Ventilatory Inefficiency and Exertional Dyspnea in Early Chronic Obstructive Pulmonary Disease

Exertional dyspnea is present across the spectrum of chronic obstructive pulmonary disease (COPD) severity. However, without realizing it themselves, patients may decrease daily physical activity to avoid distressing respiratory sensations. Dyspnea also may be associated with deconditioning. Cardiopulmonary exercise testing can uncover exertional dyspnea and its physiological determinants in patients with preserved or only mildly-reduced FEV1. Dyspnea in mild COPD can largely be explained by increased "wasted" ventilation in the physiological dead space which heightens the drive to breathe and worsens the inspiratory mechanical constraints. During incremental exercise testing, this is readily identified as an excessive ventilation-tometabolic demand, that is a high ventilation (V̇E) to carbon dioxide output (V̇CO2) relationship. Linking increases in V̇E/V̇CO2 to exertional dyspnea may provide objective evidence that patient's poor exercise tolerance is not just a consequence of deconditioning. This information should prompt a proactive therapeutic approach to increase the available ventilatory reserve, by, for example, giving inhaled bronchodilators. Considering that the structural determinants of ventilatory inefficiency (early emphysema, ventilation-perfusion mismatching, and microvascular disease) may progress despite only modest changes in FEV1, serial V̇E/V̇CO2 measurements might also prove valuable to track disease progression in these symptomatic patients.