Pulmonary Function Test


Pulmonary function tests (PFTs) are routinely used in patients with chronic respiratory disorders to monitor lung indices. They are performed to assess respiratory function and to determine the extent of dysfunction. Such tests include measurements of lung volumes, ventilatory function, and the mechanics of breathing, diffusion, and gas exchange[1]. PFTs are useful in following the course of a patient with an established respiratory disease and assessing the response to therapy. They are useful as screening tests in potentially hazardous industries, such as coal mining and those that involve exposure to asbestos and other noxious fumes, dusts, or gases. They are useful for screening patients scheduled for thoracic and upper abdominal surgery, and symptomatic patients with a history suggesting high risk.


Investigation of a patient with sign/symptoms that shows respiratory problems. e.g. wheezing, coughing, crackles and abnormal chest xray e.t.c.

Monitoring of patients with respiratory condition for disease progression and response to treatment.

Evaluation of degree of cardio-respiratory disability

Preoperative evaluation for patient that will undergo thoracic and abdominal surgery

Montoring of patients at risk of pulmonary complications

Routine assessment for individual with high exposure to pulmonary toxic agent e.g abestos, dust and fumes


Myocardial Infarction in the last month

Unstable Angina

Recent thoracic and abdominal surgeries

Recent Opthalmic surgery

Abdominal, thoracic and cerebral Aureysms

Active Hemoptysis


Different Pulmonary Function Tests

  1. Spirometry
  2. Forced Spiometry which include FVC, FEV1, and FVC/FEV1
  3. Techniques for measuring Residual volume (RV) and Functional residual capacity (FRC): Nitrogen Washout Technique, Helium Dilution Technique and Body Plethysmography
  4. Diffusing Capacity of Carbon monoxide (DLCo) Oxygen
  5. Peak Expiratory flow Meter Reading to generate a flow volume loop.
  6. Arterial Blood Gas Analysis
  7. Bronchodilator Test
  8. Cardiorespiratory Exercise Test [2]
  9. Oximetry
  10. Respiratory Muscle Function Test


  • Step 1: FEV1/FVC ratio

FEV1/FVC <70% (or less than the Lower limit of normal) : Obstructive Pattern (COPD, Asthma)

≥70%: Normal or Restrictive disease

  • Step 2:

Severity of obstruction (GOLD Criteria for COPD)

FEV1 80-100% predicted: Mild (Stage 1)

FEV1 50- 80% predicted: Moderate (Stage 2)

FEV1 30- <50% predicted: Severe (Stage 3)

FEV1 <30% predicted: Very severe (Stage 4)

FEV1 <50% with right side heart failure: Very severe (Stage 4)

Severity of obstruction (ATS General Criteria)

FEV1 over 70% predicted: MILD

FEV1 60-70%predicted: MODERATE

FEV1 50-60% predicted: MODERATELY SEVERE

FEV1 35-50% predicted: SEVERE

FEV1 <35% predicted: VERY SEVERE

  • Step 3

≥12% increase AND an absolute improvement of at least 200ml after inhaling a beta agonist.

FEV1, OR FVC is considered a significant response.

  • Step 4: Total Lung Capacity (TLC) (Normal range: 80-120% of predicted)

TLC >120 = Hyperinflation

TLC <80% = Restrictive disease (ATS criteria for severity)

70-80% predicted: MILD

60-70% predicted: MODERATE

50-60% predicted: MODERATELY SEVERE

<50% predicted: SEVERE

  • Step 5: RV/TLC ratio (Normal range: <35% or < predicted)

RV/TLC >35% or > predicted indicates Air trapping

  • Step 6: DLCO (Normal range: 80-120% of predicted)

In obstructive disease:

Decreased in Emphysema

Normal in chronic bronchitis

Normal or increased in Asthma

In restrictive disease:

Decreased in parenchymal disease

Normal in non-parenchymal (e.g. chest wall) restriction


  1. Ranu H, Wilde M, Madden B.Pulmonary Function Tests. Ulster Med J. 2011; 80(2): 84–90
  2. Guazzi M, Bandera F, Ozemek C, Systrom D, Arena R.Cardiopulmonary Exercise Testing; What Is its Value?Journal of the American College of Cardiology. 2017;70(13) DOI: 10.1016/j.jacc.2017.08.012
  3. Dweik AR. Interpretation of Common Lung Function Tests.Cleveland Clinic. 2011.https://www.clevelandclinicmeded.com/live/owork/us-state/MDpres2/16.0830.Dweik.Pulm.A.PFTs.CME.v2.pdf