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Biomedical subjects

B A Weber

Publications and source records attributed to B A Weber.

At least 19 recordsLinked to original sources
PubMed1998

The arbZ gene from Lactobacillus delbrueckii subsp. lactis confers to Escherichia coli the ability to utilize the beta-glucoside arbutin.

From a genomic library of the industrially used strain Lactobacillus delbrueckii subsp. lactis DSM7290, a gene designated arbZ (869bp; encoding a 33.5kDa protein) was isolated by screening E. coli transformants for the ability to utilize the beta-glucoside arbutin. Out of 9000 transformants nine were able to ferment arbutin, whereas no utilization of the beta-glucosides salicin, esculin or cellobiose could be detected. Overexpression of arbZ using the T7-polymerase-T7-promoter-system resulted in the formation of insoluble, catalytically inactive protein aggregates (inclusion bodies). Accordingly, overexpression was not accompanied by an increase in ArbZ activity. Induction of arbZ controlled by the lac promoter under conditions that reduce protein aggregation resulted in a 12-fold increase in arbutin hydrolyzing activity of intact cells and a 13-fold increase in phospho-beta-glycosidase activity in cell-free extracts of the respective transformants. Nucleotide sequence analysis revealed a second gene upstream of arbZ that was designated arbX (830bp). ArbX (32.6kDa) shared similarity with several glycosyltransferases involved in the biosynthesis of lipopolysaccharides in Gram-negative bacteria. In Lb. delbrueckii subsp. lactis DSM7290 two transcripts, one covering arbX together with arbZ and one covering arbZ alone were detected by Northern blot analysis.

Amino Acid Sequence↗
PubMed1998

Plano and refractive keratectomy. Comparison of the wound healing response.

PURPOSE: To compare the extension of the subepithelial low dry mass layer after plano and refractive keratectomy, in order to know more about the factors that influence the corneal wound healing response. METHODS: Thirty rabbits assigned into two groups were treated on one eye each with plano and refractive keratectomy, respectively. In each group five rabbits were sacrificed after 10 days, 4 weeks and 21 weeks, respectively. The corneal buttons were excised, freeze-sectioned and freeze-dried. On the freeze-dried sections microradiography was performed. In the treated eyes the superficial stroma showed qualitatively underneath the epithelium areas with low dry mass, whose extension was measured by a modified planimetry. RESULTS: The difference between the extension of subepithelial low dry mass areas in the plano and the refractive keratectomy group was small but statistically significant at 4 weeks. Within the refractive group the extension of low dry mass was significantly higher at 4 weeks compared to 21 weeks. CONCLUSION: A flat surface ablation may cause a less pronounced healing response when compared to a steep curve refractive treatment.

Animals↗
PubMed1997

Colocalization of hyaluronan and water in rabbit corneas after photorefractive keratectomy by specific staining for hyaluronan and by quantitative microradiography.

PURPOSE: Endogenous hyaluronan (HA) has previously been shown to be a part of corneal wound healing after photorefractive keratectomy (PRK). HA is known to bind considerable amounts of water. This study aimed to show whether HA colocalized with water in the wound area after PRK. METHODS: Five New Zealand White rabbits were subjected to PRK in one eye each. After 4 weeks, the rabbits were killed and the corneas were freeze-sectioned. The freeze-dried sections were exposed to soft x-rays generated at 3 kV and the microradiographs were evaluated densitometrically. The same sections were then stained for the presence of HA using the HA-binding region of bovine nasal cartilage proteoglycans linked to biotin. RESULTS: The microradiographs showed, in a zone underlying the epithelium, that the water content was increased. In the corresponding zone, the cornea stained positive for HA. CONCLUSION: HA that is reactively formed in the corneal wound after PRK colocalized to the hydrated area of the corresponding location as revealed by quantitative microradiography. The findings suggest that HA causes local shifts in water content in the corneal wound and thereby also local shifts in transparency.

Animals↗
PubMed1995

Use of maximum length sequence analysis in newborn hearing testing.

The use of maximum length sequence analysis (MLSA) with rapid click rates may be of clinical value in newborn hearing screening because a greater number of individual responses can be signal averaged without adding to test time. To examine the potential clinical value of MLSA in newborn screening, auditory brainstem responses (ABRs) from 50 premature newborns were studied. ABRs were acquired with conventional signal averaging at four stimulus intensity levels (50 dB, 40 dB, 30 dB, and 20 dB nHL) using a click rate of 33.3/sec. These responses were directly compared with the ABRs acquired with MLSA using a rate of 227.3/sec. MLSA and conventional signal averaging yielded similar results with no statistically significant differences in the number of responses detected. Across babies, the overall quality of the tracings slightly favored MLSA, particularly when recording conditions were poor. Though the results of this investigation do not support the use of MLSA as the primary technique in newborn screening in the neonatal intensive care unit (NICU), they do support consideration of the use of MLSA as an alternative technique when the responses obtained with conventional signal averaging are poorly defined.

Acoustic Stimulation↗
PubMed1993

Swallowing, speech, and brainstem auditory-evoked potentials in spasmodic torticollis.

To explore the controversial "brainstem theory" of spasmodic torticollis, eight consecutively referred patients were examined. Three independent examinations were conducted on the same day: a videofluoroscopic barium swallowing examination, an instrumental speech examination, and a brainstem auditory-evoked potential (BAEP) analysis. Swallowing was normal in two patients; speech physiology, in five; and BAEPs, in all. Normal BAEPs refute the brainstem theory, while abnormalities of speech and swallowing temper this conclusion. Several alternative explanations are proposed.

Adult↗
PubMed1993

Application of maximum length sequence analysis to auditory brainstem response testing of premature newborns.

The feasibility of utilizing maximum length sequence analysis (MLSA) with newborns was examined on 40 premature infants residing in a neonatal intensive care unit (NICU). Auditory brainstem responses (ABRs) were initially obtained using a conventional stimulus rate of 33.3/sec. Using MLSA, responses were also recorded using much faster stimulus rates (227.3/sec, 454.5/sec, and 909.1/sec). As expected, faster stimulus rates resulted in longer ABR component wave latencies. Less expected was the clarity of the ABRs that were obtained through MLSA. Well-defined responses were obtained from premature infants at all stimulus rates. The findings suggest that MLSA may have clinical applications to newborn hearing screening.

Acoustic Stimulation↗
PubMed1992

Application of an implantable bone conduction hearing device to patients with unilateral sensorineural hearing loss.

This investigation, comprised of five studies, was undertaken to determine if individuals with newly acquired profound unilateral hearing losses would benefit from an implantable bone-conduction hearing device. The bone conductor was implanted on the side of the deaf ear at the time of translabyrinthine acoustic tumor resection. Two areas greatly affected by unilateral hearing loss, speech recognition in noise and sound localization, were examined. No improvement in aided performance could be documented in either area.

Adult↗
PubMed1991

Implantable bone-conduction hearing device: practical considerations.

An implantable bone conduction hearing device can be of significant benefit to carefully selected patients with noncorrectable conductive hearing losses. However, for some patients the device has significant limitations. This paper presents several practical issues that need to be considered before a decision is made regarding implant surgery. It is recommended that, whenever possible, air conduction hearing aids remain the first option considered when a patient's conductive hearing loss cannot be resolved through traditional medical management.

Adult↗
PubMed1988

Comparative studies of speech processing strategies for cochlear implants.

A wide variety of speech processing strategies for multichannel auditory prostheses were compared in studies of two patients implanted with the UCSF electrode array. Each strategy was evaluated using tests of vowel and consonant confusions, with and without lipreading. Included among the strategies were the compressed analog processor of the present UCSF/Storz prosthesis and a group of interleaved pulses processors in which the amplitudes of nonsimultaneous pulses code the spectral variations of speech. For these patients, each with indications of poor nerve survival, test scores were significantly higher with the interleaved pulses processors. We believe this superior performance was a result of 1. the substantial release from channel interactions provided by nonsimultaneous stimuli and 2. a fast enough rotation among the channels to support adequate temporal and spectral resolution of perceived speech sounds.

Cochlear Implants↗
PubMed1981

The averaged evoked potential in the study of infant auditory discrimination.

This study was conducted to determine whether an averaged evoked potential technique using a random-versus-repetitive presentation mode, could be used to study auditory discrimination in infants. We were interested in which stimulus mode, random-novel or repetitive, would result in greater responsiveness in terms of central nervous system evoked potential latencies and amplitudes. Recordings were made of 20 normal full-term infants between 14 and 18 weeks of age. Two different stimuli were used to create the random and repetitive modes: a burst of 125-Hz square waves (a buzz) and a burst of white noise. Two interstimulus intervals were also used, fast (1,000 msec) and slow (1,700 msec), to determine which rate is most effective. Ten of the infants were tested at the slow rate and 10 at the fast rate. Results for the N2 component of the averaged evoked potential (AEP) showed a main effect of presentation mode with a shorter latency for random versus repetitive. The shortest onset latency was for the random stimulus at the fast rate. The mean amplitude of N2 for all repetitive presentations at the slow rate was significantly larger.

Audiometry↗
PubMed1979

Auditory brain-stem response audiometry in children.

Auditory Brain-stem Response (ABR) Audiometry, also called Brain-stem Evoked Response Audiometry, is an effective procedure for assessing the hearing of children who cannot or will not perform satisfactorily on behavioral audiometric tests. Although ABR audiometry has limitations, it does permit an estimate of hearing status in nearly all children regardless of their age or developmental level.

Aphasia↗