Optimized speech understanding with the continuous interleaved sampling speech coding strategy in patients with cochlear implants: effect of variations in stimulation rate and number of channels

The purpose of this study was to investigate the effect of systematic variations in stimulation rate and number of channels on speech understanding in 13 patients with cochlear implants who used the continuous interleaved sampling speech coding strategy. Reducing the stimulation rate from 1,515 to 1,730 pulses per second per channel to 600 pulses per second per channel resulted in decreased overall performance; the understanding of monosyllables and consonants was more affected than the understanding of vowels. Reducing the number of active channels below 7 or 8 channels decreased speech understanding; the identification of vowels and monosyllables was most affected. We conclude that vowel recognition with the continuous interleaved sampling strategy relies on spectral cues more than on temporal cues, increasing with the number of active channels, whereas consonant recognition is more dependent on temporal cues and stimulation rate.

Scala vestibuli insertion in cochlear implantation: a valuable alternative for cases with obstructed scala tympani

Insertion of a sufficient number of electrodes is important for a successful use of cochlear implants. We investigated the results of scala vestibuli insertion for cochlear implantation in cases of obstructed scala tympani. In a series of 200 cochlear implantations, scala vestibuli insertion was successfully performed in 4 cases with obstruction of the scala tympani. Etiologies included a temporal bone fracture, severe otosclerosis and malformations of the cochlea. The maximum insertion depth obtained via the scala vestibuli was 30 mm. Postoperative results were comparable to patients in whom conventional scala tympani insertion was performed. No adverse effects related to the site of insertion were observed. Scala vestibuli insertion offers a valuable alternative in cases of obstructed scala tympani that can be employed for a variety of etiologies.

Induction and repair of DNA double-strand breaks under irradiation and microgravity

The influence of microgravity on induction and repair of double-strand breaks was studied in the yeast mutant rad54-3, which is temperature-conditional for the repair of DNA double-strand breaks. The experiment was performed on the shuttle Atlantis flight STS-84. Cell samples were kept at 0-4 degrees C until they reached orbit, where they were transferred to 22 (permissive temperature for repair) and 37 degrees C (restrictive temperature). They were exposed to graded doses of beta particles from an in-built (63)Ni source during the repair period. After 152 h in microgravity, the radiation exposure was stopped, and the samples were returned to low-temperature conditions, where they remained until final evaluation in the home laboratory. The amount of double-strand breaks remaining was estimated from the differences in survival after plating and incubation at the restrictive temperature. The results show that there is no significant difference for both the induction and the repair of double-strand breaks between microgravity and terrestrial conditions.

Stochastic radial dose distributions and track structure theory

Measured single-event distributions of the specific energy deposited in cylindrical volumes with simulated diameters down to 150 nm for (4)He and (12)C ions with energies of 25 MeV/nucleon and (16)O ions with 21 MeV/nucleon and radial distances up to 12 microm are presented. The mean specific energy per ion <z(r)>, the mean specific energy per target hit z(1)(r), and the relative frequency of target hits nu(r) as a function of radial distance are evaluated and compared with the corresponding quantities of the track structure model of Kiefer and Straaten (Phys. Med. Biol. 31, 1201-1209, 1986). Though there are some discrepancies in the absolute values, the radial dependence of <z(r)>, z(1)(r) and v(r) for (12)C and (16)O ions is reproduced satisfactorily. The model fails to describe the data for (4)He ions. A more detailed comparison of the radial shape of the mean specific energies calculated from the experimental data from the present work and data from the literature reveals a significant projectile charge dependence which is not included in track structure models.

Mutation induction by different types of radiation at the Hprt locus

Mutation induction at the Hprt locus in Chinese hamster cells was studied after exposure to ultraviolet light, X-rays and alpha particles. While mutant frequency as a function of dose or fluence followed a linear-quadratic relationship with UV and X-rays, it showed a linear dependence for alpha particles. If mutant frequency is plotted vs. the logarithm of surviving fraction, a linear relationship is found in all cases although with different slopes. These are about equal with the two types of ionising radiations but about 10 times larger for UV. They can be used as a measure of mutagenic potential and are termed mutagenicity. It is shown that this parameter is correlated with the maximum of mutant yield, i.e., the number of mutants per cell at risk. It is concluded from this analysis that the maximum mutant yield is always found at doses or fluences which lead to 37% survival irrespective of the kind of radiation. If mutation induction is measured in X-irradiated cells after pre-exposure to UV, mutant frequency is higher than expected on the basis of independent action of the two radiations. Deletion spectra were determined by using multiplex polymerase chain reaction. It was found that the background of spontaneous mutants varied considerably and showed frequently repetitive patterns, presumably because of clonal expansion of pre-formed mutants. UV-induced mutants did not contain any deletions, while those with both X-rays and alpha particles the majority displayed partial and total deletions. Based on a total number of 134 X-ray- and 192 alpha-induced mutants, it is concluded that the total fraction of mutant clones without deletions (partial or total) is about 40% for X-rays and only about 20% for alpha-particles.

Radiation risk in manned space flights

This paper addresses some of the pertinent questions relating to the assessment of radiation risk for humans in space; the paper is not intended as a comprehensive review. The radiation field is briefly summarised and doses to be expected are given based on recent on-board measurements. The problems in adapting terrestrial epidemiological data to the space situation are outlined. Apart from the intrinsic uncertainties in deriving risk factors the specific difficulties are mainly concerned with the effects of energetic charged particles for which no human data exist. The necessity for continuing ground-based research is stressed. Also discussed is whether the principles of radiation protection successfully applied on Earth are really suitable for the space situation or whether they should be replaced by a different approach.

Space radiation effects and microgravity

Humans in space are exposed both to space radiation and microgravity. The question whether radiation effects are modified by microgravity is an important aspect in risk estimation. No interaction is expected at the molecular level since the influence of gravity is much smaller than that of thermal motion. Influences might be expected, however, at the cellular and organ level. For example, changes in immune competence could modify the development of radiogenic cancers. There are no data so far in this area. The problem of whether intracellular repair of radiation-induced DNA lesions is changed under microgravity conditions was recently addressed in a number of space experiments. The results are reviewed; they show that repair processes are not modified by microgravity.

Electric-acoustic stimulation of the auditory system. New technology for severe hearing loss

Various devices have been developed to overcome the widespread phenomenon of different degrees of hearing deficits between mild and profound hearing loss. Basically, we differentiate between acoustic stimulation (hearing aids), restricted to cases with a partially functioning cochlear receptor, and electrical stimulation (cochlear implants), stimulating the auditory nerve directly in cases with profound or total hearing loss. For the first time, animal data have been collected that indicate the possibility of nearly interference-free use of both stimulation types simultaneously. In addition, we have gathered the first clinical patient experience, which confirms the encouraging results. Future implications for patients with severe high-frequency hearing loss are discussed.

Eosinophilic cationic protein as a marker of nasal inflammation in patients with cystic fibrosis

OBJECTIVES

Evaluation was made of eosinophilic cationic protein (ECP) in nasal secretion for measuring the degree of nasal inflammation and monitoring response to therapy in cystic fibrosis (CF) patients with chronic rhinosinusitis. Symptoms and findings in regard to ECP levels before and after treatment were described.

STUDY DESIGN

Study was prospective, with 21 CF patients aged 4 to 19 years; 20 healthy volunteers served as controls. Collection of nasal secretion by a sponge was performed, and blood samples were obtained for serum. Cystic fibrosis (CF) patients were classified according to nasal symptoms and findings.

METHODS

ECP was measured by fluoroimmunoassay. Age, sex, nasal symptoms, and endoscopic and histological findings were obtained, and examinations were conducted before and after treatment; recurrences were recorded.

RESULTS

In CF patients with chronic nasal inflammation, increased nasal levels of ECP were detected when compared with asymptomatic CF patients or healthy nonatopic subjects. ECP concentrations were strongly related to the extent of nasal disease; patients with nasal polyps had higher levels than those without. Checked at 1 and 4 months after treatment, ECP levels declined with regression of symptoms, and in patients with exacerbation of nasal disease, ECP levels rose.

CONCLUSIONS

According to our study, there is a relationship between levels of ECP in nasal secretions and the degrees of nasal inflammation. In addition, the measurement of ECP could be useful in monitoring nasal disease in CF patients.

Repair of cellular radiation damage in space under microgravity conditions

The influence of microgravity on the repair of x-ray-induced DNA double-strand breaks was studied in the temperature-conditional repair mutant rad54-3 of diploid yeast Saccharomyces cerevisiae. Cells were exposed on the ground and kept at a low temperature until microgravity conditions were achieved. In orbit, they were incubated at the permissive temperature to allow repair. Before re-entry they were again cooled down and kept at a low temperature until final analysis. The experiment, which was flown on the shuttle Atlantis on flight STS-76 (SMM-03), showed that repair of pre-formed DNA double-strand breaks in yeast is not impaired by microgravity.

Conservation of intracellular Wnt signaling components in dorsal-ventral axis formation in zebrafish

The mechanism of early dorso-ventral axis specification in zebrafish embryos is not well understood. While beta-catenin has been clearly implicated as a determinant of the axis, the factors upstream and downstream of beta-catenin in this system are not defined. Unlike in Xenopus, where a sperm-induced cortical rotation is used to localize beta-catenin on the future dorsal side of the embryo, zebrafish do not have an obviously similar morphogenetic movement. Recently, a GSK-3 (Glycogen Synthase Kinase-3) binding protein (GBP) was identified as a novel member of the Wnt pathway required for maternal dorsal axis formation in Xenopus. GBP stabilizes beta-catenin levels by inhibiting GSK-3 and potentially provides a link between cortical rotation and beta-catenin regulation. Since zebrafish may use a different mechanism for regulating beta-catenin, we asked whether zebrafish also express a maternal GBP. We report the isolation of the zebrafish GBP gene and show that it is maternally expressed and is present as mRNA ubiquitously throughout early embryonic development. Over-expression of zebrafish GBP in frogs and fish leads to hyper-dorsalized phenotypes, similar to the effects resulting from over-expression of beta-catenin, indicating that components upstream of beta-catenin are conserved between amphibians and teleosts. We also examined whether Tcf (T cell factor) functions in zebrafish embryos. As in frogs, ectopic expression of a dominant negative form of XTcf-3 ventralizes zebrafish embryos. In addition, ectopic beta-catenin expression activates the promoter of the Tcf-dependent gene siamois, indicating that the step immediately downstream of beta-catenin is also conserved between fish and frogs.

Deletion-pattern analysis of alpha-particle and X-ray induced mutations at the HPRT locus of V79 Chinese hamster cells

To investigate the mutagenic mechanisms of low-energy alpha particles V79 Chinese hamster cells were irradiated with 241Am-alpha particles (mean LET of 112 keV/micron). Parallel experiments were performed using 300 kV X-rays. Cell inactivation and mutation induction cross sections were measured. At approximately 20%--survival level, DNA deletions were analysed at the HPRT locus by multiplex-PCR-analysis of all nine exons of 47 alpha-irradiated and 36 background mutants. 92 HPRT- mutants isolated after 300 kV-X-irradiation were analysed similarly for comparison, along with 15 corresponding background mutants. The resulting mutant deletion-pattern distributions were corrected for background mutations. alpha Particles induced a larger fraction of deletions than X-rays. Furthermore, non-contiguous partial deletions were present among the alpha-induced mutants, a type not found after X-irradiation.

Results of cochlear implantation in patients with severe to profound hearing loss--implications for patient selection

In patients with some residual hearing and minor benefit from conventional hearing aids, the benefits of cochlear implantation have to be weighed carefully against eventual adverse effects. In this study, pre- and post-operative thresholds as well as functional results after cochlear implantation are reported; 17 of 44 implanted adults had residual hearing pre-operatively (mean threshold(250 to 4000 Hz): 106 dB HL) in the implanted ear. Residual hearing in the implanted ear could not, in general, be preserved post-operatively. Seventeen of 44 implanted children had some amount of residual hearing in the implanted ear pre-operatively (implanted ear: 114 dB HL; contralateral ear: 109.9 dB HL; mean thresholds(250 to 4000 Hz))). Contrary to the results in adults, residual hearing in the implanted ear remained statistically unchanged. Hearing in the contralateral ear increased significantly from 109.9 to 101.9 dB HL post-operatively. This increase was mainly attributed to maturation of the central auditory pathway. In adults with residual hearing, the monosyllable word recognition scores increased significantly from 9 per cent pre-operatively to 42 per cent post-operatively. Children with residual hearing tended to perform better on speech-related test material compared to children without prior auditory experience. Cochlear implantation is indicated in adults and children with residual hearing and minor benefit from conventional amplification. The contralateral ear in children should be considered for additional acoustical stimulation.

A review of dsb induction data for varying quality radiations

PURPOSE

This short review summarizes the data obtained with various techniques for measuring the yields of double strand breaks (dsb) produced by particle radiations of differing linear energy transfer (LET) in order to obtain relative biological effectiveness (RBE) values.

RESULTS AND CONCLUSIONS

Studies aimed at understanding the interactions of different types of radiation with cellular DNA have monitored the yields of DNA dsb versus radiation quality. Several techniques have been used to measure dsb yields in mammalian cells, and these include: neutral sedimentation gradients, filter elution and more recently pulsed field gel electrophoresis techniques (PFGE). Recent developments in PFGE have allowed the measurement of both the yields and the distribution of breaks within the genome, which go part of the way to explaining the RBE values close to 1.0 previously measured using other approaches with various radiation qualities. It is clear that future studies to determine the effectiveness of radiations of differing LET must use techniques that determine both yields and distributions of dsb, and assays need to be developed to allow these measurements at biologically relevant doses.

Optimization of channel number and stimulation rate for the fast continuous interleaved sampling strategy in the COMBI 40+

OBJECTIVE

To investigate the interrelation between number of channels and stimulation rate in the continuous interleaved sampling strategy (CIS).

SUBJECTS AND METHODS

Three of the first recipients of the new COMBI 40+ cochlear implant participated in consonant, vowel, number, and sentence tests. Speech understanding was evaluated for different combinations of number of active channels from two to twelve and stimulation rate per channel between 1,515 and 9,090 pulses per second.

RESULTS

The results indicate that the optimum number of active channels is not necessarily the maximum number of usable channels.

Separation of PP2A core enzyme and holoenzyme with monoclonal antibodies against the regulatory A subunit: abundant expression of both forms in cells

Protein phosphatase 2A (PP2A) holoenzyme is composed of a catalytic subunit, C, and two regulatory subunits, A and B. The A subunit is rod shaped and consists of 15 nonidentical repeats. According to our previous model, the B subunit binds to repeats 1 through 10 and the C subunit binds to repeats 11 through 15 of the A subunit. Another form of PP2A, core enzyme, is composed only of subunits A and C. It is generally believed that core enzyme does not exist in cells but is an artifact of enzyme purification. To study the structure and relative abundance of different forms of PP2A, we generated monoclonal antibodies against the native A subunit. Two antibodies, 5H4 and 1A12, recognized epitopes in repeat 1 near the N terminus and immunoprecipitated free A subunit and core enzyme but not holoenzyme. Another antibody, 6G3, recognized an epitope in repeat 15 at the C terminus and precipitated only the free A subunit. Monoclonal antibodies against a peptide corresponding to the N-terminal 11 amino acids of the A alpha subunit (designated 6F9) precipitated free A subunit, core enzyme, and holoenzyme. 6F9, but not 5H4, recognized holoenzymes containing either B, B', or B" subunits. These results demonstrate that B subunits from three unrelated gene families all bind to repeat 1 of the A subunit, and the results confirm and extend our model of the holoenzyme. By sequential immunoprecipitations with 5H4 or 1A12 followed by 6F9, core enzyme and holoenzyme in cytoplasmic extracts from 10T1/2 cells were completely separated and they exhibited the expected specificities towards phosphorylase a and retinoblastoma peptide as substrates. Quantitative analysis showed that under conditions which minimized proteolysis and dissociation of holoenzyme, core enzyme represented at least one-third of the total PP2A. We conclude that core enzyme is an abundant form in cells rather than an artifact of isolation. The biological implications of this finding are discussed.

Evaluation of performance with the COMBI40 cochlear implant in adults: a multicentric clinical study

The present multicentric clinical study involves 19 centres, 16 of them in German-speaking countries, 1 British, 1 Polish and 1 Hungarian. 60 postlingually deafened adults with a mean age of 47.5 years (20-70) and mean duration of deafness of 5.3 years (0.5-20) have been evaluated with the MED-EL COMBI 40 cochlear implant which implements a high-rate continuous-interleaved-sampling strategy with 8 channels. Safety and effectiveness data have been collected. Speech perception tests include a 16-consonant, an 8-vowel, a sentence and a monosyllabic-word test in all languages and a 2-digit figure test in all languages but English. Test intervals are 1, 3, 6 months and 1 year after first fitting. 41 of the 60 postlingually deafened adult study patients have completed their 6-month evaluation. While their pre-operative monosyllabic-word score was 0%, their mean monosyllabic-word score 6 months after first fitting was 48% (8-90) with a median of 50%. The mean sentence understanding was 84% (24-100) with a median of 90%. The respective values for the 1-year evaluations with 25 patients are a mean of 50% (5-85), with a median of 60% for the monosyllables and a mean of 89% (30-100), with a median of 97%, for the sentences.

HPRT mutations in V79 Chinese hamster cells induced by accelerated Ni, Au and Pb ions

Mutation induction by accelerated heavy ions to 6-TG resistance (HPRT system) in V79 Chinese hamster cells was investigated with Ni (6-630 Me V/u), Au (2.2, 8.7 Me V/u) and Pb ions (11.6-980 Me V/u) corresponding to a LET range between 180 and 12895 ke V/microns. Most experiments could only be performed once due to technical limitations using accelerator beam times. Survival curves were exponential, mutation induction curves linear with fluence. From their slopes inactivation- and mutation-induction cross-sections were derived. If they are plotted versus LET, single, ion-specific curves are obtained. It is shown that other parameters like ion energy and effective charge play an important role. In the case of Au and Pb ions the cross-sections follow a common line, since these ions have nearly the same atomic weight, so that they should have similar spatial ionization patterns in matter at the same energies. Calculated RBEs were higher for mutation induction than for killing for all LETs.

Prescribing practice with cognition enhancers in outpatient care: are there differences regarding type of dementia?--Results of a representative survey in lower Saxony, Germany

Previous studies of cognition enhancers have mainly focused on insufficiently defined groups of cognition disorders, e.g., "cerebral insufficiency". With regard to the various biological changes in senile dementia of Alzheimer's type (SDAT) and in vascular dementia (VD), which together make up the great majority of senile dementias, many authors have encouraged different studies of these types of dementias, especially since both can be diagnosed clinically with satisfying certainty. Since primary care physicians treat the majority of elderly and demented patients, they have their own experience with cognition enhancers. We were therefore interested to know, how far these physicians differ in their treatment of SDAT and VD. We performed a representative survey (response rate 83.2%; 145 family physicians and 14 neuropsychiatrists) in the Goettingen area. A written case vignette described a 70-year-old widow with moderate dementia and vascular risk factors which are easily treated with drugs. Two versions were randomly assigned, in which (version A) either a "typical" VD history or a typical SDAT history (version B) were described. After perusal, the physician was asked whether and which drugs he would choose to treat the cognitive disorders in this patient. Most frequently, piracetam (A/B: 25.6%/30.9%), ginkgo biloba (24.4%/28.4%), and nimodipine (14.1%/25.9%) were considered. Aspirin was cited by 29.5%(A) and 17.3%(B) of the physicians respectively. As far as the type of dementia was concerned, significant differences were found only for co-dergocrine, which was preferred in SDAT. The following inter-group trends were observed: family physicians considered ginkgo biloba more often than nimodipine or co-dergocrine. The results show the apparent importance of cost-and safety aspects, while the type of dementia has hardly any impact. The latter impression corresponds to the results of drug trials demonstrating no different efficacy. In our opinion, aspirin was not sufficiently taken into consideration.