U. Schönfeld

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 μm 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.

Effects of continuous-wave laser systems on stapes footplate

The aim of the present study was to clarify which of the presently available continuous‐wave laser systems are best suited for application in stapes surgery.

Effects of pulsed laser systems on stapes footplate.

The aim of the present study was to investigate the tissue ablation capacity of various pulsed lasers at the stapes footplate.

Thermic effects in the "vestibule" during laser stapedotomy with pulsed laser systems.

Apart from the ablation properties at the stapes footplate, the degree of thermic loading in the inner ear is important in determining the suitability of pulsed lasers for stapedotomy. The aim of the study is to compare the thermic effects in the vestibule with different pulsed laser systems.

Extended High Frequency Audiometry in Pre-school Children

Since adequate and reliable earphones are now available and standards have been established, clinical audiometry can be performed at extended high frequencies (EHFs). In the present study, 47 preschool children (aged 4-7 years) were examined with EHFs (8-16 kHz) using the new Sennheiser HDA 200 earphone. The hearing thresholds correspond to those of other studies; the median thresholds and range increase with increasing frequency. The medians and quartiles were: 10 kHz: 25 (5-35) dB(SPL), 11.2 kHz: 35 (20-40) dB(SPL), 14 kHz 40 (30-50) dB(SPL) and 16 kHz: 50 (40-60) dB(SPL). The hearing thresholds could be more reliably determined in the older children (> 5 years) and were 5 dB better than in the younger ones (< 5 years). Thresholds in the 10-12.5 kHz range correspond to those of adults but are more sensitive by 5-12 dB in the 14-16 kHz range.

Influence of pulsed laser irradiation on the morphology and function of the guinea pig cochlea

Recent experimental and clinical studies have demonstrated that several pulsed laser systems are also suitable for stapedotomy. The aim of the study was to investigate morphological and functional inner ear changes after irradiating the basal turn of the guinea pig cochlea with two pulsed laser systems of different wavelengths. The Er:YSGG (lambda=2.78 mcm) and Ho:YAG (lambda=2.1 mcm) lasers were used applying the laser energies necessary for perforating a human stapes footplate. The cochleas were removed 90 min, 1 day, 2 weeks, or 4 weeks after laser application. Acoustic evoked potentials (compound action potentials) were measured before and after laser application and at the above times immediately before removal of the cochleas. The organ of Corti was examined by scanning electron microscopy. Application of Er:YSGG laser parameters effective for stapedotomy had no adverse effects on Cortis organ in the guinea pig cochlea. On the other hand, effective Ho:YAG laser parameters cause damage to the outer hair cells with fusion of stereocilia and formation of giant cilia leading to partial or total cell loss. The inner hair cells and supporting cells were usually normal. These morphological data show a good correlation with the electrophysiological measurements. Our results clearly demonstrate that, besides achieving efficient bone management, the Er:YSGG laser has high application safety. On the other hand, the Ho:YAG laser is not well tolerated in our animal study. Its use in stapedotomy would be unreliable and dangerous for the inner ear.

New Developments in CO2 Laser Stapedotomy

Summary The idea of applying the CO2 laser as a precise and contact-free instrument in middle-ear surgery and especially in stapes surgery is based on the desire to reduce the complication rate of these interventions by further optimizing the surgical techniques. Today, using high-precision micromanipulators, the laser beam can be focused to a spot diameter of 180 μm. New application modes combined with scanner systems enable an exact adjustment to the demands of stapes surgery, thus permitting the finest microsurgical work. “One shot” stapedotomy can be achieved by microprocessor-controlled movement of the focused laser beam over a defined area (diameter: 0.5 to 0.7 mm) by rotating mirrors. On the basis of experimental data, effective and safe parameters were determined with the CO2 laser and applied in the clinical routine. Compared to conventional techniques the CO2 laser irradiation enables precise and contact-free procedures on middle ear structures. The risk of chain luxation, particularly footplate mobilization (floating footplate) or damage to the adjacent middle and inner ear structures is practically impossible with the limitation of the energy parameters used here.

Der otolith-okuläre Reflexbei linearen Beschleunigungen mit niedrigen Frequenzen

ZusammenfassungHintergrund und Fragestellung. Allen bisher angewendeten Methoden zur Untersuchung des dynamischen otolith-okulären Reflexes (OOR) beim Menschen ist der limitierte untersuchbare Frequenzbereich des Stimulus gemeinsam. Patienten und Methode. Der in der vorliegenden Studie verwendete Drehstuhl mit variablem Radius ermöglicht durch sinusförmige exzentrische Bewegung des Probanden während konstanter Drehung (300°/s) um die vertikale Achse eine einseitige Otolithenreizung und die Erzeugung eines Otolithenstimulus mit extrem niedrigen Frequenzen (0,03– 1,0 Hz). Mit einem 3D-Videookulographiesystem wurde das Verhältnis der Augentorsion zum effektiven Kippwinkel (Gain) und die Phasendifferenz zwischen Stimulus und torsionaler Augenbewegungskomponente ermittelt. Ergebnisse.Über den gemessenen Frequenzbereich zeigte sich mit steigender Frequenz ein Abfall des torsionalen OOR (0,09°/° bei 0,03 Hz auf 0,009°/° bei 1 Hz) und ein Anstieg der Phasenverschiebung zwischen Stimulus und Augentorsion (Tiefpasscharakteristik). Im Vergleich mit der frequenzunabhängigen peripheren neuronalen Aktivität ergibt sich, dass die Tiefpassfilterung für den OOR in den vestibulären Nuklei stattfindet. Schlussfolgerungen. Die torsionale Otolithenantwort konnte bis zu einer Reizstärke bzw. Beschleunigung der Otolithen von 0,03 m/s2 registriert werden und liegt damit unterhalb der subjektiven Wahrnehmungsschwelle.AbstractBackground. During constant velocity rotation about the earths vertical axis, eccentric displacement of the head can be used to generate adequate stimulation of the otolith organs. More recently, studies have been performed with a variable radius rotatory chair, which permits a controlled modulation of the centripetal or radial acceleration, to achieve linear acceleration frequencies much lower than with a conventional linear sled. Methods. In the present study, frequency response and threshold testing was performed using sinusoidal modulation of the chair radius. Three-dimensional eye movements were recorded with binocular video-oculography. Results. The gain (0.09°/° at 0.03 Hz, 0.009°/° at 1 Hz) and phase relationships of the otolith-ocular response (OOR) show a low-pass characteristic over the measured range of 0.03–1.0 Hz. In comparison to the flat response of neurophysiological recordings from the otolith afferent, our findings support the idea that any low-pass filtering of otolith afferents occurs at the level of the vestibular nuclei. Conclusion. The OOR could be detected at acceleration levels of 0.03 m/s2, much lower than the subjective threshold for the perception of 0.08 m/s2

Experimentelle und klinische Erfahrungen mit dem Er:YAG-Laserotoskop

ZusammenfassungHintergrund und Fragestellung. Laserotoskope eignen sich für eine ambulante, schmerzfreie Behandlung der sekretorischen Otitis media (SOM) in Oberflächenanästhesie. Lasermyringotomieperforationen sollten einen Durchmesser von mindestens 2 mm haben, um das Mittelohr für etwa drei Wochen zu belüften. Patienten/Methodik. In dieser Arbeit wurde überprüft, inwieweit ein Prototyp eines Er:YAG-Laserotoskops (Fa. Baasel Lasertechnik, Starnberg) zur Durchführung von Lasermyringotomien an Patienten geeignet ist. In In-vitro-Experimenten mit formalinfixierten humanen Trommelfellen wurden die Parameter für den klinischen Einsatz eines Er:YAG-Otoskops erarbeitet. Mit fokussiertem Laserstrahl (Strahldurchmesser 500 μm) erzielt man ab einer Energie von 70 mJ (Energiedichte 36 J/cm2) mit einem Laserpuls Perforationen mit einem Durchmesser von 50 μm. Mit einer Energie von 100 mJ erhält man Perforationen mit einem Durchmesser von 150 μm. Die Ablationsrate des fokussierten Laserstrahls, d. h. der Schichtdickenabtrag pro Laserpuls, beträgt bei einer Energie von 70 mJ ca. 100 μm. Dies bedeutet, dass formalinfixiertes humanes Trommelfell mit einer normalen Schichtdicke von 100 μm mit einem Laserpuls zu perforieren ist. Ergebnisse. Zehn Patienten mit sekretorischer Otitis media wurden in Oberflächenanästhesie des Trommelfells (8% Tetracainbaselösung in Isopropylalkohol für 15 min) mit fokussiertem Strahl mit einer Pulsenergie von 100 mJ (Energiedichte 52 J/cm2) behandelt. Ein ausreichender Perforationsdurchmesser von ca. 2 mm konnte mit durchschnittlich 15 nebeneinander liegenden Pulsen angelegt werden, wobei das Vorgehen durch austretendes Sekret und Trommelfellblutungen behindert wurde. Zwischen den Laserapplikationen musste häufig unter otomikroskopischer Kontrolle abgesaugt werden. Die Heilungsverläufe wurden in klinischen Nachuntersuchungen kontrolliert. Die Perforationen mit einem Durchmesser von 2 mm heilten innerhalb von 14 Tagen. Bei den verwendeten Parametern wurde keine Innenohrfunktionsstörung beobachtet. Schlussfolgerungen. Eine effektive, schnelle und praktische Durchführung der Lasermyringotomie ist mit dem Er:YAG-Otoskop z. Z. noch nicht möglich.AbstractBackground and objective. Laserotoscopes are suitable for low-pain outpatient surgery of otitis media with effusion (OME) under topical anesthesia. The myringotomy perforations should have a diameter greater than 2 mm to ventilate the middle ear for approximately 3 weeks. Patients/Methods. In this study, the clinical applicability of a prototype of an Er:YAG laserotoscope (Baasel Lasertechnik, Starnberg, Germany) was tested. Formalin-fixed human tympanic membranes yielded the parameters suitable for clinical application of an Er:YAG laserotoscope in patients. With a focussed laser beam (beam diameter 500 μm), one is able to achieve perforations of 50-μm diameter with one single laser pulse applying pulse energies of 70 mJ (energy density 36 J/cm2). The ablation rate, i.e. , the tissue layer that is ablated per laser pulse, is 100 μm using pulse energies of 70 mJ. This means that formalin-fixed human tympanic membrane can be perforated with one single laser pulse. Results. Ten patients with OME (otitis media with effusion) were treated under topical anesthesia of the tympanic membrane (8% tetracainbase in Isopropanol for 15 min) with focussed laser pulses (beam diameter 500 μm) with energies of 100 mJ (energy density 52 J/cm2). A sufficient perforation diameter of 2 mm could be achieved with an average of 15 juxtaposed laser applications. The enlargement of the perforations was made difficult by extruding middle ear secretions and slight bleeding of the tympanic membrane. Between laser applications, the target tissue had to be cleaned by suctioning using the operation microscope. The healing of the tympanic membrane was verified and compared in postoperative clinical follow-ups. With a perforation diameter of 2 mm, the Er:YAG laser myringotomies healed within 14 days. The used parameters did not generate side effects such as inner ear hearing loss. Conclusions. An effective, easy, and practical performance of laser myringotomy is not currently possible with the Er:YAG laserotoscope.

IR Lasers and Application Systems for Myringotomy

Abstract.The study examines an Er:YAG laser (2940 nm) and different application systems of the CO2 laser (10 600 nm) with regard to their suitability for a one-shot laser myringotomy of an adequate perforation size (∼2 mm). The laser–tissue interaction of the Er:YAG laser and the CO2 laser in fresh tympanic membranes of horses (thickness: 80–100 µm) as well as in formalin-fixed human tympanic membranes (thickness: 100 µm) is studied correlating perforation diameters to the applied power/energy density and the effects demonstrated by light and scanning electron microscopy are analysed. Using the Er:YAG laser with a focused laser beam (spot diameter: 400 µm) or with a maximally defocused laser beam (spot diameter: 1600 µm) perforations of an adequte size (2 mm) can only be achieved with multiple laser pulses. Histological studies disclose only minimal thermic side effects in the adjacent tissue in both specimens. If the CO2 laser radiation is transmitted via a silver halide polycrystalline fibre (diameter: 900 µm) a maximal perforation diameter of 1300 µm is achieved with significant thermic side effects such as coagulation. Using an Acuspot™ 710 micromanipulator (focused beam diameter: 180 µm) combined with a SilkTouch™ scanner a maximal perforation diameters of 1700 µm can be achieved in horse tympanic membrane with one laser pulse. A prototype of a hand-held CO2 laser otoscope in combination with the SilkTouch™ scanner is suitable for performing laser myringotomies with a diameter of 2 mm with a single laser pulse in fresh horse tympanic membrane.