Measurement of lung volumes in patients with obstructive lung disease. A matter of time (constants)

A 57-year-old man with chronic obstructive pulmonary disease complains of increasing shortness of breath on exertion over the preceding 3 months. He experiences dyspnea after walking approximately 100 m, a mild productive cough, and wheezing, and he has recently gained 5 kg (11 pounds) in body weight. Physical examination demonstrates abdominal obesity, mild expiratory wheezing with a few inspiratory crackles at the lung bases, and mild lower extremity edema. He weighs 86.4 kg, and his height is 171 cm. Posterioranterior and lateral chest radiographs are suggestive of hyperinflation. When measured using the nitrogen washout technique, his TLC is also below the fifth percentile, which indicates a mixed obstructive and restrictive pattern. The patient performs normal tidal breathing and is switched to 100% O2 once a stable endexpiratory volume (FRC) has been reached.