Longitudinal measurements of distortion-product and click-evoked otoacoustic emissions of preterm infants: preliminary results.

Click-evoked and distortion-product otoacoustic emission (CEOE and DPOE) tests were performed 3-4 times on a weekly basis for 13 ears of 7 preterm infants. The CEOEs and DPOEs recorded from each individual ear were analyzed by calculating the root-mean-square (RMS) levels within half-octave bands and were also compared to the normal ranges defined by the 10th and 90th percentiles of half-octave RMS levels obtained from a group of normal full-term newborn ears. Longitudinal data showed that, in general, CEOE and DPOE RMS levels increased with increasing postconceptional age (PCA) in at least one half-octave band. Combined data from subjects who had both ears tested were collected over multiple sessions. Those data revealed statistically significant correlation between the otoacoustic emission (OE) levels in the two ears of the same individual. The analysis of the combined DPOE and CEOE data showed statistically significant correlation between the RMS DPOE and CEOE levels in each of the half-octave bands in the 2- to 4-kHz region. Pilot measurements of spontaneous otoacoustic emissions (SOEs) indicated an increase of SOE frequencies with increasing PCA of the subject. These findings support the view that postnatal changes occur in the outer, middle, and inner ear of preterm infants. The RMS OE levels of preterm infants were often above the 90th percentiles of full-term newborns suggesting that the maturation of the auditory periphery of preterm infants may possibly pursue a different time course than that of full-term infants.