BASIC MECHANISM OF IN-VITRO PULSED-DYE LASER-INDUCED VASODILATION

Vasodilation of rabbit carotid arteries induced by a pulsed-eye laser was studied in vitro to clarify the underlying mechanism. Artery segme nts were double cannulated in a pressure-perfusion apparatus which, un der physiological conditions, allows for differential application of v arious solutions, pharmacological agents, and pulsed-dye laser light. Vasoconstriction was activated using both pharmacological and nonpharm acological agonists. Laser energy at a wavelength of either 480 or 575 nm was applied intraluminally in 1-mu sec pulses, which caused dilati on of the arteries if hemoglobin was present in the lumen at sufficien t concentration. Induced vasodilation did not specifically require the presence of hemoglobin; the same phenomenon could be repeated using a n inert dye such as Evans blue as an optical absorber of laser energy. The optical density of the absorber, the number of applied laser puls es, and total amount of applied energy directly influenced the vasodil atory response. Laser-induced vasodilation was possible in both normal vessels and vessels denuded of endothelium. Pulsed-dye laser-induced vasodilation is therefore not a phenomenon mediated through chemical p rocesses, but is rather a purely physical process initiated by the opt ical absorption of laser energy by the intraluminal medium, which prob ably induces cavitation bubble formation and collapse, resulting in th e vasodilatory response of the vessel.