Spirometry

Interpretation Of Spirometry
Dr. Saumya Shishir
DM fellow
Department of pulmonary medicine
AIIMS, Jodhpur

SPIROMETRY
• Spirometry is a physiological test that measures how an
individual inhales/exhales volumes of air over a period of
time.
• It is the most commonly used pulmonary function test.
• Total volume of air that the patient can expel from lungs after
a maximal inhalation is FVC and amount of air exhaled in 1st
sec of expiration is FEV1
• It measures various volumes and capacities except functional
residual capacity, residual volume and total lung capacity.

HISTORY
• In mid 1800s, John Hutchinson developed a simple
spirometer based on water seal principle that measured the
maximum volume of air which can move in and out of lung,
vital capacity.
• Around 1950, Gansler attached a microswitch to a water seal
spirometer to time the vital capacity. He observed that healthy
people can exhale than 80% of their vital capacity in first
second and almost all the vital capacity in 3 seconds.
• In late 1950s, Robert Hyatt and others began using flow
volume display to measure lung function.
Sprigs EA. The history of spirometry. Br J Dis Chest 1978; 72: 165-180

From ‘Instruction manual for the Collins Stead-Wells Spirometer 06041″,
published 1979 by W. E. Collins, Co

Types of spirometers- Volume/ flow
• Volume Displacement Spirometers- These record the
amount of air exhaled or inhaled within a certain time.
• Flow sensing Spirometers-These measure how fast the
air flows in or out as the volume of air inhaled or exhaled
increases.
Johns DP, Pierce R. Pocket guide to Spirometry. McGraw Hill Australia, 2003

What is measured by Spirometry

Diagnostic
• To evaluate symptoms, signs or abnormal laboratory tests.
• To measure the effect of disease on pulmonary function
• To screen individuals at risk of having pulmonary disease
• To assess pre-operative risk
• To assess prognosis.
• To assess health status before beginning strenuous physical activity programmes
Monitoring
• To assess therapeutic intervention.
• To describe the course of diseases that affect lung function.
• To monitor people exposed to injurious agents.
• To monitor for adverse reactions to drugs with known pulmonary toxicity
Indications of spirometry
Standardisation of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical Statement. American Jo

Disability/impairment evaluations
• To assess patients as part of a rehabilitation programme.
• To assess risks as part of an insurance evaluation
• To assess individuals for legal reasons
Public health
• Epidemiological surveys.
• Derivation of reference equations Clinical research
Indications of spirometry
Standardisation of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society
Technical Statement. American Journal of Respiratory and Critical Care Medicine, 200(8), pp.e70-e88.

Spirometry during COVID pandemic
• ATS recommend that PFT be limited to tests that are only essential for immediate
treatment decisions, that the type of pulmonary function testing be limited to the
most essential tests when possible, and that measures to protect both the staff and
individuals being tested be put in place.
• Use of protective measures like PPE that limits aerosolized droplet acquisition for
staff.
• This is an evolving situation and the risk/benefit ratio continue to change over time.
https://www.thoracic.org/professionals/clinical-resources/disease-related-resources/pulmonary-function-laboratories.php

Bedside tests
• Sabrase breath holding test
• Single breath count
• Forced expiratory time
• Debono’s whistle blowing test
• Wright’s peak flow meter
• Wright’s respirometer

Contraindications of spirometry
• Due to increase in myocardial demand or change in blood pressure
• Acute MI within 1 wk
• Systemic hypotension or severe hypertension
• Significant atrial/ventricular arrhythmia
• Non-compensated heart failure
• Uncontrolled pulmonary hypertension
• Acute cor pulmonale
• Clinically unstable pulmonary embolism
• History of syncope related to forced expiration/cough

Due to increase in intra-cranial/ intra-ocular pressure
Cerebral aneurysm
Brain surgery within 4 wk
Recent concussion with continuing symptoms
Eye surgery within 1 wk
Due to increase in sinus and middle and middle ear pressure
Sinus or middle ear surgery or infection within 1 wk
Due to increase in intrathoracic and intraabdominal pressure
Presence of pneumothorax
Thoracic/abdominal surgery within 4 wk
Late term pregnancy
Infection control issues
Active or suspected transmissible respiratory or systemic infection like TB
Standardisation of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical
Statement. American Journal of Respiratory and Critical Care Medicine, 200(8), pp.e70-e88.

• Pneumothorax
• Increased intracranial pressure
• Syncope, dizziness, headache
• Chest pain
• Paroxysmal coughing
• Nosocomial infection
• Oxygen desaturation due to interruption of O2
• Bronchospasm
Complications of spirometry

FVC -Forced vital capacity
This is the total amount of air that one can forcibly blow out after full inspiration, measured in
liters
FEV1- Forced expiratory volume in one second
This is the amount of air that one can forcibly blow out in one second, measured in liters.
Along with FVC it is considered one of the primary indicators of lung function
FEV1/FVC
The proportion of the total volume of air that can be expired in the first second of expiration.
Test Values In Spirometry
Burrows, B., 1975. Pulmonary Terms and Symbols. Chest, 67(5), pp.583-593.

PEFR- Peak expiratory flow rate
This is the maximum speed of air moving out of the lungs at the beginning of
expiration, measured in litres per second.
FEF25-75%
or 25-50%
- Forced expiratory flow 25-75%
or 25-50%
This is the average flow or speed of air coming out of lung during the middle portion
of the expiration ( also sometimes referred to as MMEF , for maximal mid-expiratory
flow)
FIF 25-75% or 25-50%- Forced inspiratory flow 25-75%
or 25-50%
This is similar to FEF 25-75% or 25-50% except the measurement is taken during inspiration.
Important in extra thoracic disease
Burrows, B., 1975. Pulmonary Terms and Symbols. Chest, 67(5), pp.583-593.

FET -Forced expiratory time
This measures the length of the expiration in seconds.
SVC-Slow vital capacity
Total amount of air that can be exhaled slowly after full inspiration .
MVV -Maximum voluntary ventilation
The maximum amount of air that can be breathed in and out in one minute time.
In normal subjects is is FEV1 times 40.

Test Requirements and procedure
• Record the subjects age, race ,height, weight and gender for calculation of
the reference values.
• Age must be recorded in years to one decimal place, height in centimetres
to one decimal place and weight to nearest 0.5 kg be recorded.
• BMI should be calculated as kg/m2
• For kyphotic patients- arm span for height.
• The Spirometry is effort dependent test, always better to demonstrate how
to blow out.
• Use of nose clip during spirometry is not necessary
• If dentures- use them

Calibration of Spirometers
• For correct and reproducible results
• Verify calibration frequently
• Syringes- 1L and 3L

Patients should be advised to avoid the following prior to testing:
• Smoking and/or vaping and/or water pipe within 1 hour before testing
• Consuming intoxicants within 8 hours before testing.
• Performing vigorous exercise within 1 hr before testing.
• Wearing clothing that substantially restricts full chest and abdominal
expansion.
Pre Test preparation

Bronchodilator Medication Withholding Time
SABA ( albuterol or salbutamol) 4-6 h
SAMA ( ipratropium) 12 h
LAMA ( formoterol or salmeterol) 24 h
Ultra- LABA ( indacaterol, vilanterol) 36 h
LAMA ( tiotropium, umeclidinium,
glyccopyronium)
36- 48 h
Bronchodilator Withholding Times

exhalation
Inhalation
Spirometry requires a coordinated maximum effort. The three steps are:
• Step 1: Coach the patient to take as deep a breath as possible
• Step 2: Loudly prompt the patient to Blast out the air into the
spirometer
• Step 3: Encourage the patient to continue exhaling for maximum of 15 seconds.
• Step 4 : Inspiration at maximal flow back to maximum lung volume.
EXHALATION
INHALATION
Phase 1
Inhale
Phase 2
Blast
Phase 3
Keep going

Types of spirometry tracings- V-
T and F-V curves

Flow Volume Loop- Inspiratory / Expiratory limbs
• Flow volume curve provides a graphic illustration of a
patient’s spirometry efforts.
• Flow is plotted against volume to display a continuous loop
from inspiration to expiration.
• A normal flow volume loop has a rapid peak expiratory
flow rate (termed as ‘peak of the curve’). The expiratory
flow rate then falls and the tracing moves downward to
meet the volume axis. It is termed ‘the slope of the curve.
• The inspiratory portion of the loop is a deep curve plotted
on the negative portion of the flow axis. It indicates upper
airway disease.
• The overall shape of the flow volume loop is important in
interpreting spirometry results.
Peak
Slope

• Blunt peak (Sand mound): Such appearance
indicates inadequate effort and the test needs to
be repeated (Fig. 1).
• Notch: A notch in the initial part indicates a
cough or hesitant start. After the initial flow, the
first peak appears and then the glottis is closed,
leading to notch. Flow restarts making a second
peak, test should be repeated ( Fig. 2)
• Delayed peak: Sometimes, the curve starts from
zero, but the peak is delayed. This pattern
indicates defective start and the test should be
repeated (Fig. 3).
• Flat peak: Reduced flow rate along with
expiratory plateau indicates intrathoracic
obstruction (Fig. 4).
Abnormal Patterns in Peak
Fig.1 Fig.2
Fig. 3 Fig.4

• Steep Curve: In restrictive lung diseases. curve is steep
and straight ( Fig. 1)
• Rat tail appearance: characteristics of obstructive
airways, airflow starts with a sharp peak, but flow rapidly
declines due to airway collapse resulting in shift of upward
concavity proximally and a long plateau. (Fig.2)
• Notches on slope: Sometimes, the descending slope has
undulations and these are because of cough. Notches in the
proximal part indicate a need for repetition of the test, since
it can give a falsely reduced FEV1. Coughing in the later
part of the slope does not affect the results (Fig. 3).
• Abrupt termination of the slope: Instead of a slow and
smooth pattern, the tracings abruptly fall on the volume axis
after the peak. During the test, this pattern appears when the
patients stops expiration before complete exhalation.
Therefore, the test should be repeated. In such situations,
the spirometric parameters will show a typical restrictive
defect with FEV1/FVC ratio as high as 100% (Fig. 4). This
is commonly seen in children.
Abnormal patterns in slope
Fig.1 Fig.2
Fig.3
Fig.4

• The volume versus time curve is an alternative
way of plotting spirometric results.and is another
useful illustration of patient’s performance.
• It shows the amount of air expired from the lungs
as a function to time.
• The normal volume time curve has a rapid up
slope and approaches a plateau soon after
exhalation.
• The maximum volume attained represents the
forced vital capacity (FVC), while the volume
attained after one second represents the forced
expiratory volume (FEV1).
Volume Time curve

• Steep ascent: Restrictive defects. The
duration of expiration is reduced.
• Shallow ascent: In airflow obstruction, instead
of being steep, the slope is shallow due to a low
flow rate. The duration of expiration is
prolonged.
• Ledges on the slope: Because of coughing,
the ascending slope shows small edges. If these
appear in the first second, the test should be
repeated. Cough in the later part does not affect
the results.
Abnormal Patterns

Back-extraploted volume(BEV). Time 0 is found by drawing a line with a slope
equal to peak flow on V-T curve and setting Time 0 to the point where this line
intersects the time axis. The BEV is equal to volume of gas exhaled before time 0

• Repeatability criteria (applied to acceptable FVC and FEV1 values)
• Age >6 yr: The difference between the two largest FVC values must be ≤0.150
L, and the difference between the two largest FEV1 values must be ≤0.150 L
• Age ≤6 yr: The difference between the two largest FVC values must be ≤0.100
L or 10% of the highest value, whichever is greater, and the difference between
the two largest FEV1 values must be ≤0.100 L or 10% of the highest value,
whichever is greater.

Acceptability
criteria
Within the manoeuvre Between the manoeuvre
Free from artefacts
• Cough
• Glottic closure
• Early termination
• Submaximal effort
• Leaks
Having good start
Satisfactory exhalation
• Two largest value of FVC must be
within 0.15 L of each other.
• Two largest value of FEV1 must be
within 0.15 L of each other.
If FVC is < 1 L then it is 100 ml

• Both ATS and ERS recommend the use of LLN, to delineate between healthy
and suspected disease.
• These are set at the fifth percentile (equivalent to a z- score of -1.645) so that
95% of healthy population fall within the normal range and lowest 5% would be
false positive.
• The true LLN is age and/or height dependent and therefore will occur at varying
percent values in different individuals.
• The fixed values used (e.g. 80% predicted for, 0.70 for FEV1/FVC) are estimates
based on middle aged adults, and therefore erroneous clinical decisions based
on these fixed cut offs are likely to occur in children and in older shorter adults.
Using Reference Data in Interpretation of Results
Culver et al, 2017. Recommendations for a Standardized Pulmonary Function Report. An Official American Thoracic Society
Technical Statement. American Journal of Respiratory and Critical Care Medicine, 196(11), pp.1463-1472.

Algorithm for Spirometry Interpretation
Check FEV1/FVC
Normal
Reduced
Check FVC (VC)
Normal Reduced
Obstructive lung disease
VC
Low
Normal Restrictive
Lung disease
Additional testing
(lung volume)
Normal
Combined
obstructive and
restrictive disease
Pure obstructive
disease
Bronchodilator
test
Obstruction
reversible
Probably
asthma
Obstruction
not reversible
Probably
COPD

Pellegrino, R., 2005. Interpretative strategies for lung function tests. European Respiratory Journal, 26(5), pp.948-968.

PFT parameter Pure obstruction Pure Restriction Mixed
FEV1/VC N
VC N or
FEV1
INTERPRETATION OF SPIROMETRY

Bronchodilator reversibility test
• Bronchodilator reversibility (BDR) testing should be performed at baseline in all subjects
suspected or found to have airflow obstruction . However, in subsequent serial testing in
such subjects, BDR test is usually not required.
• BDR test should be performed between 15 and 20 min after administering salbutamol
(four puffs of 100 μg) or equivalent doses of levo salbutamol (4 puffs of 50 μg).
• If use of salbutamol is contraindicated, ipratropium (8 puffs of 20 μg) may be used as an
alternative with spirometry performed after 30 min.
• The bronchodilator should be delivered with a metered dose inhaler (MDI) device, ideally
with a spacer, using correct technique .
• Alternative preparations such as nebulisation or dry powder inhaler may be used in
subjects who are unable to take MDIs.

What criteria should be used to define bronchodilator reversibility?
An increase in FEV1 and/or FVC of 200 mL and 12% of the baseline should be
used as the criterion for defining BDR
The least improvement is seen when baseline values are very low ( often due
to diffuse mucous plugging ) or very high( relatively normal bronchial tone).

Severity of Obstructive lung
defect
• When FEV1/FVC is below LLN or < predicted normal.
• Based on FEV% predicted normal.
Mild 70 to < LLN
Moderate 60-69
Moderately severe 50-59
Severe 35-49
Very severe <35
Pellegrino, R., 2005. Interpretative strategies for lung function tests. European Respiratory Journal, 26(5), pp.948-968.

Assessment of severity of obstruction
in COPD ( GOLD guidelines)
• Post- bronchodilator spirometry FEV1/FVC < 0.7
• Severity assessed by FEV as % predicted normal
GOLD Stage
Degree of
obstruction
FEV1%
1 Mild > 80% predicted
2 Moderate 50- <80%
3 Severe 30- <50%
4 Very severe <30%

Severity of Restrictive lung
defect
• Most reliable is on basis of TLC measurement.
• Based on VC% of predicted normal severity of restriction
can be graded.
Degree of restriction
VC% of predicted
normal
MILD > 70 to LLN
MODERATE 50-69
SEVERE 35-49
VERY SEVERE <35
Pellegrino, R., 2005. Interpretative strategies for lung function tests. European Respiratory Journal, 26(5), pp.948-968

Diseases associated with airflow obstruction
• COPD
• Asthma
• Bronchiectasis
• Cystic fibrosis
• Post- tuberculosis
• Obliterative bronchiolitis

Diseases associated with Restrictive
Defect
Pulmonary
• Fibrosing lung disease
• Pneumoconiosis
• Pulmonary edema
• Parenchymal lung tumors
• Lobectomy or pneumonectomy
Extra pulmonary
• Thoracic cage deformity
• Obesity
• Pregnancy
• Neuromuscular disorders
• Fibrothorax

Diseases associated with Mixed Ventillatory Defects
• COPD
• Bronchiectasis
• Sarcoidosis
• Hypersensitivity Pneumonitis
• LAM
• CPFE
• OSA
• Both obstructive and restrictive disease

Spirometry in Central/ Upper Airways Lesions
• PEF may be severly affected.
• FEV1/PEF > 8 ml/L/min indicate need for inspiratory and expiratory
F/V loop evaluation.
• Extra thoracic lesions : MIF 50% is reduced.
• Intra thoracic lesions : MEF 50% is reduced.

• Vocal cord paralysis
• Sub glottic stenosis
• Goitre
Variable Intra-thoracic
Airway Obstruction
Variable Extra-thoracic
Obstruction
• Tracheomalacia
• Relapsing polychondritis
• Retrosternal goitre

FIXED UPPER OBSTRUCTION
• Cancer of vocal cord.
• Lymphoma of mid-trachea
• Idiopathic B/L vocal cord palsy with fixed stenosis
• Post-thyroidectomy B/L vocal cord palsy with fixed stenosis
• Post tracheal tube stricture

RV/TLC % predicted Severity of Air trapping
Severity of Restriction
TLC % predicted
80 to 120 % pred Normal 80-120 %
130 to 140 % pred Mild >70 %
140 to 170 % pred Moderate 60- 69 %
Above 170 % pred Severe < 60 %
Severity Assessment on Lung Volume

Spirometry

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