Identification of neonatal hearing impairment: hearing status at 8 to 12 months corrected age using a visual reinforcement audiometry protocol.

OBJECTIVES: 1) To describe the hearing status of the at-risk infants in the National Institutes of Health-Identification of Neonatal Hearing Impairment study sample at 8 to 12 mo corrected age (chronologic age adjusted for prematurity). 2) To describe the visual reinforcement audiometry (VRA) protocol that was used to obtain monaural behavioral data for the sample. DESIGN: All neonatal intensive care unit infants and well babies with risk factors (including well babies who failed neonatal tests) were targeted for follow-up behavioral evaluation once they had reached 8 mo corrected age. Three thousand one hundred and thirty-four (64.4%) of the 4868 surviving infants returned for at least one behavioral hearing evaluation, which employed a well-defined VRA protocol. VRA thresholds or minimum response levels (MRLs) were determined for speech and pure tones of 1.0, 2.0, and 4.0 kHz for each ear using insert earphones. RESULTS: More than 95% of the infants were reliably tested with the VRA protocol; 90% provided complete tests (four MRLs for both ears). Ninety-four percent of the at-risk infants were found to have normal hearing sensitivity (MRLs of 20 dB HL) at 1.0, 2.0, and 4.0 kHz in both ears. Of the infants, 2.2% had bilateral hearing impairment, and 3.4% had impairment in one ear only. More than 80% of the impaired ears had losses of mild-to-moderate degree. CONCLUSIONS: This may be the largest study to attempt to follow all at-risk infants with behavioral audiometric testing, regardless of screening outcome, in an effort to validate the results of auditory brain stem response, distortion product otoacoustic emission, and transient evoked otoacoustic emission testing in the newborn period. It is one of only a few studies to report hearing status of infants at 1 yr of age, using VRA on a clinical population. Successful testing of more than 95% of the infants who returned for the VRA follow-up documents the feasibility of obtaining monaural behavioral data in this population.

From laboratory to clinic: a large scale study of distortion product otoacoustic emissions in ears with normal hearing and ears with hearing loss.

OBJECTIVES: 1) To describe distortion product otoacoustic emission (DPOAE) measurements in large groups of subjects with normal hearing and with hearing loss, and to use these data to provide comprehensive descriptions of DPOAE test performance. 2) To describe the effects of primary frequency and audiometric threshold on the extent to which DPOAE measurements accurately identify auditory status. 3) To develop an approach that describes the probability that any measured response is coming from either a normal or an impaired ear. 4) To develop an approach for representing DPOAE data clinically. 5) To explore the relation between magnitude of hearing loss and DPOAE measurements. DESIGN: DPOAE measurements were made in 1267 ears of 806 subjects, using stimulus conditions that previously had been demonstrated to result in the greatest separation between normal and impaired ears (i.e., primary levels of 65/55 dB SPL for f1/f2; Stover et al., 1996). Subjects were recruited from local clinical populations and through local advertisements. All data were analyzed using clinical decision theory, including relative operating characteristic (ROC) curves and estimates of areas under these curves (Az). In addition, cumulative distributions were constructed of response properties from both normal and hearing-impaired ears. These cumulative distributions were used to select specific probabilities that measured responses were coming from either the normal or impaired distributions, and to develop an approach for describing clinical DPOAE data. RESULTS: For no conditions were the distributions of DPOAE responses from normal and impaired ears completely separated, meaning that optimal criterion values would still result in errors in identification of auditory status. Test performance, defined by Az, was best for mid and high frequencies and poorest for lower frequencies and for the highest frequency tested (8000 Hz). Performance was best when normal hearing was defined as audiometric thresholds between 20 and 30 dB HL, with poorer performance for more stringent or lax audiometric criteria. CONCLUSIONS: Within the limits related to the effects of primary frequency and audiometric criterion, it appears that DPOAE measurements can be used to accurately identify auditory status. An approach is described, using the present data set, that allows one to assign to any measured DPOAE value (DPOAE amplitudes, DPOAE/noise) the probability that the response is coming either from the distribution of normal or impaired responses. In addition, DPOAE/noise systematically decreases as hearing loss increases over the range of hearing losses from 0 to about 40 to 60 dB HL (depending on frequency), thus potentially enabling one to differentiate hearing losses over this range. For hearing losses greater than 50 to 60 dB HL, ears do not produce measurable DPOAEs and thus, no predictive relationship exists.

The apoenzyme of aspartate aminotransferase and alanine aminotransferase in the serum of healthy persons and patients suffering from liver diseases.

In activity determination with addition of pyridoxal 5'-phosphate (P-5-P), aspartate aminotransferase (AST) activity increases by 6.5 U/l and that of alanine aminotransferase (ALT) by 2.5 U/l in the serum of healthy persons. This corresponds to a relative stimulation of initial activity by 37% and 15.2%, respectively. ApoAST activity in patients with chronic liver diseases is not changed as compared with that of healthy persons, the relative stimulation rate, however, is significantly smaller. ApoALT activity and corresponding relative stimulation is significantly greater as compared with healthy persons. In the case of acute viral hepatitis, a decrease of AST and ALT activity is followed by a decrease of apoenzyme activity in the course of disease. Diagnostic evidence of determinations of aminotransferase activities could not be improved by addition of P-5-P.