Information About Spirometry | Jindal Chest Clinic

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Spirometry
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Why Test Pulmonary Function?

• Determine best lung function
• Subclinical disease detection
• Evaluation of treatment
• Prediction of outcomes
• Intensive monitoring
• Epidemiology and research

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Common Lung Function Tests

• Dynamic Studies
• Spirometry
• Flow-Volume Loops
• Static Lung Volumes
• FRC Measurements
• Gas Transfer
• Diffusing Capacity
• Arterial Blood Gases

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SPIROMETERS PAST AND PRESENT
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Information from Spirometry

• Volumes and capacities
• Flows
• Flow Volume loops
• Bronchodilator reversibility

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The Testing Procedure

• Patient can be seated or standing
• Nose clips are recommended
• Seal lips tightly over mouthpiece
• Begin with normal tidal volume breaths
• At end-expiration, perform a maximal inspiration
  to total lung capacity
• Then exhale as hard, as fast, and as completely
  as possible
• Measure volumes and report at BTPS

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Inspiration
IC
IRV
TLC
VC
Resting Tidal Volume
ERV
Expiration
FRC
RV
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Assessment of Test Quality

• ACCEPTABILITY
• Full inhalation prior to start of test
• Satisfactory start of exhalation
• Free from artifacts
• Satisfactory duration

• REPRODUCIBILITY
• 3 8 manoeuvres
• Two largest values for VC and FEV1 should be
  within 0.2 litres
• If criteria not met after 8 trials, interpret
  with 3 best tests

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What is Normal ?
Age group specific mean Derived from regression
model Personal best (?)
Predicted normal Lower limit of normal
Fixed percent Lower fifth percentile Lower 95th
C.I.
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Which Variables ?

• Some computerized equipments generate gt20
  spirometric variables
• Do not use more than few such variables
• Increasing the number of variables used increases
  number of false positive results
• In most cases, VC, FEV1 and FEV1/VC suffice to
  provide all the information needed to interpret a
  spirogram

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FEV1/VC
Normal
Reduced
Check VC
Check FEV1
Normal
Reduced
Reduced
Normal
Restrictive defect
Obstructive defect
Categorize based on VC
Categorize based on FEV1
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Guidelines for Interpretation

• Evaluate test quality
• Use VC, FEV1 FEV1/VC as primary guides
• Chose statistically valid lower limits of normal
• Interpret values well above or well below lower
  limits of normal with confidence
• Interpret borderline values with caution, using
  clinical information to make decisions

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Limitations of Interpretation

• Statistical estimates may not represent true
  patient status
• False positive false negative results
• Problem of mixed defects
• Borderline values
• Arbitrary categorization of severity

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58 year old male smoker with wheeze
Observed
VC (L)
2.07
Reduced
FEV1 (L)
1.31
Reduced
FEV1/VC ()
63.3
Interpretation Obstructive defect
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58 year old male nonsmoker with dry cough
Observed
VC (L)
2.67
Reduced
FEV1 (L)
2.11
Reduced
FEV1/VC ()
79.0
Interpretation Restrictive defect
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Flow Volume Loop
Expiration
Flow
Volume
Inspiration
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Peak Expiratory Flow (PEF)

• Maximal flow that can be generated by a forced
  expiratory effort following full inspiration, and
  which can be maintained for at least 10 ms
• Monitoring tool only not a diagnostic test

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Abnormal Flow Volume Loop
Expiration
Flow
Volume
Inspiration
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Abnormal Flow Volume Loop
Obstruction
Expiration
Flow
Volume
Inspiration
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Abnormal Flow Volume Loop
Restriction
Expiration
Flow
Volume
Inspiration
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Flow Volume Loops
Normal
Restrictive defect
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Flow Volume Loops
Mild obstruction
Severe obstruction
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Bronchodilator Reversibility

• No bronchodilator use for 4 hours
• Perform baseline spirometry
• Two puffs of salbutamol (100 µg each)
• Repeat spirometry after 15-30 minutes
• BDR present if increase in FEV1 and/or VC is gt12
  and gt200 mL

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Bronchodilator Reversibility
Pre Post Change
FVC 4.41 L 5.10 L 15.6
FEV1 2.96 L 3.82 L 29.1
FEV1/FVC 51.2 74.9
PEF 6.97 L/s 9.61 L/s 37.9
BDR present
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Tips to Improve Quality

• Ensure that the instrument meets standards for
  accuracy and precision
• Take care that equipment is maintained well and
  calibrated on schedule
• Enforce procedural standards while testing
• Set up monitoring and feedback mechanism
• Select appropriate reference standards and
  interpretative strategies, and be consistent