The effect of partial denaturation on Nd:YAG laser mediated stress relaxation of porcine septal cartilage

摘要

In this study, we examined 1) the effect of partial denaturation and 2) repetitive irradiation on porcine septal cartilage during Nd:YAG laser (lambda=1.32 mum,25 W/cm~2, 5 mm spot size) exposure. Diffuse reflectance from a HeNe probe laser and internal stress were measured in mechanically deformed cartilage specimens (2 x 10 x 25 mm) during Nd:YAG laser irradiation. Specimens were first partially denaturation in heated saline water baths at selected temperatures (50 deg C, 70 deg C, and 100 deg C all for 30 minutes). Native and water bath heated specimens were sequentially irradiated three times (pulse duration varying from 5-12 seconds, determiend by noting the onset of accelerated stress relaxation) with a 5 minute cooling interval between pulses. After the first laser pulse, diffuse reflectance and internal stress changes occurred synchronously (coupled); the peak in internal stress occurred within less than 1 second following observation of the peak in diffuse reflectance. With repeated laser irradiation, this time interval lengthens with eventual decoupling of the diffuse reflectance and internal stress. With decoupling, internal stress increases during laser heating, and abruptly decreases when irradiation is terminated. decoupling occurs with greater frequency in specimens pre-heated in the water bath. With the first laser exposure, only 15percent of control, 8percent of 50 deg C heated, 0percent of 70 deg C heated, and 8percent of 100 deg C specimens exhibited decoupling. However, after two laser exposures, decoupling was observed in 83percent and 60percent of specimens heated in water baths at 70 deg C (N=12) and 100 deg C (N=12), respectively; in contrast, decoupling was observed in less than 20percent of the native (N=24) and 50 deg C (N=12) water bath pre-heated specimens with two laser irradiations. The effect of partial denaturaiton using water bath immersion mimics findings observed with sequential laser irradiation. Hence cartilage likely undergoes partial denaturation during laser reshaping, and that sustained laser irradiation may result in irreversible changes in the tissue matrix.