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Biomedical subjects

T Janssen

Publications and source records attributed to T Janssen.

At least 19 recordsLinked to original sources
PubMed1991

Effect of propelling surface size on the mechanics and energetics of front crawl swimming.

In swimming the propulsive force is generated by giving a velocity change to masses of water. In this process energy is transferred from the swimmer to the water, which cannot be used to propel the swimmer. Theoretical considerations indicated that an increase of the propelling surface size should lead to a reduced loss of energy to the water. Thus, in this study, the effect of artificially enlarging the propelling surface of the hand was examined. The effect was examined in terms of the propelling efficiency during front crawl swimming using the arms alone. The legs were floated with a small buoy as previously described (Toussaint et al., J. appl. Physiol. 65, 2506-2512, 1988a). In ten competitive swimmers (six male, four female) the rate of energy expenditure (power input, Pi), power output (Po), work per stroke cycle (As), distance per stroke cycle (d), work per unit distance (Ad), and propelling efficiency (ep) were determined at various swimming speeds once with and once swimming without paddles. At the same average velocity the effect of swimming with paddles was to reduce Pi, Po, and Ad by 6, 7.6, and 7.5% respectively, but to increase ep and As by 7.8 and 7%. The increase in distance per stroke cycle and the decrease in stroke cycle frequency matched the predicted values based on the theoretical considerations in which the actual increase in propelling surface size was taken into account.

Arm↗
PubMed1991

Infrarenal aortic occlusion in the rabbit to assess the effect of flunarizine in the prevention of ischemic spinal cord injury.

Infrarenal aortic occlusion in rabbits to produce paraplegia is possible in large series and can be achieved without any side-effects of anesthetic drugs. This model was tested for its suitability to investigate the use of calcium-channel blockers, which potentially reduce or prevent ischemic spinal cord damage. In a pilot study 26 rabbits were treated with 0.1 mg/kg Flunarizine i.v. prior to occlusion and 38 animals served as control. Groups were compared where the aorta was occluded for 10, 15, 20, 25 or 30 min. No reduction of paraplegia in the Flunarizine groups was observed, apart from in the 15-min occlusion subset: here the number of unaffected animals was significantly greater (p less than 0.05). At histopathological examination the number of ischemic spinal cord segments was reduced (p less than 0.03). It is concluded that Flunarizine could not reduce the cellular damage of the spinal-cord due to complete and global ischemia after an aortic occlusion interval exceeding 15 min. The narrow interval between potential recovery (15 min) and definite paraplegia (20 min) makes this rabbit paraplegia model less appropriate for testing of calcium-channel blockers which are presumed to have a moderate effect on the reduction of spinal cord ischemia.

Animals↗
PubMed1991

[Is the duplicity theory of the hair cells still valid today?].

The "Duplizitätstheorie" of Meyer zum Gottesberge (1948) states that signal processing takes place at low sound intensities on the nerve fibers of the outer hair cells, whereas at high sound intensities on the nerve fibers of the inner hair cells. The discovery of oto-acoustic emissions by Kemp (1978) makes a modification of the "Duplizitätstheorie" necessary. The outer hair cells are supposed to be motor-drives final control elements to enhance the sensitivity of inner hair cells. Thus outer hair cells do not serve for the direct transmission of information in the sense of neural coding. Signal processing takes place at all intensities exclusively on the nerve fibers of the inner hair cells.

Acoustic Stimulation↗
PubMed1989

[Correlation of the latency shift and brain stem potentials in basocochlear hearing loss and the time course of the click stimulus-induced evoked wave in the cochlea].

Frequency-specific information on high tone loss in the inner ear can, and if so only indirectly, be obtained from changes in latency of the click-evoked brain stem potential (ABR). The relationship between latency increases of the Jewett-wave-V in basocochlear hearing loss and the time course of the travelling wave on the basilar membrane will be presented. The latency increases of basocochlear hearing loss at 2 kHz, 1 kHz and 500 Hz correspond to both the computer-simulated time course of the travelling wave and to those of the derived responses. From a pathophysiological standpoint, receptor cells in basocochlear hearing loss are not functional, beginning at the oval window, so that, dependent on the degree of inactivity, a delay corresponding to that of the time course of the travelling wave passes until active hair cells are reached and action potentials released that produce, when summed up a potential of delayed latency.

Acoustic Stimulation↗
PubMed1989

[Hypospadias: surgical aspects and personal experience].

In the last eight year period, a series of 102 hypospadias reconstruction performed in our institution were reviewed. 50% presented with marked degree of chordee. Four types of repair where used: MAGPI (n degree 18), Mathieu (n degree 41), Duckett (n degree 28), two stage repair (Duplay) (n degree 12), other procedures (n degree 3). Overall complication rate was 18% and was related to major procedure and difficult technical situations. It never compromised the final outcome of the procedure. The relatively high complication rate mentioned in the literature and in our series emphasizes that hypospadias surgery has to be done by well trained surgeons in this field.

Clinical Competence↗
PubMed1988

Click ABR intensity-latency characteristics in diagnosing conductive and cochlear hearing losses.

A schematic description of the correlation between various pathologies of hearing impairments and the behavior of auditory brainstem responses (ABR) is presented. Conductive pathology and high-frequency cochlear hearing losses prolong wave component latency due to energy loss and hair cell dysfunction. In cases of flat cochlear hearing loss latency is not affected. Prolonged interwave latencies between wave I and wave V indicate eight nerve and brainstem disorders. An algorithm was developed in the form of a flow chart for locating various malfunctions. Fields of wave V intensity-latency functions were designed for the faster detection and more precise evaluation of conductive and cochlear hearing losses.

Algorithms↗
PubMed1988

[Response latency characteristics for ENT medical assessment of auditory brain stem evoked response].

A schematic description of the correlation between the various types of hearing disorders and the behaviour of auditory brain stem responses (ABR) is presented. Conductive pathology and high-frequency cochlear hearing loss prolong wave component latency due to energy loss and hair cell dysfunction. Latency is not affected in flat cochlear hearing loss. Prolonged interwave latencies between wave I and wave V indicate eighth nerve and brain stem disorders. An algorithm in the form of a flow chart was developed for location of the malfunction. Families of characteristics of wave V intensity-latency functions were designed for faster detection and more precise evaluation of conductive and cochlear hearing losses.

Audiometry, Evoked Response↗
PubMed1988

[The significance of the family as primary caregiver for the aged in need of assistance].

This study focuses on the experiences of the primary care-giver of somatically impaired older people and intends to get a better understanding of the social conditions, difficulties and limitations of family care. Data come from qualitative in depth interviews with 52 primary care-givers: 24 spouses, 21 children (mostly daughters) and seven other women. In this article special attention is given to the importance of other people (mostly members of the family) to the primary care-giver. Fifty % of the primary care-givers experienced their situation as not so burdensome, 25% as rather and also 25% as very burdensome. Support turns out to be very important for the primary care-giver but lots of support does not always prevent a situation from becoming very burdensome. Three kinds of stress have been distinguished: care-stress, relation-stress and network-stress. Particularly network-stress turns out to be indicative for very burdensome situations. Pre-eminently one is experiencing this kind of stress if one is also experiencing care- and relation-stress. In spite of much stress and feelings of burden however, people tend to continue with caring. A strong sense of duty plays a mayor part here. Finally, the current political trend to effect a shift to more informal care, is critically evaluated in the light of the results of the research.

Aged↗
PubMed1988

[Effect of cochlear processes in generating Jewett IV and V brain stem potential components].

Polarity of the stimulus influences latency, amplitude and waveform of the human auditory brainstem response (ABR). One clear feature is the splitting of the wave complex JIV and JV in separate peaks following rarefaction stimulation. ABR was recorded using high-pass filtering to mask the basilar membrane partially to establish whether and to what extent basal hair cells contribute to waves IV and V. Wave IV disappeared in response to rarefaction stimuli with masking of the basal region. In contrast, wave V appeared with reduced amplitude and delayed latency in response to condensation stimuli. A model was developed to determine the motion of the basilar membrane and the distribution over time of the action potential on the auditory nerve fibers following rarefaction and condensation stimuli. The rarefaction stimulus produces a bifid and the condensation stimulus only a single-peaked contribution. It is suggested that the splitting of the wave complex IV and V may be traced to mechanical processing in the cochlea.

Auditory Pathways↗
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↗