Resting lung volume phenotypes in COPD: implications for exertional dyspnoea and exercise tolerance

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Medical Technology

Background:

• Lung volumes and dyspnoea (shortness of breath) vary significantly in patients with Chronic Obstructive Pulmonary Disease (COPD) at a given forced expiratory volume in 1 second.
• The added value of assessing hyperinflation, indicated by high total lung capacity (TLC), alongside inspiratory capacity (IC), in predicting mechanical-ventilatory impairment and exertional dyspnoea in COPD requires further investigation.

Purpose of the Study:

• To determine if hyperinflation (high TLC) provides additional predictive value to simpler inspiratory capacity (IC) measurements for mechanical-ventilatory impairment and exertional dyspnoea in COPD patients.
• To identify distinct lung volume phenotypes in COPD and correlate them with physiological constraints and patient-reported outcomes.

Main Methods:

• 345 patients with mild to very severe COPD underwent incremental cycling tests with dyspnoea (Borg scale) and lung volume measurements.
• Resting lung volumes (TLC, IC) were measured using body plethysmography and compared to Global Lung Initiative standards.
• A novel artificial intelligence (AI) algorithm quantified mechanical-ventilatory constraints and dyspnoea during exercise.

Main Results:

• Four lung volume phenotypes were identified: preserved IC/TLC, preserved IC/high TLC (hyperinflation), low IC/no hyperinflation, and low IC/hyperinflation.
• Patients with low IC and/or hyperinflation exhibited worse air trapping and lower transfer factors.
• Hyperinflated patients showed worse outcomes at a given IC, and patients with low IC showed worse outcomes at a given TLC. Low IC with hyperinflation was associated with the highest risk of severe mechanical constraints and dyspnoea (OR 5.2).

Conclusions:

• Combining inspiratory capacity (IC) and total lung capacity (TLC), expressed as z-scores, allows for the identification of relevant physiological phenotypes in COPD.
• These phenotypes are linked to dynamic lung mechanical abnormalities during exertion, activity-related dyspnoea, and exercise tolerance across the COPD spectrum.
• This combined approach can aid clinicians in better understanding and managing COPD patients' exercise limitations.