Restrictive/Inflammatory Lung Disease

Question 1

Restrictive vs. Obstructive Lung Disease (Compliance/Airway resistance)

Answer 1

• Obstructive ==> Increased compliance + increased airway resistance
• Restrictive ==> Decreased compliance + decreased airway resistance
• Obstructive disease primarily increases resistive pressure, P_r. Restrictive disease increases the work required to distend the lung, the P_el.

Question 2

Compliance of respiratory equation

Answer 2

• 1/C_tot = 1/C_lung + 1/C_cw
• C_tot = Compliance of the total system
• C_lung = Compliance of the lung
• C_cw = Compliance of the chest wall
• **compliance of the respiratory system may be affected by changes in compliance of either chest wall or lung or both

Question 3

Mechanisms of decreased lung compliance

Answer 3

1. Increased thickness of the lung interstitium
   
   • deposition of elastic/connective tissue (e.g. fibroblasts)
   • increase in inflammatory cells
2. Increased lung water
   
   • CHF
3. Increased alveolar surface tension
   
   • ​​==> alveolar collapse ==> reduced compliance
   • can occur due dilution from pulmonary edema
   • abnormal sufractant production/fxn

Question 4

Acute dx resulting from abnormal surfactant production

Answer 4

• Respiratory distress syndrome in premature infants is a result of inadequate surfactant production due to immature lung development.
• Acute respiratory distress syndrome (ARDS) results in dysfunctional surfactant due to injury to type 2 alveolar cells + pulmonary edema in this disorder dilutes the surfactant + inflammation and injury in the interstitium that decreases compliance.

Question 5

Restrictive Lung Disease impact on TLC, FRC, RV and PV curve

Answer 5

• TLC, FRC and RV are all decreased
• PV curve is flatter and shifted down

Question 6

Restrictive Lung disease impact on airflow measures

Answer 6

• Airflows in pulmonary fibrosis/ILD are supranormal for a given lung volume because the airways are dilated due to traction applied from adjacent parenchyma (“traction bronchiectasis”)
• Spirometry will show a normal or elevated FEV₁/FVC ratio.

Question 7

Restrictive disease impact on gas-exchange

Answer 7

• impaired gas-exchange (decrease in D_LCO) due to:
• decreased lung volumes
• decreased alveolar capillary SA
• increased wall thickness ==> decreased diffusion
• V/Q mismatch

Question 8

Mechanisms that decrease chest wall compliance

Answer 8

• burns: third degree burns form a thick eschar that limits chest wall excursion
• obesity- increases soft tissue mass and decreased ability of the chest wall to move
• kyphoscoliosis- deformity of the spine (lateral and anterior displacement)
• ankylosing spondylitis- inflammatory disease which causes ossification of the ligamentous structures of the spine (the bamboo spine). This restricts movement of the ribs.
• respiratory muscle weakness - paralysis of the muscles, neuromuscular disease
• pleural fibrosis/thickening- restricts expansion of the lung within the thoracic cavity
• pleural effusion - fluid in pleural cavity limits lung expansion

Question 9

Restrive disease due to chest wall vs. lung interstitium

Answer 9

• both: decreased lung volumes, normal airflow
  
  • except: muscular weakness ==> normal FRC but low effort-dependent PFT measures
• Lung: decreased D_LCO/V_a (gas-exchange adjusted for alveolar volume)
• Chest wall: normal D_LCO/V_a

Question 10

Technique to measure compliance of lung w/out the effects of chest wall

Answer 10

• Pressure-volume curves plotted using a manometer
• manometer is passed into the mid-esophagus ==> estimation of pleural pressure
• in the body box a patient exhales slowly from TLC and lung volumes are measured periodically using Boyle’s Law
• The volume is correlated to the pleural pressure measured by manometer

Question 11

Examples of mixed lung disorders + common PFT results

Answer 11

• combination of obstructive and restrictive
• e.g. an obese patient with asthma
• combined pulmonary fibrosis and emphysema
• Decrease in TLC or FRC (restrictive) + decrease in FEV₁/FVC ==> markedly decreased D_LCO

Question 12

ILD definition & Common causes

Answer 12

• ILD = “Interstitial Lung Disease” = generic term for heterogenous group of lung disorders
• Autoimmune disease
• Exposure to inorganic dusts (e.g. asbestos or silica)
• Exposure to organic mlx ==> hypersensitivity pneumonitis
• Drug effect
• Idiopathic

Question 13

Common approach to ILD dx

Answer 13

• “clinical-radiologic-pathologic”
  *

Question 14

Common presentation of most ILDs

Answer 14

• insidious onset of dyspnea on exertion
• nonproductive cough
• PFTs: restrictive pattern w/reduced diffusing capacity

Question 15

Common findings for IPF vs. NSIP

Answer 15

• IPF = idiopathic pulmonary fibrosis
  
  • 2-3 yr survival, unresponsive to therapy
  • CXR: traction bronchiectatsis, volume loss, honeycomb lung, paucity of ground glass
  • Histo: Usual Interstitial Pneumonia (UIP) = spacially and temporally heterogenous fibrosis + fibroblast foci
• NSIP = non-specific interstitial pneumonia
  
  • less severe than IPF
  • CXR: traction bronchiectatsis, volume loss, usually associated w/ground glass
  • Histo: spatially and temporally homogenous, generally more cellular (vs. fibrotic)