Pneumology - Lung volumes-airway-resistance

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1. Dr. Sunil Sharma
Senior Resident
Dept of Pulmonary Medicine

2. l l d b
it
fl
€
l
ung

vo
l
umes

measure
d b
y

sp
i
rome
t
ry are

use
f
u
l
for detecting, characterising & quantifying the severity of lung disease severity of lung disease
€
Measurements of absolute lun
g
volumes
,
RV
,
FRC
g,,
& TLC are technically more challenging Æ
limiting use in clinical practice €
Precise role of lung volume measurements in the assessment of disease severity, functional assessment of disease severity, functional disability, course of disease and response to treatment remains to be determined

3. Lg l f t
€
L
un
g
vo
l
ume

are

necessary
f
or

a

correc
t
physiological diagnosis in certain clinical
conditions €
Contrast to the relative simplicity of spirometric volumes variety of disparate techniques have volumes variety of disparate techniques have been developed for the measurement of absolute lung volumes
€
Various methodologies of body plethysmography, nitro
g
en washout
,

g
as dilution
,
and radio
g
ra
p
hic
g,g,gp
imaging methods
Eur
Respir
J 2005; 26: 511
–
522
Eur
Respir
J 2005; 26: 511
–
522

4. ‘‘lg l’’ ll f t th l f
€
‘‘l
un
g
vo
l
ume
’’
usua
ll
y

re
f
ers
t
o
th
e

vo
l
ume

o
f
gas within the lungs, as measured by body
plethysmography, gas dilution or washout €
Lung volumes derived from conventional chest radiographs are usually based on the volumes radiographs are usually based on the volumes within the outlines of the thoracic cage & include
volume of tissue (normal and abnormal)
ƒ
volume of tissue (normal and abnormal)
ƒ
lung gas volume
€
Lung volumes derived from CT scans can also include estimates of abnormal lung tissue volumes

5. €
There are four volume subdivisions which ƒ
do not overlap
ƒ
can not be further divided
h dd d t th l t t l l it
ƒ
w
h
en

a
dd
e
d t
oge
th
er

equa
l t
o
t
a
l l
ung

capac
it
y
€
Lung capacities are subdivisions of total
€
Lung capacities are subdivisions of total volume that include two or more
of the 4
basic lung volumes basic lung volumes

6. €
Tidal Volume
€
InspiratoryReserve Volume
€
Ex
p
irator
y
Reserve Volume
py
€
Residual Volume

7. €
Tidal volume ƒ
The amount of gas inspired or expired with each bthb
rea
th
Iit
R Vl
€
I
nsp
i
ra
t
ory
R
eserve
V
o
l
ume
ƒ
Maximum amount of additional air that can be inspired from the end of a normal inspiration inspired from the end of a normal inspiration
€
Expiratory Reserve Volume
€
Expiratory Reserve Volume ƒ
The maximum volume of additional air that can be expired from the end of a normal expiration be expired from the end of a normal expiration

8. €
Residual Volume ƒ
The volume of air remaining in the lung after a
maximal expiration
ƒ
This is the only lung volume which cannotbe meas red ith a
spirometer
meas
u
red
w
ith a
spirometer

9. €
Total Lung Capacity
€
Vital Capacity
€
Functional Residual Ca
p
acit
y

py
€
InspiratoryCapacity

10. Ttl L C it
€
T
o
t
a
l L
ung
C
apac
it
y
ƒ
volume of air contained in the lungs at the end of a
maximal ins
p
iration
p
ƒ
Sum of all four basic lung volumes
ƒ
TLC = RV + IRV + TV + ERV
€
Vital Capacity ƒ
The maximum volume of air that can be forcefully
ƒ
The maximum volume of air that can be forcefully expelled from the lungs following a maximal inspiration L t l th t b d ith
ƒ
L
arges
t
vo
l
ume
th
a
t
can
b
e

measure
d
w
ith
a

spirometer
ƒ
VC = IRV + TV + ERV = TLC - RV

11. €
Functional Residual Capacity ƒ
The volume of air remaining in the lung at the
d f l i ti
en
d
o
f
a

norma
l
exp
i
ra
ti
on
ƒ
FRC = RV + ERV
€
InspiratoryCapacity
Maximum volume of air that can be inspired from
ƒ
Maximum volume of air that can be inspired from end expiratory position
ƒ
This ca
p
acit
y
is of less clinical si
g
nificance than
py g
the other three
ƒ
IC = TV + IRV

12. €
Use a spiromete
r
IRV
VC
TV
IC
IRV
Can Use
S
p
iromenter
TLC
TV
ERV
p
RV
FRC
RV
Can’t Use a Spirometer

13. C
i
€
C
annot

use

sp
i
rometry
M FRC h
€
M
easure
FRC
,

t
h
en

use:
RV = FRC – ERV
€
Residual Volume is determined by one of 3 techniques techniques ¾
Gas Dilution Techniques |
Nitro
g
en washout
g
|
Helium dilution
¾
Whole Body Plethysmography Rdi h
¾
R
a
di
ograp
h
y

14. €
Two most commonly used gas dilution
methods for measuring lung volume
ƒ
open circuit nitrogen (N
2
) method
ƒ
closed-circuit helium (He) method
€
Both methods take advantage of ƒ
physiologically inert gas that is poorly soluble in
alveolar blood and lung tissues
both are most often used to measure functional
ƒ
both are most often used to measure functional residual capacity

15. I th
iit
th d ll h l d i
€
I
n
th
e

open-c
i
rcu
it
me
th
o
d
,

a
ll
ex
h
a
l
e
d
gas
i
s

collected while the subject inhales pure oxygen
€
Initial concentration of nitrogen in the lungs is
assumed to be about 0.81 €
rate of nitrogen elimination from blood and tissues about 30 mL/min
t f th t t l t f it
€
measuremen
t
o
f th
e
t
o
t
a
l
amoun
t
o
f
n
it
rogen

washed out from the lungs permits the calculation of the volume of nitro
g
en-containin
g

g
g
gas present at the beginning of the manoeuvre

16. 080FRC =
V
xF
MassBalance:
0
.
80

FRC

=

V
spirometer
x

F
N
2
Mass

Balance:
N2 Start N2 Finish
V
F
FRC
V
F
F
ml
Spirometer N
N
=
•
=
•
2
2
40 000 0 05
08
(spiometer)
(lung)
,.
.

17. A d t f th
i it th d i th t
A
n

a
d
van
t
age

o
f th
e

open-c
i
rcu
it
me
th
o
d i
s
th
a
t
€
permits an assessment of the uniformity of ventilation of the lungs by ventilation of the lungs by ƒ
anal
y
zin
g
the slo
p
e of the chan
g
e in nitro
g
en
yg p g g
concentration over consecutive exhalations measuring the end
expiratory concentration of
ƒ
measuring the end
-
expiratory concentration of
nitrogen after 7 minutes of washout
ƒ
by measuring the total ventilation required to reduce
end-expiratory nitrogen to less than 2%
Am Rev Respir Dis1980; 121:789-794

18. €
The open-circuit method is sensitive to ƒ
Leaks anywhere in the system –mouthpiece
ƒ
Errors in measurement of nitrogen
concentration & exhaled volume
€
If a pneumotachygraphis used attention must be paid to the effects of the change
in viscosity of the gas exhaled, because it
contains a progressively decreasing concentration of nitrogen

19. Disadvanta
g
es
g
€
Does not measure the volume of gas in poor
communication with the airways e.g. lung bullae €
Assumes that the volume at which the measurement was made corresponds to the end
expiratory point
was made corresponds to the end
-
expiratory point
€
requires a long period of
reequilibration
with room air
€
requires a long period of
reequilibration
with room air
before the test can be repeated
Measuring spirometric volumes immediately before
measuring FRC can eliminate the assumption of a
constant or reprod cible end
e pirator ol me
constant or reprod
u
cible end
-
e
x
pirator
y

v
ol
u
me

20. €
Subject rebreathea gas mixture containing
helium in a closed system until equilibriation
i hi d i
s

ac
hi
eve
d
€
Volume and concentration of helium in the gas mixture rebreathedare measured
€
Final equilibrium concentration of helium permits calculation of the volume of gas in the lungs at the start of the manoeuvre

21. Start: known ml of 10% He in Spirometer
Rebreath for 10 min (until He evenly distributed)
F
F
V
FRC
V
(
)
F
F
V
⋅
(
)
F
F
V
FRC
He He Spirometer
initial final
•
=
•
+
V
Spirometer
(
)
FVC
F
F
V
F
He He Spirometer
H
e
initial final
final
=
−
⋅
(
)
final

22. Th l
dtiit t th hli
€
Th
erma
l
-con
d
uc
ti
v
it
y

me
t
er

measures
th
e
h
e
li
um

concentration continuously, permitting return of the
sampled gas to the system €
Because the meter is sensitive to carbon dioxide it is removed from the system by adding carbon dioxide removed from the system by adding carbon dioxide absorber
€
Removal of CO
2
& O
2
consumption results in a
constant fall in the volume of gas in the closed circuit
€
An equivalent amount of oxygen is to be introduced
as an initial bolus or as a continuous flow

23. €
Closed-circuit method is sensitive to
errors from leakage of gas and alinearity
of the gas analyzer
€
Fails to measure the volume of gas in lung bullae
& ca
nn
ot be
r
epeated at s
h
o
r
t
bullae
& cannot be repeated at short
intervals
€
Test results are reproducible
Scand J Clin Lab Invest1973; 32:271-277

24. €
Three types of plethysmograph ƒ
pressure
ƒ
Volume
ƒ
pressure-volume/flow

25. €
Has a closed chamber with a
fixed volume in which the
subject breathes subject breathes
€
Volume changes associated
with compression or expansion with compression or expansion of gas within the thorax are measured as pressure changes in gas surrounding the subject
ithi th b
w
ithi
n
th
e
b
ox
€
Volume exchange between
l d b d di l l
ung

an
d b
ox
d
oes

not
di
rect
l
y

cause pressure changes
€
Thermal, humidity, & CO
2
-O
2
exchange differences between inspired and expired gas do cause pressure changes cause pressure changes

26. Th i l d i t
€
Th
orac
i
c

gas

vo
l
ume

an
d
res
i
s
t
ance

are

measured during rapid manoeuvres
€
Small leaks are tolerated or are introduced to
vent to slow thermal-
p
ressure drift
p
€
Best suited for measuring small volume changes because of its high sensitivity & excellent frequency response
€
Measurements are usually brief and are used to stud
y
ra
p
id events it need not be leak-free
,

yp
,
absolutely rigid, or refrigerated

27. €
Has constant pressure and variable volume variable volume
€
When thoracic volume changes, gas is displaced through a hole in
the box wall and is measured
ƒ
spirometer
or
ƒ
spirometer
or
ƒ
integrating the flow through a pneumotachygraph
€
Suitable for measuring small or large volume changes large volume changes

28. €
To attain good frequency response, the
impedance to gas displacement must be very
ll
sma
ll
€
Requires a
ƒ
low-resistance pneumotachygraph
ƒ
sensitive transducer
ƒ
fast, drift-free integrator, or
ƒ
meticulous utilization of special spirometers
€
Difficult to be used for routine studies

29. €
Combines features of both types
€
As the sub
j
ect breathes from
j
the room, changes in thoracic
gas volume compress or expand
the air around the subject in th b d l di l it th
e
b
ox

an
d
a
l
so
di
sp
l
ace
it
through a hole in the box wall
€
Compression or decompression of gas is measured as a pressure change
€
displacement of gas is measured ƒ
spirometer connected to the box or
ƒ
integrating airflow through a pneumotachygraph
in the opening
pneumotachygraph
in the opening

30. €
All of the change in thoracic gas volume is accounted
€
All of the change in thoracic gas volume is accounted for by adding the two components (pressure change
and volume displacement) €
This combined approach has ƒ
wide ran
g
e of sensitivities
g
ƒ
permitting all types of measurements to be made with
the same instrument (i.e., thoracic gas volume and
airway resistance, spirometry, and flow-volume curves)
€
Box has excellent frequency response and relatively modest requirements for the
spirometer
modest requirements for the
spirometer
€
The integrated-flow version dispenses with water-
filled
spirometers
and is tolerant of leaks
filled
spirometers
and is tolerant of leaks

31. C ibl g i th th h th t it
€
C
ompress
ibl
e
g
as
i
n
th
e
th
orax,

w
h
e
th
er

or

no
t it
is in free communication with airways
€
By Boyle's law, pressure times the volume of the
gas in the thorax is constant if its temperature
remains constant (PV = P
'V
')
remains constant (PV = PV)
€
At end-ex
p
iration, alveolar
p
ressure
(
Palv
)

pp(
)
equals atmospheric pressure (P) because there is no airflow & V (thoracic gas volume) is unknown
€
Airway is occluded and the subject makes small inspiratory and expiratory efforts against the occluded airway occluded airway

32. Di
iit
ff t th th l
€
D
ur
i
ng

i
nsp
i
ra
t
ory e
ff
or
t
s,
th
e
th
orax

en
l
arge

(ΔV) and decompresses intrathoracic gas, creating a new thoracic gas volume (V
'
=
V
+
ΔV)
creating a new thoracic gas volume (V V ΔV) and a new pressure (P' = P + ΔP)
€
A pressure transducer between the subject's
mouth and the occluded airway measures the
new pressure (P
’
)
new pressure (P )
€
Assumed
-
P
th
=

P
l
during
compressional
€
Assumed
P
mou
th

P
a
l
v
during
compressional
changes while there is no airflow at the mouth Æpressure changes are equal throughout a static fl id t (P l' i i l ) fl
u
id
sys
t
em
(P
asca
l'
s

pr
i
nc
i
p
l
e
)

33. l
’
dhl
€
Boy
l
e –Mariotte
’
s Law : P x V = constant un
d
er isot
h
erma
l

conditions
P
A
x TGV = (P
A
-Δ PA)(TGV + Δ V)
Expanding and rearranging equation
TGV =(Δ V / Δ P
A
)(P
A
-Δ P
A
)
Since Δ P
A
is very small compared to P
A
(<2%) it is usually
omitted in the differential term
TGV ~ (Δ V / Δ P
A
) x P
A
with P
A
= P
bar
-P
H2O
,sat
TGV ~ (Δ V / Δ P
A
) x (P
bar
-P
H2O
,sat)

34. €
The measured TGV additionally includes any
apparatus dead spaces (Vd,app) as well as any
volume inspired above resting end
expiratory
volume inspired above resting end
-
expiratory
lung volume at the moment of occlusion (Vt,occ)
€
FRC
pleth
can be derived from TGV by subtraction
of these two volume components of these two volume components
FRC
lh
= TGV
-
V
d
-
V
FRC
p
l
et
h
= TGV
V
d
,app
V
t,occ

35. Th th i l ll d i
€
Th
e
th
orac
i
c

gas

vo
l
ume

usua
ll
y

measure
d i
s

slightly larger than FRC unless the shutter is closed precisely after a normal tidal volume is closed precisely after a normal tidal volume is exhaled
€
Connecting
ƒ
the mouth-piece assembly to a valve and spirometer (or
pneumotachygraph
and integrator)
(or
pneumotachygraph
and integrator)
ƒ
using a pressure-volume plethysmograph
makes it possible to measure TLC and all its
subdivisions in conjunction with the measurement of
thoracic
g
as volume
g

36. Problems €
Effects of Heat, Humidity, and Respiratory Gas Exchange Ratio
€
Changes in Outside Pressure
€
Cooling
€
Underestimation of Mouth Pressure
€
Compression Volume

37. €
In uncooperative subjects radiographic lung
volumes may be more feasible than physiological
measurements
€
The definition of the position of lung inflation at the time of image acquisition is clearly essential
€
Volumes measured carry their own assumptions
and limitations and cannot be directly and limitations
,
and cannot be directly
compared with volumes measured by the other techniques techniques

38. €
The
p
rinci
p
le is to outline the lun
g
s in both A-P & lateral
pp g
chest radiographs, and determine the outlined areas ƒ
assuming a given geometry or
ƒ
using
planimeters
in order to derive the confined volume
using
planimeters
in order to derive the confined volume
€
Adjustments are made for
magnification factors
ƒ
magnification factors
ƒ
volumes of the heart
ƒ
intrathoracic tissue and blood if di h i
ƒ
i
n
f
ra
di
ap
h
ragmat
i
cspaces
€
In the determination of TLC
,
6–25% of sub
j
ects differed b
y

,
jy
>10% from plethysmographic measurements in adult subjects
Academic Press Inc New York 1982; pp 155
163
Academic Press Inc
.,
New York
,
1982; pp
.
155
–
163

39. €
In addition to thoracic cage volumes, CTs can provide
€
In addition to thoracic cage volumes, CTs can provide estimates of ƒ
lung tissue and air volumes
ƒ
volume of lung occupied by
ƒ
volume of lung occupied by |
Increased density (e.g. In patchy infiltrates) or
|
Decreased density (e.g. in emphysema or bullae)
€
In a study of children, comparable correlations were
observed for CT and radio
g
ra
p
hic measurements as
gp
compared with plethysmographicTLC
A J
Ri
Cit
C M d 1997 155 1649
1656
A
m
J
R
esp
i
r
C
r
it
C
are
M
e
d 1997
;
155
:
1649
–
1656
€
Disadvantage Æhigh radiation dose

40. €
MRI offers the advantage of a large number of
images within a short period of time, so that
volumes can be measured within a single breath volumes can be measured within a single breath
€
Potential for scanning specific regions of the
€
Potential for scanning specific regions of the lung, as well as the ability to adjust for lung water and tissue water and tissue
€
despite the advantages of an absence of
€
despite the advantages of an absence of radiation exposure its use for measuring thoracic gas volume is limited by its considerable cost

41. Resistive Forces €
Inertia of the res
p
irator
y
s
y
stem
pyy
(negligible)
€
Friction
€
Friction ¾
lung & chest wall tissue surfaces gliding past
¾
lung & chest wall tissue surfaces gliding past each other
¾
lung tissue past itself during expansion
¾
lung tissue past itself during expansion
¾
frictional resistance to flow of air through the
airwa
y
s
(
80%
)
y( )

42. Airflow in the Airways Exists in Three Patterns
ƒ
Laminar
ƒ
Turbulent
ii l [di ib d l i ]
ƒ
Trans
i
t
i
ona
l [di
str
ib
ute
d l
am
i
nar
]

43. €
Reynolds number

ρ
X
Ve
X D
€
Reynolds number
=

ρ
X
Ve
X D
η
ρ= density
Ve= linear velocity of fluid
D = diameter of tube
η =
viscosity of fluid
η =
viscosity of fluid
€
Turbulent flow tends to take place when gas density, linear velocity & tube radius are large velocity & tube radius are large
€
Linear velocity (cm/sec) of gas in the tube is calculated by diidi th fl t (L/ ) b tb (
2
)
di
v
idi
ng
th
e
fl
ow

ra
t
e
(L/
sec
) b
y
t
u
b
e

area
(
cm
2
)
€
Tube area refers to total cross sectional area of the
f
airways

o
f
a

given

generation

44. €
Airflow is transitional throughout most
€
Airflow is transitional throughout most of tracheobronchial tree E i d t d thi fl i
€
E
nergy

requ
i
re
d t
o

pro
d
uce
thi
s
fl
ow
i
s

intermediate between laminar and
turbulent €
Many bifurcations in tracheobronchial tree flow becomes laminar at very low tree
,
flow becomes laminar at very low
Reynolds number in small airways distal to the terminal bronchioles
€
Flow is turbulent only in the trachea where the radius is large and linear velocities reach high values [during velocities reach high values [during exercise, during a cough]

45. €
Airway resistance is easy to measure
repeatedly & is always related to the
lung volume at which it is measured
•
Measurements of R
AW
useful in differential
diagnosis of
|
type of airflow obstruction
|
localization of the major site of obstruction
•
Measured during airflow & represents the ratio of the driving pressure and instantaneous airflow the driving pressure and instantaneous airflow

46. €
R
AW
is determined by
i th l (β)
measur
i
ng
th
e

s
l
ope
(β)
of a curve of plethysmograph
pressure
plethysmograph
pressure
(x-axis) displayed against airflow (y
-
axis)
against airflow (y
axis)
on an oscilloscope during
r
ap
i
d, s
h
allow b
r
eat
hin
g
apd, s allow b eat g
through a p
neumotach
yg
ra
p
h
pygp within the plethysmograph

47. €
Shutter is closed across the mouth-piece, and
the slope (α) of plethysmographic pressure (x-
axis) displayed against mouth pressure (y
axis) is
axis) displayed against mouth pressure (y
-
axis) is
measured during panting under static conditions
€
Because P
mouth
equals P
alv
in a static system it
serves two purposes serves two purposes ƒ
Relates changes in plethysmographic pressure
to chan
g
es in
P
alv
in each sub
j
ect
g
alv
j
ƒ
Relates R
AW
to a particular thoracic gas volume

48. Ph
y
siolo
g
ic factors affectin
g

p
leth
y
smo
g
ra
p
hic measurement
yg g
pygp
of R
AW
Airflow €
R
AW
p
ertains to a
p
articular flow rate durin
g
continuous
pp g
pressure-flow curves, so the slope may be read at any
desired airflow rate €
R
AW
is measured at low flows, at which transmural
compressive pressures across the airways are small and the
relation to Palv is linear
€
Airway dynamics measured during forced respiratory maneuvers is associated with ƒ
large transmural compressive pressures across the airways
ƒ
maximal dynamic airway compression limiting airflow rates and
ƒ
possible alterations in airway smooth muscle tone
nder s ch circ mstances R
AW
ma be increased markedl
u
nder s
u
ch circ
u
mstances
,
R
AW
ma
y
be increased markedl
y

49. VlV
o
l
ume
N TLC i i ll b RV
€
N
ear
TLC
,

res
i
stance
i
s

sma
ll
,
b
ut

near
RV
,

resistance is large
€
Lung volume may be changed voluntarily to
evaluate R
AW
at lar
g
er or smaller volumes in
g
health and disease
€
As a first approximation, airway conductance (G
AW
), the reciprocal of R
AW
, is proportional to
lung volume lung volume

50. Transpulmonary
Pressure
Transpulmonary
Pressure
€
R
AW
is related more directly to lung elastic recoil pressure
th t l l th
an
t
o
l
ung

vo
l
ume
€
Subjects with increased lung elastic recoil have a higher G
i l l b f i d i
G
AW
at

a

g
i
ven
l
ung

vo
l
ume
b
ecause

o
f i
ncrease
d
t
i
ssue

tension pulling outward on airway walls
€
Loss of elastic recoil results in loss of tissue tension and
decreased traction on airway walls, so G
AW
is decreased
€
This relationship may be used to analyze the mechanism of airflow limitation in various obstructive ventilatory defects (e.g., bullous lung disease)

51. Airway Smooth Muscle Tone Airway Smooth Muscle Tone
.
€
Airways affected markedly by smooth muscle tone,
depending on the state of inflation and volume
hi thi
s
t
ory
€
R
elat
i
o
n
s
hi
ps a
r
e
r
eleva
n
t to d
i
seases
in
w
hi
c
h

elat o s ps a e eleva t to d seases w c
ƒ
smooth muscle tone is increased (e.g., asthma)
ƒ
low lung volumes are encountered (e.g., during cough, when
pneumothorax
is present)
when
pneumothorax
is present)
€
Bronchoconstriction is not demonstrable temporarily after a deep breath or at TLC in healthy subjects after a deep breath or at TLC in healthy subjects
€
R
AW
in healthy subjects may be greater when a given
l l i hd f R h f C l
ung

vo
l
ume
i
s

reac
h
e
d f
rom
R
V

t
h
an
f
rom

TL
C

52. Panting Panting €
Panting minimizes changes in the plethysmograph caused
by thermal, water saturation, and carbon dioxide-oxygen
exchange differences during inspiration and expiration exchange differences during inspiration and expiration
€
Improves the signal-to-drift ratio, because each respiratory cycle is completed in a fraction of a second cycle is completed in a fraction of a second
€
gradual thermal changes and small leaks in the box become insignificant compared with volume changes become insignificant compared with volume changes attributable to compression and decompression of alveolar gas
€
Glottis stays open, rather than partly closing and varying
position, as it does during tidal breathing

53. DBi
d ll d ib d ill t
€
D
u
B
o
i
san
d
co
ll
eagues
d
escr
ib
e
d
an

osc
ill
a
t
ory

method to measure the mechanical properties of the lung and thorax the lung and thorax
EurRespirJ1996; 9:1747-1750
€
Use an external loudspeaker or similar device to generate and impose flow oscillations on generate and impose flow oscillations on spontaneous breathing
€
Impulse oscillometry measures R
AW
and lung
compliance independently of respiratory muscle
strength and patient cooperation

54. Sd t i f i (3
20 H )
€
S
oun
d
waves

a
t
var
i
ous
f
requenc
i
es
(3
-
20 H
z
)
are applied to the entire respiratory system
€
piston pump can be used to apply pressure waves
around the bod
y
in a whole-bod
y
res
p
irato
r
y
yp
€
Slow frequency changes in pressure, flow, and
volume generated by the respiratory muscles during normal breathing are subtracted from the Raw data Raw data
€
p
ermittin
g
anal
y
sis of the
p
ressure-flow-volume
pgy p
relationships imposed by the oscillation device

55. Th l ti f f th l d h t ll
€
Th
e

e
l
as
ti
c
f
orces

o
f th
e
l
ungs

an
d
c
h
es
t
wa
ll
oppose

the volume changes induced by the applied pressure
& decrease as the frequency of oscillation increases €
The total force or pressure that opposes the driving pressure applied by the loudspeaker can be measured pressure applied by the loudspeaker can be measured as peak-to-peak pressure difference divided by peak- to-peak flow Æcombination of the resistance and
t
reac
t
ance
€
This resistance is proportional to the R
AW
in healthy
€
This resistance is proportional to the R
AW
in healthy
subjects and patients, although it does include a
small component of lung tissue and chest wall
resistance as well as the resistance of the airways resistance as well as the resistance of the airways

56. High f ill ti g i fl i li d t
€
High f
requency

osc
ill
a
ti
n
g
a
i
r
fl
ow
i
s

app
li
e
d t
o

the airways
€
Resultant pressure & airflow changes are
measured €
Applying a/c theory Raw can be measured contineousl
yy
J Appl Physol1970; 28: 113-16
€
Measures total respiratory resistance through out
the vital capacity – displaying resistance as
function of lung volume function of lung volume