Pulmonary
function tests
Content
• Pulmonary
function tests
• Role
of PFT in lung disorders
Objective
After completion of this lecture, student will be able
to:
• Explain
the pulmonary function tests
• Describe
the role of PFT in lung disorders
Pulmonary function tests
Pulmonary function tests (PFT’s) are useful
• In
diagnosis of various pulmonary diseases
• Management
of patients with lung disease
Clinical
uses of PFTs:
a) Evaluate respiratory symptoms
b) Screen for respiratory diseases
c) Assess disease severity
d) Monitor the cause of disease
e) Evaluate the response to therapy
f) Assess the risk of pulmonary
exposure to environmental toxins
Definitions
• Ventilation
à The movement of air
into and out of the lungs
• Perfusionà Movement of blood
through the lungs
• Air
travels via laminar flow through the conducting airways comprised of the
following:
• Trachea
• Lobar
bronchi
• Segmental
bronchi
• subsegmental bronchi
• small
bronchi
• Bronchioles
• and
terminal bronchioles
• The
airways then branch further to become transitional/respiratory bronchioles
• The
transitional/respiratory zones are made up of respiratory bronchioles, alveolar
ducts, and alveoli
• Gas
exchange takes place in the acinus
• This
is defined as an anatomical unit of the lung made of structures supplied by a
terminal bronchiole
Pulmonary Function Tests
• Spirometry
• Lung
volume
• Lung
Flow
• Airway
reactivity
• Diffusing
Capacity of Carbon Monoxide (DLCO)
• Compliance
• Resistance
and conductance
Spirometry
• Spirometry is the most widely
available and useful PFT
• It takes only 15 to 20 minutes, carries no
risks, and provides information about obstructive and restrictive disease
• it also allows assessment of FEV1
and FEF25%–75%
• Spirometry
measurements can be reported
in two different formats— standard spirometry
and the flow–volume loop
• In standard spirometry- the volumes
are recorded on the vertical (y) axis and the time on the horizontal (x) axis
• In flow–volume loops- volume is
plotted on the horizontal (x) axis, and flow is plotted on the vertical (y)
axis
• The
shape of the flow – volume loop can be helpful in differentiating obstructive
and restrictive defects and in
diagnosing upper airway obstruction
Tests
Respiratory
function assessed by:
• lung
volume tests
• lung
flow tests
Lung volume tests
a) Tidal volume (TV)
b) Inspiratory capacity (IC)
c) Inspiratory reserve volume (IRV)
d) Expiratory reserve volume (ERV)
e) Slow vital capacity (SVC)
f) Residual volume (RV)
g) Functional residual capacity (FRC)
h) Total lung capacity (TLC)
Lung volumes and
Capacities
} 4
volumes:
◦
Inspiratory reserve volume
◦
tidal volume
◦
expiratory reserve volume
◦
residual volume
} 4
capacites:
◦
vital capacity
◦
inspiratory capacity
◦
Functional residual capacity
◦
total lung capacity
Tidal
volume:
• Amount of air inhaled or exhaled at
rest
• Reference range : 500 to 750 ml
• It is infrequently used as a measure
of respiratory disease
Inspiratory reserve volume
• The maximal volume of air inhaled
above tidal volume.
• Reference range: 3.1 L
• Amount of air that is inhaled with
maximal inhalation after the normal inhalation
Expiratory reserve volume
• The maximal air exhaled below tidal volume is the expiratory
reserve volume (ERV)
• Amount of air that is exhaled with
maximal expiration after the normal exhalation
• Reference range: 1. 2 L
Residual
volume
• Amount of air that is left in the
lungs after full exhalation
• Reference range: 1. 2 litre
• RV unmeasurable by spirometry but
measurable by body plethysmography
• Without
the RV the lungs would be like deflated ballons
• In
diseases like Asthma & COPD the RV
increases (air trapped in lungs)
Capacities
•
The combinations or sums of two or more lung volumes
are termed capacities
Vital Capacity
• Vital capacity (VC) is the maximal
amount of air that can be exhaled after a maximal inspiration
• It is equal to the sum of IRV, TV, and ERV
Forced vital capacity (FVC)
• It is the total unit of air exhaled
as hard & as fast as possible after a maximal inhalation
Slow
vital capacity
• When the full inhalation-exhalation
procedures is repeated slowly – instead of forcefully and rapidly – it is known
as SVC
• This value is the maximum amount of
air exhaled after a full and complete inhalation
• In
patients with normal airway function, SVC and FVC are usually similar
• In
patients with diseases, such as COPD during the initial stages of disease, the
FVC decreases before the SVC
Inspiratory
capacity
•
The volume measured from the point of the TV where
inhalation normally begins to maximal inspiration
•
Sum of TV +
IRV
•
Reference range: 500 ml + 3.1 L = 3.6 L
Functional residual capacity
•
It is the sum of the ERV and RV [2.4L]
•
Increased FRC usually represents hyperinflation of
the lungs and indicates airway obstruction
•
Decreased FRC occurs in restrictive diseases
especially due to pulmonary fibrosis and
pneumonia
Total lung capacity
•
It is the total amount of gas contained in the lungs
at maximal inhalation
•
It is the sum of the
four primary lung volumes (IRV, TV, ERV, and RV)
•
Reference range: 6 L
Body Plethysmography
•
Also
known as body box
•
Used to
obtain lung volume measures
•
Patient
sits in air-tight chamber
•
Uses
Boyle’s law
–
Pressure
& volume vary inversely if temperature is constant
–
Used to
measure FRC and other lung volumes
LUNG FLOW TESTS
Forced expiratory volume
•
FEV0.5, FEV1, FEV3
are the amounts of air exhaled after 0.5 , 1 and 3 seconds respectively
•
Of these, FEV1 has the most clinical
relevance and primarily the indicator of airway function
•
Volume
of air exhaled in the first second under force after a maximal inhalation
•
The
normal value for FEV1 is 0.75 – 5.5 L & this wide variation is due to
physical variables among patients
•
A value
of >80% of predicted value is considered normal
FEV1/ FVC Ratio
•
The ratio of FEV1 to the FVC is another
way to estimate the presence and amount of obstruction in the airways
•
In healthy individuals, the normal value is FVC 0.5 = 50%; FVC1 = 80%; FVC3
= 98%
•
In patients with restrictive disease it is usually
normal/ high because FVC is reduced
•
In patients with obstructive disease, this ratio
will decrease
Diffusion capacity tests
•
Patient deeply inhales a mixture of 0.3% CO, 10%
helium and air
•
After holding
the breath for 10 seconds, the patient exhales fully and the concentration of
CO and helium are measured during the end of the expiration
•
Concentrations
are compared with the inspired concentrations to determine the amount diffusing
across alveolar membrane
Airway reactivity tests
•
Bronchodiolators studies
i.
patient performs spirometry and plethysmography
immediately before and after the administration of inhaled beta 2 agonist. If
the airflow /volume improved – candidate for therapy
ii.
Drugs tested – beta 2 agonist, theophylline (asthma)
anti cholinergics (COPD)
Compliance
•
The elasticity of lung or thorax is measured by
pulmonary compliance
•
Compliance is the change in volume divided by the
change in pressure
•
Decreased compliance observed in patients with
decreased volume secondary to pulmonary fibrosis, edema and pneumonia
Resistance
Airway resistance = Change in pressure / Change
in flow
•
Useful in differentiating obstructive from
restrictive disease or from normal pulmonary function
•
In obstructive, resistance increases due to blockage
of airflow
Summary
•
Lung
volume tests include measuring
•
IRV
•
ERV
•
TV
•
RV
•
Lung
flow tests include measuring FEV1: FVC ratio and PEF
