The effect of temperature and other factors on selective microvascular damage caused by pulsed dye laser

Brief pulses of 577-nm radiation have recently been shown to selectively damage superficial cutaneous blood vessels, resulting clinically in purpura. There was a sharp threshold of exposure dose necessary for causing purpura in any given subject, which correlated with histologic evidence of extravasation and specific vascular injury. As a means of studying mechanisms for such damage, heat, cold, pressure, suction, UV radiation, and intradermal epinephrine were used to alter human cutaneous microvasculature prior to and during 577-nm pulsed dye laser exposures. When compared with control sites, only cooling of the skin significantly affected the exposure dose needed to cause purpura. The magnitude of this effect is quantitatively most consistent with intravascular microvaporization as the cause of vessel rupture and hence purpura.