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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.

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lung volumes and gas distribution

Lung Volumes and Gas Distribution

RET 2414

Pulmonary Function Testing

Module 3.0

lung volumes gas distribution
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 distribution1
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 distribution2
Lung Volumes / Gas Distribution
  • Direct Spirometry
    • Used to measure all volumes and capacities EXCEPT for RV, FRC and TLC
lung volumes gas distribution3
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 distribution4
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 distribution5
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 = C2 V2

lung volumes gas distribution6
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 V2

C1

lung volumes gas distribution7
Lung Volumes / Gas Distribution
  • Gas dilution techniques
    • Can only measure lung volumes in communication with conducting airways !!!
lung volumes gas distribution8
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 distribution9
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 distribution10
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 distribution11
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
lung volumes gas distribution12
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
lung volumes gas distribution13
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 distribution14
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 distribution15
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 distribution16
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 distribution17
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
        • FRC determination is based on the following equation:

VFRC = (CExhN2)(VExh)

CAlvN2

lung volumes gas distribution18
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 distribution19
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 distribution20
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 distribution21
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 distribution22
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 distribution23
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
lung volumes gas distribution24
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
lung volumes gas distribution25
Lung Volumes / Gas Distribution
  • Open-Circuit Nitrogen Washout
    • Leak
lung volumes gas distribution26
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 distribution27
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 distribution28
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 distribution29
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 distribution30
Lung Volumes / Gas Distribution
  • Closed-Circuit Helium Dilution

FRC

lung volumes gas distribution31
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 distribution32
Lung Volumes / Gas Distribution
  • Closed-Circuit Helium Dilution

C1 V1 = C2 V2

(C1 initial He concentration)(V1 system volume)

lung volumes gas distribution33
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 distribution34
Lung Volumes / Gas Distribution
  • Closed-Circuit Helium Dilution

O2 Added

CO2 Absorbed

H2O Absorbed

lung volumes gas distribution35
Lung Volumes / Gas Distribution
  • Closed-Circuit Helium Dilution

He Concentration

System Volume

lung volumes gas distribution36
Lung Volumes / Gas Distribution
  • Closed-Circuit Helium Dilution
lung volumes gas distribution37
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 recorded
  • The FRC can then be calculated

FRC

lung volumes gas distribution38
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 distribution39
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 distribution40
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 distribution41
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 distribution42
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 distribution43
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 distribution44
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 distribution45
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 distribution46
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 distribution47
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 distribution48
Lung Volumes / Gas Distribution
  • Single-Breath Nitrogen Washout
    • Measures Distribution of Ventilation
    • Closing Volume
    • Closing Capacity
lung volumes gas distribution50
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 distribution51
Lung Volumes / Gas Distribution
  • SBN2

Phase I: upper airway gas from anatomical dead space (VDanat), consisting of 100% O2

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

lung volumes gas distribution52
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 distribution53
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 distribution54
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 distribution55
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 distribution56
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 distribution57
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 distribution58
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 distribution59
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