[The influence of conductive hearing loss on DPOAE-threshold. The effect of an individually optimized stimulation]. / Der Einfluss einer Schallleitungsstörung auf die DPOAE-Schwelle. Möglichkeiten einer individuell optimierten Auslösung.

BACKGROUND: The DPOAE-threshold, estimated from extrapolated I/O functions, allows an objective assessment of the mechanical sensitivity of the inner ear. In children, the specificity of this diagnostic tool is impaired by conductive hearing loss. METHODS: In this study, we propose an individual optimization of the primary tone level ratio. This procedure allows the detection of a conductive hearing loss that can be accounted for when estimating the DPOAE-threshold. By means of a simulation using DPOAE-data from 22 normally hearing subjects, the effects of this procedure on the estimation of the DPOAE-threshold are examined. RESULTS: An individually optimized DPOAE stimulation distinctly improves the signal-to-noise ratio of the DPOAE which enables an estimation of the DPOAE-threshold for sound conductive losses up to 15 dB. The DPOAE-threshold only worsens in individual cases. CONCLUSIONS: An individually optimized stimulation paradigm may improve the specificity of inner ear diagnostics with the DPOAE-threshold. A clinical evaluation of the method in children, however, is necessary.

Concentrations of insulin-like growth factor (IGF)-I, -II, and IGF binding protein-4, and -5 in human bone cell conditioned medium do not change with age.

We examined the effects of age on the secretion of insulin-like growth factor (IGF)-I, -II, and IGF binding protein-4, and -5 in long-term bone cell cultures from 71 female donors, aged 28-79 years. Our results suggest that under basal conditions, the intrinsic capacity of human bone cells to produce these IGF components is largely preserved with age.

Transforming growth factor beta (TGF-beta) levels in the conditioned media of human bone cells: relationship to donor age, bone volume, and concentration of TGF-beta in human bone matrix in vivo.

Transforming growth factor-beta (TGF-beta) is thought to play an important role in human bone remodeling. In the present study, we examined constitutive differences in TGF-beta levels in primary bone cell cultures from the iliac crest of 112 women, aged 28-79 years. TGF-beta1 was the major TGF-beta isoform in the conditioned media, as determined by neutralizing TGF-beta activity with specific antibodies against TGF-beta1-3 in the mink lung cell bioassay, and by enzyme-linked immunoassay (ELISA). TGF-beta1 levels in the conditioned media did not change with donor age. There was a lack of association between TGF-beta levels in vitro and the concentration of matrix-associated TGF-beta in vivo. TGF-beta1 levels failed to be associated with the local trabecular bone volume in the complete study population (r = +0.15, p = 0.16, n = 89). A significant association between TGF-beta1 levels and bone volume was present in premenopausal women (r = +0.39, p = 0.02, n = 33), but was largely accounted for by the two samples with the highest TGF-beta concentrations. In conclusion, our data suggest that TGF-beta1 is the major TGF-beta isoform produced by human bone cells in vitro, and that the constitutive secretion of TGF-beta by bone cells does not change with age. Whether constitutive differences in TGF-beta secretion may be a determinant of human bone mass remains to be clarified in further studies.

Vibration-induced nystagmus - A sign of unilateral vestibular deficit.

Vibrations of 60 Hz and 100 Hz were applied on the mastoid of healthy subjects, patients with unilateral peripheral vestibular lesions, with central lesions of different localizations, and patients with benign paroxysmal positioning vertigo (BPPV). In patients with unilateral peripheral deficit a horizontal nystagmus with a small torsional component beating generally to the not affected side could be observed. This nystagmus did not show adaptation during 40 s. The occurrence was more frequent using 60-Hz stimulations. This vibration-induced nystagmus did never occur in healthy subjects, seldom in patients with central vertigo, and only exceptionally in patients with BPPV. It is concluded that the finding of a vibration-induced nystagmus reflects a side difference of peripheral vestibular excitability.

Obligatory urinary and fecal nitrogen losses in young women, older men, and young men and the factorial estimation of adult human protein requirements.

Obligatory urinary and fecal nitrogen losses and urinary urea nitrogen and creatinine excretion levels were determined in 11 young women (four of whom used oral contraceptives), eight older men, and five young men. Values for obligatory nitrogen losses in the young women who did not use oral contraceptives were similar to those observed previously in young women and lower than those reported for young men. Our values for older men were lower than previously reported values for obligatory losses observed in young and elderly men, but similar to previously reported values for young women and to values for our women who did not use oral contraceptives. The four oral contraceptive users had significantly higher levels of total urinary and fecal obligatory nitrogen losses than the nonusers in our study. When values from our study and values from other recent studies are considered, variations in obligatory nitrogen losses appear to be larger among individuals within an age-sex group than the observed differences between groups. When the intakes of protein recommended as safe by the Food aculated from obligatory nitrogen losses per se, the recommended levels appear to be only marginally adequate.