Spirometry
(Pulmonary Function Tests)
By:
A. H. Mehrparvar, M.D.
References
1. M. R. Miller, et al. “ATS Standardisation of Spirometry”. Eur
Respir J. 2005, 26: 319-338.
2. “Lung Function Testing: Selection of Reference Values and
Interpretative Strategies”, ATS, 2003.
3. NIOSH Spirometry Training Guide, 2003.
4. Spirometry Handbook. National Asthma Council (Australia),
2004.
Definition
A physiological test for measuring
volumes inhaled or exhaled by an
individual as a function of time
Indications
• Not a screening test for general
population
• Diagnostic
• Monitoring
• Impairment evaluation
• Public health
Indications (diagnostic)
• Evaluation of symptoms and signs
• Measuring the effect of dis. on
pulmonary function
• Screening individuals at risk for
pulmonary dis.
• Assess preoperative risk
• Assess health status before physical
activities (e.g. work)
Indications (monitoring)
• Assess therapeutic intervention
• Monitor people exposed to injurious
agents
Spirometry standards
• ATS (American Thoracic Society)
• ERS (European Respiratory Society)
Spirometry standardisation steps
Equipment performance criteria
Equipment validation
Quality control
Subject maneuvers
Measurements procedures
Acceptability
Repeatability
interpretation
Spirometry maneuvers
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FVC
VC and IC
PEF
MVV
FVC maneuver
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Requirements of spirometer:
1.
2.
3.
Accumulating volume for at least 15 s
Measuring volumes at least 8 lit (BTPS)
Accuracy of at least ± 3% or ±0.050 lit with
flows between 0 and 14 lit/s
Showing both volume-time and flow-volume
curves
Showing EV value
4.
5.
Test procedure
1. Maximal inspiration
2. A blast of exhalation
3. Complete exhalation to the end of
test
Spirometry curves
Spirometric indices
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FVC (forced vital capacity)
FEV1 (forced expiratory volume in 1 s)
FEV1/FVC
FEVt (forced expiratory volume in t s)
FEF25-75 (maximum midexpiratory flow)
PEF (peak expiratory flow)
Within maneuver evaluation
• Start of test criteria
- back extrapolation (EV < 5% of FVC or 150 ml)
● End of test criteria
- the subject cannot or should not continue
- exhalation at least 6s (in children under 10, 3s)
- no change in volume (<0.025 lit) for at least 1s
* In obstruction or older subjects more than 6s exhalation (till
15s)
Acceptability
● Start of test criteria
● End of test criteria
● cough especially during first second
● Valsalva maneuver (glottis closure)
● Leak from the mouth
● Obstruction of the mouthpiece
● Extra breath during the maneuver
Repeatability
• At least three acceptable maneuvers
Maximum difference between the largest and next
largest FVC and FEV1 = 150ml (If FVC <1lit, this
value is 100ml)
● At
the most eight tests should be
performed
Flow chart of criteria
Perform FVC
Acceptability criteria
3 acceptable maneuvers
Repeatability criteria
Largest FVC and largest FEV1
Maneuver with largest FVC + FEV1 for other indices
Reversibility testing
1. Stop drugs (short-acting for 4 h,
long-acting for 12h) before test
2. Stop smoking for 1 h. before test
3. Perform baseline test
4. Administer drug
5. Perform test after 10 – 15 min. (for
salbutamol) or after 30 min. (for
ipratropium)
Reversibility criteria
1. VC (forced or slow) and FEV1 the
primary indices for bronchodilator
response.
2. A 12% increase, and a 200-ml increase
in either FVC or FEV1
3. FEF25-75 should be used secondarily in
evaluating bronchodilator response.
4. Ratios such as FEV1/VC should not be
used to judge bronchodilator response.
VC maneuver
1. Two types (IVC and EVC)
2. Perform this test prior to FVC
3. Perform not more than 4 tests (at
least 1 min. apart)
4. Surely use nose clip
Interpretation
Key Notes
1. be conservative in suggesting a specific
diagnosis based only on pulmonary
function abnormalities.
2. Interpret borderline normal values with
caution.
3. First step = to evaluate and comment on
the quality of the tests.
Key Notes
4. The number of test indices (e.g., FVC, FEV1,
etc.) used in interpretation should be limited to
avoid an excessive number of false positive
results.
5. The primary guides for spirometry
interpretation should be VC (slow or forced),
FEV1, and FEV1/VC.
6. FEV1/VC should be the primary guide for
distinguishing obstructive from nonobstructive
patterns.
Key Notes
7. If FEV1/VC is borderline, use
Instantaneous and mid flows to confirm
airway obstruction.
8. Don’t use FEF25-75 and the
instantaneous flows to diagnose small
airway disease.
9. The pattern of a low FEV1/VC and
greater than average VC and FEV1
should be recognized as one that may
occur in healthy individuals.
Key Notes
10. The severity of airway obstruction should be
based on FEV1.
11. When FEV1 and FEV1/VC are normal, don’t use
FEF25-75 for grading the severity of obstruction.
12. A reduced VC and normal FEV1/VC suggest but
not diagnose the presence of restriction.
13. The severity of restriction should be based on
TLC. If VC is used, severity may be based on VC.
Lower Limits of Normal
1. Normal ranges should be based on
calculated fifth percentiles.
2. Lower limits of normal are variable.
3. The use of 80% of predicted for adult
pulmonary function parameters is not
recommended. This criterion works only
for average persons and for a limited
number of parameters.
LLN
• FEV1 and FVC = 80%
• FEV1/FVC = 70-75%
• FEF25-75 = 50-60%
Interpretation
A. Normal: both the VC and the FEV1/VC ratio
are normal.
B. Obstructive: FEV1/VC ratio is below the
normal range.
The severity of the abnormality is graded:
- % Pred FEV1 > 100 = May be a physiological
variant
- % Pred FEV1 < 100 and > 70 = Mild
- % Pred FEV1 < 70 and > 60 = Moderate
- % Pred FEV1 < 60 and > 50 = Moderately severe
- % Pred FEV1 < 50 and > 34 = Severe
- % Pred FEV1 < 34 = Very severe
Interpretation
C. Restrictive: This is most reliably interpreted on
the basis ef TLC. If this is not available, one may
interpret a reduction in the VC without a reduction
of the FEV1/VC ratio as a restriction
The severity of the abnormality might be graded as
follows:
- % Pred VC < LLN and > 70 = mild
- % Pred VC < 70 and > 60 = Moderate
- % Pred VC < 60 and > 50 = Moderately severe
- % Pred VC < 50 and > 34 = Severe
- % Pred VC < 34 = Very severe
TLC
TLC
IC
VC
Vt
ERV
RV
RV
FRC
VC
RV
Normal
Vital capacity is reduced in both
obstructive and restrictive diseases
VC
VC
VC
RV
RV
RV
Obstructive
Normal
Restrictive
An Algorithm for Spirometry
Is maneuver acceptable?
no
yes
Is the FEV1/FVC
lower than predicted?
yes
This is the definition of
obstruction
Mild
FEV1 >70%
Moderate FEV1 60-70%
Mod severe FEV1 50-60%
Severe
FEV1 <50%
Very severe FEV1 <40%
Interpretation may be
limited by falsely low
FVC
no
Is FVC reduced?
no
yes
Restriction may be present;
Need TLC to definitively
diagnose restriction
Normal pulmonary
mechanics
Restriction
Spirometry:
Severity is determined
by the reduction in VC
Mild
70-80%
Moderate
60-70%
Severe
<60%
Lung volumes:
Severity determined by
the reduction in TLC
Mild
65-80%
Moderate
50-65%
Severe
<50%
Extrathoracic/upper airway
obstruction (stridor)
Fixed upper airway obstruction
Case 1
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A 38 year-old male
Height: 171, weight: 82
FVC = 4.53 (100%)
FEV1 = 3.35 (89%)
FEV1/FVC = 74%
FEF25-75 = 2.85 (65%)
Case 2
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A 53 year-old male
Height: 180, weight: 73
FVC = 4.51 (97%)
FEV1 = 3.18 (86%)
FEV1/FVC = 70.50%
FEF25-75 = 2.26 (58%)
Case 3
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A 41 year-old male
Height: 171, weight: 65
FVC = 4.77 (115%)
FEV1 = 3.50 (101%)
FEV1/FVC = 73.40%
FEF25-75 = 2.74 (66%)
Case 4
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A 52 year-old male
Height: 181, weight: 95
FVC = 3.81 (81%)
FEV1 = 2.38 (63%)
FEV1/FVC = 62.5%
FEF25-75 = 1.72 (41%)
Case 5
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A 39 year-old male
Height: 184, weight: 83
FVC = 5.82 (111%)
FEV1 = 4.98 (116%)
FEV1/FVC = 85.6%
FEF25-75 = 5.25 (114%)
Case 6
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A 44 year-old male
Height: 185, weight: 92
FVC = 3.93 (76%)
FEV1 = 2.75 (66%)
FEV1/FVC = 70%
FEF25-75 = 1.91 (43%)
Case 7
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A 54 year-old male
Height: 178, weight: 80
FVC = 4.56 (121%)
FEV1 = 3.10 (102%)
FEV1/FVC = 68%
FEF25-75 = 1.83 (51%)