Pulmonary function testing may suggest, if not establish, the diagnosis of large airway obstruction. In our patient, spirometry revealed a near-normal FEV1 in the setting of a decreased MVV and elevated Raw, which by itself is an unusual pattern. Our patient also exhibited a flattening of the inspiratory flow-volume loop at a mean flow of 2 L/s (Fig 1), which is highly suggestive of large airway obstruction.11 Prior studies2,12 have reported the diagnostic utility of “truncation” of the inspiratory flow-volume loop. Newman and colleagues2 reported this finding in 23% of their patients with VCD, making it a common finding, but not a sensitive indicator of VCD. Kryger et al11 also highlighted the utility of the mid-VC values of the expiratory/inspiratory flow ratio to differentiate extrathoracic from intrathoracic variable obstruction.11 In healthy patients, this ratio is approximately 0.9, with a ratio of > 2 indicating extrathoracic obstruction and a ratio of < 0.5 indicating intrathoracic obstruction. In our patient, the ratio was 5.9, indicating the extrathoracic origin of the variable large airway obstruction. Newman et al2 reported a statistically significant elevation in this ratio compared with asthmatic control subjects, but the actual number was not reported. Thomas and colleagues7 reported that in seven patients with pseudosteroid-resistant asthma the presence of normal Raw may be a defining feature of VCD. This, however, proved not to be the case for the patient reported herein.