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

       Explain two advantages of
        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
            measurements are made
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


  O2 Added


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
  dead space (VDanat),
                      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
    healthy adults; up to
    3% in older adults

    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
    adults range from
    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

    In healthy adults,
    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
    may added to it
    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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