Pulmonary Function

Robert C. Strunk, MDStrominger Professor of Pediatrics

Washington University School of Medicine

St. Louis Children’s Hospital

Division of Allergy, Immunology, and

Pulmonary Medicine

Disclosures

Employment Washington University School of Medicine

Research Interests NHLBI

Financial Interests 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 creativeUse incentivesEven with the best of environments and coaching, a

child may not be able to perform spirometry.

ATS Acceptable CriteriaWithin 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 CriteriaWithin 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:• 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

• FVC nl or↓• FEV1 ↓• FEF25-75% ↓ • FEV1/FVC ↓• TLC nl or ↑

Restrictive Disorders• 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 % predictedMild >70Moderate 60-69Mod severe 50-59Severe 35-49Very 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 restrictionRV/TLC above 30% for air trapping

Degree of severity FEV1 % predictedMild > 70Moderate 50-70Severe < 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

-

-

Vocal Cord Dysfunction

Patient example

12 year old boy presents with exercise-induced wheeze for 1 year

Not responsive to bronchodilator used pre-exercise, 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 yearsIntubated at scene of accidentComatose 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 sizeDifferences 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/FVCFEV-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 HistoryPulmonary 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 monthsIntubation admission was #28, with first

documented hypercarbia with exac at age 4 years

Spirometry History

Age FVC % pred FEV-1 % pred FEV-1/FVC

6 143 126 79

7 157 115 65

8 149 119 72

9 159 129 73

10 127 95 66

11 147 96 58

12 119 91 67

13 100 77 71

14 78 57 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