Pulmonary function tests (PFTs) measure lung function in three categories: dynamic air flow, lung volumes and capacities, and gas diffusion. PFTs identify and quantify changes from pulmonary disease, evaluate therapy effectiveness, and assess postoperative risk. Spirometry is the most common PFT and measures forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) to detect airway obstruction. Other PFTs include slow vital capacity, maximal voluntary ventilation, flow-volume loops, and reversibility testing with bronchodilators. PFT interpretation considers ratios like FEV1/FVC and compares values to predicted normals to diagnose obstructive or restrictive lung disease.

1. *
Dr.IFRA KHAN
ASSISTANT PROFESSOR

2. INTRODUCTION
-It is a group of procedures that measures the function of
the lungs.
-Pulmonary function tests can provide valuable information
about the important individual processes that support gas
exchange.
CATEGORIES OF PFT
There are 3 categories of PFT measuring
i. Dynamic flow rates of gases through airways.
ii. Lung volumes and capacities.
iii. The ability of the lungs to diffuse gases.

3. PURPOSE OF PFT
- To identify and quantify the changes in pulmonary function
due to any disease.
- Evaluate effectiveness of therapy.
- Perform epidemiological surveillance for pulmonary disease.
- Assess patients for risk of postoperative complications.
- Determine pulmonary disability.

4. PATHOPHYSIOLOGY
*Pulmonary disease are divided into two major categories:
-Obstructive pulmonary disease. Eg. COPD
-Restrictive pulmonary disease. Eg. Asthma
-Some pulmonary disease can cause both obstructive and
restrictive pulmonary disease.
*Comparison of obstructive & restrictive pulmonary disease

5. Fig. Obstructive Pulmonary Disease
* Obstructive pulmonary disease
- The primary problem in obstructive pulmonary disease is
an increased airway resistance (Raw).
- In simple terms difficulty in expiration.

6. Fig. Restrictive Pulmonary Disease
* Restrictive pulmonary disease
- The primary problem in restrictive pulmonary disease is
reduced lung compliance, lung volume or both.
- In simple terms difficulty in inspiration.

7. PULMONARY FUNCTION TEST EQUIPMENT
• Two general types of measuring devices exist, those that:
- Measure volume
- Measure flow
• Volume-measuring devices - spirometers
• Flow-measuring devices - pneumotachometers
• Every measuring device has capacity, accuracy, error,
resolution, precision, linearity, & output

8. SPIROMETRY
*It is the measurement of air entering and leaving lungs
which includes measurement of several values of forced
airflow and volume during inspiration and expiration.
• Tests of pulmonary mechanics:
-Forced vital capacity (FVC)
-Forced expiratory volume in 1 second (FEV1)
-Other forced expiratory flow measurements
-Maximum voluntary ventilation
• These measurements assess ability of lungs to move large
volumes of air quickly through airways

9. PURPOSE/IMPORTANCE OF SPIROMETRY
• The purpose of spirometry is to assess the ability of the
lungs to move large volumes of air quickly through the
airways to identify airway obstruction.
• Measuring flow rates is a surrogate for measuring airway
resistance.
• To a lesser extent spirometry can also identify and quantify
a restrictive type of pulmonary disease.

10. TYPES OF SPIROMETRY
-Computerized spirometer
-Incentive spirometer
-Tilt compensated spirometer
-Windmill type spirometer
-Tank type spirometer

11. Computerized spirometer Incentive spirometer Windmill type spirometer
Tilt compensated spirometer
Tank type spirometer

12. INDICATIONS OF SPIROMETRY
It should be especially indicated for persons with complaint
of shortness of breath.
-Asthma evaluation
-COPD diagnosis
-Screening for occupational lung disease
-Pre-operative evaluation
-Chronic cough
-Unexplained dyspnoea
-Smoking cessation
-Nonspecific

13. CONTRAINDICATIONS OF SPIROMETRY
It should not be indicated for persons with,
-Haemoptysis of unknown origin
-Pneumothorax
-Unstable angina pectoris
-Recent myocardial infarction
-Thoracic aneurysms, abdominal aneurysms, cerebral
aneurysms.
-Recent eye surgery ( intraocular pressure during forced
expiration)
-History of syncope associated with forced expiration
-Patient with active Tuberculosis should not be tested

14. PRECAUTIONS TO BE TAKEN FOR SPIROMETRY
-Persons with high blood pressure
-Semi-comatic patients
-Patients with age of 80yrs or more
-The subject should be healthy (free from asthma)
-No air leaks in the apparatus (or else will give inaccurate
readings)
-The mouth piece should be sterilized
-The water chamber should not be overfilled (or it may
enter air tubes)

15. TERMINATION CRITERIA FOR SPIROMETRY
-Feeling of giddiness
-Gasping
-Dyspnoea
-Hesitation or false starts
-Coughs
-Variable efforts
-Glottis closure
-Air leaks
-Early termination before a plateau (6s) reached
-Laughing

16. TECHNIQUES OF PFT
*Spirometry
*Helium dilution method
- Based on fact that known amount of helium will be diluted by
size of patient’s RV
*Nitrogen washout method
- Based on fact that 79% of RV is nitrogen
- Volume of nitrogen exhaled ÷ 0.79 = RV
*Whole body plethysmography
- Boyle’s law
Unknown lung gas vol = Gas pressure of the box
Known box gas vol Gas pressure of the lungs

17. *Helium Dilution Method

18. *Nitrogen Washout Method

19. *Body Plethysmography

20. PARAMETERS OF PFT
-Forced vital capacity (FVC)
-Slow vital capacity (SVC)
-Maximal voluntary ventilation (MVV)
*Forced vital capacity
-Most common test of pulmonary mechanics
-Many measurements are made while patient is performing
FVC maneuver
-FVC is an effort-dependent maneuver requiring careful
patient instruction & cooperation
-To ensure validity, each patient must perform at least 3
acceptable FVC maneuvers

21. *Forced vital capacity (cont.)

22. *Forced vital capacity for Obstructive and Restrictive Disease

23. *Slow vital capacity
-Slow Vital Capacity is a spirometry test that displays the
volume of gas measured on a low complete expiration
after a maximal inspiration without forced or rapid effort.
-Ensure that at least four consecutive tidal breaths are
stable before beginning SVC.
-SVC’s should agree within 5% or 150ml.
-SVC’s can be performed as inspiratory, expiratory or mixed
IC/ERV efforts.

24. *Slow vital capacity (cont.)

25. *Maximal voluntary ventilation
-Effort-dependent test: the patient should be instructed
to breathe as rapidly and as deeply as possible for at
least 12 seconds.
-The patient’s breathing is measured on a spirogram or
electronically for the specific number of seconds (t) and
the volume (V) breathed when the MVV is converted to
liters per minute.
• Results reflect:
-Patient effort
-Function of respiratory muscles
-Ability of chest wall to expand
-Patency of airways

26. *Maximal voluntary ventilation (cont.)
-Normal MVV for males is 160 to 180 L/min & slightly lower in
females
-MVV is reduced in patients with moderate to severe
obstructive lung disease
-MVV may be normal or slightly reduced in patients with
restrictive disease
-Undernourished patients may have reduced MVV

27. LUNG VOLUMES AND CAPACITIES
There are four lung volumes and four lung capacities. A lung
capacity consists of two or more lung volumes.
*Lung Volumes *Lung Capacities
- Tidal volume - Total lung capacity
- Inspiratory reserve volume - Inspiratory capacity
- Expiratory reserve volume - Functional residual capacity
- Residual volume - Vital capacity

28. LUNG VOLUMES AND CAPACITIES (cont.)

29. FLOW VOLUME LOOP
-The flow-volume loop is a plot of inspiratory and
expiratory flow (on the Y-axis) against volume (on the X-
axis) during the performance of maximally forced
inspiratory and expiratory maneuvers
-The normal expiratory portion of the flow-volume curve is
characterized by a rapid rise to the peak flow rate
followed by a nearly linear fall in flow as the patient
exhales toward RV.
-The inspiratory curve, in contrast, is a relatively
symmetrical, saddle-shaped curve.
*NOTE – Answer is given above for the question how flow
volume loop is produced?

30. FLOW VOLUME LOOP (cont.)

31. FLOW VOLUME LOOP FOR OBSTRUCTIVE AND RESTRICTIVE
DISEASE

32. REVERSIBILITY TEST
-If obstruction is present, reversibility must be evaluated
-Done by performing spirometry before & after therapy
-Bronchodilator is administered by small-volume nebulizer
or MDI
-Reversibility indicates effective therapy
-Reversibility is defined as 15% or greater improvement in
FEV1 & at least 200-ml increase in FEV1

33. PFT REPORT INTERPRETATION
-FEV1/FVC ratio is good place to start with; reduced
(<70%) with obstructive lung disease
-If TLC less than 80% of predicted normal & FEV1/FVC is
normal - restrictive disease is present
*If DLCO is <80% of normal - diffusion defect is present
-Reduced surface area = emphysema
-Thickened AC membrane = pulmonary fibrosis

34. PFT REPORT INTERPRETATION (cont.)

35. CONCLUSION
-Pulmonary function tests are an important tool in the
assessment of patients with suspected or known respiratory
disease.
-They are also important in the evaluation of patients prior to
major surgery.
-Interpretation of the tests, which requires knowledge of normal
values and appearance of flow volume curves, must be
combined with the patient’s clinical history and presentation.
REFERENCE:
-Egan’s Fundamentals of respiratory care
-PDF-Slow Vital Capacity - UTMB.edu
-Pubmed-www.ncbi.nlm.nih.gov/pmc/articles/PMC3229853/
-www.uptodate.com/contents/flow-volume-loops
-Article- Spirometry in the evaluation of pulmonary function

36. THANK YOU!