Resting Lung Volumes

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					Resting Lung Volumes

An Introduction to Spirometry
Spirometer Tracing
            Measurement
• Static lung volumes can be measured
  using a spirometer creating a paper trace
• Residual lung volume measurement is
  difficult because the volume can not be
  exhaled
  We will use a method known as nitrogen
  dilution
      Residual Lung Volume
• The volume of air left in the lungs after a
  maximal expiration
• Small passageways close before all of the
  air from the alveoli is expelled
• If the alveoli were to be completely
  emptied, they would stick together and be
  very difficult to reopen
         Why measure RV?
• Basic scientific interest
• Get an accurate density from hydrostatic
  weighing
• Determine whether or not it aids
  performance in sports (especially of
  interest are water sports)
• Determine whether it is anatomical or can
  change based on training
          Basic Procedure
• Subject maximally expires to residual
  volume
• Subject breathes in and out 100% oxygen
  from a spirometer (of a known volume)
• After an equilibrium has been reached the
  Nitrogen level in the spirometer is
  measured
   Nitrogen Dilution Technique
• Nitrogen is metabolically inert (it is neither
  produced nor consumed by the body)
• Nitrogen dilution is merely balancing an
  equation


Initial Amount of N2 = Final Amount N2
Components of Initial Amount of N2
• Nitrogen in the Spirometer
   FN2ispirometer x Vispirometer
  *Spirometer Volumes include the bell
   volume and the dead space
• Nitrogen in the Lungs
    FN2iLung x RV
  – FN2iLung is the fraction of Nitrogen inspired
    (79%)
  – RV is the Residual Volume
Components of Final Amount of N2
• Nitrogen in the connected system of the
  spirometer and lungs measured during
  equilibrium
    FN2f x Vf
  – FN2f
     • The fraction of nitrogen in the lungs and spirometer
       at equilibrium
     • A measured variable
  – Vf
     • The sum of the volume of the spirometer (including
       both the dead space and the bell) and the Residual
       Volume
Distribution of Nitrogen in the
            System
             Calculating RV
• Using the information on the last three
  slides RV can be calculated from the three
  measured variables (initial fraction N2, final
  fraction N2, and initial spirometer volume)
• The BTPS correction factor must be used
  to determine the actual volume of gas in
  the conditions inside the lungs
     Dynamic Lung Volumes
• Forced Expiratory Volume in 1.0 seconds
  (FEV 1.0)
• Forced Expiratory Volume in 3.0 seconds
  (FEV 3.0)
• Maximum Voluntary Ventilation (MVV)
   Forced Expiratory Volumes
• The percent of vital capacity expelled in a
  set time period
• Give indications of health problems not of
  fitness or training
• FEV 1.0 normal value ~80% of FVC
• FEV 3.0 normal value ~98% of FVC
FEV Spirometer Examples
Maximum Voluntary Ventilation
• Maximum amount that can be exhaled per
  unit time
• Usually measured over 12 seconds
• Units are in L/min
• Debatable application to fitness, training
  status, or athletic performance
       Factors Influencing Lung
               Volumes
•   Height
•   Gender
•   Age
•   Ethnic Background
•   Disease
•   These factors are used in determining
    prediction equations for lung volumes
  Standardizing Gas Volumes
• Gas volumes change as temperature and
  pressure change
• These relationships are determined by
  Charles’ Law and Boyle’s Law
      Water Vapor Pressure
• The amount of water vapor that can be
  held in the air increases as temperature
  increases
• This increases the pressure measured
• Therefore when gas volumes are
  measured the water vapor pressure must
  be taken into account as part of the
  pressure change
         Correction Factors
• The difference in conditions between the
  lab (where the volume is measured) and
  inside the body (the volume we are hoping
  to determine) must be corrected for
      BTPS/STPD Correction
• The conditions in the lab are called ATPS or
  ambient temperature pressure and saturation
• In order for comparison of volumes in different
  circumstances STPD or the standard
  temperature and pressure dry is used
• In order to determine the actual volume of air
  that the lungs contain, BTPS or body
  temperature pressure and saturation conditions
  are used

				
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posted:8/10/2011
language:English
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