Identification of photoacoustic transients during pulsed laser ablation of the human temporal bone: an experimental model

Penetration of CO2 laser into the otic capsule using a hand-held, flexible-fiber delivery system

BACKGROUND AND OBJECTIVE

Recently, a new, flexible-fiber, CO2 laser delivery system has been FDA-cleared for clinical use. However, for otologic surgery, no data have been reported correlating power settings to depth of penetration into the otic capsule-the bone that covers the inner ear. This was the goal of our study.

STUDY DESIGN/MATERIALS AND METHODS

Eight cadaveric temporal bones were procured as per our institution's protocols. For each specimen, nine different laser holes were burned into the otic capsule using the flexible-fiber CO2 laser delivery system. Power settings were varied from 10 to 20 W in 2 W increments, and duration of exposure was 100, 200, 300, 400, or 600 milliseconds. Each setting (power and duration) was tested on two specimens. Following laser exposure, each specimen was scanned in a microCT scanner, and the depth of penetration measured from these images.

RESULTS

Of the 72 laser shots, 8 were excluded due to double hits (4), oblique hits (3), or complete penetration (1). After excluding these 8, bone penetration was found to vary from 160 to 670 microm based on power and time settings. Spearman analysis on ranked data showed that time had a greater impact on depth than power. The correlation coefficients for time and power were 0.84 (P = 0.013) and 0.40 (P<0.001), respectively.

CONCLUSION

The flexible-fiber CO2 laser is effective for otic capsule ablation in this model. High power setting and long pulse duration can lead to complete penetration of the otic capsule potentially causing damage of underlying structures such as the facial nerve, horizontal semicircular canal, and cochlea.

Nuclear transport by laser-induced pressure transients

PURPOSE

Control of the transport of molecules into the nucleus represents a key regulatory mechanism for differentiation, transformation, and signal transduction. Permeabilization of the nuclear envelope by physical methods can have applications in gene therapy. Laser-induced pressure transients can produce temporary aqueous pores analogous to those produced by electroporation and that the cells can survive this procedure. In this study, we examine the role of the pressure transients in creating similar pores in the nuclear envelope.

METHODS

The target human peripheral blood mononuclear cells in a 62 microM 72 kDa fluoresceinated dextran solution were exposed to the pressure transients generated by laser ablation. An in vitro fluorescence confocal microscope was used to visualize and quantify the fluoresceinated dextran in the cytoplasmic and nuclear compartments.

RESULTS

In contrast to electroporation, the pressure transients could deliver 72 kDa fluoresceinated dextrans, which are normally excluded by the nucleus, across the nuclear envelope into the nucleus. In addition to creating pores in the plasma membrane, temporary pores were also created in the nuclear envelope following exposure to pressure transients.

CONCLUSION

The production of temporary nuclear pores could provide a unique resource for drug-delivery and gene therapy.