Emphysema

Introduction

A condition characterized bydilation of air spaces (with ↓ elasticity and ↑ compliance)
- due to alveolar wall destruction
  - normally, elastin in the wall functions to keep alveoli open
- capillaries are destroyed along with the alveoli
Causes
- smoking
  - most common cause
- α₁-antitrypsin (AAT) deficiency
  - AD disorder (codominant)
    - MM phenotype is normal
    - ZZ phenotype results in disease
  - AAT normally inhibits the action of elastase
  - without AAT elastase is unchecked and destroys the elastic tissue of the alveoli
  - as a result emphysema develops at early age
may also develop cirrhosis due to the inability to release an abnormal form of AAT from the liver resulting in hepatotoxicity

Classification

Centriacinar
- dilated respiratory bronchiole
- most common presentation of emphysema due to smoking
  - result of inhaled tobacco toxins arriving first in the respiratory bronchioles before traveling to the alveolus
- most commonly in the upper lobes
  - result of upper lobes receiving exposure to smoke
Panacinar
- dilated alveoli
- most common presentation of AAT deficiency
  - also due to a functional AAT deficiency as a result of smoking
    - oxidants and inflammatory reaction of smoke can destroy AAT
    - smoking exacerbates effects of genetic AAT deficiency
- most commonly in the lower lobes
  - result of lower lobes recieving ↑ perfusion allowing more immune cells to traffic into the alveoli
Paraseptal
- most commonly involves young, otherwise healthy males
- does not obstruct the airway
  - associated with bullae
  - found near the pleura
increased risk for spontaneous pneumothorax

Presentation

Symptoms
- dyspnea
- classic pursed-lip breathing
  - results in increased airway pressure and prevents airway collapse during exhalation
Physical exam
- decreased breath sounds on auscultation
- increased anterior-posterior diameter (barrel chest)
- hyperresonant to percussion
“pink puffer” (end-stage)

Imaging

Chest radiograph
- increased AP diameter with flattened diaphragms
- hyperinflated lungs
- loss of lung markings
elongated heart

Evaluation

Labs
- ABG during exacerbation shows hypoxemia and acute respiratory acidosis
- AAT shows no α-globin peak on electrophoresis
Pulmonary function tests
- decreased FEV_{1 sec} / FVC
- increased TLC and RV
decreased diffusion capacity from destruction of capillaries

Treatment