Lung function changes following methacholine inhalation in COPD.

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Bronchial hyper-responsiveness in COPD is often linked to reduced airway caliber.
• This study investigates the mechanisms behind FEV1 decline in severe COPD during methacholine challenge.

Purpose of the Study:

• To determine if FEV1 decline in severe COPD is due to increased airway resistance or changes in lung volumes.
• To compare the response to methacholine in severe COPD patients versus asthmatic subjects.

Main Methods:

• Spirometry and oscillatory mechanics were measured in 25 moderate to severe COPD patients and 10 asthmatics.
• Measurements were taken before and after methacholine challenge, at a 20% fall in FEV1 (PC(20)FEV1).

Main Results:

• In COPD patients, methacholine challenge led to significant decreases in FVC, SVC, and IC, with no change in FEV1/FVC ratio or TLC.
• Total respiratory system resistance remained unchanged, but reactance decreased significantly in COPD subjects.
• Asthmatics showed increased obstruction, with a smaller lung volume fall and increased R(5).

Conclusions:

• Methacholine-induced FEV1 fall in moderate to severe COPD is primarily driven by increased residual volume.
• These changes in lung volumes may indicate airway closure and new expiratory flow limitation.
• COPD and asthma exhibit distinct responses to methacholine challenge, highlighting different pathophysiological mechanisms.