These results demonstrate that significant thermal damage is concurrent with clinically relevant shape change. This contradicts previous notions that there is a privileged laser dosimetry parameter where clinically relevant shape change and tissue viability coexist.

Background and Objectives Chondrocyte viability following laser irradiation and reshaping has not been established for human nasal septal cartilage. Knowledge of the relationship between thermal injury and laser dosimetry is needed in order to optimize septal laser cartilage reshaping. The objective of this study was to determine the depth and width of thermal injury in human septal cartilage following laser irradiation. Study Design/Materials and Methods Excess fresh nasal septal cartilage sections from rhinoplasty or septoplasty operations were irradiated using a 1.45 μm diode laser 1.25–3.6 W (2.8 mm spot diameter) with 1 second fixed exposure time, and then at exposure times of 1–4 seconds for a fixed power of 1.25 W. An infrared camera recorded surface temperature profiles during irradiation, and the temperature data were incorporated into a rate process model to numerically estimate thermal damage. Calcein AM and ethidium homodimer-1 fluorescent dyes combined with confocal laser microscopy (CLM) were used to measure thermal damage. Results CLM demonstrated clear demarcation between dead and living cells following irradiation. The extent of non-viable chondrocyte distributions increased with power and exposure time. The maximum depths of injury were 1,012 and 1,372 μm after 3.6 W 1 second and 1.25 W 4 seconds irradiation respectively. The damage predictions made by the rate process model underestimated thermal injury when compared with CLM measurements. Conclusions The assay system identified regions of non-viable chondrocytes in human septal cartilage and defined how thermal injury varies with dosimetry when using a 1.45 μm diode laser.

Background and Objectives Trauma, emergent tracheostomy, and prolonged intubation are common causes of severe deformation and narrowing of the trachea. Laser technology may be used to reshape tracheal cartilage using minimally invasive methods. The objectives of this study were to determine: (1) the dependence of tracheal cartilage shape change on temperature and laser dosimetry using heated saline bath immersion and laser irradiation, respectively, (2) the effect of temperature on the mechanical behavior of cartilage, and (3) tissue viability as a function of laser dosimetry. Materials and Methods Ex vivo rabbit trachea cartilage specimens were bent and secured around a cylinder (6 mm), and then immersed in a saline bath (45 and 72°C) for 5– 100 seconds. In separate experiments, tracheal specimens were irradiated with a diode laser (λ = 1.45 μm, 220–400 J/cm2). Mechanical analysis was then used to determine the elastic modulus in tension after irradiation. Fluorescent viability assays combined with laser scanning confocal microscopy (LSCM) were employed to image and identify thermal injury regions. Results Shape change transition zones, between 62 and 66°C in the saline heating bath and above power densities of 350 J/cm2 (peak temperatures 65±10°C) for laser irradiation were identified. Above these zones, the elastic moduli were higher (8.2±4 MPa) than at lower temperatures (4.5±3 MPa). LSCM identified significant loss of viable chondrocytes within the laser-irradiation zones. Conclusion Our results indicate a change in mechanical properties occurs with laser irradiation and further demonstrates that significant thermal damage is concurrent with clinically relevant shape change in the elastic cartilage tissues of the rabbit trachea using the present laser and dosimetry parameters.