First biocompatibility margins for optical stimulation at the eardrum via 532-nm laser pulses in a mouse model

Hearing impairment affects ∼460 million people worldwide. Conservative therapies, such as hearing aids, bone conduction systems, and middle ear implants, do not always sufficiently compensate for this deficit. The optical stimulation is currently under investigation as an alternative stimulation strategy for the activation of the hearing system. To assess the biocompatibility margins of this emerging technology, we established a method applicable in whole-mount preparations of murine tympanic membranes (TM). We irradiated the TM of anesthetized mice with 532-nm laser pulses at an average power of 50, 89, 99, and 125 mW at two different locations of the TM and monitored the hearing function with auditory brainstem responses. Laser-power-dependent negative side effects to the TM were observed at power levels exceeding 89 mW. Although we did not find any significant negative effects of optical stimulation on the hearing function in these mice, based on the histology results further studies are necessary for optimization of the used parameters.

Frequency-specific activation of the peripheral auditory system using optoacoustic laser stimulation

Hearing impairment is one of the most common sensory deficits in humans. Hearing aids are helpful to patients but can have poor sound quality or transmission due to insufficient output or acoustic feedback, such as for high frequencies. Implantable devices partially overcome these issues but require surgery with limited locations for device attachment. Here, we investigate a new optoacoustic approach to vibrate the hearing organ with laser stimulation to improve frequency bandwidth, not requiring attachment to specific vibratory structures, and potentially reduce acoustic feedback. We developed a laser pulse modulation strategy and simulated its response at the umbo (1-10 kHz) based on a convolution-based model. We achieved frequency-specific activation in which non-contact laser stimulation of the umbo, as well as within the middle ear at the round window and otic capsule, induced precise shifts in the maximal vibratory response of the umbo and neural activation within the inferior colliculus of guinea pigs, corresponding to the targeted, modelled and then stimulated frequency. There was also no acoustic feedback detected from laser stimulation with our experimental setup. These findings open up the potential for using a convolution-based optoacoustic approach as a new type of laser hearing aid or middle ear implant.

Bacterial keratitis: Photodynamic inactivation reduced experimental inflammation

The successful treatment of bacterial keratitis remains an unsolved clinical problem. The current study aimed to establish a murine keratitis model and to investigate the effect of chlorin e6 (Ce6) and photodynamic inactivation (PDI) on corneal inflammation. The cornea of anesthetized mice was scratched and covered with a bacterial suspension of Pseudomonas aeruginosa. A paste containing Ce6 was applied to the cornea with subsequent exposure to specified light. Two days later the animals were sacrificed, and the globes were processed for light microscopy. Evaluation parameters were the maximal corneal thickness and the severity of the hypopyon. The maximal corneal thickness of 290±16 µm in the infected and untreated group was significantly reduced to 220±8 µm in the infected and treated group (P<0.05). In addition, the hypopyon was less severe in the infected and treated group. In conclusion, the present study indicates that PDI using Ce6 may be a potential approach to treat patients suffering with severe bacterial keratitis.

Chlorin e6 mediated photodynamic inactivation for multidrug resistant Pseudomonas aeruginosa keratitis in mice in vivo

Following corneal epithelium scratches, mouse corneas were infected with the multidrug resistant (MDR) P. aeruginosa strain PA54. 24 hours later, 0% (for control group), 0.01%, 0.05% or 0.1% Chlorin e6 (Ce6), a second generation photosensitizer derived from chlorophyll, was combined with red light, for photodynamic inactivation (PDI). 1 hour or 2 days later, entire mouse eyes were enucleated and homogenized for counting colony forming units (CFU) of P. aeruginosa. For comparison, 0.1% Ce6 mediated PDI was started at 12 hours post infection, and 0.005% methylene blue mediated PDI 24 hours post infection. Clinical scores of corneal manifestation were recorded daily. Compared to the control, CFU 1 hour after PDI started 24 hours post infection in the 0.01% Ce6 and 0.05% Ce6 groups were significantly lower (more than one log₁₀ reduction), the CFU 2 days post PDI higher in the 0.1% Ce6 group, clinical score lower in the 0.1% Ce6 group at 1 day post PDI. These findings suggest that PDI with Ce6 and red light has a transient efficacy in killing MDR-PA in vivo, and repetitive PDI treatments are required to fully resolve the infection. Before its clinical application, the paradoxical bacterial regrowth post PDI has to be further studied.

Pharmacokinetics of the photosensitizers aminolevulinic acid and aminolevulinic acid hexylester in oro-facial tumors embedded in the chorioallantois membrane of a hen's egg

BACKGROUND

Oral squamous-cell carcinoma is a frequent form of cancer in the head and neck region. The survival rate is poor. Therapy success is highly dependent on the stage of cancer development at which diagnosis is made. The disease is mostly diagnosed at a late stage. Photodynamic diagnosis is a new tool for screening examinations. This technique calls for reliable photosensitizers, such as aminolevulinic acid (ALA) and aminolevulinic acid hexylester (h-ALA). ALA and h-ALA are the source material for the synthesis of protoporphyrin IX in tumor cells. Protoporphyrin IX has a high detection rate for tumor tissue within a reasonable period of time.

METHODS

Tumor specimens were harvested from oral carcinomas and basaliomas of the face. The vital cells of the specimens and the human tumor cell line (CLS- 354) were cultured in a 90% RPMI and 10% fetal bovine serum medium. A constant number of 50,000 cells from each specimen and the cell line were transferred to an in vivo model on the hen's egg model. The grown specimens were tested for tumor fluorescence with ALA and h-ALA. The intensity of tumor fluorescence during the following 24 hours was measured spectroscopically as the degree of concentration of protoporphyrin IX within the cells.

RESULTS

All tumors showed higher protoporphyrin IX enrichment and fluorescence, compared to healthy tissue. Using h-ALA, the peak concentration of protoporphyrin IX was achieved 20%-25% more quickly with 3- or 6-mM solutions than with ALA. The highest contrast between tumorous and healthy tissue achieved owing to fluorescence was 1:11 using h-ALA, compared to 1:5 using ALA with the peak concentrations of protoporphyrin IX.

CONCLUSIONS

Using h-ALA, the peak concentration of protoporphyrin IX, compared to ALA, is achieved 20% percent more quickly and with twice as much contrast between tumorous and healthy tissue (1:11 compared and 1:5, respectively). This facilitates a faster, better discrimination between tumorous and healthy tissue.

Ablation of vitreous tissue with erbium:YAG laser

PURPOSE

Using a noncontact erbium (Er):yttrium--aluminium--garnet (YAG) laser, ablation of vitreous was compared to distilled water in vitro.

METHODS

The porcine vitreous body and distilled water were ablated in vitro at different pulse lengths and pulse energies. Selected pulse energies were 25, 35, 45, 75, and 100 mJ (pulse rate: 1 Hz; laser beam diameter at the surface of the sample: 2 mm). Pulse lengths were at 140 +/- 3 microsec, 190 +/- 4 microsec, and 240 +/- 5 microsec. The loss of weight in vitreous tissue and distilled water was measured using precision scales and corrected for evaporation, respectively. The Mann-Whitney U test was used to assess the significance of differences in ablation rates of water and vitreous. P < 0.05 was considered statistically significant.

RESULTS

Reproducible and constant ablation rates were found in both vitreous and distilled water in each of 10 consecutive series of 50 laser pulses at constant laser parameters. Ablation rates per pulse (microg/microsec) of vitreous tissue were as follows: 3.0 microg to 45.8 microg (140 microsec), 10.4 microg to 53.8 microg (190 microsec), and 17.9 microg to 24.2 microg (240 microsec). The ablation rates exhibited a linear correlation with increasing pulse energies and also with decreasing pulse lengths. Considering the pulse lengths of 190 microsec and 240 microsec with all pulse energies tested, the ablation rates of distilled water were significantly higher (P < 0.05) than ablation of vitreous tissue. The ablation rates at a pulse length of 140 microsec were not significantly different. The differences per pulse were as follows: 0.5 microg to 2.1 microg (140 microsec), 1.9 microg to 6.0 microg (190 microsec), and 3.5 microg to 8.7 microg (240 microsec).

CONCLUSIONS

Vitreous ablation is possible using Er:YAG laser. The ablation characteristics of vitreous have proved to be similar but not equal to that of water.

Laser Resistance of Endotracheal Tubes II: ObservedTemperature Rise and Theoretical Explanation

An infrared camera was used to measure the temperature rise which takes place in endotracheal tubes exposed to a 20 W CO2 laser beam. It was seen that a metallic tube was heated up within 1 s to temperatures of 200-300°C which was very destructive to the PVC conduits inside the tube. A compound tube, on the other hand, reached temperatures of only 60°C at its inner surface after an exposure of 20 s. The experimental results can be explained by a physical model which uses the heat conduction and the heat capacities of both tubes. Whereas heat conduction in the metal tube is isotropic, heat conduction in the compound tube is anisotropic with a high conductivity along the outer surface and a low conductivity to the inside. This anisotropy and the cooling mechanism in the compound tube due to vaporising water are the reason for the high laser resistance of the tube.

Photoablation of meningiomas and neurinomas by Holmium Yag laser radiation

Cranial rat bone was irradiated by 2.1 microns Holmium Yag laser radiation. Quantitative edge rates were calculated. Histologic sections were investigated by light and electron microscopy. Eighteen cases of hard fibrous or calcified spinal and cranial meningiomas and neurinomas were operated upon using pulsed laser beam. In rat cranial bone ablation rate ranged between 0.3-0.5 mm per pulse. Perifocal thermal damage was observed in a zone of 20-90 microns around the lesion. In all human cases tumors could be removed totally without additional neurological deficit. In vivo heat development was measured by an i.r.-camera.

Interaction of holmium laser radiation and cortical bone: ablation and thermal damage in a turbid medium

The ablation of cortical bone by holmium laser radiation is described by experimental values of the ablation rate, the depth of tissue damage, and the tissue temperature. An ablation model is presented on the basis of photon diffusion in a turbid medium. When this model is compared with experimental results for the ablation rate, the penetration depth is determined. The expansion of the laser-induced heat can be explained by a point heat source located in a distance beneath the surface equal to the ablation depth. The accumulation of heat as a function of the repetition rate of the laser leads to a limitation of the repetition rate. In order to avoid traumatic heat accumulation, a maximum repetition rate should not be exceeded.

Effects of simmer current on flash-lamp impedance and their combined influence on the output of the Ho,Cr,Tm:YAG laser

The increase in slope efficiency and the reduction of the laser threshold of a flash-lamp-pumped Ho,Cr,Tm:YAG laser that are due to increased flash-lamp efficiency when the current of the dc simmer is increased are described. Investigations of the electrical characteristics of the flash lamp as a function of the simmer current prove that the flash-lamp impedance decreases to a constant value when the dc simmer current is increased. As a consequence an increase of the peak current through the flash lamp is observed, which improves the flash-lamp efficiency.

[Measuring vibrations by laser doppler vibrometry of the human tympanic membrane after stapes fixation]

At times preoperative diagnosis of otosclerosis can prove difficult. Even the objective measurement of the stapes reflex is not very conclusive in patients suffering from more severe hearing loss. Laser-Doppler vibrometry measures the velocity or amplitude of the tympanic membrane (umbo) vibrations. Laser-Doppler vibrometry has a sensitivity that is highly by the factor 10(4) than tympanometry. The herewith presented examinations show, that there is a correlation between the frequency patterns of the displacement amplitudes and experimentally simulated otosclerosis.

Middle ear transmission disorders--tympanic membrane vibration analysis by laser-Doppler-vibrometry

Laser-Doppler-vibrometry is a useful method to measure vibrations of the tympanic membrane. It is suitable to objectively diagnose the middle ear. In comparison to tympanometry, laser-Doppler-vibrometry has greater sensitivity. Temporal bone specimens were specially prepared to simulate middle ear disorders like middle ear effusion, fixation of the malleus head, fixation of the stapes footplate and removal of the incus. A correlation between the displacement function of the umbo and the experimentally produced middle ear disorders could be demonstrated. For the first time it was possible to measure the vibration of the tympanic membrane by using a laser-Doppler-vibrometer in a healthy 25-year-old male.

[Laser Doppler vibrometry of the tympanic membrane. Possibilities for objective middle ear diagnosis]

In the diagnosis of hearing disorders, the laser velocimeter can be used to advantage. In contrast to previously published studies on measurements at exposed middle and inner ear structures of the human temporal bone, we used a clinically more practical method to obtain results through the intact auditory meatus. We used a laser intensity of less than 1 mW. The measurements were performed in a room with unlimited sound transmission of frequencies between 0.5 and 8 kHz. The signals from the vibration of the tympanic membrane, obtained by this touch-free method, were analyzed by Fourier transform, showing only the fundamental oscillation but not the higher harmonics. Experimental data on middle ear effusions, obtained by fixation of the malleus head and by drilling the temporal bone, are presented.