• Respiratory diseases account for the majority
of all paediatric hospital visits and
hospitalizations all over the world, with
significant morbidity and mortality.
• Children have a dynamic developmental phase
during which lung volume size and airway size
change with increasing age.
• Spontaneous breathing is defined as
movement of air into and out of the lungs as a
result of work done by an individual’s
• The air that we breathe contain approximately
What you can control in Ventilation
• Volume V : how much air will get in and out of
• Pressure P: how much pressure will get in and
out of patient .
• Rate R.R: how fast the patient will breath? Breath
• Flow rate F.R: Flow = Volume Time. How fast
the patient will push the volume in & out.
• Oxygen O : how much oxygen the patient will put
Lung volumes and lung capacities
• Lung volumes and lung capacities refer to the
volume of air associated with different phases
of the respiratory cycle.
• Lung volumes are directly measured;
• Lung capacities are combination of two or
more lung volumes
• Static Lung volumes: volumes & capacities
• Depend on Expiration & inspiration but not on
• Dynamic lung volumes: volume& velocity
• Are the one that are depend on the rate at
which they happen.
Tidal volume Normal volume of air inspired or expired during
quiet breathing (500 mL in males and 400 mL in
females )TV = 5-8cc/kg
Extra volume of air inhaled after tidal volume by
max inspiratory effort (3000 mL in males and
2100 mL in females) 20‐25 ml/kg
Extra volume of air that can be exhaled after
tidal volume by max expiratory efforts (1100 mL
in males and 800 mL in females)
Volume of the air left out in lungs after forceful
expiration or complete expiration (1200 in a
normal adult, 20‐25 ml/kg)
• These are combinations of two or more lung
• 1. Inspiratory capacity
• 2. Functional residual capacity
• 3. Vital capacity
• 4. Total lung capacity
Inspiratory capacity Max volume of air that can be inspired after
normal tidal expiration IC = TV+IRV
Volume of air remaining in lungs after normal
tidal expiration (FRC= ERV + RV)
Vital capacity Max Amount of air expelled after deepest
possible inspiration (VC = TV+IRV+ERV)
Total lung capacity Volume of air present in lung after max inspiration
( TLC = VC + RV )
Dynamic lung volumes
• Forced vital capacity or FVC
• The forced expiratory volume in 1
• Peak expiratory flow rate (PEFR)
• forced expiratory flow at 25-75
capacity or FVC
is volume of the air that can be expired rapidly with max
force following a max inspiration, and its timed by a
in 1 second (FEV1)
is the volume of air (in liters) exhaled in the
first second during forced exhalation after maximal
inspiration. Normally, at least 80% of
the forced vital capacity (FVC) is exhaled in the
flow rate (PEFR)
is the maximum flow rate generated during a forceful
exhalation, starting from full lung inflation.
flow at 25-75%
the average flow rate measured over the middle half of
Pulmonary function tests (PFTs)
• noninvasive tests that show how well the
air ways & lungs are working.
• The tests measure lung volume, capacity,
rates of flow, and gas exchange.
• PFT can be done with two methods.
• Spirometry is a simple test used to help
diagnose and monitor certain lung
conditions by measuring how much air
you can breathe out in one forced
• It's carried out using a device called a
spirometer, which is a small machine
attached by a cable to a mouthpiece.
• Spirometry parameters are influenced by
weight, height, age, sex, environmental factors,
ethnicity, patient cooperation and effort, and
• Most children are able to perform good
quality spirometry/flow volume loops from 5
years of age.
• Although it is not difficult to perform spirometry
in children in the primary care office setting.
• it is frequently underused in the paediatric age
• A published survey revealed that only half of
physicians in paediatric primary care who were
treating children with asthma were using
spirometry and nearly half did not interpret the
spirometry results correctly.
Indications for spirometry in
• Spirometry is commonly indicated for children with chronic cough,
persistent wheezing, and for the diagnosis and monitoring of asthma and
• Reviewing asthma control and disease activity.
• It is frequently used to measure lung function in a number of diseases that
affect the lungs including haematological disorders such as transfusion-
dependent thalassaemia majorand sickle cell anaemia, haemato-oncology
conditions, connective tissue disorders, ataxia telangiectasia, and chest
deformities such as pectus excavatum.
• Spirometry is helpful in ascertaining preoperative lung function in flaccid
neuromuscular scoliosis (e.g. muscular dystrophy, spinal muscular atrophy,
and cerebral palsy).
Contraindications to spirometry
• Although there is no absolute contraindication for
• the following conditions are considered relative
• presence of respiratory tract infection (e.g. influenza),
• haemoptysis of unknown origin,
• uncontrolled hypertension,
• recent thoracic, abdominal, eye surgery
• nausea, vomiting or pain,
• confusion or dementia
Preparing for the test
• The patient should avoid strenuous exercise
or eating large meals for a few hours before
• It's best to wear loose, comfortable clothing
on the day of the test.
• If the child use bronchodilator
medication ,you may advice to stop using it
What happens during a
• The patient will be seated during the test and a soft clip will be placed on
his nose to stop air escaping from it.
• The tester will explain what you need to do, and you may be asked to have
a few practice attempts first.
• When you're ready for the test, you'll be asked to:
• inhale fully, so your lungs are completely filled with air
• close your lips tightly around the mouthpiece
• exhale as quickly and forcefully as you can, making sure you empty your
• blowing out candles on a cake : The instructions should be “take in a deep
breath and blow, blow, blow…” until the test is completed.
• This will normally need to be repeated at least 3 times to ensure a reliable
• producing results within less than 5% error.
• Spirometer can measures all volume &
capacities except :
• Residual volume
• Total lung capacity
• Functional residual capacity
Predicted Normal Values
• Reference values for spirometry are derived from
studies of specific populations of healthy people
like National Health and Nutrition Examination
• Predicted : what the patient should have
depending on Age, Hight, Sex, Weight & ethnicity.
• When performing PFT , three measures will
• Actual : what the patient performed
• Predicted : what the patient should have
depending on Age, Hight, Sex, Weight & ethnicity.
• % predicted : a comparison of the Actual value to
the Predicted value
• In general, parameters above 80% of predicted (and an FEV1/FVC
ratio >80%) are considered normal results.
Loops & Curves
• Flow-Volume Loops: flow-volume loop will show the vital
capacity on the horizontal axis and the peak flow on the
vertical axis. The slope of the curve is an indication of the
• FEV1 : can be determined from the volume-time curve.
• Flow-Volume Loops:
• The flow-volume loop must be examined to ensure the
validity of the test.
• It should rapidly rise to a sharp peak, have a smooth
expiratory curve, and not terminate until full exhalation
has been achieved.
• Cough, sudden termination of exhalation, and uneven
expiratory effort are common errors seen in flow-volume
Obstructive airway vs Restrictive lung
Obstructive Lung Disease
• Obstructive lung disease is characterized by decreased airflow, as
measured by FEV1 and FEF25%–75%.
• The FVC is usually normal in mild disease, but with more severe disease,
air trapping causes the vital capacity to decrease as the residual volume
• if the ratio of FEV1/FVC ratio is less than 80%, obstructive lung disease is
• When the FEV1 and FEF25%–75% are diminished, the flow-volume loop
will have a scooped out appearance because of lower flow rates .
• Obstructive lung conditions other than asthma include chronic obstructive
pulmonary disease, bronchiolitis, bronchiectasis, cystic fibrosis, congestive
heart failure, sarcoidosis, or pulmonary embolism.
• In general, an increase in FEV1 of greater than 12% (for low lung volumes,
minimum change of 200 mL) and/or an increase in FEF25%–75% of greater
than 20% is considered a significant positive response to a bronchodilator.
Restrictive Lung Disease
• The defining characteristic of restrictive lung disease is decreased lung
• The FVC decreases, whereas the measures of airflow, FEV1, and FEF25%–
75% are preserved. The key to recognition may lie in the ratio of FEV1/FVC,
which increases as the denominator (the FVC) decreases.
• In addition, severe restriction will make all parameters decrease, except the
• The flow-volume loop retains its normal shape but becomes smaller as the
vital capacity diminishes.
• Examples of restrictive lung diseases include muscular dystrophy, scoliosis,
pulmonary fibrosis, and other types of pneumoconiosis.
Vocal Cord Dysfunction
• Vocal cord dysfunction is a condition in which a patient attempts to inhale
against partially or totally closed vocal cords, resulting in inspiratory
• This results in flattening of the lower (inspiratory) limb of the flow-volume
• Vocal cord dysfunction is often misdiagnosed as asthma, with which it is often
• It occurs as the result of paradoxical closure of the vocal cords on inspiration,
which produces stridor, dyspnea, and noises that are often misinterpreted as
Comparison of Test Results
• The usual convention for defining significant
change between test results is to have measured
volumes (FVC and FEV1) change by more than 10%
and FEF25%–75% by 20% to 30%
• Multiple research studies have provided
evidence indicating that as hypertension is
managed by measuring blood pressure regularly
and diabetes is managed by checking blood
glucose levels, so should lung diseases should
be managed by performing spirometry in