People with mild chronic obstructive pulmonary disease (COPD) can have significant physiological abnormalities and breathing inefficiency which become more pronounced during the stress of exercise, leading to intolerable breathing discomfort (dyspnea). To better understand the mechanisms of respiratory symptoms and exercise limitation in mild COPD, we will examine detailed lung function tests and other important measurements during rest and exercise in people with mild COPD compared with healthy non-smokers. This will be the first study to uncover the fundamental causes of breathing inefficiency and the related shortness of breath during physical exertion in patients with mild COPD. We hope to demonstrate that one simple measurement during exercise [the relation (ratio) between the total amount of air breathed (ventilation) and the amount of carbon dioxide breathed out] gives meaningful information about the extent of damage to the small airways and blood vessels in mild COPD and the overall gas exchanging function of the lungs, without the need for an arterial blood sample.

This is a case-controlled observational study not involving an intervention. Participants will complete 2 visits approximately 1 week apart, each conducted at the same time of day. Visit 1 will consiste of screening for iligibility, symptom and activity assessments, pulmonary function tests and an incremental cycle cardiopulmonary exercise test (CPET) for familiarization purposes. Visit 2 will include spirometry followed by an incremental cycle CPET with detailed measures of ventilatory, gas exchange, sensory-perceptual and arterial blood gas responses.

Inclusion Criteria:

• Stable symptomatic patients with GOLD grade 1B mild COPD;
• at least 50 years of age;
• a cigarette smoking history ≥20 pack-years;
• a Baseline Dyspnea Index focal score ≤9;
• post-bronchodilator forced expiratory volume in 1 second (FEV1) ≥80 %predicted and an FEV1/forced vital capacity (FVC) ratio <0.7 and < lower limit of normal.

Exclusion Criteria:

• clinically significant comorbidities;
• contraindications to exercise testing;
• history/clinical evidence of asthma;
• body mass index <18.5 or >30 kg/m2;
• use of supplemental oxygen.

Patients fitting GOLD grade 1B criteria for mild COPD