Developmental changes of distortion product and transient evoked otoacoustic emissions in different age groups

The developmental changes of distortion product otoacoustic emissions (DPOAEs) and transient evoked otoacoustic emissions (TEOAEs) were evaluated in 275 normal subjects aged from 1 month to 39 years. The DP-grams showed an M-shaped pattern with peaks at 1587 Hz and 5042 Hz for all age groups. In subjects younger than 3 years, low frequency DPOAEs did not rise above the noise floor. The DP levels at high frequency (5042 Hz) did not change much from infancy to young adulthood (12.9-16.5 dB SPL), however, those at low and middle frequency significantly decreased with age. Total echo power (TEP) of TEOAE was greatest in early infancy, decreased rapidly before 6-7 years old, and then decreased gradually (TEP = 16.6 - 1.9 X ln (age)). Wave reproducibility was constant across age. The frequency area peak power (FAPP) to middle and high frequency sounds changed little with age, however, FAPP at low frequency sounds dramatically increased with age. FAPP at 5000 Hz was relatively depressed levels at each age. The TEOAE value was more prominent at middle and low frequencies while DPOAE was predominant at high frequencies. These two measurements may reflect different functions of outer hair cells in the developing cochlea.