Peripheral airways dysfunction measured by oscillometry differentiates asthma from inducible laryngeal obstruction.

BACKGROUND

Inducible laryngeal obstruction (ILO, also called vocal cord dysfunction) can be difficult to distinguish clinically from asthma. Limited studies have explored the use of respiratory oscillometry to detect changes unique to ILO, but more study is needed to determine if routine oscillometry can differentiate these two clinical entities.

OBJECTIVE

Determine if impedance variables measured on routine oscillometry over tidal breathing vary between individuals with asthma and ILO.

METHODS

Subjects with asthma and ILO were recruited to participate in a single-center, observational study at the University of Rochester Medical Center. Oscillometry measurements were obtained over tidal breathing according to technical standards. Exploratory oscillometry variables were analyzed, as well as standard oscillometry variables including measures of peripheral airways dysfunction.

RESULTS

25 subjects (12 with asthma and 13 with ILO) were recruited and included in the analysis. Measures of peripheral airways dysfunction including frequency dependence of resistance (R5-R20), area under the reactance curve (AX), and reactance at 5 Hz (X5) were significantly more abnormal in asthma subjects compared to ILO subjects (p = 0.039, p = 0.008, and p = 0.0327 respectively). Resistance at 5 Hz (R5) was not statistically different between asthma and ILO (p = 0.301). Exploratory variables, including inspiratory impedance and the standard deviation of impedance, were not significantly different between asthma and ILO.

CONCLUSION

Measures of peripheral airways dysfunction by oscillometry were significantly different in subjects with asthma compared to ILO and more significant in subjects with poor asthma control. There were no exploratory oscillometry variables that were significantly different between ILO and asthma.