Wideband Middle-Ear Measures in Aminoglycoside-Exposed Adults with Cystic Fibrosis

Cystic fibrosis (CF) affects sinus and lung function, yet little is known about middle-ear function in relation to disease severity. Wideband (WB) absorbance measures are a more sensitive and specific metric of middle-ear function than traditional, single-frequency tympanometry. WB tympanometric measures were used to study middle-ear function in normal-hearing persons with CF and varying degrees of exposure to intravenous aminoglycoside (IV-AG) antibiotics as a proxy for disease severity compared with age-matched persons without CF.

Middle-ear function was assessed in normal-hearing adult participants with (N = 57) and without CF (N = 29). Four groups were examined: (1) CF with a history of greater than 40 doses of IV-AGs (CF high IV-AG), (2) CF with fewer than 40 doses of IV-AGs (CF low IV-AG), (3) CF with no previous IV-AG exposures (CF no IV-AG), and (4) Healthy controls without CF or history of IV-AG exposure (non-CF). Clinical tests included pure-tone air (250 to 8000 Hz) and bone conduction audiometry (250 to 4000 Hz) and 226 Hz tympanometry. Experimental WB downswept tympanometry was also conducted for 250 to 8000 Hz. Hearing thresholds, air-bone gaps, and 226 Hz static acoustic admittance were compared between groups. WB tympanometric absorbance and peak-to-tail differences were compared between groups at half-octave frequencies, as was the tympanometric width (TW) of the low-frequency averaged absorbance tympanogram (from 380 to 2000 Hz) around its tympanometric peak pressure.

Air conduction thresholds were elevated for patients with CF for 250 to 2000 Hz compared with control participants. Broader absorbance TW was found for the CF participants relative to the non-CF control participants ( p < 0.05). Specifically, non-CF controls demonstrated smaller TW compared with the CF no IV-AG ( p = 0.015), CF low IV-AG ( p = 0.011), and CF high IV-AG ( p < 0.001) groups. WB peak-to-tail differences further revealed statistically significant group mean differences between the CF no IV-AG and CF high IV-AG groups from 500 to 1000 Hz ( p < 0.05) and non-CF controls and CF high IV-AG group at 2000 and 5660 Hz ( p < 0.05). There were no statistically significant differences at the p < 0.05 level for mean static acoustic admittance ( Ytm ) obtained from the 226 Hz tympanogram between non-CF controls and the three CF IV-AG exposure groups ( p = 0.076).

Novel findings from this investigation revealed that participants with CF regardless of AG dosing had greater WB TW compared with non-CF controls. Greater WB TW along with poorer (elevated) low-frequency audiometric thresholds and lower absorbance peak-to-tail differences compared with non-CF controls suggest increased middle-ear stiffness in individuals with CF. These differences are subtle as reflected in the higher air conduction thresholds at low frequencies, despite absent air-bone gaps. Additional studies of middle-ear function in CF patients with a history of middle-ear disorders are needed to determine the clinical implications of these findings.