Pulmonary Function Tests: Airway Resistance and Compliance

Introduction

Pulmonary function tests (PFTs) are essential in assessing respiratory mechanics. Two critical components—airway resistance and lung compliance—play a significant role in pulmonary health.

Airway Resistance

Definition

Airway resistance (Raw) refers to the opposition to airflow within the respiratory tract. It is influenced by airway diameter, viscosity of inspired air, and flow dynamics.

Factors Affecting Airway Resistance

• Bronchoconstriction due to asthma or allergies
• Inflammation caused by infections like bronchitis
• Mucosal edema or excessive mucus production
• Obstruction from tumors or foreign objects

Compliance

Definition

Compliance (C) is the ability of the lungs and thoracic cavity to expand and recoil during breathing. It is measured as the ratio of lung volume change to pressure change.

Types of Lung Compliance

• Static Compliance: Measured when there is no airflow, assessing lung elasticity.
• Dynamic Compliance: Measured during active breathing, influenced by airway resistance.

Clinical Significance

Reduced compliance is seen in conditions like pulmonary fibrosis, where lung tissue stiffens. Increased compliance occurs in emphysema, where elastic recoil is diminished.

Diagnostic Approaches

PFTs such as spirometry, body plethysmography, and lung volume measurements help evaluate airway resistance and compliance, aiding in the diagnosis of obstructive and restrictive lung diseases.

Conclusion

Understanding airway resistance and lung compliance is crucial for diagnosing respiratory conditions and optimizing patient management strategies.