Understanding the Context

What Is Lung Compliance?

Lung compliance (also known as lung elasticity or compliance index) refers to the ability of the lungs to stretch and expand in response to pressure changes. When lungs are healthy, they are highly compliant — meaning they easily fill with air when inhaled. However, decreased lung compliance indicates stiff lung tissue that resists expansion, requiring greater effort to breathe.

Compliance is typically measured in liters per millimeter of mercury (L/mmHg) or cm⁻¹ (in relative terms). Normal lung compliance ranges around 75–100 cm⁻¹, but this varies based on patient age, morphology, and clinical context.

Key Insights

Causes of Decreased Lung Compliance

Decreased lung compliance often stems from structural or physiological changes in pulmonary tissue. Common causes include:

1. Pulmonary Fibrosis

Scarring and thickening of lung tissue lead to stiffness, impeding normal expansion. Conditions like idiopathic pulmonary fibrosis (IPF) or asbestos-related fibrosis result in progressive decreased compliance.

2. Atelectasis

Collapsed lung regions restrict volume expansion, causing localized stiffness and reduced compliance in affected areas.

3. Acute Respiratory Distress Syndrome (ARDS)

A severe condition marked by fluid buildup and inflammation in alveoli leads to stiff, non-compliant lungs.

Final Thoughts

4. Obesity Hypoventilation Syndrome

Excess adipose tissue around the thorax restricts diaphragmatic movement, reducing expansion and decreasing compliance.

5. Pneumonia and Lung Infections

Inflamed lung tissue loses elasticity, contributing to stiff lungs and limited airflow.

6. Neuromuscular Diseases

Conditions like muscular dystrophy or amyotrophic lateral sclerosis (ALS) impair respiratory muscle function, indirectly reducing lung compliance over time.

Key Symptoms of Decreased Lung Compliance

When lung compliance is lowered, breathing becomes more laborious. Symptoms may include:

• Shortness of breath (dyspnea), especially with activity
  
• Rapid, shallow breathing (tachypnea)
  
• Fatigue and reduced endurance
  
• Chest tightness or discomfort
  
• Cyanosis (bluish tint of lips or fingertips) in severe cases
  
• Cough or prolonged expiration