Influence of tissue desiccation on critical temperature for thermal damage during Er:YAG laser skin treatments.

OBJECTIVES: Erbium lasers have become an accepted tool for performing both ablative and non-ablative medical procedures, especially when minimal invasiveness is desired. Hard-tissue desiccation during Er:YAG laser procedures is a well-known phenomenon in dentistry, the effect of which is to a certain degree being addressed by the accompanying cooling water spray. The desiccation of soft tissue has attracted much less attention due to the soft tissue's high-water content, resulting in a smaller effect on the ablation process. MATERIALS AND METHODS: In this study, the characteristics of skin temperature decay following irradiations with Er:YAG laser pulses were measured using a fast thermal camera. RESULTS: The measurements revealed a substantial increase in temperature decay times and resulting thermal exposure times following irradiations with Er:YAG pulses with fluences below the laser ablation threshold. Based on an analytical model where the skin surface cooling time is calculated from the estimated thickness of the heated superficial layer of the stratum corneum (SC), the observed phenomena is attributed to the accelerated evaporation of water from the SC's surface. By using an Arrhenius damage integral-based variable heat shock model to describe the dependence of the critical temperature on the duration of thermal exposure, it is shown that contrary to what an inexperienced practitioner might expect, the low-to-medium level fluences may result in a larger thermal damage in comparison to treatments where higher fluences are used. This effect may be alleviated by hydrating the skin before Er:YAG treatments. CONCLUSION: Our study indicates that tissue desiccation may play a more important role than expected for soft-tissue procedures. It is proposed that its effect may be alleviated by hydrating the skin before Er:YAG treatments.

Minimally invasive, non-ablative Er:YAG laser treatment of stress urinary incontinence in women--a pilot study.

The study presents an assessment of mechanism of action and a pilot clinical study of efficacy and safety of the Er:YAG laser for the treatment of stress urinary incontinence (SUI). The subject of this study is a treatment of SUI with a 2940 nm Er:YAG laser, operating in a special SMOOTH mode designed to increase temperature of the vaginal mucosa up to maximally 60-65 °C without ablating the epidermis. Numerical modelling of the temperature distribution within mucosa tissue following an irradiation with the SMOOTH mode Er:YAG laser was performed in order to determine the appropriate range of laser parameters. The laser treatment parameters were further confirmed by measuring in vivo temperatures of the vaginal mucosa using a thermal camera. To investigate the clinical efficacy and safety of the SMOOTH mode Er:YAG laser SUI treatment, a pilot clinical study was performed. The study recruited 31 female patients suffering from SUI. Follow-ups were scheduled at 1, 2, and 6 months post treatment. ICIQ-UI questionnaires were collected as a primary trial endpoint. Secondary endpoints included perineometry and residual urine volume measurements at baseline and all follow-ups. Thermal camera measurements have shown the optimal increase in temperature of the vaginal mucosa following treatment of SUI with a SMOOTH mode Er:YAG laser. Primary endpoint, the change in ICIQ-UI score, showed clinically relevant and statistically significant improvement after all follow-ups compared to baseline scores. There was also improvement in the secondary endpoints. Only mild and transient adverse events and no serious adverse events were reported. The results indicate that non-ablative Er:YAG laser therapy is a promising minimally invasive non-surgical option for treating women with SUI symptoms.