Abstract
Forced expiratory volume in 1 second (FEV1) has served as an important diagnostic measurement of chronic obstructive pulmonary
disease (COPD) but has not been found to correlate with patient-centered outcomes
such as exercise tolerance, dyspnea, or health-related quality of life. It has not
helped us understand why some patients with severe FEV1 impairment have better exercise tolerance compared with others with similar FEV1 values. Hyperinflation, or air trapping caused by expiratory flow limitation, causes
operational lung volumes to increase and even approach the total lung capacity (TLC)
during exercise. Some study findings suggest that a dyspnea limit is reached when
the end-inspiratory lung volume encroaches within approximately 500 mL of TLC. The
resulting limitation in daily physical activity establishes a cycle of decline that
includes physical deconditioning (elevated blood lactic acid levels at lower levels
of exercise) and worsening dyspnea. Hyperinflation is reduced by long-acting bronchodilators
that reduce airways resistance. The deflation of the lungs, in turn, results in an
increased inspiratory capacity. For example, the once-daily anticholinergic bronchodilator
tiotropium increases inspiratory capacity, 6-minute walk distance, and cycle exercise
endurance time, and it decreases isotime fatigue or dyspnea. Pulmonary rehabilitation
and oxygen therapy both reduce ventilatory requirements and improve breathing efficiency,
thereby reducing hyperinflation and improving exertional dyspnea. Thus, hyperinflation
is directly associated with patient-centered outcomes such as dyspnea and exercise
limitation. Furthermore, therapeutic interventions—including pharmacotherapy and lung
volume–reduction surgery—that reduce hyperinflation improve these outcomes.
Keywords
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© 2006 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
