Spirometry
(Pulmonary Function Tests)
By:
A. H. Mehrparvar, M.D.
Yazd University of Medical Sciences
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 maneuvers
•
•
•
•
FVC
VC and IC
PEF
MVV
FVC maneuver
•
Requirements of spirometer:
1.
2.
3.
Accumulating volume for at least 15 s
Measuring volumes at least 8 lit
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
Contraindications of Spirometry
• Uncontrolled hypertension
• Suspected presence of active TB or other
communicable respiratory disease
• Thoracic or abdominal surgery within recent 3
wks
• MI or unstable angina within recent 6 wks
• Respiratory distress
• Active hemoptysis
• Recent eye/ear surgery
• Abdominal or thoracic aortic aneurysm
Interfering condition
• Acute illness or cold during the past
few days
• Any respiratory infection during the
past 3 weeks
• Heavy meal during the past 1-2 hour
• Cigarette smoking during the past 1
hour
Spirometric indices
•
•
•
•
•
•
FVC (forced vital capacity)
FEV1 (forced expiratory volume in 1 s)
FEV1/FVC
FEVt (forced expiratory volume in t s)
FEF25-75 (maximum mid-expiratory flow)
PEF (peak expiratory flow)
FVC
• Definition:
– maximal amount of air that can be exhaled
forcefully after a maximal inspiration or the
most air a person can blow out after taking the
deepest possible breath.
FEV1
• Definition:
– The volume of air exhaled during the first second of a
forced expiratory maneuver
FEV1/FVC%
• Definition:
– The value expresses the volume of air the worker exhales in one
second as a percent of the total volume of air that is exhaled.
Spirometry Performance Steps
• Equipment performance criteria
• Equipment quality control ( calibration &
leak )
• Contraindications & interfering condition
• Age, height, race, gender
• Selection of appropriate reference value
• Patient maneuver
• Acceptability criteria
• Reproducibility criteria
• Selection of best curve and best result
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
Measuring lung volumes (RV, FRC,
TLC)
•
•
•
•
Nitrogen washout
Helium dilution
Body plethysmography
Diffusing Capacity
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
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
Case 1
• A 60 year old man with a 60 pack/year
smoking history and dyspnea on
exertion
• FVC = 73% , FEV1 = 23%
FEV1/FVC = 25% FEF25-75 = 6%
TLC = 150% DLCO = 19%
Answer
• This patient has emphysema. His
FEV1/FVC ratio is < 70% which indicates
obstruction. His FEV1 is < 34% of
predicted which indicates very severe
obstruction. His TLC is elevated and his
diffusing capacity is very low. We consider
PFTs consistent with emphysema if there is
(1) non-reversible obstruction, (2) elevated
lung volumes, (3) low diffusing capacity,
and (4) an adequate smoking history
Case 2
• 50 year old man with a 65 pack/year
smoking history and a cough. His
chest x-ray shows a diffuse
reticulonodular pattern
• FVC = 62% , FEV1 = 42%
FEV1/FVC = 56% FEF25-75 = 11%
TLC = 64% DLCO = 29%
Answer
• First, he is obstructed because the
FEV1/FVC ratio is < 72%. Second, he is
restricted since the TLC is < 80%. Third, he
has a low diffusing capacity. The
differential diagnosis of combined
restrictive & obstructive defects includes
cystic fibrosis, bronchiectasis,
lymphangioleimomatosis, eosinophilic
granuloma, and interstitial disease +
COPD. This patient has eosinophilic
granuloma
Case 3
• A 22 year old woman with dyspnea on
exertion. She also notes dyspnea when
exposed to cats. On physical exam, she
is wheezing
• FVC = 83% , FEV1 = 60%
FEV1/FVC = 61% FEF25-75 = 23%
TLC = 100% DLCO = 122%
•
Answer
• This is pretty typical for asthma. The
FEV1/FVC ratio is < 75% so she is
obstructed. The FEV1 puts her in the
moderate obstruction category. She is not
restricted and the diffusing capacity is
increased. The reason why the diffusing
capacity is increased in asthma is not fully
known but it has been suggested that there
is increased pulmonary blood flow, allowing
increased carbon monoxide extraction from
the carbon monoxide inhalation.
Case 4
• 43 year old woman with progressive
dyspnea on exertion. Chest x-ray
shows bilateral reticular infiltrates,
especially in the lung bases
• FVC = 51% , FEV1 = 49%
FEV1/FVC = 78% FEF25-75 = 35%
TLC = 52% DLCO = 51%
Answer
• This is characteristic for interstitial
lung disease. The FEV1/FVC ratio is >
73% so she is not obstructed. The
TLC is 35% of predicted so she falls
in the severe restriction category. The
diffusing capacity is low indicating
impairment to gas transport