Pulmonary Function Test Concepts

S. Krishnamurthy

Group Clinical Pharmacist, Kauvery Hospital, Trichy

Definition

Pulmonary function tests (PFTs) are a group of tests that measure lung function. They help diagnose lung conditions, monitor treatment, and assess risk factors for lung disease.

Purpose

  • Diagnose and monitor respiratory diseases like asthma and emphysema
  • Assess treatment for chronic lung problems
  • Evaluate patients before surgery
  • Monitor the progression of lung disease
  • Identify non pulmonary disease processes.

Types of PFTs

  • Spirometry: Measures how much air one can breathe in and out, and how fastone can exhale
  • Body plethysmography: Measures lung volume by having one sit in a clear box and breathe into a mouthpiece
  • Diffusion capacity: Measures how well oxygen enters the bloodstream
  • Pulmonary exercise tests: Measures how well our lungs work when we are active
  • Pulse oximetry: Measures the levels of oxygen in our blood

Spirometry: Measures the rate of air flow and estimates lung size. For this test, client will breathe multiple times, with regular and maximal effort, through a tube that is connected to a computer. Some people feel lightheaded or tired from the required breathing effort

Forced Vital Capacity (FVC): Volume of air that is exhaled after maximum inhalation

Forced expiratory volume (FEV): Volume of air exhaled in one breath      

Forced expiratory flow: Air flow in the middle of exhalation

 Peak expiratory flow (PEF): Rate of exhalation

Maximum voluntary ventilation (MVV) :Volume of air that can be inspired and expired in 1 minute

Slow vital capacity (SVC: Volume of air that can be slowly exhaled after inhaling past the tidal volume

Total lung capacity (TLC): Volume of air in the lungs after maximum inhalation

Functional residual capacity (FRC) :Volume of air left in the lungs after normal expiration

Residual volume (RV) : Volume of air in the lungs after maximum exhalation

Total lung capacity (TLC) : Maximum volume of air that the lungs can hold

Expiratory reserve volume (ERV) : The volume of air that can be exhaled beyond normal exhalation

Gas Diffusion

Instrument: Blood gas analyzer

Arterial blood Gases: Concentration of oxygen and carbon dioxide in the blood

FEV1/FVC ratio

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

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 SEVER

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

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

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

References

Nightingale Journals

Kauvery Hospital
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