Clinical presentation

A 34-year-old woman with atopic asthma since the age of 16 years presented with increasing exertional dyspnoea and wheeze over a period of 12 months. She had no symptomatic benefit from escalation of bronchodilator therapy and her peak expiratory flow (PEF) remained reduced despite multiple courses of oral corticosteroid. Lung function at rest showed mild air flow obstruction with forced expiratory volume in 1 s (FEV₁) of 2.27 l (75% predicted), forced vital capacity (FVC) of 3.13 l (89% predicted) and a FEV₁/FVC ratio of 73%. Both inspiratory and expiratory limbs of the flow-volume loop (FVL) had a flattened appearance. She was also noted to have a right-sided aortic knuckle on chest x-ray.

To determine the mechanisms of exercise limitation, she underwent an incremental cardiopulmonary exercise test on a cycle ergometer with …