1 - Respiratory Mechanics ( III )

Question 1

Objectives: Define factors affecting FRC

Lung Resection

Kyphgoscoliosis (Chest Wall defects)

Emphysema / COPD

Answer 1

• Lung Resection:
  
  • FRC / RV both decreased
• Kyphoscoliosis:
  
  • Underventilation of the lungs
  • FRC / RV both decreased
• Emphysems / COPD:
  
  • More space from loss of tissue
  • FRC / RV both increased

Question 2

Objectives: Define obstructive vs restrictive lung disease

Answer 2

• Obstructive: High Airway Resistance
  
  • ​Asthma
  • Bronchitis (upper airways)
  • Cystic Fibrosis
  • COPD (Emphysema + chronic Bronchitis)
• Restrictive: Low Lung Compliance or Increased Stiffness and Increased Lung Recoil
  
  • ​Pulmonary Fibrosis (scar tissue stiffens)
  • Sarcoidosis (stiffens lungs)
  • Silicosis, Asbestosis (build up of scar tissue)
  • Wegener’s Granulomatosis (“coin lesions” in lungs)

Question 3

Objectives: How is FEV1 a measure of airway resistance in the lung?

Answer 3

• Maximal forced exhalation from total lung capacity–the amount exhaled in 1 sec is FEV1 (total volume of gas is FVC)
  
  • For a normal person ~ 80% or greater
• Low FEV1 = Obstructive Pulmonary Disease
  
  • ​Airways collapse, resistance increases, can’t get air out
  • Note axes on these plots, pay attention to time on X-axis
  • Airway obstruction will result in a less steep slope

Question 4

Objectives: How do airways collapse during forced expiration?

Question 5

Objectives: How do lung diseases affect lung volumes?

Question 6

Objectives: How are flow volume loops used in lung disease?

Answer 6

Shifts in their position of shape vs normal can be indicative of major lung disease

• Left, Rapid Decline = Obstructive
  
  • ​Emphysema
  • Larger Volumes (left shift)
  • Rapid decline from Dynamic Collapse
• Right, Leveled Decline = Restrictive
  
  • ​Asthma, COPD, bronchitis
  • Smaller Volumes (right shift)
  • Rates not as affected vs obstructive

Question 7

Objectives: How are flow-volume loops used in upper airway diseases?

(Thoracic Location Variants)

Answer 7

• Cross section area of obstruction is dependent on inspiratory or expiratory effort
• Variable Intrathoracic Lesion - Obstruction inside thoracic cage - Staying at the “Inn”
  
  • Affected greater by expiration
  • ​Flow Volume Loop will have flattened expiration (upper) portion
  • Ex: Tumor of Lower Trachea
• Variable Extrathoracic Lesion - Obstruction outside thoracic cage - Extra Bowl of Cereal
  
  • Affected greater by inspiration
  • Flow Volume Loop will have flatted inspiration (lower) portion
  • Ex: Fat Deposit, Vocal Chord Paralysis, Obstructive Sleep Apnea
• Fixed Intra/Extra Thoracic Lesion - Obstruction fixed in airway​
  
  • ​Both inspiration and expiration flattened
  • Ex: Tumor in central airway, fibrotic lesion, tracheal stenosis

Question 8

Objectives: Explain the protocol for Methacholine Challenge Testing

Answer 8

• Used to detect hyperreative airways, useful for Asthma

1. Started when baseline spirogram is normal
2. Inhalation Challenge performed w/varying [Methacholine] by dosimeter
3. Each [Methacholine] stage is ended with spirometry
   
   1. 20% reduction in FEV1, test terminated and positive for airway hyperreactivity
   2. [Methacholine] for this is labeled PC₂₀
4. Given bronchodilator for recovery (so they don’t die)

• PC_20FEV1 less than 8 mg/ml suggests airway hyperreactivity; 8-16 = negative

Question 9

How must your normalize FEV1?

How does this ratio change with obstructive and restrictive diseases?

Answer 9

• Measured as ratio against FVC (e.g. body size)
• FEV₁ / FVC = 80% (healthy)
• Obstructive: Decrease FEV₁ / FVC​
  
  • ​Low FEV1/FVC – Think obstructive!
• Restrictive: Increase FEV₁ / FVC
  
  • ​Normal ~ Higher
  • Compliance is lower, so some air can get out fast

Question 10

What additional lung volume / capacities do you mainly look at for the following diseases to differentiate?

Fibrosis

Emphysema

Asthma

Answer 10

• Fibrosis: Diffusing Capacity (DLCO) and TLC
• Emphysema: TLC
• Asthma: Methacholine Challenge Test

Question 11

What are the main differences in Obstructive vs Restrictive PEF Graphs?

What are PEF graphs?

Answer 11

• PEF Graphs are just the top have of flow volume loops
  
  • ​PEF = Peak Expiratory Flor (apex of graph)
• Obstructive: Left Shift
  
  • ​Lower Amplitude
  • Smaller Area (loss of tissue)
  • Steep decent due to dynamic collapse
• Restrictive: Right Shift
  
  • ​Lower Amplitude
  • Smaller Area (stiff lungs, harder to inflate)
  • Slightly convex decent, steeper slope “Witch Hat”

Question 12

What are three important things to consider for Methacholine Challenge Test?

Answer 12

1. Positive tests may not have asthma; COPD, smokers, allergic rhinitis will test positive
2. Asthma patients on anti-inflammatory drugs may test negative
3. Those triggered by specific agents (cold, allergens) may test negative

Question 13

How do you read Methacholine Challenge Tests?

Ex: Test performed

FEV1_Control = 3.8

Answer 13

• PC₂₀ = 20% Reduction in FEV1
  
  • Take Control, Subtract 20% of this value
    
    • Draw Horizontal line to graph
  • Draw vertical line to x-axis from this value, estimate [Methacholine] dosage
• If this value is < 8 mg/ml, +Test

Ex: 20% x 3.8 = 0.76 ; 3.8-0.76 = 3.04

Draw vertical line down from 3.04; determined [Methacholine]; is < 8 mg/ml = +Test

Question 14

What is the first step in any Methacholine Challenge Test graph?

Answer 14

1. Look at baseline based on control
2. Subtract 20% (or look for 20% reduction)
3. Determine [Methacholine] at that level
4. If < 8 = +Test