Search PubMed⌕ Search

Biomedical subjects

H Scherer

Publications and source records attributed to H Scherer.

At least 73 records · Page 4Linked to original sources
PubMed1996

[Thermal stress on the inner ear in laser stapedotomy].

Apart from ablation properties at the stapes footplate, the degree of thermal stress of the inner ear is important when considering the suitability of pulsed lasers for stapedotomy. The aim of the present study was to compare the heating of cochlear structures with presently available pulsed laser systems during stapedotomy under reproducible conditions. Temperature increases and heat-exchange processes were examined in a physiologic model of the cochlea using various laser parameters effective for footplate perforations. With all systems, increases in energy density, number of pulses and resultant total energy led to higher temperatures. In the effective energy density range, the highest temperature increases achieved with the requisite number of pulses at a distance of 2 mm behind the footplate perforation were 30 degrees and 26 degrees C with the pulsed CO2 and Ho:YAG lasers, respectively. The lowest temperature recorded was 5.5 degrees C with the Er:YAG and <5 degrees C with the Er:YSGG laser. The excimer laser investigated at only one energy density showed maximum temperatures of 10 degrees C. With regard to possible inner ear damage from thermal stress during laser stapedotomy, the Er:YSGG laser can be used safely over a relatively broad energy density range. The Er:YAG laser investigated also appears suitable for stapedotomy when considering thermal effects. In contrast, application of the pulsed CO2 laser at parameters effective for stapedotomy leads to high temperatures and wide scattering to compromise its use. The Ho:YAG laser also appears to be unsuitable because of the higher energy density and pulse rate required for sufficient perforation and the resultant higher temperature increases in the perilymph. Although footplate perforations can be achieved with only slight temperature increases in the fluid of the cochlea model, the excimer laser does not seem to be appropriate for stapedotomy because of the long period of heat exposure required and the lower ablation rates at the stapes.

Body Temperature↗
PubMed1995

Experimental studies on the suitability of the erbium laser for stapedotomy in an animal model.

Animal experiments in mature guinea pigs were devised to determine whether and to what extent inner ear damage can be caused by in vivo use of the erbium laser for stapedotomy. The present study examined the laser effect in connection with perforation of the basal convolution of the cochlea and subsequent application in the opened cochlea. Acoustic evoked potentials as compound action potentials (CAP) were recorded for changes in inner ear function. Findings demonstrated that five applications of the erbium:YSGG (yttrium-scandium-gallium-garnet) laser (energy, 85 mJ/pulse; energy density, 36 J/cm2) were needed to create a footplate perforation of 500-600 microns and did not lead to CAP alteration in any animal (n = 20). An increase of the repetition rate from 1 to 5 Hz likewise caused no CAP alteration (n = 17). Application of high total energies in the open cochlea (n = 5) to determine the safety of the laser system for stapedotomy revealed that a 10-fold increase in the total energy required for adequate perforation led to irreversible CAP alterations and no CAP could be recorded at a 15-fold increase in total energy. In contrast, a 5-fold maximum increase in total energy caused no CAP alterations. These results demonstrate the safety of the Er:YSGG laser comparable to that of the CO2 laser for stapedotomy, supporting its utility as an alternative method for surgery.

Acoustic Stimulation↗
PubMed1995

[Animal experiment studies on CO2 laser stapedotomy].

Experiments were performed in guinea pigs to clarify which, if any, of the CO2 lasers used can damage the inner ear on application of the laser parameters required for stapedotomy. A further aim was to determine their application safety. The basal convolution of the guinea-pig cochlea was chosen as the application site, since its thickness is similar to that of the human stapes base. We examined the laser effect in connection with perforation of the basal convolution and subsequent application in the open cochlea. Acoustic evoked potentials (compound action potentials [CAP]) yielded information on inner-ear function. Animals without laser treatment were used as controls. Perforation of the basal convolution and laser applications in the open cochlea with the same parameters did not lead to a measurable CAP alteration with the CO2 cw laser (power: 8 W, pulse duration: 50 ms, power density: 3200 W/cm2). An increase of the laser power to 15 W (power density: 6000 W/cm2) and of the pulse duration to 200 and 500 ms (energy: 3 J and 7.5 J) caused partly irreversible CAP alterations; finally, no potential could be recorded any more at a maximal laser power and pulse duration (15 W and 500 ms). Examination of high power densities (40,000 and 60,000 W/cm2) through reduction of the laser beam diameter to 180 microns yielded comparable results.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Imaginary gaze effects on eye movements induced by linear acceleration: involvement of vestibular induced smooth pursuit eye movement.

We investigated smooth eye movements elicited i) by linear acceleration in a space-fixed imaginary gaze condition (smooth component of eye movement induced by linear motion: LSEM) and ii) during acoustic pursuit of a moving sound source (smooth component of eye movement induced by acoustic pursuit of a sound source: SSPEM). The two conditions were examined using the same test subjects. LSEM and SSPEM performance was found to be positively correlated across the subject population. From the comparison of LSEM and SSPEM we propose the following hypothesis: LSEM consists not only of a pure translational vestibular-ocular reflex (tVOR) component but also of a component based on the perception of otolithic information. Accordingly, this second component is instrumental in the pursuit of an imaginary visual target during linear self-motion.

Acceleration↗
PubMed1995

[Revision of the stapes foot plate with various laser systems. 1: Continuous laser irradiation].

During stapedotomy, the small dimensions and highly sensitive anatomic structures present require the highest degree of precision and safety. The risk of damage to middle and inner ear structures through manipulation with conventional instruments can be reduced by non-contact perforation of the footplate with the laser beam. The present study was devised to clarify which of the presently available laser systems was best suited for use in stapes surgery and thus represent a significant alternative to conventional stapedotomy. Isolated human stapes and bovine compact-bone platelets were used to investigate the connections between the parameters of various laser systems and their effects on bone tissue. The aim was to optimize the laser parameters required to achieve a perforation of 500 microns to 600 microns in diameter. In addition, the thermal effects of laser irradiation were assessed. Three different systems were employed: the argon and CO2 lasers in continuous wave (cw) modes and the CO2 laser in superpulse mode. The lasers investigated offered the advantage of achieving an adequately large perforation with one or a few juxtaposed applications but caused in part extensive thermal side effects at the stapes footplate. To reduce thermal effects, footplate perforation was best performed by several juxtaposed single shots at low power, short pulse duration and small beam diameter. The suitability of the argon laser for stapedotomy was rendered doubtful in view of the lower absorption coefficient of the stapes for the argon laser beam and the considerable influence exerted by the degree of pigmentation of the irradiated tissue sites with a resultant poor reproducibility of the perforation diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

[Modifying the stapes footplate with various laser systems. II. The pulsed laser].

The object of the present study was to examine the tissue ablation capacity of various pulsed lasers at the stapes footplate. Isolated human stapes and bovine compact-bone platelets (thickness 90 microns) were used to determine effective laser parameters for achieving a perforation measuring 500 microns to 600 microns in diameter. Apart from achieving the perforation diameters, particular attention was given to the form and quality of the perforations, reproducibility of the perforation effect and the thermally altered border zones occurring at the footplate. Four pulsed laser systems were used: excimer, Ho:YAG, Er:YSGG and CO2 lasers. An adequately large perforation generally could only be achieved by several repeated shots at the same application site, since only a small amount of tissue was ablated per application. The mechanism of the photoablation caused the extent of the thermal side effects to be markedly lower than with the continuous wave (cw) and superpulse systems. For this reason and because of their highly reproducible perforation effect, they were basically better suited for stapedotomy than the cw systems. It was possible, however, that as a result of the longer application time and the need to repeatedly irradiate the same application site, the higher pulse counts could prove to be disadvantageous in clinical practice. Among the pulsed laser systems, the Er:YSGG laser had the highest ablation rate at the stapes and was thus the most effective laser for interventions at the footplate. Although somewhat less effective than the Er:YSGG laser in our studies, the Ho:YAG and pulsed CO2 lasers also appear to be suitable for stapes surgery. On the other hand, we did not consider the excimer laser (308 nm) to be particularly effective at the footplate because of its low ablation rates.

Animals↗
PubMed1995

[Thermal stress of the inner ear during laser stapedotomy. I: Continuous-wave laser].

As a consequence of perforating the footplate during laser stapedotomy, direct radiation to the inner ear will warm perilymph and adjacent structures. To determine the possible thermal dangers to cochlear structures from different laser parameters, heat transport mechanisms, temperature increases and temperature fields were investigated in a model system approximating caloric and physiologic changes in the inner ear. The temperature-time course of local cochlear warming showed a rapid convection-dependent increase that reached a peak at about the end of the laser impulse. An increase in power density caused an elevation of the temperature in all laser systems used. Maximum temperatures varied widely for CO2 lasers at the same wave-length, but a different beam-time behavior was found at a distance of 2 mm behind the perforation by using low-power densities. Heat values were lowest at a pulse duration of 50 ms in the superpulse (< 5 degrees C) and continuous wave (cw) modes (< 9 degrees C), while the highest value was found in the pulser mode (to 21 degrees C). After argon laser irradiation at high-power densities, temperatures were nearly independent of location (5.5-13 degrees C). When considering risks of possible inner ear damage from thermal stress during laser stapedotomy, application of the CO2 superpulse and cw laser appears to be safe over a large power-density range. Low energies using a small-beam diameter and short pulse durations (50-100 ms) are recommended. In contrast, use of the CO2 laser in a pulser mode may result in inner-ear damage because of the high temperatures produced. Structures located at a greater distance can be endangered by direct irradiation with the argon laser.

Body Temperature Regulation↗
PubMed1994

[Current status of laser surgery in the area of the soft palate and adjoining regions].

The amount of different clinically available lasers is increasing. The ENT surgeon can therefore use the best laser for the planned operation. As the resources of the hospital do not increase with the laser technology, a decision has to be made whether in addition to the universal CO2-laser other types must be acquired and which type is best. This paper presents the characteristics and typical tissue interactions of several lasers for the area of the soft palate. Typical operative examples are shown, e.g. partial resection of the soft palate in patients with bronchopathy and sleep apnoea syndrome, tonsillectomy, tonsillotomy and adenotomy in adults.

Adenoidectomy↗
PubMed1993

Vestibulo-oculomotor testing during the course of a spaceflight mission.

The experimental concept and findings from a recent manned orbital spaceflight are presented. In a single-case, longitudinal study, vestibulo-oculomotor function was examined by caloric testing and active head oscillations. The results from preflight, inflight, and postflight measurements of the human vestibulo-ocular reflex, together with those of ongoing terrestrial studies, should enable separation of the canalicular and otolithic contributions to ocular torsion. This analysis enables an accurate evaluation of the adaptation of the otolithic system to the inflight microgravity and, after landing, to the 1-g force environment. Video-oculography was employed throughout for the comprehensive measurement of eye and head movements. Caloric testing involved air insufflation at 15 degrees C over 90 s, followed by an observation interval of 2 min. During inflight testing this was continued with a 30-s free-floating interval. Active head oscillations were performed at four discrete frequencies (0.12, 0.32, 0.80, 2.0 Hz) and over a frequency sweep between 0.1 and 2.0 Hz. These head oscillations were performed in yaw, pitch, and roll and for three visual conditions (head-fixed target, space-fixed target, no target). The concomitant stimulation of the semicircular canals and otolithic receptors during these oscillations should yield different oculomotor responses under 1-g and 0-g adaptations. Both the short-form caloric test and the active head movement test were performed on 4 of the 5 available mission days. The results of the caloric tests yield a caloric nystagmus intensity (slow-phase velocity) of approximately 60% of that measured before flight and indicate an adaptation in response over the 10-day period after landing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1993

Dynamic analysis of ocular torsion in parabolic flight using video-oculography.

Dynamic ocular torsion was investigated in a group of healthy subjects during the course of parabolic flight by means of our video-based eye movement recording method-video-oculography. This technique enables a non-invasive dynamic measurement of all three dimensions of eye movement in a harsh experimental environment such as parabolic flight. The test subjects were positioned so that the changing resultant gravito-inertial field in the aircraft was aligned with their interaural (y) axis, primarily stimulating the utricular organs. The analysis of the torsional component of eye movement during the change of gravity between 1.8-0 and 0-1.8 g demonstrated a static component--well known as the ocular counter roll--and a dynamic component, which leads to a slight overshoot in the torsional response. These static and dynamic component of ocular torsion correlate with previous neurophysiological findings.

Acceleration↗
PubMed1993

Three-dimensional aspects of caloric nystagmus in humans: I. The influence of increased gravitoinertial force.

The influence of increased gravitoinertial force on the horizontal vertical and torsional components of caloric nystagmus response was examined. Video-oculographic (VOG) recordings were made on a group of 10 human subjects so that all three components of eye movement could be evaluated. The caloric nystagmus response at all tested g-levels included nystagmus components around all three rotation axes. Over the tested range of 1.0 g to 3.0 g, the results demonstrate that nystagmus intensity does not increase linearly with effective gravitoinertial force but appears to saturate at levels of 2.0 g and beyond. It is proposed that the vertical and torsional nystagmus components were elicited both by caloric stimulation to the (anterior) vertical canals and direct thermal mediation to the otolithic sensory cells. Vertical LZ-nystagmus response was also observed during centrifuge runs (previous to caloric irrigation) at all g-levels and in all subjects. The caloric-induced vertical nystagmus response was also clearly recognisable. The observation of a reduction and inversion of nystagmus intensity during g-transitions agrees with earlier findings and is attributable to the stimulation to the canals during centrifuge acceleration, respectively deceleration.

Caloric Tests↗
PubMed1993

Three-dimensional aspects of caloric nystagmus in humans: II. Caloric-induced torsional deviation.

The oculomotor response to caloric stimulation was recorded using video-oculography (VOG), yielding measures of eye rotation about all three orthogonal axes. During an ongoing caloric nystagmus response, a slow torsional deviation of the eye in the direction of the slow phase of the torsional component of nystagmus was observed. The effect appeared to be systematically influenced by the gravitoinertial force employed during a centrifuge study (see Part I, this issue), and was observed in all tested subjects. Furthermore, in subsequent laboratory tests warm and cold irrigations elicited opposite responses, as did stimulation to right and left ears. Testing in the supine and prone positions, however, did not lead to a reversal of direction, as is the case with the horizontal, vertical and torsional nystagmus components as such. The rate of torsional deviation was of the order of 0.05 degrees/s, well below the physiological transduction range of the cupular organs. Testing with a torsional optokinetic stimulus produced only the expected OK nystagmus without any slow deviation. This would argue against a central vestibular integratory, or oculomotor origin for the phenomenon. It is proposed that this caloric-induced, torsional deviation is of peripheral otolithic origin, most likely elicited by way of direct thermal stimulation to the hair cells of the utricular maculae.

Caloric Tests↗
PubMed1993

Evaluation of the torsional VOR in weightlessness.

The experimental concept and findings from a recent manned orbital spaceflight are described. Together with ongoing terrestrial and parabolic studies, the present experiment is intended to further our knowledge of the sensory integrative processing of information from the semicircular canals and the otolithic receptors, and to quantify the presumed otolithic adaptation to altered gravito-inertial force environments in a more reliable manner than to date. The experiment included measurement of the basic vestibulo-oculomotor response during active head rotation about each of the three orthogonal axes. Priority was given to the recording of ocular torsion, as elicited by head oscillation about the roll axis, and thus due to the concomitant stimulation of the semicircular canals and otolith receptors. Videooculography was employed for the measurement of eye movements; head movement was measured by three orthogonally arranged angular rate sensors and a triaxial linear accelerometer device. All signals were recorded synchronously on a video/data recorder. Preliminary results indicate alterations in the torsional VOR under zero-g conditions, suggesting an adaptive modification of the torsional VOR gain over the course of the 6-day orbital flight. In addition, the inflight test findings yielded discrepancies between intended and performed head movement, indicating impairment in sensorimotor coordination under prolonged microgravity conditions.

Aerospace Medicine↗
PubMed1991

A compact equipment package for vestibular experiments during spaceflight.

A compact measurement and stimulus equipment package for vestibular testing is described. The package is designed on a modular concept so that a customised version can be assembled for each experimental situation. Although primarily conceived for space-related research, the equipment has also been introduced successfully into the clinical diagnostic procedure. An essential function of the equipment is the recording and evaluation of eye movements. This is performed by a video-based measurement system which permits evaluation of horizontal, vertical and torsional components of eye movement. Objective testing of the vestibulo-ocular reflex in all three orthogonal planes is therefore possible. Furthermore evaluation of the otolithic function in weightlessness is made feasible by the possibility of measuring dynamic ocular counterrolling. Some applications of the equipment are described.

Equipment Design↗
PubMed1991

31P nuclear magnetic resonance spectroscopy, histology and cytokinetics of a xenografted hypopharynx carcinoma following treatment with cisplatin: comparison in three sublines with increasing resistance.

The changes in the phosphorus metabolism of a xenografted hypopharynx carcinoma (Hyp 1), sensitive to cisplatin (CDDP), were compared to those occurring in two sublines of the tumour, characterised by moderate or high resistance to CDDP (Hyp 1/H and Hyp 1/R) following, i.p. administration of 4, 8 or 12 mg CDDP/kg-1. The investigations were performed by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Parallel to the NMR experiments, the cytokinetic and histological alterations in the tumours were studied under the same experimental conditions. No mentionable differences in the levels of the main phosphorus-containing metabolites could be detected between the three tumour lines before treatment. Following application of CDDP, the alterations in the NMR spectra were clearly related to the degree of tumour response. The most sensitive and earliest marker of tumour regression was a decrease in the phosphomonoester/phosphodiester ratio, parallelled by a gradual increase in the phosphocreatine/inorganic phosphorus quotient. In the resistant tumour lines Hyp 1/H and Hyp 1/R non-responding tumours showed alterations in the 31P NMR spectrum which were similar to those observed during uninfluenced tumour growth. Marked changes in the 31P NMR spectrum were always associated with severe cytotoxic lesions following therapy. The results suggest that the changes detected by 31P NMR spectroscopy following chemotherapy with CDDP are response-specific.

Animals↗