Proteoglycan synthesis in porcine nasal cartilage grafts following Nd : YAG (lambda=1.32 mu m) laser-mediated reshaping

Mechanically deformed morphologic cartilage grafts undergo temperature-depe ndent stress relaxation during sustained laser irradiation resulting in sta ble shape changes. In this study, porcine nasal septal cartilage specimens were evaluated for viability by measuring the incorporation of (Na2SO4)-S-3 5 into proteoglycan (PTG) macromolecules in whole tissue culture following laser-mediated reshaping. Synthesis rates of PTG were determined by scintil lation counting lyophilized specimens and normalizing these values by total protein content. Positive controls were established by inducing chondrocyt e apoptosis using prolonged exposure to nitric oxide (NO), In chondrocytes, apoptosis induced using NO resulted in significantly lower PTG synthesis r ates compared to untreated native specimens. Cartilage specimens were irrad iated with light emitted from a Nd:YAG laser (25 W/cm(2), lambda = 1.32 mu m) while recording simultaneously radiometric surface temperature, internal stress and backscattered light intensity from a probe laser. Each specimen received one, two or three sequential laser exposures. The duration of eac h exposure was determined from real-time measurements of characteristic cha nges in back-scattered light intensity that correlate with accelerated stre ss relaxation. A 5 min time interval between each laser exposures allowed t he cartilage specimen to return to thermal equilibrium. Average PTG synthes is rates decreased with successive laser exposures, though these were alway s higher than baseline rates established for NO-treated tissues, suggesting that laser-mediated cartilage reshaping acutely does not eliminate the ent ire population of viable chondrocytes, The reduction in PTC synthesis is co rrelated with the time-temperature-dependent heating profile created during laser irradiation, supporting our hypothesis that careful monitoring of la ser dosimetry is required to ensure chondrocyte viability.