This 60-year-old woman was very dyspneic even when at rest; treatment with systemic corticosteroids did not bring about any improvement.
Inspiratory and expiratory flow-volume curves were recorded when she was at rest. She was then asked to exhale forcefully and fully after a normal inspiration. During thissi maneuver a flow-limiting segment develops in intrathoracic airways from the moment a very low peak expiratory flow is produced: forced expiratory flow is the same as that obtained during a normal expiration. During exercise such patients can barely increase oxygen uptake and carbon dioxide delivery, as they (nearly) function at the top of their ventilatory reserves.
FRC = functional residual capacity