Alterations in the mechanical properties of the lung during dyspnea in chronic obstructive pulmonary disease.

The mechanical properties of the lungs in seven patients with chronic obstructive pulmonary disease (COPD) were measured before and during dyspnea on exertion, as well as when relief with added oxygen was obtained. Mean pulmonary dynamic compliance was 0.091 liters/cm of H(2)O before dyspnea, 0.057 during dyspnea, and 0.101 liters/cm H(2)O during relief. During dyspnea there was an increase in the total respiratory work (both elastic and nonelastic work) and this fell during relief with oxygen. Nonelastic resistance and respiratory rate were not significantly different during the three periods. In five similar patients a progressive increase in the instantaneous rate of change of transpulmonary pressure (dP/dt) was observed during exercise and this was markedly increased during dyspnea. These changes in dP/dt during exercise could explain the observed fall of pulmonary dynamic compliance.