Does the respiratory system limit exercise in mild chronic obstructive pulmonary disease?

Area of Science:

• Pulmonary Physiology
• Exercise Science
• Respiratory Medicine

Background:

• Investigating exercise limitation in mild chronic obstructive pulmonary disease (COPD) is crucial.
• Abnormal dynamic respiratory mechanics may limit exercise capacity in mild COPD.
• Failure to increase ventilation and tidal volume (Vt) with dead space (DS) loading indicates ventilatory limitation.

Purpose of the Study:

• To compare the effects of dead space (DS) loading during exercise on ventilation, breathing pattern, lung volumes, and dyspnea in mild COPD and healthy subjects.
• To determine if ventilatory mechanics limit exercise in individuals with mild COPD.

Main Methods:

• Twenty subjects with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage I COPD and 20 healthy controls underwent incremental cycle exercise tests.
• Tests were performed with and without added dead space (DS) of 0.6 L in a randomized order.
• Measurements included ventilation, breathing pattern, operating lung volumes, and dyspnea intensity.

Main Results:

• Peak oxygen uptake and ventilation were significantly lower in COPD patients compared to healthy controls.
• Added DS reduced peak work rate and did not significantly increase peak ventilation in either group.
• Healthy subjects increased peak Vt and end-inspiratory lung volume with DS, while COPD patients did not, experiencing greater dyspnea.

Conclusions:

• The respiratory system reaches or approaches its physiological limit at lower peak work rates and ventilation in mild COPD compared to healthy individuals.
• Dynamic respiratory mechanics appear to limit exercise in mild COPD.
• Registered clinical trial: NCT 00975403.