Cryogen spray cooling during laser tissue welding

Cryogen cooling during laser tissue welding was explored as a means of redu cing lateral thermal damage near the tissue surface and shortening operativ e time. Two centimetre long full-thickness incisions were made on the epilated back s of guinea pigs, in vivo. India ink was applied to the incision edges then clamps were used to appose the edges. A 4 mm diameter beam of 16 W, contin uous-wave, 1.06 mu m, Nd:YAG laser radiation was scanned over the incisions , producing similar to 100 ms pulses. There was a delay of 2 s between scan s. The total irradiation Lime was varied from 1-2 min. Cryogen was delivere d to the weld site through a solenoid valve in spurt durations of 20, 60 an d 100 ms. The Lime between spuns was either 2 or 4 s, corresponding to one spurt every one or two laser scans. Histology and tensile strength measurem ents were used to evaluate laser welds. Total irradiation times were reduced from 10 min without surface cooling to under 1 min with surface cooling. The thermal denaturation profile showed less denaturation in the papillary dermis than in the mid-dermis. Welds cre ated using optimized irradiation and cooling parameters had significantly h igher tensile strengths (1.7 +/- 0.4 kg cm(-2)) than measured in the contro l studies without cryogen cooling (1.0 +/- 0.2 kg cm(-2)) (p < 0.05). Cryogen cooling of the tissue surface during laser welding results in incre ased weld strengths while reducing thermal damage and operative times. Long -term studies will be necessary to determine weld strengths and the amount of scarring during wound healing.