Comparison of free radicals produced by laser and ultrasound ablation of cardiovascular tissue

Pulsed UV laser generated short-lived free radicals from biological samples

EPR characterization of the short-lived free radicals generated by pulsed UV laser ablation of biological samples has been investigated using a spin trap method. The obtained EPR spectra suggest that the trapped short-lived free radicals generated by excimer laser ablation of collagen and myocardium are identical. The obtained results are discussed in association with the production scheme of free radicals and an empirical mechanism of laser generated short-lived free radicals.

Electron spin resonance investigation of laser and heated metal-tip-induced free radical formation in various tissues

The short-lived free radical formation accompanying laser irradiation and laser-heated metal tip contact was examined using electron spin resonance (ESR) spin-trap methodology. Various tissues (canine myocardium, human aorta, liver, and spleen) were irradiated by argon-ion (continuous wave [CW] and pulse) and YAG (CW) lasers employing both naked fiber and a laser-heated metal tip. All showed the formation of primarily carbon-centered, not oxygenated, free radicals, together with some minor unidentified species. This implies that the backbones of amino acids, lipids, or other biological building blocks are cleaved during the irradiation or thermal treatment. Different tissues produce similar radicals but with different amounts when irradiated by argon-ion, YAG, and laser-heated metal tip sources. The amount of the free radicals formed depends on the laser power (within 5-15 W). Compared to the naked fiber, the laser-heated metal tip shows the generation of at least twice the amount of free radicals. The possible relationship of the free radical formation to tissue injury is briefly discussed.

Hydrogen atom formation by ultrasound in D2O solutions of nitrone spin traps

To elucidate the mechanism of ultrasonically induced H atom formation in D2O solutions of nitrone spin traps, alpha-phenyl-N-tert-butylnitrone (PBN) and alpha-(4-pyridyl-1-oxide)- N-tert-butylnitrone (POBN) were exposed to 50 kHz ultrasound in the presence of Ar, and the ratio of the ESR signal of the H-spin adduct to that of the D-spin adduct (H/D ratio) was examined. The H/D ratio increased with the concentration of the spin traps. The magnitude of the H/D ratios correlates with the hydrophobicity of the spin traps. The H/D ratios for the more hydrophobic spin trap, PBN, are larger than those for POBN at all concentrations. Xenon, which has a lower thermal conductivity than argon, was employed for creating higher final temperatures of the cavitation bubbles. For the less hydrophobic spin trap POBN the H/D ratio is lower for xenon than for argon. A similar result was found for PBN at lower concentrations. These results show that the H adducts of PBN and POBN are formed from the spin traps or their decomposition products by homolytic scission of C-H bonds due to pyrolysis.