Search PubMed⌕ Search

Biomedical subjects

T Janssen

Publications and source records attributed to T Janssen.

72 records · Page 4Linked to original sources
PubMed1987

Auditory brainstem responses to single-slope stimuli. The influence of steepness and polarity.

Click polarity has little influence on brainstem potentials. We applied an auditory stimulus similar to a step function generated in a closed acoustic system. The influence of stimulus onset steepness (comprising rise time and intensity) on wave V latency and amplitude was investigated. A remarkable latency prolongation was observed for condensation (C) compared with rarefaction (R), if a sharp bend at the foot of the slope was avoided. The C latency lag was nearly the amount of rise time. The effect can be explained by cochlear travel time. Wave V amplitude for R slopes was significantly enhanced. At high intensity and short rise time, it reached twice the values found with C slopes, or with clicks of either polarity. Although the explanations found are not yet satisfactory, a clinical application in cochlear diagnosis is predictable.

Adult↗
PubMed1987

Lateral ligament injury of the knee.

Injury to the lateral ligament complex is an injury of greater magnitude than that seen with anterior cruciate or medial collateral ligament. The prognosis is influenced adversely by the associated injuries. Lateral ligament tear is often associated with anterior cruciate ligament tear. Results from this study indicate that if associated injuries permit, patients should have acute repair.

Adolescent↗
PubMed1987

[Spatial representation of basilar membrane movement with 3D computer graphics].

A mathematical model of the cochlea was implemented on a computer. The basilar membrane motion was computed for single, two, and multi-tone stimuli as well as for musical sounds and vowels. The pattern of the travelling waves were presented in three-dimensional color computer graphics. The high performance 3D graphics system performs local hidden surface removal, 3D geometric transformations and supports local lighting models to generate truly realistic shading for complex 3D objects. An addressable 1280 by 1024 pixel matrix assures crisp, precise resolution of the finest detail in the graphic images. The spatial pattern of basilar membrane motion conveys an impression of the image of acoustic stimuli on the basilar membrane. Firstly, the motion pattern of the travelling wave to a single tone is presented. The superposition of several tones (two-tone, multi-tone) causes a superposition of the travelling waves along the basilar membrane whereby the place principle in the cochlear partition becomes more clearly recognizable. Sounds (flute and violin) and vowels (German "u" and "i") evoke a complex motion pattern on the basilar membrane. The realization of the chronological order of movements on the basilar membrane can be made by computer animation. This enables the analysis of the space-time patterns of complex acoustic stimuli.

Basilar Membrane↗
PubMed1987

Gouty tenosynovitis and compression neuropathy of the median nerve.

Two cases of gouty tenosynovitis were associated with carpal tunnel syndrome. Both patients had carpal tunnel release with good relief of symptoms. In one patient, gout was not suspected before operation; this patient developed wound dehiscence with tophaceous urate crystal drainage that eventually disappeared. Proper preoperative antigout therapy may have prevented this complication. Carpal tunnel syndrome associated with gout is rare. Preoperative investigations for gout may be indicated in patients with carpal tunnel syndrome.

Carpal Tunnel Syndrome↗
PubMed1985

Brainstem and cochlea potentials evoked by rarefaction and condensation single-slope stimuli. A preliminary report.

Influences of stimulus polarity on Jewett wave V are rather small when using clicks which produce two or more polarity changes within a short time interval. In order to separate pressure changes towards rarefaction (R) and towards condensation (C) we applied steep single-slope stimuli returning very slowly to baseline. Brainstem responses recorded from 8 human subjects differed markedly for R and C onset. Amplitudes were much higher for R than for C onset. The main C response was double-peaked with the first peak appearing about 0.5 ms earlier and the second, higher one, 1 ms later than the predominant R wave. The transition from single-slope to click stimulation was investigated by combining R and C slopes. For large time intervals, independent responses to either slope were observed. Down to an on/off interval of 1 ms, the on-response predominated. For still shorter intervals an equalization of R and C responses and a graduation towards click responses was found. Using the same stimuli, cochlear microphonics (CM) and compound action potentials (CAP) were recorded from 7 guinea pigs. The CM did not replicate the slow off-motion of the single-slope stimulus, but returned back to baseline after 0.6 ms. The C compared with R latency of the CAP (peak N1) was also delayed by 0.6 ms. This delay, and that of human peak V, may be explained by CAP initiation only by one direction of basilar membrane motion.

Acoustic Stimulation↗
PubMed1985

[Latency behavior of early acoustic evoked potentials in inner ear hearing loss].

In 101 patients suffering from sensory hearing loss the latency of the auditory evoked brain stem potentials was investigated. In case of minor and moderate pancochlear deafness latency is found to be within normal range. In severe pancochlear hearing loss above 80 dB latency is significantly delayed. In basocochlear hearing disorders the latency-delay is depending on the extent of the frequency loss and on the degree of pure tone threshold shift. If the patient is suffering from a high frequency hearing loss, normal latency will be found in the higher stimulus levels whereas within low levels latency tends to be delayed depending on the cut-off frequency. A general prolongation of latency across all sound pressure levels will take place in cases with steep forms of high frequency hearing loss. For the purpose of investigating the wave-I-latency we used an earcanal electrode in some patients. It can be shown, that in cochlear hearing disorders the latency of wave V is delayed to the same extent as the latency of wave V. After discussing model studies reference values of wave-V-delay as a function of the degree of high frequency disorders are listed

Audiometry, Pure-Tone↗
PubMed1982

[Use of a body acoustic probe and the conduction of brain stem potentials for the determination of sound conduction during tympanoplasty].

A new procedure of evoking brain stem potentials is introduced. Contrary to evoking brain stem potentials by acoustic stimulation via earphone or loudspeaker, we touch the middle ear apparatus at various locations using a piezoelectric transducer with a screwed-on probe, thus causing physiological movements within the sound conducting structures (Fig. 3). As a reaction to this kind of stimulation--1000 clicks with a duration of 0.1 ms were given--far field brain stem potentials can be recorded. The calibration of this special sound probe--not bigger than a pencil (Fig. 1)--was made by equalizing the mechanically and acoustically evoked guinea-pig brain stem potentials (Fig. 2). The intraoperative control of sound transmission to the inner ear is ascertained by the mechanically evoked potential's latency and amplitude. In order to apply the procedure in tympanoplasty we made a number of recordings after having simulated various kinds of middle ear pathology in the guinea pig. Four cases of various kinds of ear disease (interruption of the ossicular chain - Fig. 4 -, soft tissue bridge between incus and stapes - Fig. 5 -, otosclerosis - Fig. 6 -, Torp prosthesis - Fig. 7 -) are presented. As a result of our intraoperative recordings we can demonstrate that the presented method may be a valuable contribution to the examination of acoustic transmission through the middle ear during tympanoplasty under general anesthesia.

Animals↗
PubMed1981

[Measurements of the acoustic reflex at variable static pressures (author's transl)].

Acoustic reflex measurements are made on thirty normal and three early stage otosclerotic ears at different static pressures in the ear canal and recorded as reflex-tympanogram at 200 Hz and 660 Hz probe-tone frequency. Acoustic reflexes were elicited contralaterally with a pure-tone stimulus at 2,000 Hz. This stimulus was chosen to avoid technical artifacts. An example of a normal acoustic reflex pattern as a function of variable static pressure is presented (Fig. 1). This record was made at 20 dB above the subjects reflex threshold, using 660 Hz probe-tone frequency. The reflex deflection of susceptance is positive up to pressures of plus or minus 50 mm H2O and then becomes negative. The reflex deflection of conductance is negative in the total range. A stiffened middle-ear system shows negative reflex deflection of both admittance components. The reflex-tympanograms (Fig. 2) show the admittance component curves as a function of variable static pressure with and without eliciting the acoustic reflex in case of a normal ear, using probe-tone frequencies of 220 Hz and 660 Hz at 10 dB and at 20 dB above the subjects reflex threshold. The reflex-tympanogram in case of an early stage otosclerotic ear shows negative reflex deflection of susceptance within the total pressure range indicating pathological stiffness (Fig. 3). The reflex related change of the dynamic properties was stimulated in a mathematical model of the middle-ear (Fig. 4). The measurements could be explained in a mathematical approach.

Audiometry↗
PubMed1981

[A practical application of brainstem evoked response audiometry (author's transl)].

After a brief review of Brainstem Evoked Response Audiometry (BERA) for clinical diagnosis of middle and inner ear hearing losses (Fig. 2, 3) and retrocochlear damages a new practical application is presented: Brainstem Evoked Response Audiometry in Tympanoplasty. Recordings of acoustically evoked brainstem potentials have been made in middle ear surgery in order to get direct objective information about the mobility of the stapes (Fig. 4) and the sound conducting mechanism of the middle ear after tympanoplasty (Fig. 5). Because of the damping factor of the middle ear after tympanoplastic reconstruction quantitative evaluation of sound transmission to the internal ear. Via brainstem potentials evoked by loudspeakers or probe tubes is difficult. Therefore, a special mechanical vibrating system for direct stimulation of the middle ear apparatus at various locations will have to be developed.

Audiometry↗
PubMedDate not supplied

Pharmacokinetics, acetylation-deacetylation, renal clearance, and protein binding of sulphamerazine, N4-acetylsulphamerazine, and N4-trideuteroacetylsulphamerazine in 'fast' and 'slow' acetylators.

Sulphamerazine shows a clear acetylator phenotype. The half-life of elimination of sulphamerazine is 12 h in 'fast' and 24 h in 'slow' acetylators. N4-Acetylsulphamerazine is eliminated biphasically, characterized by half-lives of 5 and 12 h in 'fast' and 5 and 24 h in 'slow' acetylators. Protein binding of sulphamerazine (86 per cent) and N4-acetylsulphamerazine (92 per cent) is independent of acetylator phenotype or the origin of the compound, whether it is present in the body as parent compound or metabolite. The renal clearance of sulphamerazine (20 ml min-1) and N4-acetylsulphamerazine (300-500) ml min-1) is independent of the acetylator type and the origin of the compound. The existence of an acetylation-deacetylation equilibrium in the metabolism of sulphamerazine has been demonstrated with the test drug N4-trideuteroacetylsulphamerazine, which inhibits the renal excretion and clearance of N4-acetylsulphamerazine.

Acetylation↗
PubMedDate not supplied

Confirmation of G. von Békésy's theory of paradoxical wave propagation along the cochlear partition by means of bone-conducted auditory brainstem responses.

In order to investigate the propagation time of the traveling wave in the cochlea after bone-conduction stimulation of the inner ear, bone-conducted auditory brainstem responses (ABRs) were recorded in 6 normally hearing subjects after masking the basal cochlear region using high-pass filtered noise. As in air-conducted ABRs, Jewett V wave latency is delayed corresponding to the propagation time of the traveling wave front traversing the desynchronized hair cell region. These results support the theory of paradoxical wave propagation proposed by von Békésy in 1952, who postulated that wave motion always starts from the stiffest part of the basilar membrane, independent of the location of the vibrating force. In addition, we also found a latency delay of the Jewett V wave of bone-conducted ABRs in 8 patients with high-frequency hearing loss which corresponded to the severity of their hearing impairment.

Adolescent↗
PubMedDate not supplied

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.

Adult↗
PubMedDate not supplied

[Volvulus of the gallbladder. Apropos of 2 new cases].

Acute torsion or volvulus of the gallbladder is a rare entity, which is seldom diagnosed before operation. Cholecystectomy, which must be performed without delay, is generally easy. Detorsion of the involved organ before cholecystectomy is recommended. The process occurs primarily in the aged. An increased incidence is noted in keeping with more enhanced longevity. Two new cases are reported. The literature is reviewed.

Acute Disease↗
PubMedDate not supplied

[Prostate-specific antigen: the most useful marker for prostate cancer].

Fifteen years after its discovery, Prostate Specific Antigen (PSA) remains the most useful marker for prostate cancer. We summarise the biomolecular characteristics of PSA and the available assays for its measurement. We define its role in the diagnosis of prostate cancer, and discuss its value in the monitoring of patients under therapy.

Biomarkers, Tumor↗
PubMedDate not supplied

[Laparoscopy: new technique in urology].

Laparoscopic surgery in urology is in a testing and development phase. The technique is currently used by some urologists to evaluate non-palpable testes and to perform varicocelectomy or pelvic lymphadenectomy. Other standard open surgical procedures are experimentally being performed with the laparoscope. Owing to technological advances laparoscopic surgery might become a part of routine urological care. We review the current impact of laparoscopy on urology, we emphasise the advantages but also the risks of this new approach, and discuss the benefit of these technical feats.

Adrenal Glands↗