Identification of neonatal hearing impairment: Distortion product otoacoustic emissions during the perinatal period

Objectives: 1) To describe distortion product otoacoustic emission (DPOAE) levels, noise levels and signal to noise ratios (SNRs) for a wide range of frequencies and two stimulus levels in neonates and infants. 2) To describe the relations between these DPOAE measurements and age, test environment, baby state, and test time. Design: DPOAEs were measured in 2348 well babies without risk indicators, 3 53 well babies with at least one risk indicator, and 4478 graduates of neon atal intensive care units (NICUs). DPOAE and noise levels were measured at f(2) frequencies of 1.0, 1.5, 2.0, 3.0, and 4.0 kHz, and for primary levels (L-1/L-2) of 65/50 dB SPL and 75/75 dB SPL. Measurement-based stopping rul es were used such that a test did not terminate unless the response was at least 3 dB above the mean noise floor + 2 SDs (SNR) for at least four of fi ve test frequencies. The test would terminate, however, if these criteria w ere not met after 360 sec. Baby state, test environment, and other test fac tors were captured at the time of each test. Results: DPOAE levels, noise levels and SNRs were similar for well babies w ithout risk indicators, well babies with risk indicators, and NICU graduate s. There was a tendency for larger responses at f(2) frequencies of 1.5 and 2.0 Hz, compared with 3.0 and 4.0 kHz; however, the noise levels systemati cally decreased as frequency increased, resulting in the most favorable SNR s at 3.0 and 4.0 kHz. Response levels were least and noise levels highest f or an f(2) frequency of 1.0 kHz. In addition, test time to achieve automati c stopping criteria was greatest for 1.0 kHz. With the exception of "active /alert" and "crying" babies, baby state had little influence on DPOAE measu rements. Additionally, test environment had little impact on these measurem ents, at least for the environments in which babies were tested in this stu dy. However, the lowest SNRs were observed. for infants who were tested in functioning isolettes, Finally, there were some subtle age affects on DPOAE levels, with the infants born most prematurely producing the smallest resp onses, regardless of age at the time of test. Conclusions: DPOAE measurements in neonates and infants result in robust re sponses in the vast majority of ears for f(2) frequencies of at least 2.0, 3.0 and 4.0 kHz. SNRs decrease as frequency decreases, making the measureme nts less reliable at 1.0 kHz. When considered along with test time, there m ay be little justification for including an f(2) frequency at 1.0 kHz in ne wborn screening programs. It would appear that DPOAEs result in reliable me asurements when tests are conducted in the environments in which babies typ ically are found. Finally, these data suggest that babies can be tested in those states of arousal that are most commonly encountered in the perinatal period.