3. Lung function tests, types, indications, devices, and minimal requirement of acceptability

Question 1

Different types of LFTs used in daily practice

Answer 1

• Spirometry
• Full-body Plethysmography
• Single Breath Diffusion Capacity
• Bronchial Challenge/Bronchiodilator Responsiveness Testing
• Respiratory Muscle Function Testing

Bolded tests are the most common used

LFTs alone cannot give dx. Patient history, physical examination and imaging studies in addition to LFTs will allow a definitive diagnosis

Question 2

What can Spirometry not measure

Answer 2

It measures Static and Dynamic lung volumes, however it cannot measure Residual Volume and Total Lung Capacity

This is because it is impossible to exhale out RV even on forced expiration

Lung capacities and Airflow

We thus can measure, Tidal Volume, Inspiratory Reserve Volume, Vital Capacity and Expiratory Reserve Volume

Question 3

Indications for Spirometry

Answer 3

• Chest pain
• Dysnpea
• Difficulty taking a deep breath
• Chronic cough
• Wheezing

It is the best initial test for evaluation of pulmonary function and determine a differential dx, especially recognize Obstructive vs Restrictive diseases.

It is also the best test to monitor pulmonary function throughout a therapy, autoimmune diseases that affect lungs, etc

Question 4

What do we interpret in Spirometry

Answer 4

Flow-Volume loops graphically and its numerical measurements

Question 5

What are the things to monitor to ensure good spirometry results

Answer 5

• Good test initiation [quick and forceful onset of exhalation]
• No coughing
• Smooth curves
• Absence of early termination of expiration [minimum exhalation of 6 seconds with no change in volume for the last second]
• Patient cooperation by accurate demonstration

Question 6

Indications for Full-body Plethysmography

Answer 6

• Patients who cannot actively participate in Spirometry
• Obstructive diseases to evalute root cause
• Restrictive diseases to distinguish external vs internal causes
• Measure Residual Volume and Total Lung Capacity

Patients are put in an airtight sealed chamber with a mouth piece. Patient inhales causing decrease in pressure inside chest and simultaneous Increase in pressure inside the chamber.
Follows Boyle’s Law