# Lung Volumes and Gas Distribution by ggl16746

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```									Lung Volumes and Gas Distribution

RET 2414
Pulmonary Function Testing
Module 3.0
Lung Volumes / Gas Distribution

   Objectives

   Describe the measurement of lung
volume using direct and indirect
spirometry

measuring lung volumes using the
body plethysmograph
Lung Volumes / Gas Distribution

   Objectives

   Calculate residual volume and total
lung capacity from FRC and the
subdivisions of VC

   Identify restriction from measuring
lung volumes
Lung Volumes / Gas Distribution
   Direct Spirometry
   Used to measure all volumes and
capacities EXCEPT for RV, FRC and TLC
Lung Volumes / Gas Distribution
   Indirect Spirometry

   Required for the determination of
RV, FRC and TLC

   Most often, indirect spirometry is
performed to measure FRC volume

   FRC is the most reproducible lung
volume and it provides a consistent
baseline for measurement
Lung Volumes / Gas Distribution

   Indirect Spirometry

   Two basic approaches

   Gas dilution

   Body plethysmography

   Measurements are in Liter or Milliliters
   Reported at BTPS
Lung Volumes / Gas Distribution
   Gas dilution techniques
   All operate on a principle SIMILAR to
Boyle’s Law (P1 V1 = P2 V2), which
states,
In isothermic conditions, the volume of a gas varies
inversely with its pressure

Fractional concentration of a known gas is
used instead of its partial pressure

C1 V1 = C 2 V2
Lung Volumes / Gas Distribution

   Gas dilution techniques

   By having a known (or measured)
gas concentration at the start and
end of the study and a single known
volume, the unknown volume can be
determined. For example:

V1 = C2 V 2
C1
Lung Volumes / Gas Distribution

   Gas dilution techniques

   Can only measure lung volumes in
communication with conducting
airways !!!
Lung Volumes / Gas Distribution
   Gas dilution techniques

   Obstruction or bullous disease can have
trapped, noncommunicating air within the
lungs

   FRC may be measured as being less than its
actual volume
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
   The natural volume of nitrogen in the
subject’s lungs at FRC is washed out
and diluted with 100% oxygen

   Test must be carefully initiated from
the FRC baseline level
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   All exhaled gas is collected in a Tissot
(large volume) spirometer for
measurement of its volume

   Analyzer in the breathing circuit
monitors nitrogen concentrations
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   Approximately 3-7 minutes of
breathing 100% O2 to wash out N2
from the lungs

   If oxygen-induced hypoventilation is a
documented problem (as in COPD), a
different method of FRC determination
is needed
Lung Volumes / Gas Distribution
   Open-Circuit Nitrogen Washout

   Test is successfully completed when
the N2 levels decrease to become less
than 1.5% for at least 3 successive
breaths (subjects without obstructive
disorders)

   Premature discontinuation may occur
due to:
   System leak
   Patient unable to continue
   Tissot spirometer is full
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   The FRC has a N2 concentration of
approximately 0.75, based on the
atmospheric nitrogen minus CO2 and
water vapor at BTPS:

(CAlvN2) = 0.75
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   The final collected volume of exhaled
gas in the Tissot spirometer

(VExh)

   Has a measurable concentration of N2

(CExhN2)
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   FRC determination is based on the
following equation:

VFRC = (CExhN2)(VExh)
CAlvN2
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   In the actual FRC determination by
this method, the calculation is more
complex

Do not get scared !
You will not be asked to do
the calculation!
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   The small final concentration of
alveolar N2 remaining in the lung
needs to be subtracted from the
original CalvN2

   Deep breath of O2 at the end of the test
and slowly exhaled. The end-
expiratory CN2 is used as the CFN2
(This volume should not be exhaled into the
spirometer)
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   The second correction is the volume of
nitrogen released from the body
tissues during the washout procedure
(body tissue N2 factor or BTN2)

   Rages from 30 – 50 ml/minute of the
washout procedure (TTest)
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   Final Calculation

VFRC = (CExhN2 X (VExh +VD) ) - BTN2 Factor X TTest
CAlvN2 – CFN2

   Must be BTPS converted
   Test can be repeated after 15 minutes (longer if COPD)
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout

   Modern computer-operated
pneumotachometer systems do not
require collection of total VExh or
measurement of the CExhN2

   Breath-by-breath CExhN2 and VExh
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
Lung Volumes / Gas Distribution

   Open-Circuit Nitrogen Washout
   Leak
Lung Volumes / Gas Distribution
   Open-Circuit Nitrogen Washout

Criteria for Acceptability

   The washout tracing/display should
indicate a continually falling
concentration of alveolar N2

   The test should be continued until the
N2 concentration falls to <1.5% for 3
consecutive breaths
Lung Volumes / Gas Distribution
   Open-Circuit Nitrogen Washout
Criteria for Acceptability

   Washout times should be appropriate
for the subject tested. Healthy
subjects should washout N2
completely in 3-4 minutes

   The washout time should be reported.
Failure to wash out N2 within 7
minutes should be noted
Lung Volumes / Gas Distribution
   Open-Circuit Nitrogen Washout
Criteria for Acceptability

   Multiple measurements should agree
within 10%

   Average FRC from acceptable trials should
be used to calculate lung volumes

   At least 15 minutes of room-air breathing
should elapse between repeated trials, >1
hour for patients with severe obstructive
or bullous disease
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

   FRC is calculated indirectly by
diluting the gas in the lungs at the
end-expiration level with a known
concentration of helium (an inert
gas)
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

FRC
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution
Procedure
•Spirometer is filled with a
known volume of air with
added oxygen of 25 – 30%

•A volume of He is added so
that a concentration of
approximately 10% is
achieved

•System volume (spirometer,
tubing) and He concentration
are measured
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

C1 V1 = C2 V2

(C1 initial He concentration)(V1 system volume)
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution
Procedure
•The patient breathes through
a free-breathing valve that
allows either connection to
both room air or the
rebreathing system

•The patient is switched into
the rebreathing system at
end-expiration level (FRC)

•The patient rebreathes the
gas in the spirometer, until
the He concentration falls to a
stable level
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

CO2 Absorbed
H2O Absorbed
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

He Concentration

System Volume
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution
Procedure
•Once the He reaches
equilibrium between the
spirometer and the patient,
the final concentration of He is   FRC
recorded

•The FRC can then be
calculated
Lung Volumes / Gas Distribution

   Closed-Circuit Helium Dilution

C1 V1 = C2 V2

(CIHe)(SV) = (CFHe)(FRC)

FRC = (%HeInitial - %HeFinal) x System volume
%HeFinal
Lung Volumes / Gas Distribution
   Closed-Circuit Helium Dilution

Volume Corrections

   A volume of 100 ml is sometimes subtracted
from the FRC to correct loss of He to the
blood

   The dead space volume of the breathing
valve and filter should be subtracted from
the FRC
Lung Volumes / Gas Distribution
   Closed-Circuit Helium Dilution

Criteria for Acceptability

   Spirometer tracing should indicate no leaks
(detected by a sudden decrease in He),
which would cause an overestimation of FRC

   Test is successfully completed when He
readings change by less than 0.02% in 30
seconds or until 10 minutes has elapsed
Lung Volumes / Gas Distribution
   Closed-Circuit Helium Dilution

Criteria for Acceptability

   Multiple measurements of FRC should agree
within 10%

   The average of acceptable multiple
measurements should be reported
Lung Volumes / Gas Distribution
   Body Plethysmography (BP)

   Measurement of FRC by body
plethysmograph is based on an
application of Boyle’s law

P1V1 = P2V2
or
V1 = P2V2
P1
Lung Volumes / Gas Distribution
   Body Plethysmography (BP)

   Unlike gas dilution tests, BP includes both air in
communication with open airways as well as air
trapped within noncommunicating thoracic
compartments

   In patients with air trapping, plethysmography
lung volumes are usually larger those measured
with gas dilution methods

   Volume measured is referred to as thoracic gas
volume (TGV or VTG)
   ATS is recommending term be dropped and changed
to “plethysmographic lung volume” (VL, pleth), and
“FRC by body plethysmography” or TGV at FRC
(FRCpleth)
Lung Volumes / Gas Distribution

   Body Plethysmography (BP)
Procedure

•Patient is required to support
cheeks with both hands and pant
with an open glottis at a rate of
0.5 - 1 Hz (30 – 60 breaths/min)
•BP shutter is suddenly closed at
end-expiration prior to
inspiration
•Panting is continued for several
breaths against closed shutter
(no air flow)
Lung Volumes / Gas Distribution

   Body Plethysmography (BP)
Procedure

•The thoracic-pulmonary volume
changes during panting produce
air volume changes within the BP
cabinet

•Decreases in cabinet volume are
an equal inverse response to
thoracic volume increase (As
thoracic volumes increase with
panting inspiration, BP cabinet
volume decreases and visa versa)
Lung Volumes / Gas Distribution

   Body Plethysmography (BP)

Criteria of Acceptability

•Panting maneuver shows a
closed loop without drift
•Tracing does not go off the
screen
•Panting is 0.5 – 1 Hz
•Tangents should be within 10%
•At least 3 FRCpleth values
should agree within 5% and the
mean reported
Lung Volumes / Gas Distribution

   Body Plethysmography (BP)

   Airway Resistance (Raw) and Specific
Airway Conductance (SGaw) can be
measured simultaneously during open-
shutter panting (1.5-2.5 Hz)

   Most plethysmographs have built-in
pneumotachometers and allow VC
maneuvers to be performed during the same
testing session
Lung Volumes / Gas Distribution

   Single-Breath Nitrogen Washout

   Measures Distribution of Ventilation

   Closing Volume

   Closing Capacity
Lung Volumes / Gas Distribution

   SBN2 (SBO2)

   Equipment
Lung Volumes / Gas Distribution
   SBN2
Procedure
   Patient exhales to RV

   Inspires a VC breath of
100% O2

   Patient exhales slowly
and evenly (0.3-
0.5L/s)

   N2 concentration is
plotted against volume
Lung Volumes / Gas Distribution

   SBN2
Phase I: upper airway
gas from anatomical
O2
consisting of 100% N2

Phase II: mixed airway
gas in which the
relative concentrations
of O2 and N2 change
abrubtly as VDanat
volume is expired
Lung Volumes / Gas Distribution

   SBN2
Phase III: a plateau
caused by the
exhalation of alveolar
gas in which relative
O2 and N2
concentrations change
slowly and evenly

Phase IV: an abrupt
increase in the
concentration of N2
that continues until RV
is reached
Lung Volumes / Gas Distribution
   SBN2
% N2 750 – 1250
Is 1.5% or less in

Increased % N2 750
– 1250 is found in
diseases characterized
by uneven distribution
of gas during
inspiration or unequal
emptying rates during
expiration.

Patients with severe
emphysema may
exceed 10%
Lung Volumes / Gas Distribution

   SBN2
Slope of Phase III

Is an index of gas
distribution

Values in healthy
0.5% to 1.0%
N2/L of lung
volume
Lung Volumes / Gas Distribution
   SBN2
Closing Volume
The onset of Phase
IV marks the lung
volume at which
airway closure
begins

airways begin
closing after 80-
90% of VC has
been expired,
which equates to
30% of TLC

Reported as a
percentage of VC
Lung Volumes / Gas Distribution
   SBN2
Closing Capacity

If RV has been
determined, CV
and expressed at
Closing Capacity
(CC)

CC is recorded as
a percentage of
TLC
Lung Volumes / Gas Distribution
   SBN2
Normal Values for CC and CV
________________________________
Male       Female

CV/%VC      7.7%     8.7%

CC/%TLC     24.8%    25.1%
Lung Volumes / Gas Distribution
   SBN2
   CV and CC may be increased, indicating
earlier onset of airway closure in:

   Elderly patients

   Smokers, early obstructive disease of small
airways

   Restrictive disease patterns in which FRC
becomes less than the CV

   Congestive heart failure when the caliber of
the small airways is compromised by edema
Lung Volumes / Gas Distribution

   SBN2
   Acceptability Criteria
   Inspired and expired VC should be
within 5% or 200 ml
   The VC during SBN2 should be within
200 ml of a previously determined VC
   Expiratory flows should be maintained
between 0.3 and 0.5 L/sec.
   The N2 tracing should show minimal
cardiac oscillations

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