Abstract
We studied vasodilatation effect and its mechanism of the bubble generated by Ho:YAG (Holmium-yttrium-aluminum-garnet) laser (λ=2.1μm) irradiation in vessel. We employed two different kinds of optical fiber tip arrangement, i.e., the bare optical fiber alone and the optical fiber tip located in the sheath. The Ho:YAG laser-induced bubbles shape generated by these optical fiber arrangement were observed along the time. The Ho:YAG laser energy was delivered by a silica-glass optical fiber of which core diameter was 600μm. The laser-induced water-vapor bubble was generated in the extracted fresh porcine carotid artery with warmed and pressurized saline perfusion in a heat bath. When the laser energy was ranging to 200-800mJ per pulse, the outer diameter of the vessel after the laser bubble loading of 200 pulses was expanded to 1.1-1.5 times comparing with that of before the laser bubble loading. The expanding rate of the estimated internal diameter from measured outer diameter was 1.3-2.2. To investigate the mechanism of this vasodilatation, the Young′s modulus of the vessels were measured before and after the laser bubble loading. The Young′s modulus of elastic fibers and collagen fibers were increased after the laser bubble loading. We think that simultaneous loading of stress/temperature elevation by the expansion/generation of the laser bubble stretched elastic fibers with collagen fibers softening and degenerated collagen fibers thermally to keep elastic fibers stretching. When we employed the bubble which was made by the arrangement of the optical fiber tip located in the sheath, thermal effect of the vessel might be decreased although vasodilatation effect was almost same as that by the bare optical fiber alone. We found that the elastic lamina was stretched just after the laser bubble loading and keep stretched even 1week after the laser bubble loading in rabbit aorta in vivo. We suppose it is likely to be possible to use the Ho:YAG laser irradiation as a temporary vasodilator tool.
