Pulmonary Function Tests Overview

Pulmonary Function Tests

• Pulmonary function tests (PFTs) are investigations used to evaluate the airways, respiratory musculature, and lung tissues.
• PFTs measure lung volumes and capacities, gas flow rates, gas diffusion and distribution.
• PFTs are used to classify lung diseases into obstructive, restrictive and mixed categories.

Intended Learning Outcomes

• Students will be able to recognize and distinguish different pulmonary function tests.
• Students will understand how to conduct an accurate spirometry test.
• Students will interpret numerical and graphical spirometry data.
• Students will recognize spirometry patterns associated with restrictive and obstructive lung diseases.
• Students will appreciate the American Thoracic Society recommendations for presenting spirometry data.
• Students will appropriately use spirometry data to evaluate physiotherapy interventions.

Lung Diffusion Capacity Test (DLCO)

• DLCO is a measurement to assess the lung's ability to transfer gas from inspired air to the bloodstream.
• It's called the diffusing capacity of the lungs for carbon monoxide (DLCO).
• Inhaled carbon monoxide (CO) is used because it has a higher affinity for hemoglobin than oxygen (O2).
• The test requires the patient to hold their breath for 10 seconds to measure the CO uptake.

Fick's Equation

• Factors affecting gas diffusion across the alveolar membrane:
  • Surface area of the membrane
  • Membrane thickness
  • Solubility of the gas
  • Driving pressure/pressure gradient

DLCO Results

• DLCO is indicated to evaluate parenchymal and non-parenchymal lung diseases, such as obstructive, restrictive, and pulmonary vascular diseases.
• Results are interpreted in conjunction with spirometry and TLC values.
• Normal DLCO is >75% predicted, up to 140%.
• Mild DLCO is 60% to LLN.
• Moderate DLCO is 40% to 60%.
• Severe DLCO is <40%.

How DLCO is Conducted

• Techniques include single breath method, intrabreath method, and rebreathing technique.
• The patient sits with a clip on the nose.
• A mouthpiece is attached for the test gas.
• The patient takes a few normal breaths.
• The patient exhales completely, inhales deeply, and holds the breath for 10 seconds.
• The patient then exhales for 3-5 seconds.

What is Spirometry?

• Spirometry is the study of gas flow and lung volumes (ventilatory function).
• It measures the flow and volume of air entering and leaving the lungs.
• It compares lung function results to reference values.
• It measures the impact of pulmonary diseases (e.g. asthma, COPD, cystic fibrosis).
• It detects early changes in lung function (e.g., airway narrowing).
• It evaluates the response to medicine (e.g., bronchodilator).
• It determines the ability to tolerate medical or surgical procedures

Spirometry (Physiological Test)

• Spirometry involves measuring the maximal volume of air inhaled and exhaled.
• It also measures volumes as a function of time, elastic resistance and airway resistance.

Indications for Spirometry

• General respiratory health screening.
• Identifying individuals at risk for pulmonary disease.
• Assessing pre-operative risk.
• Evaluating disease prognosis.
• Assessing disease effects on lung function.
• Evaluating disability/impairment.
• Monitoring disease progression and exacerbation.
• Evaluating the response to interventions (e.g., exercise programs, medications, surgery).
• For surveys and pre-employment/at-risk occupations lung health monitoring.

Spirometry Precautions

• Spirometry involves physical effort, increasing myocardial demand and causing the generation of intrathoracic/intra-abdominal/intracranial pressure.
• Risks are related to the impact on thoracic organs, venous return, and systemic blood pressure and chest wall and lung expansion.

Relative Contraindications for Spirometry

• Pain.
• Recent eye, thoracic, or abdominal surgery.
• Recent myocardial infarction, uncontrolled hypertension or embolism.
• Recent cerebrovascular hemorrhage or known cerebral/abdominal aneurysm.
• Pneumothorax.
• Haemoptysis of unknown origin.
• Acute disorders affecting test performance (e.g., fever, vomiting, dizziness, nausea).

Preparing for a Spirometry Test

• Environment:

  • Stable temperature.
  • Standardized pressure (barometer).
  • Quiet and comfortable.

• Hygiene:

  • Hand hygiene.
  • Disposable and single-patient filters/gloves.

• Equipment:

  • Calibrated spirometry machine.
  • Arm chair (sitting).
  • Nose clip.
  • Filter and turbine (or combined).

How to perform a Spirometry Test

• Patient performs 3 trials, choosing the best, including maximal inspiration & expiration, with appropriate instructions/prompting.
• Common errors include incorrect inspiration to TLC, premature expiration and variable effort.

Procedures for Forced Vital Capacity (FVC) Maneuvers

• Dispenses hand sanitizer and confirms patient details (including allergies and respiratory symptoms).
• Checks the requisition for relative contraindications.
• Informs the patient how to position and breathe.
• Demonstrates correct test procedure with verbal encouragement.
• Records three trials, choosing the best.

Spirometry Test Results

• Volume refers to the amount of air contained in the lungs and expelled at various times in a respiratory cycle.
• Speed refers to how fast air is expelled from the lungs at different times in the respiratory cycle.

Spirometric Report Format

• Shows numerical values (e.g., FVC, FEV1, FEV1/FVC).
• Includes a flow-volume loop graph.
• Uses reference values from the American Thoracic Society(ATS) or another relevant organization.

Obstructive Lung Disease

• A group of diseases causing airway obstruction and airflow restriction.
• Conditions that cause obstructive lung diseases are chronic bronchitis, asthma, emphysema and bronchiectasis
• Characterized by difficulty/inability to exhale air from the lungs.

Obstructive Lung Disease Characteristics

• Problems primarily in expiration.
• Impaired expiratory airflow.
• Impaired carbon dioxide elimination.
• Nonuniform alveolar ventilation.
• Thoracic cage assumes inspiratory position.
• Diaphragm lowers and bulges.
• FVC is normal or decreased.
• FEV1/FVC ratio is decreased.
• FRC is increased.

Obstructive Lung Disease: Flow-Volume Loop

• Concavity in the expiratory limb.
• Reduced FEV1.
• Reduced FEV1/FVC ratio.

Restrictive Lung Disease

• A group of diseases causing decreased lung compliance and reduced lung expansion.
• Characteristics of restrictive lung diseases include various causes, conditions such as intrinsic lung diseases (interstitial lung disease, sarcoidosis, and pneumonitis), and extrinsic lung diseases such as pleural tissue, pleural effusion, pleuritis, neuromuscular disorders, scoliosis, ascites, obesity and abdominal tumors.
• Causes decreased lung elasticity and compliance, hindering full expansion.

Restrictive Lung Disease Characteristics

• Reduced total lung capacity (TLC).
• Reduced lung compliance.
• FVC is reduced.
• FEV1/FVC ratio is normal.

Restrictive Lung Disease: Flow-Volume Loop

• Narrowed loop, relatively higher peak flow.
• Normal looking spirometry; but abnormal flow-volume loop.
• Reduced FVC.
• Relatively high PEF.
• Steep end expiratory phase.

Monitoring Disease Progression

• Obstructive diseases:

  • Weekly FEV1 changes ≥ 12% in healthy subjects or ≥ 20% in COPD patients.
  • Yearly changes in FEV1 should not exceed 15%.

• Restrictive diseases:

  • ≥ 10% FVC reduction reflects disease progression.
  • Declining FVC is a strong indicator of disease progression in neuromuscular diseases.

How to Interpret Spirometry Results and Reference Values

• Use appropriate reference values (e.g., ATS/ERS 2021).
• Consider patient characteristics (e.g., age, sex, height).
• Understand the normal distribution of healthy lung function data in defining normal range.

Classification of COPD Severity

• Mild (FEV1 ≥ 70% predicted).
• Moderate (FEV1 60-69% predicted).
• Moderate to severe (FEV1 50-59% predicted).
• Severe (FEV1 35-49% predicted).
• Very severe (FEV1 < 35% predicted).

Classification of Restriction Severity

• Normal (≥ 80% predicted).
• Mild (70-79% predicted).
• Moderate (50-69% predicted).
• Severe (<50% predicted).

Pulmonary Function Test Terminologies

• Lung volumes and capacities include:
  • Tidal, expiratory reserve volume, inspiratory reserve volume and residual volume.
• Forced expiratory volume (FEV1).
• Forced expiratory volume during 6 seconds (FEV6) ratio.
• Peak expiratory flow (PEF or PEFR or MEF).
• Forced mid-expiratory flow (FEF25-75%)