Pulm Function Testing

Question 1

6 Indications for PFTs

Answer 1

• Categorize
  
  • Obstructive v. restrictive
  • Asthma v. emphysema
• Objective Assessment
  
  • Document an abnormality - “disability”
  • Distinguish from psych problem –> SOB
• Document Progression
  
  • COPD
  • ALS
• Document Response to Therapy
  
  • Asthma control
  • Lung volume reduction surgery
• Preoperative
  
  • Want to make sure you have enough lung reserve to undergo lung cancer resection
  • Timing of lung transplant
• Screen for sub-clinical disease
  
  • May screen for emphysema in smokers or in those w/ occupation risk

Question 2

What does spirometry measure?

Answer 2

1- Exp Volumes

• Forced vital capacity (FVC) if max effort
• Slow vital capacity (SVC) if slow and steady exhalation

2- Exp Rate

• FEV1 - volume expired in 1st sec
• FEF 25-75 -flow rate b/n 25-75% forced vital capacity
• FEV1/FVC

Question 3

What are the normal spirometry values? Which ones fluctuate and how?

Answer 3

• normal FEV1/FVC > or = .7 regardless of demographics
• Whereas FEV1 and FVC individually fluctuate by demographics (dec w/ age, lower in females, lower in asians/blacks, inc w/ height)
  • Normal = w/in 20% of predicted values (80-120% range)

Question 4

Why are flow-volume curves superior to volume-time curves for spirometry results?

Answer 4

• Better for detecting patterns
• Better for detecting quality control

**Should be … 4 seconds long, 3 acceptable loops w/ less than 5% difference b/n them

Question 5

Fixed Upper Airway Obstruction Pattern

Variable Extra-Thoracic Airway Obstruction Pattern

Intra-Thoracic Upper Airway Obstruction Pattern

Answer 5

• Fixed Upper Airway Obstruction - inspiratory and expiratory plateaus
  
  • Ex) fixed tracheal stenosis
• Variable Extra-thoracic Obstruction - normal expiratory loop but inspiratory plateau
  
  • Ex) glottic tumor or redundant tissue in obesity/sleep apnea
• Intra-thoracic Upper Airway Obstruction - have expiratory plateau but normal inspiration curve
  
  • Ex) tracheal tumor OR chondromalacia

Question 6

Bronchodilator Response

Answer 6

• Determine reversibility of airway obstruction by comparing spirometry b/f and after bronchodilator med (usually beta-agonist)
• Pos - if inc FEV1 by 12%+ OR if inc FVC by 200 mL+
• Pos response to bronchodilator can dx asthma

Question 7

Bronchial Challenge

Answer 7

• For episodic symptoms you can induce them in office (chemicals, particulates, methacholine, histamine-derivative which induces bronchospasm only in those w/ asthma) OR give portable device to use at home or work
• 20% reduction in any parameter (FVC, FEV1 or peak expiratory flow) is positive

Question 8

Obstructive v. Restrictive Disease on Spirometry

Answer 8

OBSTRUCTIVE

• Normal volume expired but takes longer to come out due to resistance
• FEV1/FVC < .7
• Maybe first noticed as normal FEVI/FVC but FEF25-75 <65% predicted value
• Can have dec FVC (air trapping)

RESTRICTIVE

• Lower volume expired but normal rate
• Dec FVC and dec TLC
• BUT normal FEV1/FVC b/c both decrease in proportion (normal rate)

Question 9

2 Tests to Meas Vol in Lung

Answer 9

(RV, TLC, FRC)

• 1- Helium Dilution
  
  • Use a closed system w/ helium of known amount into spirometer
  • Conc1 x V1 = Conc2 x V2
  • If you can meas change in helium conc then you can calculate the change in total gas volume when pt breaths in
  • Use helium because it is not soluble so does not move into blood like oxygen or carbon dioxide would
• 2- Body Plethysmography
  
  • Access pressure shift at mouth against closed airway (tells you change in pressure)
  • Access change in box pressure (tells you change in lung volume)
  • P1V1=P2V2
  • Larger lung volume will cause huge dec in pressure w/ expansion (volume inc) v. smaller lung volume will cause smaller dec in pressure w/ expansion (volume inc)
    
    • Look at change in mouth pressure and use this to determine original lung volume

Question 10

How do you measure diffusion capacity?

Answer 10

• Meas gas exchange NOT ventilation
• Give mix of small quantity of CO, helium and oxygen
• Helium tells you how much dilution there is
• CO tells you how much diffusion by meas conc of CO b/f and after (use CO b/c binds Hb and has high P gradient)
• Abnormal if less than 80% predicted value