Experimental in vivo fenestration of guinea pig cochlea using 2.79 Μm laser radiation

Abstract

Abstract. Erbium-YSGG laser systems are promising tools in ear, nose and throat (ENT) surgery. The high absorption in biological tissues, resulting in precise tissue ablation with minimal thermal tissue damage, and the possibility to guide the radiation through optical fibres make the 2.79 ~m wavelength a favourite for microsurgery.In order to simulate the fenestration of the human stapes foot plate required for prosthesis implantation when treating otosclerosis, five guinea pig cochleae were irradiated in vivo until perforation was achieved. The laser-induced temperature rise and pressure transients evoke activity in the inner hair cells that was investigated by micro-iontophoresis.Perforation of the cochlea bone (hole diameter of 350/~m) can be performed with a few laser pulses and high precision with a thermal damage zone of <100~m. The bone ablation rate is 10 + 2 ~m pulse -1 at a radiant exposure of 12 J cm-2. The functionality of the afferent inner hair cells in the guinea pig cochlea was verified before and after laser treatment using glutamate receptor agonists AMPA and NMDA. For the above selected laser parameters, the induced 15-min enhanced activity was blockable with the specific reversible AMPA and NMDA antagonists CNQX and AP-7.Micro-iontophoresis confirms the reversibility of cochlea functionality after its perforation with Er-YSGG laser pulses. A limit of radiant exposure around 12 J cm -2 is found for safe fenestration. It is demonstrated that the Er-YSGG laser is a precise and safe instrument whilst still using adequate laser parameters. On the other hand, this study demonstrates the potential of uncontrollable and unintended induced damage, resulting from vapour channel formation in the perilymph, if a high laser radiant exposure is applied.

Erbium: Yttrium‐Aluminum‐Garnet Laser Application in Stapedotomy

“…Therefore, in the last 2 decades, more than a few experimental and clinical studies to establish the safety of different lasers and to find the "ideal laser" for primary and revision stapedotomy have been performed. [13][14][15][16][17][18][19][20] Comparison of preoperative with early (3 days) and late (12 months) postoperative bone conduction, assessed up to 4000 Hz, showed in most of the patients unchanged or slightly improved values, both in the early and in the late measurements. Only 1 patient showed a deterioration of more than 10 dB, also in the late measurement, and it was related to the high number of pulses (the highest of our study group) that were applied to perforate his thick footplate.…”

“…With laser pulses between 10 and 17 J/cm 2 , it is possible to perforate the stapes without damaging the cochlear function. 11,20 Other experimental studies show that during laser application, sudden molecular disruption produces an acoustic shock with varying sound levels for different laser systems. Measurement using sound pressure level (SPL) recording equipment to record laser beam noises on bovine stapes revealed sound levels of 133 dB SPL for erbium laser, 135 dB SPL for CO 2 , and 92 dB SPL for argon.…”

“…However, several risks for the inner ear, such as heat diffusion and temperature increase in the perilymph, damage to organs positioned near the foot plate by direct energy irradiation, and destruction of the sensory hair cells by acoustic shock, appear to be associated with laser‐performed stapedotomy. Therefore, in the last 2 decades, more than a few experimental and clinical studies to establish the safety of different lasers and to find the “ideal laser” for primary and revision stapedotomy have been performed 13–20 …”

“…Experimental in vivo studies substantiate these statements, showing that laser pulses with a power density of 10 J/cm 2 produce only a transient increase in postsynaptic inner hair cell receptor activity. With laser pulses between 10 and 17 J/cm 2 , it is possible to perforate the stapes without damaging the cochlear function 11,20 . Other experimental studies show that during laser application, sudden molecular disruption produces an acoustic shock with varying sound levels for different laser systems.…”

Advantages and Dangers of Erbium Laser Application in Stapedotomy

“…All patients suffered from classical otosclerosis and had a moderate conductive hearing loss with negative Rinne preoperatively. J/cm 2 ) applied to the inner ear liquid destroyed the cochlea (18). Based on these results, we concluded that the maximum erbium laser power allowed for use in stapes surgery was 10-17 J/cm 2 .…”