Pulmonary Function
Robert C. Strunk, MD
Strominger Professor of Pediatrics
Washington University School of Medicine
St. Louis Children’s Hospital
Division of Allergy, Immunology, and
Pulmonary Medicine
Disclosures
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Employment
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Research Interests
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NHLBI
Financial Interests
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Washington University School of Medicine
None
Chair, Pediatric Adjudication Committee,
GSK study of safety and benefit of
FP/salmeterol vs. FP
Spirometry
For now, spirometry is best test to:
• Monitor asthma status
• Look for evidence of asthma
• Look for evidence of other diagnoses
Volume-Time Plot
Forced Vital Capacity Maneuver
Airflow,
L/sec
Lung volume
Definitions
 FVC – Forced Vital Capacity
Volume of air exhaled after a maximal inspiration to total lung capacity.
This volume is expressed in Liters
 FEV1 – Forced Expiratory Volume in 1 second
Volume of air exhaled in the first second of expiration.
This volume is expressed in Liters
 FEF 25-75%
Mean expiratory flow during the middle half of the FVC maneuver;
reflects flow through later emptying airways, not necessarily the small
airways
 FEV1/FVC – Ratio (%)
Volume of air expired in the first second, expressed as a percent of FVC
Performance of FVC maneuver
Patient assumes the position (typically standing)
• Puts nose clip on
• Inhales maximally
• Puts mouthpiece in mouth and closes lips around
mouthpiece (open circuit)
• Exhales as hard and fast and long as possible
• Repeat instructions if necessary – effective coaching
is essential
• Give simple instructions
• Repeat minimum of three times (check for
repeatability)
Special Considerations in Pediatric
Patients
Ability to perform spirometry dependent on
developmental age of child, personality, and
interest.
Patients need a calm, relaxed environment
and good coaching. Patience is key.
Be creative
Use incentives
Even with the best of environments and
coaching, a child may not be able to perform
spirometry.
ATS Acceptable Criteria
Within Maneuver
 Free from artifacts, such as
•
•
•
•
•
•
Cough during the first second of exhalation
Glottis closure that influences the measurement
Early termination or cut-off
Effort that is not maximal throughout
Leak
Obstructed mouthpiece
 Good starts
• Extrapolated volume < 5% of FVC or 0.15 L, whichever is greater
 Satisfactory exhalation
• Duration of ≥ 6 s (3 s for children < 10) or a plateau in the volume–
time curve or
• If the subject cannot or should not continue to exhale
ATS Acceptable Criteria
Within Maneuver
 After three acceptable spirograms have been obtained, apply the
following tests
• The two largest values of FVC must be within 0.150 L of each other
• The two largest values of FEV1 must be within 0.150 L of each other
 If both of these criteria are met, the test session may be
concluded
 If both of these criteria are not met, continue testing until
• Both of the criteria are met with analysis of additional acceptable
spirograms
 or
• A total of eight tests have been performed (optional) or
• The patient/subject cannot or should not continue
 Save, as a minimum, the three satisfactory maneuvers
Spirometry Interpretation: So what
constitutes normal?
Normal values vary and depend on:
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•
•
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Height
Age
Gender
Ethnicity
Spirometry Interpretation: Obstructive
vs. Restrictive Defect
 Obstructive Disorders
• Characterized by a limitation of
expiratory airflow so that
airways cannot empty as rapidly
compared to normal (such as
through narrowed airways from
bronchospasm, inflammation,
etc.)
Examples:
• Asthma
• Emphysema
• Cystic Fibrosis
 Restrictive Disorders
• Characterized by reduced lung
volumes/decreased lung
compliance
Examples:
• Interstitial Fibrosis
• Scoliosis
• Obesity
• Lung Resection
• Neuromuscular diseases
• Cystic Fibrosis
Spirometry Interpretation: Obstructive
vs. Restrictive Defect
 Obstructive Disorders
•
•
•
•
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FVC nl or↓
FEV1 ↓
FEF25-75% ↓
FEV1/FVC ↓
TLC nl or ↑
 Restrictive Disorders
•
•
•
•
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FVC ↓
FEV1 ↓
FEF 25-75% nl to ↓
FEV1/FVC nl to ↑
TLC ↓
Severity of any spirometric abnormalities
based on the FEV1
Degree of severity FEV1 % predicted
Mild
>70
Moderate
60-69
Mod severe
50-59
Severe
35-49
Very Severe
< 35
based on ATS/ERS criteria
Criteria Used at
Washington University PFT Lab
FEV1 Normal (82-118% predicted)
FVC Normal (82-118% predicted)
TLC < 80 % predicted for restriction
RV/TLC above 30% for air trapping
Degree of severity
Mild
Moderate
Severe
FEV1 % predicted
> 70
50-70
< 50
When you see the tracings below, which of
these prompts should you give the
participant
 Take in a deeper breath
 Blow out harder
and faster
 Try not to cough
 Blow out longer
 Good Test
The flow volume loop below is
representative of
 Extrapolation or time
zero error
 Clipped inspiratory loop
 Obstructive pattern
 Restrictive pattern
 Glottic closure
When you see the tracings below, which of these
prompts should you give the participant
Blow out longer
Good Test
Take in a deeper
breath
Try not to cough
Blow out harder and
faster
When you see the tracings below, which of these
prompts should you give the participant
 Take in a deeper breath
 Blow out harder
and faster
 Try not to cough
 Blow out longer
 Good Test
The flow volume loop below is
representative of
 Extrapolation
or time zero error
 Clipped inspiratory loop
 Obstructive pattern
 Restrictive pattern
 Glottic closure
Back Extrapolation
Exhalation Time During Obstruction
Spirometry-Induced Bronchospasm
Coaching is Key
Bronchodilator Response
Obstruction
Restrictive Pattern
Patient example
Child with inspiratory stridor
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Vocal Cord Dysfunction
Patient example
12 year old boy presents with exerciseinduced wheeze for 1 year
Not responsive to bronchodilator used preexercise, ICS, OCS
Fixed airway obstruction
Obstruction due to abnormalities of the vocal
cords after trauma of intubation and
prolonged intubation
Additional history
Automobile accident at age 11 years
Intubated at scene of accident
Comatose for 1 month, followed by complete
neurologic recovery
FEF 25-75%
What is it?
What does it measure?
Is it a measure of small airways?
FEF 25-75%
 What is it?
• Mean expiratory flow during middle half of FVC maneuver
 What does it measure?
• Flow from airways that empty in the middle half of FVC
maneuver
 Is it a measure of small airways?
• Maybe in normals
• In asthma, or obstructive disease, it measures flow from
more obstructed airways which could be small or larger
with more obstruction
A problem with FEF: Variability
Dysanapsis
 Green, Mead, Turner. Variability of maximum expiratory
flow-volume curves. J Appl Physiol 1974 37:67-74
• Variability in flows among healthy adults not altered when
flows were corrected for vital capacity
• Lung static recoil and bronchomotor tone contributed little
to variability
Concluded that variability in flows between individuals
due to differences in airway size independent of
lung/parenchyma size
Differences may have embryological basis, reflecting
disproportionate but physiologically normal growth within
an organ
Dysanapsis
Mead.
Dysanapsis in normal lungs assessed by the
relationship between maximal flow, static recoil, and vital
capacity. Am Rev Respir Dis 1980 121:339-342
• “There is no association whatsoever between
airway diameter and lung size.”
• There are differences between men and women
(men 17% larger than women) and between boys
and men (boys in late teens similar to girls,
suggesting that growth in males occurs late)
Measures Of Dysanapsis
Mead used maximal expiratory flow/static
recoil pressure at 50% VC
Weiss and coworkers have used
FEF25-75/FVC as a surrogate
FEF25-75/FVC is correlated with
FEV-1/FVC
FEV-1/FVC is the best measure: obtained from
spirometry and normal values available
Dysanapsis Is Affected By Asthma
 Weiss et al. Effects of asthma on pulmonary function in
children. A longitudinal population-based study. Am Rev
Respir Dis 1992 145:58-64.
• East Boston cohort of 5-9 year old school children followed
prospectively until age 13 years
• Active asthma
• Yes to “Has a doctor ever told you that your child has asthma.”
• Wheezing symptoms present in that study year
• Boys with asthma had significantly larger FVC, but normal
FEV-1
• Girls with asthma had significantly lower FEV-1, but normal
FVC
Compared to children with no history of asthma, after adjusting for
previous level of pulmonary function, age, height, and personal and
maternal smoking
Clinical Correlates Of Asthma
Related To Dysanapsis
Studies of East Boston cohort of school
children by Weiss and colleagues
Degree of response to eucapneic
hyperventilation:
• Correlated with FEF25-75/FVC, but not FEF25-75
• Correlated with FVC (higher levels associated
with increased response)
In both studies, response also correlated with
current asthma and report of a respiratory
illness that led to activity restriction
Case History of dysanapsis
Pulmonary function results at age 7
• FVC 157% predicted
• FEV-1 115% predicted
Case History
Pulmonary function results at age 7
• FVC 157% predicted (82-120%)
• FEV-1 115% predicted (82-120%)
Case History
Pulmonary function results at age 7
• FVC 157% predicted (82-120%)
• FEV-1 115% predicted (82-120%)
• FEV-1/FVC = 65% (> 80%)
Case History
Pulmonary function results at age 7
• FVC 157% predicted
• FEV-1 115% predicted
• FEV-1/FVC = 65%
Results obtained 1 month after severe
exacerbation requiring intubation and
ventilation
1st admission occurred at age 21 months
Intubation admission was #28, with first
documented hypercarbia with exac at age
4 years
Spirometry History
Age
FVC % pred
FEV-1 % pred FEV-1/FVC
6
7
8
9
10
11
12
13
14
143
157
149
159
127
147
119
100
78
126
115
119
129
95
96
91
77
57
79
65
72
73
66
58
67
71
68
Conclusions
Spirometry is:
• Useful in asthma diagnosis and management
• Useful in diagnosis of conditions that can present
with wheezing, or airway noise that can be hard
to distinguish from wheezing
• Requires considerable expertise, particularly in
children
FEF25-75% does not measure small airways,
but instead airways more obstructed that
empty later in exhalation