Pulmonary function tests

Pulmonary function tests


       Pulmonary function tests

       Role of PFT in lung disorders


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


       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: 


       Lobar bronchi

       Segmental bronchi

        subsegmental bronchi

       small bronchi


       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


       Lung volume

       Lung Flow

       Airway reactivity

       Diffusing Capacity of Carbon Monoxide (DLCO)


       Resistance and conductance


       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


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)


       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


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)


       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


                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  


       Lung volume tests include measuring





       Lung flow tests include measuring FEV1: FVC ratio and PEF

For PDF Notes Click on Download Button

Post a Comment