The influence of ultrasound and temperature on the cochlear microphonic response following a round window irradiation

Long-term follow-up after "one-shot" CO2 laser stapedotomy: is the functional outcome stable during the years?

The use of "one-shot" CO₂ laser technique for a primary small-fenestra stapedotomy is well established, but few papers report the long-term functional results. We retrospectively reviewed medical records of 198 patients, treated for otosclerosis from January 2008 to December 2011, at the Department of Head and Neck Surgery, Catholic University of Rome. Statistical comparison between audiological thresholds obtained 24 h preoperatively, at early (4 weeks) and late postoperative examinations (mean time 45 months), was performed. Comparison of preoperative vs both early and late postoperative ACPTA showed a statistically significant difference (respectively 55 vs 33 and 31 dB; p < 0.001). No statistical difference was observed between preoperative, early and late postoperative BCPTA (respectively 23 vs 23 and 22 dB; p > 0.05). Both early and late postoperative ABG improved significantly compared to the preoperative one (respectively 10 and 9 vs 32 dB; p < 0.001). No statistical difference was found in comparison of early vs late postoperative ACPTA (respectively 33 vs 31 dB; p > 0.05), early vs late postoperative ABG (respectively 10 vs 9 dB; p > 0.05) and early vs late ABG gain (respectively 22 vs 23 dB; p > 0.05). No subjects developed postoperative complications requiring revision surgery or late deterioration of hearing threshold. The analysis of our data suggests that "one-shot" CO₂ laser stapedotomy is an effective and safe procedure: it allows a rapid stapedotomy without damages for the inner ear and optimal functional results that remain stable during the years.

Comparing mechanical effects and sound production of KTP, thulium, and CO2 laser in stapedotomy

HYPOTHESIS

The mechanical and acoustic effects that occur during laser-assisted stapedotomy differ among KTP, CO2, and thulium lasers.

BACKGROUND

Making a fenestration in stapedotomy with a laser minimizes the risk of a floating footplate caused by mechanical forces. Theoretically, the lasers used in stapedotomy could inflict mechanical trauma because of absorption in the perilymph, causing vaporization bubbles. These bubbles can generate a shock wave, when imploding.

METHODS

In an inner ear model, we made a fenestration in a fresh human stapes with KTP, CO2, and thulium laser. During the fenestration, we performed high-speed imaging from different angles to capture mechanical effects. The sounds produced by the fenestration were recorded simultaneously with a hydrophone; these recordings were compared with acoustics produced by a conventional microburr fenestration.

RESULTS

KTP laser fenestration showed little mechanical effects, with minimal sound production. With CO2 laser, miniscule bubbles arose in the vestibule; imploding of these bubbles corresponded to the acoustics. Thulium laser fenestration showed large bubbles in the vestibule, with a larger sound production than the other two lasers. Each type of laser generated significantly less noise than the microburr. The microburr maximally reached 95 ± 7 dB(A), compared with 49 ± 8 dB(A) for KTP, 68 ± 4 dB(A) for CO2, and 83 ± 6 dB(A) for thulium.

CONCLUSION

Mechanical and acoustic effects differ among lasers used for stapedotomy. Based on their relatively small effects, KTP and CO2 lasers are preferable to thulium laser.

Comparison of KTP, Thulium, and CO2 laser in stapedotomy using specialized visualization techniques: thermal effects

High-speed thermal imaging enables visualization of heating of the vestibule during laser-assisted stapedotomy, comparing KTP, CO2, and Thulium laser light. Perforation of the stapes footplate with laser bears the risk of heating of the inner ear fluids. The amount of heating depends on absorption of the laser light and subsequent tissue ablation. The ablation of the footplate is driven by strong water absorption for the CO2 and Thulium laser. For the KTP laser wavelength, ablation is driven by carbonization of the footplate and it might penetrate deep into the inner ear without absorption in water. The thermal effects were visualized in an inner ear model, using two new techniques: (1) high-speed Schlieren imaging shows relative dynamic changes of temperatures up to 2 ms resolution in the perilymph. (2) Thermo imaging provides absolute temperature measurements around the footplate up to 40 ms resolution. The high-speed Schlieren imaging showed minimal heating using the KTP laser. Both CO2 and Thulium laser showed heating below the footplate. Thulium laser wavelength generated heating up to 0.6 mm depth. This was confirmed with thermal imaging, showing a rise of temperature of 4.7 (±3.5) °C for KTP and 9.4 (±6.9) for Thulium in the area of 2 mm below the footplate. For stapedotomy, the Thulium and CO2 laser show more extended thermal effects compared to KTP. High-speed Schlieren imaging and thermal imaging are complimentary techniques to study lasers thermal effects in tissue.

What is ultrasound?

This paper is based on material presented at the start of a Health Protection Agency meeting on ultrasound and infrasound. In answering the question 'what is ultrasound?', it shows that the simple description of a wave which transports mechanical energy through the local vibration of particles at frequencies of 20 kHz or more, with no net transport of the particles themselves, can in every respect be misleading or even incorrect. To explain the complexities responsible for this, the description of ultrasound is first built up from the fundamental properties of these local particle vibrations. This progresses through an exposition of the characteristics of linear waves, in order to explain the propensity for, and properties of, the nonlinear propagation which occurs in many practical ultrasonic fields. Given the Health Protection environment which framed the original presentation, explanation and examples are given of how these complexities affect issues of practical importance. These issues include the measurement and description of fields and exposures, and the ability of ultrasound to affect tissue (through microstreaming, streaming, cavitation, heating, etc.). It is noted that there are two very distinct regimes, in terms of wave characteristics and potential for bioeffect. The first concerns the use of ultrasound in liquids/solids, for measurement or material processing. For biomedical applications (where these two processes are termed diagnosis and therapy, respectively), the issue of hazard has been studied in depth, although this has not been done to such a degree for industrial uses of ultrasound in liquids/solids (sonar, non-destructive testing, ultrasonic processing etc.). However, in the second regime, that of the use of ultrasound in air, although the waves in question tend to be of much lower intensities than those used in liquids/solids, there is a greater mismatch between the extent to which hazard has been studied, and the growth in commercial applications for airborne ultrasound.

Laser irradiation of the guinea pig basilar membrane

BACKGROUND AND OBJECTIVES

The cochlea is the part of the inner ear that transduces sound waves into neural signals. The basilar membrane, a connective tissue sheet within the cochlea, is tonotopically tuned based on the spatial variation of its mass, stiffness, and damping. These biophysical properties are mainly defined by its constituent collagen fibers. We sought to assess the effect of laser irradiation on collagen within the basilar membrane using histological analysis.

STUDY DESIGN/MATERIALS AND METHODS

Four excised guinea pig cochleae were stained with trypan blue. From these, two were irradiated with a 600 nm pulsed dye laser and two were used as controls. Collagen organization was visualized using polarization microscopy.

RESULTS

Laser irradiation reduced the birefringence within the basilar membrane as well as within other stained collagen-containing structures. Larger reductions in birefringence were measured when more laser pulses were given. The effects were similar across all turns of each cochlea.

CONCLUSIONS

Laser irradiation causes immediate alterations in collagen organization within the cochlea that can be visualized with polarization microscopy. These alterations may affect cochlear tuning. Ongoing research is aimed at analyzing the effect of laser irradiation on cochlear function. It is conceivable that this technique may have therapeutic benefits for patients with high-frequency sensorineural hearing loss.

Biological effects of ultrasound: development of safety guidelines. Part I: personal histories

After the end of World War II, advances in ultrasound (US) technology brought improved possibilities for medical applications. The first major efforts in this direction were in the use of US to treat diseases. Medical studies were accompanied by experiments with laboratory animals and other model systems to investigate basic biological questions and to obtain better understanding of mechanisms. Also, improvements were made in methods for measuring and controlling acoustical quantities such as power, intensity and pressure. When diagnostic US became widely used, the scope of biological and physical studies was expanded to include conditions for addressing relevant safety matters. In this historical review, a major part of the story is told by 21 investigators who took part in it. Each was invited to prepare a brief personal account of his/her area(s) of research, emphasizing the "early days," but including later work, showing how late and early work are related, if possible, and including anecdotal material about mentors, colleagues, etc.

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

BACKGROUND AND OBJECTIVE

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.

STUDY DESIGN/MATERIALS AND METHODS

Temperature increases and heat exchange processes in the fluid (physiological saline) were examined in a calorically and physiologically approximated cochlea model for applying the laser parameters effective in creating footplate perforations.

RESULTS

With all systems, increases in the energy density, number of pulses, and thus resultant total energy lead 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 perforation are 26 degrees C with the Ho:YAG laser. The lowest temperature maxima are 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 maximal temperatures of 10 degrees C.

CONCLUSION

The Er:YSGG and Er:YAG laser can be applied in laser stapedotomy in a relatively broad energy density range without a risk of inner ear damage by thermic loading. On the other hand, the Ho:YAG laser is not recommended for stapedotomy because of the higher energy density and pulse rate required for sufficient perforation and the resultant higher temperature increases in the perilymph. Though likewise achieving perforations with only slight temperature increases in the fluid of the cochlea model, the excimer laser does not seem appropriate for stapedotomy because of the long period of heat exposure (ca. 60 s) due to the lower ablation rate at the stapes necessitating a longer application time.

Influence of argon laser stapedotomy on cochlear potentials. I: Alteration of cochlear microphonics (CM)

In guinea pigs the cochlea microphonics (CM) were recorded during and after argon laser stapedotomy. Short termed drastic depression of CM was observed. This effect involved the entire frequency range of the cochlea. The recovery was mostly complete and often started already during laser irradiation or at the end of the laser exposure. A marked sensitivity loss of the cochlea only occurred with large stapedotomy holes followed by massive perilymph leakage. A momentary heat related instability of the entire stapes is suggested to cause the CM depression. In addition we observed a thermoacoustic effect on the CM. This laser evoked response seems to cause no harm to the cochlea.