Lung Tests

Question 1

Spirometry

Answer 1

• Steps:
  
  • Take 3 resting breathes to establish Normal Tidal Volume
  • Max inhale to Total Lung Capacity
  • Max Exhale to Residual Volume
• RV and capacities that contain RV cannot be measured
  
  • FRC
  • TLC
• Inspiration: Up
• Expiration: Down

Question 2

Helium Dilution: Steps

Answer 2

• Spirometer is filled with helium-insoluble in blood
• Patient inhales until the helium is in equilibrium with the lungs

Question 3

Helium Dilution: What is measured?

Answer 3

• measures
  
  • FRC
    
    • then derives RV & TLC
      
      • RV=FRC-ERV
      • TLC=RV+VC
  • the volume of contiguous airspace
    
    • doens’t measure obstructed airways=underestimate the residual volume
• Volume in lungs when the test is started is the volume being measured

Question 4

Plethysmography: Steps

Answer 4

• In sealed box and starts at FRC
• Shutter on breathing tube is closed
• Measure pressure of:
  
  • mouth pressure
  • Box pressure
• No air is moving, so mouth pressure=alveolar pressure
• patient inhales
  
  • chest wall expands out
  • Lungs expand out
    
    • Pressure decreases
    • Lung Volume Increases

Question 5

Plethysmography

Answer 5

• Measures all airspace in the lungs, even trapped gas (Behind an obstruction)
  
  • more accurate at measuring FRC
• Measures FRC more accurately
  
  • then derive RV and TLC

Question 6

FEV1

Answer 6

• Forced Expiratory Volume in 1 Second
• estimates airflow through large airways
• dependent on effort

Question 7

FEF_25-75

Answer 7

• Forced Expiratory Flow b/w 25%-75%
• Estimates average expiratory flow
  
  • measures small airways
• related to:
  
  • intrinsic recoil
  • dynamic compression
• Independent of effort

Question 8

Flow-Volume Curves

Answer 8

• Easy to visualize dynamic obstruction
• Maximal Effort:
  
  • Peak Expiratory Flow (up)
  • Peak Inspiratory Flow (down)
• Area independent of effort
  
  • minimal and moderate efforts
  • measures smaller airways (FEF_25-75)

Question 9

Intrathoracic vs Extrathoracic Obstruction

Answer 9

• Intrathoracic obstruction
  
  • most severe during expiration
  • relieved during inspiration
• Extrathoracic Obstruction
  
  • increased during inspiration
    
    • bc atmospheric pressure compress trachea below site of obstruction