Experimental study on the vascular thermal response to visible laser pulses

Port Wine Stains (PWS) are congenital vascular malformations that progressively darken and thicken with age and laser therapy is most effective in clinical practice. Using dorsal skin chamber, this study evaluated thermal response of blood vessel to a 595 nm pulsed dye laser (PDL) with controlled energy doses and pulse durations. Totally 32 vessels (30∼300 μm in diameter) are selected from the dorsal skin of the mouse to match those in port wine stain. The experimental results showed that the thermal response of the blood vessels to laser irradiation can be recognized as coagulation, constriction with diameter decrease, disappearance, hemorrhage and collagen damage in the order of increasing laser incident fluence. Blood vessels with small diameter would response poor and survive from the laser heating because their thermal relaxation time is much shorter than the pulse duration. For PDL, vessel hemorrhage is the dominant thermal responses that appear in 15 of 32 blood vessels, and the consequent purpura can be used as treatment endpoint in clinical practice for 595nm PDL. The optimal incident fluence is from 10 to 12 J/cm2 under 6 ms pulse duration without considering the epidermal light absorption, while the optimal pulse duration is 6ms which is close to the thermal relaxation time of the blood vessels with average diameter of 110 μm.