Mechanisms of Microvascular Response to Laser Pulses

Abstract

"Selective photothermolysis" is widely used for treating vascular lesions. In order to understand mechanisms of response, we investigated fast events during pulsed laser treatment of microvessels. A high-speed (2000 fps) CCD camera and microscope were used to image hamster cheek pouch microvessels during and after 532 nm and 1064 nm laser pulse exposures. Pulse duration and fluence were varied systematically (1-50 ms, 0-600 J per cm2). Threshold fluences for fast events were determined. On a millisecond time-scale, a specific series of fast events occur, which are wavelength, fluence, irradiance, and pulse duration dependent. In order of increasing fluence we observed: blood coagulation, vasoconstriction, thread-like appearance of the treated vascular segment, vessel disappearance, intravascular cavitation, bubble formation, vessel wall rupture and hemorrhage, and shrinkage of perivascular tissue. With increasing pulse duration, the threshold fluences for coagulation, vessel disappearance, and cavitation increase, and cavitation becomes less violent, conforming to the vessel lumen. Intravascular cavitation did not always rupture the vessel wall, and is not the mechanism for immediate vessel disappearance, a desired endpoint for treating vascular lesions. The apparent mechanism for immediate vessel disappearance is contraction of intravascular blood and perivascular collagen after thermal denaturation. This study suggests that detecting fast events in humans, in real time, may provide useful feedback signals for "smarter" laser devices.

Optimal pulse durations for the treatment of leg telangiectasias with a neodymium YAG laser

“…The final result is replacement of the vessel by fibrous tissue [8,11]. Previously, it had been speculated that vessel cavitation with intraluminal steam bubble formation was necessary for vessel disappearance [9]. More recently it has been shown that the mechanism for vessel disappearance is not Fig.…”

“…Thrombosis begins immediately after the laser insult but may not resolve for weeks [9,[12][13][14]. Most likely, both mechanisms are involved in the great majority of laser leg vein interventions.…”

“…The neodymium:yttrium aluminum garnet (Nd:YAG) laser has proven effective in leg veins [1,3,[5][6][7][8]. Compared to green and yellow light, 1,064 nm light penetrates deeper and is less absorbed by melanin [7,9]. These two features allow larger veins and darker skin to be treated [1,5,[7][8][9].…”

“…Compared to green and yellow light, 1,064 nm light penetrates deeper and is less absorbed by melanin [7,9]. These two features allow larger veins and darker skin to be treated [1,5,[7][8][9]. A number of studies describe Nd:YAG laser treatment of leg veins, however an optimal pulse duration has not been established.…”

Investigation of Laser Induced Inhibition and Simulation in Biological Samples

“…Karu [6,13] has shown that visible and near-infrared radiation is absorbed in the respiratory chain molecules in the mitochondria (e.g., cytochrome), which results in increased metabolism, which leads to signal transduction to other parts of the cell, including cell membranes, and ultimately to the photoresponse (e.g., stimulation of growth) [8,12]. Laser irradiation as a phototherapeutic modality for the induction or acceleration of wound healing was first introduced by Mester et al [4,14] in the 1970s but still is not an established therapy.…”