simple interpretation of pulmonary function tests
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Spirometry of Obstructive
Lung Diseases
Gamal Rabie Agmy, MD, FCCP Professor of Chest Diseases, Assiut University
Pulmonary Disorders Effects on
Pulmonary Function Obstructive:
Any process that interferes with air flow either into or out of the lungs.
Large or small airways.
Restrictive:
Any process that interferes with the bellows action of the lungs or chest wall.
Reduced lung volumes.
Differential Diagnosis:
COPD and Asthma COPD Onset In mid-life
Symptoms slowly progressive
Long smoking history
Dyspnea during exercise
Largely Irreversible airflow limitation
Asthma Onset early in life (often
childhood)
Symptoms vary from day to day
Symptoms at night/early morning
Allergy, rhinitis, and/or eczema also present
Family history of asthma
Largely reversible airflow limitation
Inflammatory Cascade in
COPD & Asthma
Measures of Assessment and
Monitoring of Asthma
Asthma diagnosis criteria:
Repeated variability in well-performed spirometic values (increase in FEV1 or FVC).
Positive bronchodilator (BD) responses (increase in FEV1 or FVC ⩾12% and 200 mL from baseline).
Positive methacholine challenge (20% fall in FEV1 at a dose ⩽8 μg/mL).
Objective lung function
measurements in Asthma
Spirometry:
▫ Forced Expiratory Maneuvers.
Exhaled Nitric Oxide.
Peak Flows.
GOLD 2013: Diagnosis of COPD
SPIROMETRY REQUIRED TO DIAGNOSE COPD Presence of a post-bronchodilator FEV1/FVC < 0.70 confirms the presence of persistent airflow
limitation and thus of COPD.
Key Indicators to Consider COPD Diagnosis:
1
• SYMPTOMS • Dyspnea-progressive (worsens over time and with exercise) • Chronic cough • Sputum
2
• HISTORY OF EXPOSURE TO RISK FACTORS
• Tobacco smoke • Smoke from home cooking/heating fuels • Occupational dusts and chemical
3 • FAMILY HISTORY OF COPD
Adapted from GOLD 2013
Simple Interpretation of
Pulmonary Function Tests
Gamal Rabie Agmy, MD, FCCP Professor of Chest Diseases, Assiut University
Anatomy
Lungs comprised of
Airways
Alveoli
http://www.aduk.org.uk/gfx/lungs.jpg
Weibel ER: Morphometry of the Human
Lung. Berlin and New York: Springer-
Verlag, 1963
The Airways
Conducting zone: no
gas exchange occurs
Anatomic dead
space
Transitional zone:
alveoli appear, but are
not great in number
Respiratory zone:
contain the alveolar
sacs
The Alveoli
Approximately 300
million alveoli
1/3 mm diameter
Total surface area if
they were complete
spheres 80 sq.
meters (size of a
tennis court)
Murray & Nadel: Textbook of Respiratory
Medicine, 3rd ed., Copyright © 2000 W. B.
Saunders Company
Mechanics of Breathing
Inspiration
Active process
Expiration
Quiet breathing: passive
Can become active
Pulmonary Function Tests
Airway function
Simple spirometry
Forced vital capacity
maneuver
Maximal voluntary
ventilation
Maximal
inspiratory/expiratory
pressures
Airway resistance
Lung volumes and
ventilation
Functional residual
capacity
Total lung capacity,
residual volume
Minute ventilation,
alveolar ventilation,
dead space
Distribution of
ventilation
Pulmonary Function Tests
Diffusing capacity
tests
Blood gases and gas
exchange tests
Blood gas analysis
Pulse oximetry
Capnography
Cardiopulmonary
exercise tests
Metabolic
measurements
Resting energy
expenditure
Substrate utilization
Chemical analysis of
exhaled breath
Terminology
Forced vital capacity
(FVC):
Total volume of air that can
be exhaled forcefully from
TLC
The majority of FVC can be
exhaled in <3 seconds in
normal people, but often is
much more prolonged in
obstructive diseases
Measured in liters (L)
FVC
Interpretation of % predicted:
80-120% Normal
70-79% Mild reduction
50%-69% Moderate reduction
<50% Severe reduction
FVC
Terminology
Forced expiratory volume in 1 second: (FEV1) Volume of air forcefully
expired from full inflation (TLC) in the first second
Measured in liters (L)
Normal people can exhale more than 75-80% of their FVC in the first second; thus the FEV1/FVC can be utilized to characterize lung disease
FEV1
Interpretation of % predicted:
>75% Normal
Mild 70-75%
Mod 50-69 %
Severe 35-49%
Very severe < 35%
FEV1 FVC
Terminology
Forced expiratory flow 25-
75% (FEF25-75)
Mean forced expiratory flow
during middle half of FVC
Measured in L/sec
May reflect effort
independent expiration and
the status of the small
airways
Highly variable
Depends heavily on FVC
FEF25-75
Interpretation of % predicted:
>60% Normal
40-60% Mild obstruction
20-40% Moderate obstruction
<20% Severe obstruction
Acceptability Criteria
Good start of test
No coughing
No variable flow
No early termination
Reproducibility
Changes in Lung Volumes in
Various Disease States
Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003
TLC
TLC < 80% of predicted value = restriction.
TLC > 120% of predicted value =
hyperinflation.
Lung Volumes
Spirometry
Spirometry should be performed after the
administration of an adequate dose of a short acting inhaled bronchodilator (e.g. 400 ᶙg salbutamol) to minimize variability.
A post-bronchodilator FEV 1/FVC <0.70 confirms the presence of airflow limitation that is not fully reversible.
Where possible, values should be compared to age-related normal values to avoid over- diagnosis of COPD In the elderly.
Why Do We Need Spirometry
in COPD?
Spirometry is useful for:
Screen individuals at risk for pulmonary disease.
Confirmation of COPD diagnosis.
Assessing severity of pulmonary dysfunction.
Guiding selection of treatment.
Assessing the effects of therapeutic interventions.
Who Should Be Screened for
COPD?
Consider COPD, and perform spirometry, if any of these indicators are present in an individual over age 40.
▫ Dyspnea that is progressive, usually worse with exercise, and persistent.
▫ Chronic cough (may be intermittent and unproductive).
▫ Chronic sputum.
▫ History of tobacco smoke exposure.
▫ Exposure to occupational dusts and chemicals.
▫ Risk factors.
▫ Exposure to smoke from home cooking and heating fuels.
Spirometry Origin
Most basic of Pulmonary Function Tests
Clinical Tools Origin - Mid 1800' s
▫ John Hutchinson.
▫ Water-sealed spirometry to measure vital capacity (VC).
Reasons for Performing
Spirometry
Diagnostic Purposes.
Monitoring Lung Disease.
Assessing Disability.
Spirometry
Spirometry with flow volume loops assesses the
mechanical properties of the respiratory system by measuring expiratory volumes and flow rates.
▫ Maximal inspiratory and expiratory effort.
▫ At least 3 tests of acceptable effort are performed to ensure reproducibility.
21st Century Spirometry
Measurements of:
Forced Vital Capacity (FVC).
Forced Expiratory Volume in one second (FEV1).
Forced Expiratory Volume in six seconds (FEV6).
Forced Expiratory Flow over various Intervals (FEFx).
Peak Expiratory Flow (PEF).
Definitions and Terms
FEV1 - forced expiratory volume 1 - the volume of
air that is forcefully exhaled in one second.
FEV6 - forced expiratory volume 6 - the volume of
air that Is forcefully exhaled in six seconds.
FVC- forced vital capacity- the volume of air that
can be maximally forcefully exhaled.
FEV1/FVC- ratio of FEV1 to FVC, expressed as a percentage.
Definitions and Terms
FEV/FVC- ratio of FEV6 to FVC, expressed as a percentage.
FEF25 -75 - forced expiratory flow - the average
forced expiratory flow during the mid (25 - 75%) portion of the FVC.
PEF- peak expiratory flow rate - the peak flow rate
during expiration.
Spirometry
Flow volume loops provide a graphic illustration
of a patient's spirometric efforts.
Flow is plotted against volume to display a continuous loop from inspiration to expiration.
The volume versus time curve is a an alternative way of plotting spirometric results.
The overall shape of the flow volume loop is important in Interpreting spirometric results.
Acceptability & Repeatability
Acceptability
At least three (3) acceptable maneuvers
Good start to the test.
No hesitation or coughing for the 1st second.
FVC lasts at least 6 seconds with a plateau of at least 1 second.
No valsalva maneuver or obstruction of the mouthpiece.
FIVC shows apparent maximal effort.
Repeatability
Repeatability criteria act as guideline to
determine need for additional efforts.
▫ Largest and 2nd largest FVC must be within 150 mL.
▫ Largest and 2nd largest FEV 1 must be 150 mL.
▫ PEF values may be variable (within 15%).
If three acceptable reproducible maneuvers are not recorded, up to B attempts may be recorded.
Spirometry Value
Spirometry is typically reported in both absolute values and as a predicted percentage of normal.
Normal values vary and are dependent on:
▫ Gender,
▫ Race,
▫ Age, and
▫ Height.
Reporting Standards
Largest FVC obtained from all acceptable efforts
should be reported.
Largest FEV1 obtained from all acceptable trials should be reported.
May or may not come from largest FVC effort.
All other flows, should come from the effort with the largest sum of FEV 1 & FVC.
PEF should be the largest value obtained from at least 3 acceptable maneuvers.
Results Reporting
Example
Report Format
Report should also include:
▫ Age on testing day.
▫ Height (standing without shoes).
▫ Weight (without shoes).
▫ Gender.
▫ Race or ethnic origin.
▫ Technologist comment section.
FEV1 Results for Asthma
FEV 1 Severity Results for Asthma
At Risk for COPD
Spirometric classification of airflow limitation (in patients with FEV1/FVC<0.70).
▫ GOLD 1 (Mild; FEV1 ≥80% predicted).
▫ GOLD 2 (Moderate; 50% ≤FEV1 <80% predicted).
▫ GOLD 3 (Severe; 30% ≤FEV1 <50% predicted).
▫ GOLD 4 (Very severe; FEV1 <30% predicted).
Adapted from GOLD 2013
Pre & Post Bronchodilator
Studies
B-Adrenergic aerosols are most common form
for testing.
Standardize.
▫ Drug.
▫ Dosage.
▫ Delivery Device.
Minimum of 15 minutes between pre and post tests.
Pre & Post Bronchodilator
Studies: Withholding Medications
Pre & Post Bronchodilator
Studies: Interpretations
Determined based on improvement of FEV1.
Commonly expressed as Percent Change.
% Change = Post FEV 1 - Pre FEV1 x 100
Pre FEV1
Reversibility
Reversibility of airways obstruction can be
assessed with the use of bronchodilators.
> 12% increase in the FEV1 and 200 ml
improvement in FEV1
OR
> 12% increase in the FVC and 200 ml
improvement in FVC.
Spirometry
Asthma Challenge Testing
Spirometry can be used to detect the bronchial
hyperreactivity that characterizes asthma.
Increasing concentrations of histamine or methacholine.
Patients with asthma will demonstrate symptoms and produce spirometric results consistent with airways obstruction at much lower threshold concentration than normals.
Bronchial Provocation for Asthma
Spirometry
Indications — Diagnosis
Evaluation of signs and symptoms
- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Monitoring pulmonary drug toxicity
Abnormal study
- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Spirometry
Indications — Diagnosis
Evaluation of signs and symptoms
- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Monitoring pulmonary drug toxicity
Abnormal study
- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Smokers > 45yo
(former & current)
Spirometry
Indications — Diagnosis
Evaluation of signs and symptoms
- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Evaluation of occupational symptoms
Monitoring pulmonary drug toxicity
Abnormal study
- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Spirometry
Indications — Prognostic
■ Assess severity
■ Follow response to therapy
■ Determine further treatment goals
■ Referral for surgery
■ Disability
1-First Step, Check quality of the test
1- Start:
*Good start: Extrapolated volume (EV) < 5% of FVC or 0.15 L
*Poor start: Extrapolated volume (EV) ≥5% of FVC or ≥ 0.15 L
2- Termination:
*No early termination :Tex ≥ 6 s
*Early termination : Tex < 6 s
2- Look at …………FEV1/FVC
< N(70%)
Obstructive or Mixed
≥ N(70%)
Restrictive or Normal
3- Look at FEV1 To detect degree Mild > 70% Mod 50-69 % Severe 35-49% Very severe < 35%
4- Postbronchodilator FEV1/FVC
> 70% asthma
< 70% COPD
5- Reversibility test of FEV1
> 12%, 200 ml Reversible (asthma)
< 12% ,200 ml Ireversible (COPD)
6- Look at TLC
≥ 80-120% Pure obstruction
< 80% Mixed
2- Look at …………FEV1/FVC
< N(70%)
Obstructive or Mixed
≥ N(70%)
Restrictive or Normal
3- Look at FVC
≥ N(80%) < N(80%) Normal or SAWD
4-Look at FEF25/75
> 50% Normal < 50% SAWD
Restrictive
Patterns of Abnormality
Restriction low FEV1 & FVC, high FEV1%FVC
Recorded Predicted SR %Pred
FEV 1 1.49 2.52 -2.0 59
FVC 1.97 3.32 -2.2 59
FEV 1 %FVC 76 74 0.3 103
PEF 8.42 7.19 1.0 117
Obstructive low FEV1 relative to FVC, low PEF, low FEV1%FVC
Recorded Predicted SR %Pred
FEV 1 0.56 3.25 -5.3 17
FVC 1.65 4.04 -3.9 41
FEV 1 %FVC 34 78 -6.1 44
PEF 2.5 8.28 -4.8 30
high PEF early ILD
low PEF late ILD
Patterns of Abnormality
Upper Airway Obstruction low PEF relative to FEV1
Recorded Predicted SR %Pred
FEV 1 2.17 2.27 -0.3 96
FVC 2.68 2.70 0.0 99
FEV 1 %FVC 81 76 0.7 106
PEF 2.95 5.99 -3.4 49
FEV 1 /PEF 12.3
Discordant PEF and FEV1
High PEF versus FEV1 = early interstitial lung disease (ILD)
Low PEF versus FEV1 = upper airway obstruction
Concordant PEF and FEV1
Both low in airflow obstruction, myopathy, late ILD
Common FVL Shapes
Volume
Flo
w
Normal Young or quitter Poor effort
Hesitation Knee Coughing
Asthma
0 1 2 3 4 5 60
2
4
6
8
10
12
Flo
w in L
/s
Litres
concave FV curve
intrapulmonary airflow obstruction
Restrictive
0 1 2 3 4 5 6
-8
-6
-4
-2
0
2
4
6
8
10
12 F 19 yrs 1.64m
FVC 2.41 L -3.42 SR
FEV 2.41 L -2.62 SR
FEV% 100 +2.23 SR
PEF 5.55L/s -2.00 SR
F/P 7.2 RT 116 ms
Flo
w in
L/s
Litres
COPD
0 1 2 3 4 5
-6
-4
-2
0
2
4
6
8
10
Flo
w in
L/s
Litres
pressure dependent airways collapse
Poorly co-ordinated start
0 1 2 3 4 5 6
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
Flo
w in
L/s
Litres
EV = large
Rise Time = 496 ms
Irregular shape
Poorly repeatable
Upper Airway Obstruction
0 1 2 3 4 5 6
-6
-4
-2
0
2
4
6 Age 40 yrs
FVC 3.52 L 0.84 SR
FEV1 3.0 L 0.74 SR
PEF 4.57 L/s -2.18 SR
FEV/PEF = 10.9
Inspiratory
Expiratory
Flo
w in
L/s
Volume in Litres
FEV1 in mls
PEF in L/min > 8
Upper Airway Obstruction
0 1 2 3 4 5 6
-6
-4
-2
0
2
4
6
8
10
12
Flo
w in
L/s
Volume in Litres
Male aged 62 Height 1.68m
Recorded Predicted Range SR
FEV 1 2.23 2.94 2.1 to 3.8 -1.4
FV C 3.40 3.71 2.7 to 4.7 -0.5
FEV 1% FV C 66 76 64 to 88 -1.5
PEF 2.85 7.81 5.8 to 9.8 -4.1
FEV 1/PEF 13.1
Inspiration
-ve
-ve
Expiration
+ve
+ve
Extra-thoracic UAO
worse on insp. Intra-thoracic UAO
worse on exp.
Variable UAO
Intra-thoracic UAO
0 1 2 3 4 5 6
-8
-6
-4
-2
0
2
4
6
8
10
12F
low
in
L/s
L ite rs
Age 65 Female
FVC 2.97 L 1.3 SR
FEV1 2.26 L 0.6 SR
FEV1% 76% -0.1 SR
PEF 3.4 L·s-1 -2.5 SR
F/P 11.1 RT 455 ms
Upper Airway Obstruction
• Variable extrathoracic obstructions 1. vocal cord paralysis,
2. thyromegaly,
3. tracheomalacia, or
4. Neoplasm
• Large airways variable intrathoracic obstructions 1. tracheomalacia or
2. neoplasm
• Fixed obstruction 1. tracheal stenosis,
2. foreign body, or
3. neoplasm.
Obstruction, Restriction, Mixed
Variable Extrathoracic Upper Airway Obstruction
Fixed Upper Airway Obstruction
True Restrictive Disorders
Intraparenchymal
Interstitial Infilterative Diffuse alveolar
Chest Wall
Pleural Skeletal Neuromuscular
Reduced TLC.FRC,RV,VC and normal to high FEV1/FVC
DLVA,Dlcoc or both DLVc parynhymal If normal Chest wall or neuromuscular
Pseudorestrictive Disorders
Normally: IC/ERV=2-3/1
True restrictive: IC/ERV=<2/1
Pseudorestrictive: IC/ERV=6/1
Pseudorestrictive Disorders
Asthma is a disorder characterized by increased reactivity of the
airways. Patients with asthma have recurrent or persistent airflow
obstruction, which is reversible either spontaneously or with
appropriate therapy. An obstructive pattern is most often present,
recognized by reduced forced expiratory volume in 1 s (FEV1), and
FEV1 to forced vital capacity (FEV1/FVC) or FEV1/vital capacity
(VC) ratio. Patients may have normal spirometry between attacks.
In some patients, the FVC may be reduced due to air trapping,
resulting in pseudorestriction on spirometry in the presence of
increased or normal total lung capacity (TLC), increased functional
residual capacity (FRC) and increased residual volume (RV). We
have reported 12 asthmatic patients with reduced VC and no
increase in RV, i.e., a true restrictive impairment [Gill et al. Chest
2012)
Pseudorestrictive Disorders
Obesity:
*Early airway closure (low ERV & high RV)
*FRC is more reduced than TLC&VC
*Low FEF50% , FEF75%, FEF25-75%,
Pseudorestrictive Disorders
Neuromuscular Disease:
*FRC normal
*IC&ERV decreased
*Decreased TLC
*Increased RV
*A-aO2 gradient normal
*MIP&MEP decreased
Pseudorestrictive Disorders
Asthma:
*FRC &TLC increased
*Improvement of FEV1&FVC with bronchodilators
*Positive bronchoprovacation test
*Increased diffusing capacity and DLco/VA
Pseudopseudorestrictive
Patients with obstructive diseases who do not
complete expiratory effort of FVC. This may
lead to a below normal FEV1 and FVC with
pseudonormalization of ratio.
Mixed Disorder
*Sarcoidosis
*Rhematoid
*Advanced IPF
*Bronchiectasis
*BOOP in smokers
Obstructive Pattern
■ Decreased FEV1
■ Decreased FVC
■ Decreased FEV1/FVC
- <70% predicted
■ FEV1 used to follow severity in COPD
Obstructive Lung Disease —
Differential Diagnosis
Asthma
COPD
- chronic bronchitis
- emphysema
Bronchiectasis
Bronchiolitis
Upper airway obstruction
Restrictive Pattern
Decreased FEV1
Decreased FVC
FEV1/FVC normal or increased
Restrictive Lung Disease —
Differential Diagnosis
Pleural
Parenchymal
Chest wall
Neuromuscular
Spirometry Patterns
Bronchodilator Response
Degree to which FEV1 improves with inhaled
bronchodilator
Documents reversible airflow obstruction
Significant response if:
- FEV1 increases by 12% and >200ml
Request if obstructive pattern on spirometry
Flow Volume Loop
“Spirogram”
Measures forced inspiratory and expiratory
flow rate
Augments spirometry results
Indications: evaluation of upper airway
obstruction (stridor, unexplained dyspnea)
Flow Volume Loop
Upper Airway Obstruction
Variable intrathoracic obstruction
Variable extrathoracic obstruction
Fixed obstruction
Upper Airway Obstruction
Lung Volumes
Measurement:
- helium
- nitrogen washout
- body plethsmography
Indications:
- Diagnose restrictive component
- Differentiate chronic bronchitis from emphysema
Lung Volumes – Patterns
Obstructive
- TLC > 120% predicted
- RV > 120% predicted
Restrictive
- TLC < 80% predicted
- RV < 80% predicted
Diffusing Capacity
Diffusing capacity of lungs for CO
Measures ability of lungs to transport inhaled gas
from alveoli to pulmonary capillaries
Depends on:
- alveolar—capillary membrane
- hemoglobin concentration
- cardiac output
Diffusing Capacity
Decreased DLCO
(<80% predicted)
Obstructive lung disease
Parenchymal disease
Pulmonary vascular
disease
Anemia
Increased DLCO (>120-140% predicted)
Asthma (or normal)
Pulmonary hemorrhage
Polycythemia
Left to right shunt
DLCO — Indications
Differentiate asthma from emphysema
Evaluation and severity of restrictive lung disease
Early stages of pulmonary hypertension
Bronchoprovocation
Useful for diagnosis of asthma in the setting of normal pulmonary function tests
Common agents:
- Methacholine, Histamine, others
Diagnostic if: ≥20% decrease in FEV1
PFT Patterns
Emphysema
FEV1/FVC <70%
“Scooped” FV curve
TLC increased
Increased compliance
DLCO decreased
Chronic Bronchitis
FEV1/FVC <70%
“Scooped” FV curve
TLC normal
Normal compliance
DLCO usually normal
PFT Patterns
Asthma
FEV1/FVC normal or decreased
DLCO normal or increased
But PFTs may be normal bronchoprovocation