essay 18 - basic mechanisms disturbing lung function and gas exchange - restrictive disorders. obstructive disorders. Mixed disorders

general mechanisms

• obstruction= increased resistance

• restriction= decreased lung compliance or chest wall expansion

• pulmonary blood flow deficit = decreased perfusion

• altered control of breathing = decreased respiratory centre

what's our restrictive disorders

• conditions that reduce lung compliance or expansion, resulting in decreased total lung capacity and vital capacity

restrictive diseases of the lung

1. interstitial pulmonary fibrosis

• a chronic progressive lung disease with excessive fibrosis scarring of the interstitium, leading to stiff lungs

• aetiology - autoimmune disease, occupational/environmental exposure, idiopathic

• pathogenesis= injury to alveolar epithelium → inflammatory cytokines → fibroblast proliferation → collagen deposition → thickened alveolar walls

• symptoms= progressive Dyspnea, dry cough, inspiratory crackles

2. pulmonary edoema

• accumulation of fluid alveoli and interstitial tissue impairing gas exchange

• aetiology=
  - cardiogenic= increase in pulmonary venous hydrostatic pressure
  - non cardiogenic = increase in capillary permeability

• Pathogenesis =
  - interstitial fluid accumulation
  - alveolar flooding
  - severe oxygen impairment

• Symptoms = dyspnea, cough with frothy sputum, sianosis

restrictive diseases of the chest wall

1. kyphosis and scoliosis

• structural spinal deformities(kyphosis = posterior curve, scoliosis = lateral curve) that mechanically restricts chest expansion

• aetiology = congenital, degenerative bone disease, trauma, neuromuscular conditions

• pathogenesis= deformity of thoracic cage → stiff chest wall → decreased thoracic cavity volume

• symptoms= Dyspnea on excursion, fatigue

2. Flail chest

• the loss of chest wall stability due to multiple rib fractures >/= 2 places, Creating a Free Floating Segment.

• aetiology = severe blunt trauma (Car accident, fall)

• pathogenesis = paradoxical movement → fractured segments are sucked inward on inspiration, bulges outward on expiration

• symptoms= severe pain, dyspnea, paradoxical chest movement

What Is Obstructive Disorders (ventilation disorders)

• disorders causing increased airway resistance, mainly during expiration.

• mechanisms= airway inflammation, smooth muscle hyperreactivity, mucous hyper secretion, alveolar wall destruction

list the obstructive disorders

• Asthma

• chronic obstructive pulmonary disease (COPD)

• chronic bronchitis (A type of COPD)

• emphysema (type of COPD)

describe asthma

• a chronic inflammatory disease characterised by reversible airway obstruction and hyperreactivity

• etiology/triggers = allergens, respiratory infections, cold air, exercise, pollutants, stress

• types:
  - allergic (extrinsic) = IgE-mediated, allergen-driven
  - non-allergic (intrinsic) = treated by infection, cold air, stress, chemicals

• pathogenesis = trigger→ mast cell activation→ bronchospasm + mucosal edema + mucus hypersecretion

• symptoms = wheezing, dyspnea, cough, chest tightness

• consequences = airway modelling, chronic inflammation, risk of permanent narrowing, in severe cases → status asthmaticus and death

describe chronic obstructive pulmonary disease (COPD)

• progressive, irreversible air flow limitation due to chronic airway inflammation and alveolar destruction

• etiology = cigarette smoking(main), recurrent infections, alpha1-antitrypsin deficiency, aging

• pathogenesis = chronic irritation → airway narrowing + alveolar damage → obstruction + decrease recoil → air trapping

• consequences = progressive hypoxemia, hypercapnia, respiratory acidosis, cor pulmonale (right sided heart failure)

describe chronic bronchitis (type of COPD)

• Chronic productive cough for >/=3months in 2 consecutive years

• etiology = smoking, industrial pollution

• pathogenesis = chronic irritation → mucus gland hypertrophy, mucus hypersecretion, airway narrowing

• symptoms = productive cough with purulent sputum, cyanosis, frequent infections

• consequences = hypoxia + hypercapnia, pulmonary hypertension, cor pulmonale

emphysema (type of COPD)

• abnormal, permanent enlargement of distal airspaces with destruction of alveolar walls

• etiology = smoking (protease-antiprotease imbalance), alpha1-antitrypsin deficiency.

• pathogenesis = elastin destruction → loss of recoil → hyperinflation and air trapping

• symptoms = progressive dyspnea, minimal cough initially, later “barrel chest”, use of accessory muscles, pursed-lip breathing

• consequences = hypoxemia, hypercapnia, cachexia, cor pulmonale in advanced disease

mixed disorders

• definition = disorders with features of both obstruction and restriction

• examples:
  - COPD with pulmonary fibrosis (obstruction + stiff lungs)
  - cystic fibrosis (mucus plugging+ lung scarring)
  - obesity hypoventilation syndrome:
  - restrictive = chest wall compression by fat → decreased compliance
  - obstructive = sleep apnea due to pharyngeal collapse