Effect of tissue pressure on contact laser insults.

The effect of variations in tissue pressure transmitted through contact laser probes during tissue ablation has been investigated. Weights of 10 and 50 g were transmitted through the tip of the probes onto the gastric and colorectal wall. At all laser energies the depth of tissue vaporization was significantly greater at the higher tissue pressure with perforation of the viscus occurring at laser energies above 10 J. The lateral zones of thermal tissue necrosis were not influenced by tissue pressure. Deformation of the wall of the viscus under the pressure of the probe was identified as a sign of excessive tissue pressure likely to result in perforation of any tissue of similar thickness to the normal gastric or colorectal wall.