ABSTRACT
BACKGROUND: Laser light is known to stimulate nerves. This study investigated alternative wavelengths for nerve stimulation. MATERIALS AND METHODS: The sciatic nerves of rats were irradiated with four different lasers-a Ho:YAG (2100 nm), a Yb:glass fiber laser (1495 nm) and diode lasers (1450 nm and 1540 nm). RESULTS: All lasers evoked a visible leg twitch response, and electromyography confirmed muscle activation. The Yb:glass laser at 1495 nm delivered through a single mode fiber was found to be the most effective stimulus. The stimulation threshold for a 2 millisecond pulse from the Yb:glass laser was determined to be 3.7+/-2.8 mJ/cm(2). CONCLUSIONS: The Yb:glass laser has the potential for use in neurostimulation, as an alternative to electrical stimulation.
Subject(s)
Electric Stimulation Therapy/instrumentation , Lasers, Semiconductor , Lasers, Solid-State , Low-Level Light Therapy/instrumentation , Sciatic Nerve/radiation effects , Animals , Electromyography , Neural Conduction/radiation effects , Rats , Rats, Sprague-Dawley , Sciatic Nerve/physiopathologyABSTRACT
A femtosecond laser, normally used for LASIK eye surgery, is used to perforate cadaveric human stapes. The thermal side effects of bone ablation are measured with a thermocouple in an inner ear model and are found to be within acceptable limits for inner ear surgery. Stress and acoustic events, recorded with piezoelectric film and a microphone, respectively, are found to be negligible. Optical microscopy, scanning electron microscopy, and optical coherence tomography are used to confirm the precision of the ablation craters and lack of damage to the surrounding tissue. Ablation is compared to that from an Er:YAG laser, the current laser of choice for stapedotomy, and is found to be superior. Ultra-short-pulsed lasers offer a precise and efficient ablation of the stapes, with minimal thermal and negligible mechanical and acoustic damage. They are, therefore, ideal for stapedotomy operations.
Subject(s)
Laser Therapy/instrumentation , Laser Therapy/methods , Osteotomy/instrumentation , Osteotomy/methods , Stapes Surgery/instrumentation , Stapes Surgery/methods , Stapes/cytology , Animals , Humans , In Vitro Techniques , SwineABSTRACT
OBJECTIVE: A nerve stimulator based on a CO2 laser has been developed for use in human pain research. A flattened irradiance profile was generated for safer and more uniform pain stimulation. The pain evoked by the flattened profile was compared to a TEM00 profile. BACKGROUND DATA: The CO2 laser normally operates in TEM00 mode. This is not ideal for thermal stimulation, since the beam will generate a temperature that has a peak in the center of the irradiance profile. This will result in non-uniform activation of nerve fibers. MATERIALS AND METHODS: A lens system has been designed to redistribute the energy of the beam to produce a flattened supergaussian irradiance profile for uniform heating of the skin. The lenses work by refracting the more intense central part of the beam towards the periphery. Psychophysical techniques were used to compare the pain evoked with a flattop irradiance profile and a TEM00 profile. RESULTS: It was found that the supergaussian beam evokes pain at a lower energy level than a TEM00 beam. CONCLUSION: A flattop irradiance profile is a safer source than a gaussian beam for evoking pain in human pain studies.
Subject(s)
Lasers, Gas , Nociceptors/physiology , Physical Stimulation/instrumentation , Skin/innervation , Humans , Nociceptors/radiation effects , TemperatureABSTRACT
OBJECTIVE: This study identifies the presence of photoacoustic waves during excimer laser treatment of porcine otic capsule bone. BACKGROUND DATA: Pulsed ultraviolet lasers have been suggested for use in middle ear surgery due to their potential for fiberoptic delivery, decreased thermal trauma, and precise ablation characteristics. However, the short pulse width of excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen. MATERIALS AND METHODS: A XeCl (lambda = 308 nm, tau = 12 ns) excimer laser was used to ablate wafers of bone with energies of 90, 35, 13, 5, and 1.8 mJ/pulse. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the slices of bone. During ablation photoacoustic signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope. RESULTS: Photoacoustic waves were clearly identified. Stress wave amplitude increased with laser fluence. CONCLUSION: A laser fluence must be found that compromises between an increased ablation rate and increased stress wave amplitude. The acoustic power levels generated during ablation are below maximum exposure limits.
