Anatomy WK 6 (3/13) | Lung Diseases and ARDS Overview

Exam Guidelines for Extra Time

  • Extra time during lab quizzes will be applied to exams similarly.
  • In-person attendance is mandatory for lab exams; TLC can't be done in this context.

Understanding Lung Diseases

  • The discussion focuses on expanding understanding of lung diseases, particularly pneumonia and ARDS (Acute Respiratory Distress Syndrome).
  • Inflammation in the lungs can cause fluid build-up in the alveoli.

Key Concepts in Lung Function

  • Surfactant: A fluid in the alveoli that reduces surface tension. When inflammation occurs, surfactant function diminishes, leading to:
    • Increased water = more surface tension.
    • Deactivation of type II alveolar cells.
  • This situation can result in alveolar collapse (atelectasis).
Consequences of Alveolar Collapse
  • Once an alveolus collapses, it becomes difficult or impossible to force air into it, obstructing gas exchange.
  • Severe cases (like ARDS) involve large portions of lung tissue, leading to significant hypoxemia and potential fatality.

The Role of White Blood Cells in Lung Injury

  • White blood cells in the alveoli during infections (like pneumonia or ARDS) can lead to:
    • Scar tissue formation.
    • Fibrin accumulation (a protein similar to collagen) as a part of the immune response.
  • Scar tissue negatively impacts gas exchange, leading to long-term lung damage.
ARDS and COVID-19
  • ARDS is a significant factor in the pandemic, leading to severe lung complications in COVID-19 patients due to:
    • Massive immune response causing inflammation and fluid accumulation.
    • Risk of lung tissue damage from excess fluid and inflammatory cells.
  • Treatment Focus: Find ways to reopen collapsed alveoli, which often involves mechanical ventilation.

Difference Between Pneumonia and ARDS

  • Pneumonia: Slower onset, less severe lung involvement.
  • ARDS: Rapid onset affecting a majority of lung tissue; higher mortality risk associated with severe cases.

Mechanism and Treatment of ARDS

  • Hypoxemia: ARDS can lead to refractory hypoxemia — inability to correct low oxygen levels with supplemental oxygen.
  • Treatment includes:
    • Recruitment of collapsed alveoli through mechanical ventilation using higher pressure.
    • Care must be taken to avoid barotrauma (lung injury due to excessive pressure).

Recruiting Collapsed Alveoli

  • Improved lung function may also involve patient positioning and adjustments in where blood and air flow within the lungs.

Understanding Pleural Dynamics

  • Pleural effusions (excess fluid) can increase pressure, leading to lung collapse.
  • Pneumothorax (air in pleural space) has a similar effect.

Emergency Interventions

  • Chest Tubes: Introduced to manage pleural effusions and pneumothorax, helping re-establish negative pressure and lung inflation.

Summary of Lung Pressure Dynamics

  • Inhalation occurs when lung pressure decreases below atmospheric pressure (normal = 760 mmHg).
  • Exhalation results from relaxation of the diaphragm, increasing lung pressure.
  • The pleural cavity should always maintain lower pressure than lung pressure to prevent collapse.

Important Airway Structures

  • Respiratory Tract: Divided into:
    • Upper: Nose, pharynx, larynx
    • Lower: Trachea, bronchi, lungs
  • Lined with respiratory mucosa that contains cilia and goblet cells for mucus production to trap dust and pathogens.

Pathological Conditions

  • Dysfunctional cilia lead to excess mucus in lungs, contributing to respiratory diseases like cystic fibrosis or chronic obstructive pulmonary disease (COPD).

Autonomic Regulation of Breathing

  • The diaphragm, a skeletal muscle, operates both consciously and autonomously to control breathing, influenced by various receptors monitoring oxygen levels.