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.