Pulmonary function tests measure how well the lungs work by assessing how much air they can hold and exhale. There are various lung volumes and capacities that are measured, including tidal volume, inspiratory reserve volume, and total lung capacity. Spirometry is the main test used, which measures exhaled air volumes over time. It can help diagnose obstructive lung diseases like asthma which show decreased FEV1/FVC ratio, versus restrictive diseases which show increased FEV1/FVC ratio. Other tests include diffusing capacity to measure gas exchange, body plethysmography to measure total lung capacity, and inhalational challenges to identify allergens.

1. PULMONARY FUNCTION TESTS
Def : Pulmonary function tests or Lung function tests are a group of tests that
measure how well your lungs works, how well the lungs take in and exhale air,
& how efficiently they transfer oxygen into the blood.
 PFT are useful in assessing the functional status of the respiratory
system both in physiological and pathological condition.
OBJECTIVE :
• To understand the performance of lungs.
• Able to differentiate the obstructive and restrictive lung diseases.
• To estimate the prognosis of lung diseases.
PFT’S CAN HELP DIAGNOSE :
PFT’S can help diagnose lung diseases, measure the severity of lung problems,
and check to see how well treatment for a lung disease is working.
PFT’S can help diagnose lung diseases and disorders like :
• Asthma
• Chronic bronchitis
• Respiratory infections
• Lung fibrosis
• Bronchiectasis
• Allergies
• Emphysema
• Cystic fibrosis
• Asbestosis
• sarcoidosis
• Pulmonary tumors

2. LUNG VOLUMES AND CAPACITIES :
LUNG VOLUMES:
Lung volumes are also known as respiratory volumes. It refers to the volume of
gas in the lungs at a given time during the respiratory cycle.
Lung volumes are :
• Tidal volume
• Inspiratory reserve volume
• Expiratory reserve volume
• Residual volume
TIDAL VOLUME:
• The volume of air inhaled and exhaled at each breath during normal quiet
breathing.
• It measures around 500 ml in an average healthy adult male and
approximately 400ml in a healthy female.
INSPIRATORY RESERVE VOLUME:
• The volume of air that can be forcefully inspired following a normal quiet
breathing.
• The normal adult value is 1900 – 3300 ml.

3. EXPIRATORY RESERVE VOLUME:
• The volume of air that can be forcefully expired after a normal or resting
expiration.
• The average ERV volume is about 1000mL to 1100mL.
RESIDUAL VOLUME:
• The volume of air remaining in the lungs after a forceful expiration.
• The normal residual volume is about 1100mL to 1200mL.
LUNG CAPACITIES:
Lung capacities are derived from a summation of different lung volumes.
Lung capacities are :
• Vital capacity
• Inspiratory capacity
• Expiratory capacity
• Total lung capacity
• Functional residual capacity
• VITAL CAPACITY :
• The maximum amount of air that can be exhaled after the fullest
inspiration possible.
• VC = TV + ERV + IRV.
• INSPIRATORY CAPACITY :
• The maximum amount of air that can be inhaled after a normal
exhalation.
• IC = TV + IRV .
• EXPIRATORY CAPACITY :

4. • The maximum amount of air that can be expired after a normal
inspiration.
• EC = TV + ERV .
• TOTAL LUNG CAPACITY :
• The volume of air in the lungs upon the maximum inspiration.
• TLC = VC + RV.
• FUNCTIONAL RESIDUAL CAPACITY :
• The amount of air remaining in the lungs after a normal expiration.
• FRC = ERV + RV.
SPIROMETRY:
Spirometry is the physiological test that measures the volume of air an
individual inhales or exhales as a function of time.
It is carried out by using SPIROMETER.
TEST PROCEDURE :
• A spirometry test usually takes about 15 min.
1. Patient will be seated in a chair. A cup like breathing mask is placed
around patient mouth.
2. A deep breath is being taken and hold for 6 sec and then exhale into the
same mouth mask which is connected to a electronic recording device
SPIROGRAM.
3. This is to be repeated for about 3 times and the average reading is to be
recorded.
4. Lung volume and peak expiratory flow rate (PEF or PEFR ) are measured
to differentiate obstructive or restrictive problems.
5. FEV1 : Volume of air that is being exhaled at one min.
6. FVC : Volume of air that can forcibly blown out after full inspiration.

5. 7. FEV1/FVC RATIO (FEV1%) : Ratio of FEV1 to FVC . In healthy
adults this should be approximately 75 – 80 % .
INTERPRETATION OF RESULTS:
FEV1 FVC FEV1 / FVC
OBSTRUCTIVE Decreased Decreased Decreased
RESTRICTIVE Increased Decreased Increased
OBSTRUCTIVE PROBLEMS:
• Obstructive diseases (Asthma,COPD, Chronic bronchitis, emphysema)
air flow reduces because of narrowing of airways.
• FEV1 is reduced because of increased airway resistance to expiratory
flow.
• Spirogram is continued to 6 sec to empty lung,FVC also reduced because
gas is trapped behind the obstructed bronchi and premature closure of
airway in expiration.
• Cardinal feature of obstructive defect is reduction in the FEV1/FVC
RATIO.

6. RESTRICTIVE PROBLEMS:
• Restrictive disorders can be caused by disease of the lung parenchyma
and chest wall.
• This prevent the full expansion of the lungs therefore FVC maybe
reduced.
• FEV1 will be increased because of the stiffness of the fibrolytic lungs
increases the expiratory pressure.
• Hence expired air comes out very quickly resulting with a high
FEV1/FVC ratio.
GAS DIFFUSION TEST
• Gas diffusion test is performed to check the alveolar capacity of lungs
(diffusion of gases from blood to lungs (Co2) and lungs to blood (O2).
• It measures the amount of carbon dioxide and oxygen gases crossing
membrane of air sacs per minute.

7. • It is carried out to calculate the arterial amount of different gases in the
body and how efficiently lung transfers very small amount of carbon
monoxide (CO) into the blood stream.
• Carbon monoxide diffusing capacity which measures how well your
lungs transfer a small amount of carbon monoxide into the blood.
• Two different methods are used for this test.
1. If SINGLE – BREATH or BREATH – HOLDING METHOD is used
, you will take a breath of air containing a very small amount of carbon
monoxide from a container while measurements are taken.
• You hold your breath for 10 seconds, then rapidly blow it out (exhale).
2.In the STEADY – STATE METHOD, You will breath air containing a very
small amount of carbon monoxide from a container.
• The amount of carbon monoxide in the breath you exhale is then
measured.
• Diffusing capacity provides an estimate of how well a gas is able to move
from your lungs into your blood.
BODY PLETHYSMOGRAPHY:
• Body plethysmography test is performed to measure the Total lung
capacity of the patient.
• The patient is allowed to sit in a closed chamber called Plethysmograph
and allowed to breathe out in a mouth piece and the other end is joined to
the Spirogram which will measure the flow and interpreted.
• This method is appropriate for patients who have air spaces within the
lung that do not communicate with the bronchial tree.
• There are two types of plethysmographs :
1. Flow Plethysmograph
2. Pressure Plethysmograph
INHALATIONAL CHALLENGE TEST:

8. • This test is performed to check that the patient is stimulated by what type
of allergen and in what quantity.
• It is also called as Proactive studies.
• For this test the patient is made to inhale the allergen as an inhaler using
nebulizer.
• It is slightly inhaled by the patient followed by spirometry at regular
intervals of time.
• Also Histamines and methacholines are induced in the body at regular
intervals of time.
• In very rare cases bronchospasm may occur but it is immediately treated
with effective bronchodilators.
• It is normally employed in the diagnosis of Occupational rhinitis.
EXCESSIVE STRESS TEST:
• This test is performed to check how much sudden and continuous stress
lung has the capacity to tolerate.
• For this the patient is made to do a stressful exercise continuously.
• After some interval of time spirometry is done.