Significance of upper airway influence among patients of vocal cord dysfunction for its diagnosis: Role of impulse oscillometry

Lung India. 2009 Jan;26(1):5-8. doi: 10.4103/0970-2113.45197.


Background: To identify the patients of bronchial asthma (suspected or proven), not responding to optimal therapy, for the presence of vocal cord dysfunction (VCD) and to compare the diagnostic ability of flow volume (FV) loop and impulse oscillometry (IOS).

Materials and methods: Fifty one patients of suspected/proven bronchial asthma not responding to optimal therapy were included for the study. Each patient was subjected to both FV loop and IOS studies. Direct visualization of the vocal cords with flexible fiberoptic bronchoscope for the presence of inspiratory vocal cord adduction during quiet respiration, with speech, and while performing provocative maneuvers was carried out. All patients were subjected to simple pulmonary function tests and recording of FV loop. IOS was performed on each patient to look for the site of obstruction and upper airway influence. The observations of both FV loop and IO studies were compared.

Results: Among 51 patients participated, 12 (23.53%) had bronchoscopical evidence of VCD and were labeled as VCD-positive group and rest 39 were designated VCD negative. No statistically significant difference in pulmonary function test (prereversibility) results between the VCD-positive and VCD-negative patients was found. Reversible airway obstruction was observed in 75% of the patients of VCD-positive group and 67.65% of the patients in the VCD-negative group. Only one patient in the VCD-positive and none in VCD-negative group had inspiratory limb flattening of FV loop. Upper airway influence was evident by IOS in 58.3% of patients in the VCD-positive group and in 15.4% of patients in the VCD-negative group. This difference was statistically significant (P< 0.005).

Conclusion: VCD was a common finding in patients with symptoms suggestive of asthma and frequently coexists with asthma. IOS was found to be a useful screening test for VCD and was more sensitive than FV loop.

Keywords: Forced oscillation technique; flow volume loop; impulse oscillometry; pulmonary function tests; vocal cord dysfunction.