The role of pulse length in limiting distant damage to vascular tissue caused by the Nd-YAG laser

The total damage caused by equivalent doses of energy given to human cadaver vascular tissue over the same time scale from three Nd-YAG lasers of different pulse lengths is quantified. The continuous wave (c.w.) laser produces vacuolation and coagulation around a vaporized crater; the 100 μs pulsed laser produces less surrounding damage and the 10 ns pulsed laser none at all. The areas of damage in five craters made with 10 J energy were measured from histology slides using a digitising platten, and it was found that in each case the total amount of damage was the same, even though the depth of the craters made varied. The dose response for vaporization of the 10 ns pulsed laser was the greatest at 35 μm/J and that of the c.w. laser was least at 8 μm/J. A pulse length of 100 μs may not be the optimum for limiting surrounding tissue damage during laser angioplasty but it produces much less damage than a c.w. laser and unlike the 10 ns pulses is easily transmissible down an optical fibre.