Obstructive diseases (Chapter 4) Flashcards
Areas that can cause increased resistance to airflow
1) Inside the lumen
2) in the wall of the airway
3) in the peribronchial region
Causes of resistance to airflow in lumen
Due to partial obstruction of the airway lumen
- excessive secretions (chronic bronchitis)
- pulmonary edema (acutely)
- aspiration of foreign material
- postoperatively with retained secretions
Causes of resistance to airflow in the wall of the airway
- contraction of bronchial smooth muscle (asthma)
- hypertrophy of mucous glands (chronic bronchitis)
- inflammation and edema (bronchitis and asthma)
Causes of resistance to airflow in the peribronchial region
- destruction of lung parenchyma may cause loss of radial traction and consequent narrowing (i.e. emphysema)
- bronchus compressed locally by an enlarged lymph node or neoplasm
- peribronchial edema can cause narrowing
Chronic obstructive pulmonary disease
- term applied to patients who have emphysema, chronic bronchitis or a mixture of the two
- it is often hard to distinguish between chronic bronchitis and emphysema –> therefore COPD is convenient, nondescript label that avoids making false diagnosis
Emphysema -what characterizes it
-enlargement of the air spaces distal to the terminal bronchiole with destruction of their walls (anatomic definition - diagnosis is presumtive in living patient - can’t dissect when living!!)
Typical histologic appearance of emphysematous lung
- loss of alveolar walls and consequent enlargement of airspaces
- destruction of part of the capillary bed
- strands of parenchyma containing blood vessels coursing across large dilated airspaces
- small airways are narrowed, tortuous and reduced in number
- thin, atrophied walls of small airways
- some loss of larger airways
- structural changes well seen with naked eye
What structures are affected in emphysema (location)
The parenchyma distal to the terminal bronchioles (the acinus)
Types of emphysema
- acinus may not be damaged uniformly - how it is damaged categorizes the type of emphysema
1) Centriacinar emphysema - destruction limited to the central part of the lobule (peripheral alveolar ducts and alveoli unscathed)
2) Panacinar emphysema -distension and destruction of the whole lobule
3) Paraseptal emphysema - disease most marked in the lung adjacent to the interlobular septa
4) Bullous emphysema-large cystic areas or bullae develop
Topographic distribution of centriacinar emphysema
- more marked in the apex of the upper lobe
- spreads down the lung as the disease progresses
Why centriacinar emphysema starts in the apex - hypothesis
-higher mechanical stresses in this area which predispose to structural failure of the alveolar walls
Panacinar emphysema topographic distribution
-no regional preference or possibly is more common in the lower lobes
When is it difficult to distinguish between the two types of emphysema
When emphysema is severe + these may coexist in one lung
Emphysema associated with alpha1-antitrypsin deficiency
- in patients who are homozygous for the Z gene
- frequently develop severe panacinar emphysema which usually begins in the lower lobes
- disease usually becomes evident by age 40 and often occurs without a cough or smoking history
- heterozygotes do not seem to be at risk
Pathogenesis of emphysema
hypothesis..
-excessive amounts of the enzyme lysosomal elastase are released from the neutrophils in the lung
-results in destruction of elastin = important structural protein
+
-neutophil elastase cleaves type IV collagen (important in determine the strength of the thin side of the pulmonary capillary and therefore the integrity of the alveolar wall)
Cigarette MOA development emphysema
1) stimulates macrophages to release neutrophil chemoattractants (such as C5a)
2) reduces the activity of elastase inhibitors
3) Exagerration
