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We studied Ho:YAG laser irradiation in blood vessel as a vasodilator ex vivo. We thought that the Ho:YAG
laser-induced bubble expansion might be able to dilate the vessel because we found the vessel wall expansion after the
Ho:YAG laser irradiation, that is steady deformation, in the vessel ex vivo. There have been many reports regarding to
the Ho:YAG laser irradiation in the vessel. Most of studies concentrated on the interaction between Ho:YAG laser
irradiation and vessel wall to investigate side effect on Ho:YAG laser angioplasty. We proposed to use the Ho:YAG
laser-induced bubble expansion as a vasodilator. We studied vasodilation effect of the Ho:YAG laser-induced bubble
ex vivo. The flash lamp excited Ho:YAG laser surgical unit (IH102, NIIC, Japan) (&lgr;=2.1&mgr;m) was used. The laser
energy was delivered by a silica glass fiber (outer diameter: 1000&mgr;m, core diameter: 600&mgr;m). The laser-induced
bubble was generated in the extracted fresh porcine carotid artery with the warmed saline perfusion. The laser energy
at the fiber tip was ranging from 170-1300mJ per pulse. Number of the laser irradiation was ranged from 20pulses to
100pulses. The outer diameter of the vessel was observed. To examine the change in mechanical properties of the
vessel wall, the stress-strain curve of the laser-irradiated vessel was measured. Birefringence observation and
microscopic observation of staining specimen were performed. When the laser energy was set to 1300mJ per pulse,
the outer diameter of the vessel after the laser irradiation was expanded by 1.4 times comparing with that of before the
laser irradiation and the dilatation effect was kept even at 10minutes after the irradiation. The elasticity modulus of
the artery by collagen was changed by the laser irradiation. In the polarized microscopic observation, the brightness of
the intimal side of the vessel is increased comparing with that of the normal. We think this brightness increasing may
be attributed to birefringence change by the arrangement of stretched collagen fiber. We suppose it is likely to be able
to use the Ho:YAG laser irradiation as a temporary vasodilater tool in spite of further study should be performed.
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