during
by
Flow was measured
to partial
considerations
prevailing
to drop
against
the
paralyzed
principles
of spontaneous
very
pressure
to
same
is produced
degree
Paw
alveolar
the
to
suddenly
a measurable
extended
Trantec
between
by
physiology
1), we
pressure)
97
44
ARF-BP
=
ones
measured
acute
respiratory
or selected
115
91
83
64
38
43
39
40
failure/bacterial
during
PSV
pneumonia;
clinical
ARF-PT
=
acute
respiratory
failure/
management.
CHEST
I 102
Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21654/ on 06/16/2017
/ 3 / SEPTEMBER,
1992
919
Table
Patient
2-Relevant
of
Parameters
No.
the
1
Sex
2
M
Age
(yr)
Weight
(kg)
Height
(m)
level
(cm
35
47
81
72
90
85
60
56
75
1.85
1.73
1.78
P0
P0
ARF-PT
P0
5
15
5
10
H20)
8.1
9.6
ARF-NHL
18
7.7
15
20
56.4
30.3
33.7
H,0)
3
4
7
2
12
2
12
0.4
0.21
0.4
0.3
(abdominal
ARF-BP
0.50
98
130
162
110
105
39
40
41
40
37
36
51
ARF-PT
respiratory
acute
=
respiratory
failure/bacterial
failure/polytrauma;
pneumonia.
ARF-NHL
Respiratory
parameters
acute
=
are
the
respiratory
ones
failure/non-Hodgkin
measured
or selected
during
PSV
management.
to occlude
or
during
flow.
The
either
inspiration
occlusion
was
or expiration
maintained
for
at
3.
2 to
spiratory
the
From
the
analysis
of the
we obtained
1.PA
linear
the
was
ranging
from
0.080
inspiratory
muscles.
and
The
s, and
its adequacy
3.
Pmusc,aw
was
in
relaxed
the
inspiration,
by the
the
PA. This
respiratory
was
pressure
5.
measured
the
Pel,rs,
difference
length
by inspection
as
state,
difference
and
measures
the
computed
was
as:
does
not
man
usually
by
resistance
(Fig
and
1).
pressure
during
pressure
as Paw(i)-PA,
just
before
computed
as
where
Paw(i)
is the
occlusion.
DP,intlflow,
in
which
flow
was
first
just before the occlusion.
Validation
The
of the
Method
validation
different
and
of
occluder
the
occluder
complementary
method
was
obtained
by
approaches.
were
Pressure
In six patients
airway
Protocol
(Table
occlusion
obtained
by the
and
relative
to
measurements.
were
breaths
the
compared
20
selected
the
Pes.
results
support
value),
for
breaths
by
CMV
volume
each
(0,
respiratory
a total
were
+5
of 93
allowed
following
equations
the
=
Pes(i)
+
Pel,lung
=
Pes(i)
+
Pel,rs
Pes(i)
Pel,rs,
is the
pressure
is the
computed
Likewise:
therefore,
from
is zero,
the
airway
during
possible
equation
pressure,
the
and
plateau
to
2 with
at the
is the
of occlusion,
esophageal
and
0.15
actual
the
theoretical
PA measured
PA value
at occlusion.
the
level
when
of
required
level
and
occluded
the
Interrupter
linear
inspiratory
Technique
and
normal
support
respiratory
rate
of muscle
of the
airway
in
several
its
decay
in
for Measuflng
Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21654/ on 06/16/2017
total
volume.
tidal
of Pel,rs,
The
volume)
and
El,rs,
over
(Table
mode
PEEP
to
was
volume.
ventilatory
same
adjusted
level,
reach
a
2). A maximum
function,
adjustment
peak
Mechanics
of
function.
nonconsecutive
from
In so
(ie, at 0.05,
cardiorespiratory
Respiratory
after
Three
patient,
the
was
stabilization
flow,
CMV
maintaining
for recovery
the
at
from
allowed
volume
individual
Measurements:
pressure
each
computed
at each
at each
regression
to PSV,
range
Pel,rs)/flow”
-
averaged
In each
Ventilation
CMV
VE minute
sedation
then
of the
we
(Pmax
Pel,rs,
up to the
flow.
slope
from
satisfactory
We
so on,
Support
changed
while
the
Land
as the
and
and
In
breaths
entire
were
volume,
as
performed
constant
mode.
the
breaths
inspired
Rrs,cmv,
patients
at
steps.
normal
(Rrs,cmv)
b2).
The
in different
to cover
The
proposed
(v.i.
CMV
the
were
hi).
the
paralysis
the
charge
in
(vi.
using
and
in 50-mI
each
inspiratory
of 4 h was
phase.
compare
the
Pel,cw,
time
At
in
step
conditions
in
and
mechanics
h
airway
selected
volume
were
Pressure
pressure
the
uninterrupted
we measured
at constant
was
Pel,cw,
-
esophageal
plateau
measured
is,
airflow
flow)
resistances
computed
1. PA
where
when
apply;
2.
PA
occlusion,
tidal
ten
physician
Measurement:
sedation
of 75
(Table
diagnoses
a routine
4
support
wave
block
techniques
within
wall
patients
Respiratory
occluded
volumes,
normal
measurements
0.1
following
(square
Another
the
standard
under
chest
is variable
various
PSV,
Ventilation
while
occlusion.
doing,
by
pressure
repeatedly
least
when
to
in
as suggested
in seven
with
institution.
repeated
inspired
0 to the
At
occlusions.
Immediately
different
Occlusions
inspiratory
of pressure
uninterrupted
obtained
with
of the
levels
clinically
least
results
at increasing
at different
the
At
PSV
measurements
in different
L steps),
between
technique
simultaneous
performed
-5
1) undergoing
we
study
were
flow
patient
ICU
analysis
wall.
obtained
CMV
Mechanical
inspiratory
Esophageal
chest
mode.
the
under
can
which
of
Protocol:
CMV
from
during
ventilated
We
at interruption
to the
in the
at our
method
Controlled
two
admitted
procedure
measured
by flow.
wall,
Moreover,
of the
was
entered
measurements
the
This
chest
contribution
Ventilation
a change
weaning
to
minus
muscles
Pmusc,aw.
of the
measured
compliance
been
patients
Pes[i])
inspiratory
with
the
drop
ventilated
anticipated
divided
negligible.
measurements
had
The
pressure
Mechanical
being
Pel,cw)
resistance
or even
on the
occlusion
2). They
the
Whittenberger,”
Controlled
PSV
generated
and
depends
the
account
to the
-
by the
Pmusc,es,
is small’
Mead
for a plateau
into
(Paw[iI
in-
is equal
Pes(i).
-
compared
take
-
generated
Pel,cw
=
we
(Pel,rs
(Rlung)
Rlung.
pressure
Pmusc,es
Therefore
reached
of the
between
the
the
were
measured
Rint
usually
relaxation
Moreover
be measured
resistance
pressure
[ie, the
Pel,cw])/flow,
-
flow
pressure
with
[Pel,rs
-
airway
transpulmonary
Rint
4.
Pes[i]
-
and
transpulmonary
start
muscles.
DP,int,
4.
airway
plateau,
the
judged
the
to occlusion
as PA.
acceptable
computed
static
by
(Paw[i]
=
pulmonary
dynamic
most
identified
s following
taken
from
the
indicating
was
The
was
0.250
-
Rlung
compared
extrapolation.
decay
value
during
1):
backextrapolated
minimum
0.25
pressure
back
then
recorded
(Fig
to 0.160
was
regression,
tracings
Paw
Pel,rs
was measured
1.5 s from
occlusion,
within
flow
postocclusion
Pressure
by linear
and
parameters
by linear
of the
occlusion.
2.
Paw
following
determined
portion
inspection,
920
0.30
102
surgery);
acute
=
0.6
121
3s.
It
10.1
25
volumes
and
5
6.8
12
Hg)
selected
(at 0.1
10
7.5
20.8
programmed
were
ARF-BP
19.6
lymphoma;
the
1.76
P0
20
*P#{216}
=
postoperative
was
1.63
18
mm)
PaCO2(mmllg)
time
1.64
28.2
(mm
of the
M
F
14
17
(cm
PSV,
M
7
18.0
per
clinical
M
6
73
Flo,
Pa02
5
H20/L)
RR (breaths
PEEP
M
M
8.5
(cm
4
Patients*
21
VE (lJmin)
El,rs
3
Protocol
53
1.79
support
Ventilation
62
Diagnosis
Pressure
Mechanical
Controlled
breaths
to
the
end-
(Pesenti
eta!)
ESTPA
Pel,rs,
15
o/
the
0
.5
0.
volume
15
of the
Comparisons
The
and
0q
-10
ESTDP
-
an estimated
and
ESTPeI,rs,
El,rs,
obtained
computed
duriisg
from
CMV.
Measurements
00
/
0
>
occlusion
Paw(i)
=
with
RESULTS
0
5
U
actual
compared
/f
10
E
was
these
data
and
inspiratory
an
#{176}
main aim of our experiments
Pel,rs,
measured
under
PSV
respiratory
resistance,
work
accurate
respiratory
elastance
(taking
for granted
can be derived
enough
measurement
Pressure
Protocol
was to validate PA
conditions.
From
of flow and airway
pressure).
-20
-10
10
0
Pes(i)
PeI,Iung
+
20
Esophageal
(cmH2O)
The regression
between
PA and
the corresponding
value estimated from the Pes(i) plus the transpulmonary pressure
measured
during
the occluded
plateau
phase (PeI,rs - Pel,cw) was very close to the identity
FIGURE 2. Relationship
between
PA measured
from airway
tracing
and
PA estimated
from
Pes(i)
plus
the transpulmonary
pressure
measured
during
the occluded
plateau
phase
(Pel,lung).
The computed
equation
is: PA= -0.11+1.09
* (Pes[i}+Pel,Iung);
r0.98;
n = 93.
line (Fig 2). Likewise,
inspiratory
in use
the
value,
during
upward
inspiration.
Adequate
spike
of
The
be
with
obtained
levels
possible,
pressure
near-end-expiratory
We therefore
data
obtained
and
(±
the
closure
during
early
took
phase
place
Each
10 percent)
PSV
and
was
of
not
under
of
figure
measurements
were
support.
measured
repeated
subject
the
CMV
the
measurements
estimated
from
conditions.
resistive
obtained
actual
positive
by
a brief
of PA and
In the first place
we computed
drop
(ESTDP),
occlusions
matched
were
using
the
for flow
flow.
compared
compared
also
with
=
with
the
Paw(i)
-
actual
measurement:
PA.
an estimated
value,
PSV
average
inspiratory
average
volume
r=0.97;
over
(Pmusc,aw=
n=93).
the
Ventilation
Protocol
occlusions
flow
of
were
performed
of 0.666±0.
0.204
0.22
±
theoretical
value
1 L. The
resistance
proximately
(Rrs,cmv)
the
as:
1.06
±
*
and
flow
ESTDp;
r= 0.88;
n
total
to the
inspiratory
75). In each
the average R,int, value measured
pared
very
closely
with the Rrs,cmv,
20
at occlusion
during
CMV
(at
volume)
(Dp,int
=
an
at an
regressions
correlated
from
measured
same
and
the identity
PeI,rs, and
to
measured
strictly
computed
at
141 [is
PA
ESTPe1,rs, is shown in Fig 4.
The resistive
pressure
drop
during
PSV (DP,int)
also
was
0.34
obtained
of Riung
held true for Pmusc
Pmusc,es;
and ESTPA
was
very
close
line (Fig 3). The correlation between
Pel,rs,
mechanics
CMV
same
*
During
at
respiratory
pressure
the
from
=
Mechanical
between
values
DP,int
was
=
identity. The
Controlled
those
Intrinsic
in each
ESTDP=Rrs,cmv*
estimates
Palv
(r
the regression
an intercept of 1.52 and a slope of 0.82
93), which defined a line ciose to the
(± 25
between
volume:
These
showed
0.87, n
Rint
-0.64+1.05
occlusion
volume
selected
pressure
was
compared
the corresponding
estimate
occlusion
flow
occlusion.
with
Rrs,cmv,
valve
very
measured.
occlusion
of inspiratory
end-expiratory
an
the
inspiratory
CMV.
clinically
different
the
but just
for flow
to the
avoided
during
at which
corresponding
during
When
software
flow
PSV
matched
the
(± 10 percent)
the
volume
during
then
ml)
close
CMV.
predetermined
could
came
during
ap=
subject
PSV
measured
comduring
15
25
10
o
0
I
E
U
a,
>
a,
.5
0.
20
15
10
-10
200
DO
0
.
0
,‘
15
5
-20
-20
-10
0
ESTPaIv
10
20
(cmH2O)
0
n
10
20
ESTPeI,rs
FIGURE 3. Relationship
between
PA measured
during
PSV by an
occlusion
maneuver,
and PA estimated
from
resistance
and flow
measured
during controlled
mechanical
ventilation
at approximately
the same
flow and volume
(ESTPA).
The computed
equation
is:
PA”0.05+0.95
* ESTPA;
r0.98;
n=75.
FIGURE 4. Relationship
between
relaxed
plateau
following
occlusion
from elastance
measured
during
equation
is: Pel,rs = 1.63 +0.99
CHEST
*
Pel,rs,
measured
from
the Paw
during
PSV, and PcI ,rs, estimated
CMV (ESTPeI,rs).
The computed
ESTPeI,rs;
r = 0.90; n = 75.
/ 102
Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21654/ on 06/16/2017
30
(cmH3O)
/ 3 I SEPTEMBER,
1992
921
3-Respiratory
Table
Mechanical
Measured
Patient
during
Resistances
and
Ventilation
Pressure
at Similar
Volumes
(cm
might
Ventilation
R,intt
I120/Us)
(cm
H50/L/s)
No.
1
6.09
2
13.74
5.68±0.99
3
8.44
8.16±2.03
4
13.66
14.35±3.70
8
5
12.29
13.39±2.90
12
6
13.12
13.44±2.19
7
10.50
10.62±
13.22±
be provided
8
1.72
13
14
11
1.50
improve
figures.
to the
one
of three
tMean
CMV
(Table
measurements.
occlusion
during
the
for
been
generally
esophageal
the
in spite
the
test
replaced
by
occlusion
breathing
of
alter
the
the
tipper
resistance
in
ported
resistance
values
airway:
we
specific
tance
purposes,
computation
The
with
been
posed
surprising,
since
of the airway
condition
to
spontaneously
of the artificial
by the high complimay
substantially
pressure
and
subjects.
the
this
compute
R,int,
patients
were
comparable
‘
resistance
form
respiThe reof the
of presenting
under
reported
Rint
variance
we
Rlung
922
the
between
to be
against
“esophageal”
and Pmusc
various
to be
found
standard
measurement.’6
Hint
measured
experimental
in all cases
a very
close
average
close
and
system,
the
infla-
yielded
a line
in the
individual
Rrs,cmv,
measured
(Table
3). As suggested
volumes
namely
CMV
PA was used to
values
to
true
and
chest
at
as described,
of the respi-
ohmic
than
agreement
and Rint. A possible explanation
and
tissues
the
lung.
component,
originally
proposed
as a measure
Mead
claimed
and Whittenberger
that the measurement
tissue
and
an
undefined
Lately,
et
alas
of airway
as
et
At
between
of this finding
that
in intact
Rint
summary,
Rlung
measured
It
chest
wall
et al’s
represent
and
pure
with data obtained
at
includes
Bates
least
during
a substantial
et
by
alas
spontacompo-
the chest wall.
from
In
line.
to
However,
animals,
Hint
of
Liistro
al,21
claimed
methods.
expiration,
resistance.’#{176}
well as Frank
et alm
includes
airway,
lung
proportion
Jackson
plethysmographic
nent
they
Hint,
include
the early ohmic
therefore be systemati-
Rint is very similar to Rlung during spontaneous
breathing,
while
it is on average
very comparable
to
Rrs,cmv.
The meaning
of Hint has been
the subject
of
some
uncertainties
for many
years:
the method
was
to assess
Rlung.
constant
lower
than Rrs,cmv.
Nonetheless,
we found
that
the individual
average
value
for Hint was comparable
to the corresponding
Rrs,cmv.
At this time, however,
we are unable to provide a definite explanation of why
neous
Frank
in ten
time
reasoning
cally
showed
swings
to
By analog
measured
during
PSV, should
components
only and should
occluded
conditions:
higher
wall
within
airway resistance, as compared
values is not
the identity
between
pressure
arid esophageal
line under
is in itself an accepted
subjects
the
very
flows
Chowienczyk
the validity of the esophageal
et al20 compared
Rlung
to
ESTPA
very close to the identity line. When
ratory
encouraged
our
which
PA
flow
inequalities
include
relationship
constant
over
obtained
lung
in
selected
patients.
of PA
and
body plethin ICU
pa-
Protocol
close
data
PSV ventilation
from respiratory
reproduci-
and
nonintubated
and the directly measured
during
measured
resistances.
Esophageal
mechanics
by Bates et al,asRrs,cmv, when measured
should
include all resistive components
that the patient has to breathe. For
however,
intrinsic
respiratory
resiswould
be more correct.
resistance
respiratory
at
has
it
the data since we felt this kind of measurement
the one clinically most important. It is indeed
total
Protocol
popularity
of alveolar
ratory
artificial
phases);
patients
presence
airways,
measurement
Ventilation
in avoiding
have
the
since
airway avoids the problems
ance
involved
and
are applicable
is regaining
technique
patients,
al.21
the principle
as developed
positioning,
motion,
we
rather
could
made
up in turn
of airway,
lung
and
chest
wall
resistance to flow, plus a frequency-dependent
component, related to the viscoelastic properties of the
balloon
However,
(both
plethysmographic
in proper
to cardiac
to
CMV
expiratory
breathing
esophageal
time.
physiol-
technique
during
and
spontaneously
artifacts due
in
a major
mechanics
of the
one
of classic respiratory
of difficulties
bility
been
balloon techniques.’7”
While
cannot
be routinely
applied
ysmography
tients,
has
remains
it
inspiratory
variance
compared
tion in the same
The
regression
method
principle,
respiratory
et
who
al21
ventilation.
Mechanical
mechanics
earliest developments
ogy10 In
measure
that
the interrupter method
during
with the theoretical values computed
3).
airway
et
reduce
resistance
method
similar
by
DiscussioN
The
of PA and
extrapolation
by Jackson
confirm
method
during partial support
Controlled
of Jackson
9
SD.
±
proposed
Our data
the occluder
work
extrapolation
procedure
of the pressure
tracings
the determination
We used a back
We
*Aserage
by the
showed
how
a back
than crude
inspection
and Flows
Rrs,cmv*
No.
Controlled
Support
should
we
be
method
to measure
breathing.
However,
were
on average
Interrupter
Technique
found
Hint
at the same
noted
resistive
that
Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/21654/ on 06/16/2017
Rlung
work
Hint values
very
similar
for Measuring
to be very similar
to
time by means of a Pes
is a reference
during
spontaneous
obtained
to total
Respiratory
Mechanics
during
PSV
inspiratory
(Pesenhi eta!)
resistances
measured
CMV
during
not
more
tance
4 h
than
earlier.
of Elastic
Respiratory
The
to
very
the
adult
anesthetized
accepted
Pel,rs
during
CMV
(Fig
based
4). The
was judged
during
adequacy
from
respiratory
subjects.
distress
Am
Rev
syndrome
Respir
Dis
1991;
of
explanation
(less
it
of the
next
inspiratory
presence
the
in obtaining
11
able
artificial
problem
of glottis
that all patients
studied
of sedation,
a common
ment
In
ill patients.
conclusion,
we
old method
ventilatory
but
principles,
degrees
clinical
manage-
in the
propose
a new
Biased
based
it
major
and
variable
to the
on
allows
sound
at
respiratory
perhaps
by
and
least
classic
a gross
mechanical
J.
14
15
a
Rahn
H,
16
Shee
Otis
physiologic
the
pressure
volume
curves.
J, Benito
2 Mancebo
compliance
in
respiratory
failure.
3 Gattinoni
D,
L,
Marcolin
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1988;
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static
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1989;
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1946;
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skillful
technical
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I 3 / SEPTEMBER,