## 4 Discussion  
Lung parenchyma can be separated either by means of a laser without tissue contact using a focusing handpiece or by means of a laser fiber with direct tissue contact (so-called bare fiber). The laser fiber is  
Figure 4: Histological presentation of the size of the vaporization and coagulation zone in the histological section (haematoxylin and eosin stain, magnification 12.5): (**A**) Laser power 120 W, motion speed 5 mm/s, direct contact of the tip of the bare fiber with the lung surface; (**B**) Laser power 120 W, motion speed 5 mm/s, distance of the tip of the bare fiber to the lung surface 5 mm; (**C**) Laser power 120 W, motion speed 5 mm/s, distance of the tip of the bare fiber to the lung surface: 10 mm. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Motion Speed (mm/s)/Distance of the** & & \\
**Bare Fiber to the Lung Surface (mm)** & & \\ \hline
5/0 & 2126.0 \(\pm\) 1.4 & 450.5 \(\pm\) 1.8 \\
5/5 & 994.7 \(\pm\) 1.8 & 223.2 \(\pm\) 2.1 \\
5/10 & 408.0 \(\pm\) 1.2 & 66.96 \(\pm\) 2.4 \\
10/0 & 1514.0 \(\pm\) 1.7 & 263.1 \(\pm\) 2.8 \\
10/5 & 764.5 \(\pm\) 0.6 & 126.5 \(\pm\) 2.2 \\
10/10 & 287.8 \(\pm\) 0.7 & 63.7 \(\pm\) 2.4 \\
20/0 & 863.1 \(\pm\) 1.7 & 102.2 \(\pm\) 2.4 \\
20/5 & 435.9 \(\pm\) 1.3 & 64.2 \(\pm\) 2.3 \\
20/10 & 182.0 \(\pm\) 1.5 & 38.3 \(\pm\) 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Depth of the vaporization and coagulation zone (\(\mu\)m) at a laser power of 120 W of the 600 \(\mu\)m bare fiber. guided across the lung parenchyma like a scalpel under visual control. Due to the strong development of local heat, a part of the lung parenchyma is vaporized, and the resection edges are coagulated. A hollow is thus created at the cut lung parenchyma, which is coagulated along the edge. It is therefore possible to work completely without blood loss. The laser fiber is thus not only suitable for open, but also for minimally invasive surgical procedures. As a general rule, thicker bare fibers are used for applications involving the lung parenchyma, like the 600 \(\upmu\)m fiber we used in our study. The aim of our study was to assess the local effects of the bare fiber on the lung parenchyma at various laser powers, operating speeds and distances of the tip of the bare fiber to the surface of the lungs. The greatest effect in terms of the size of the vaporization and coagulation zone was observed at a maximum laser power of 120 W, at a low operating speed of 5 mm/s and with direct tissue contact. The lowest effect was observed at a motion speed of 20 mm/s, with direct tissue contact and a laser power of 20 Watt. The fact that a vaporization effect was no longer detectable at distances of 5 mm and 10 mm of the tip of the bare fiber to the lung surface was interesting. With increasing operating speeds and unchanged laser power, the effect of the laser on the lung parenchyma is markedly reduced. This is logical, as less thermal energy per unit of time is lost to the lung parenchyma. At a constant operating speed, an increase of the laser energy leads to an increase in both the cutting and the coagulation effect. This effect can be further optimised by using a slower operating speed. As a fact the depth of the coagulation zone is responsible for the air tightness of the lung parenchyma after laser resection. Compared to our own studies, it was shown that--at a consistent energy level--the depth of the vaporization zone and of the coagulation zone is nearly twice as wide using the bare fiber with direct contact to the lung parenchyma compared to the focusing handpiece [5]. Therefore as a conclusion for clinical practice our work indicates that it is possible to cut deeper into the lung parenchyma with the bare fiber without the need for suture. This aspect has to be proven in an experimental setting with living animals, which we have planned to do in a further study. It is possible that both direct contact of the laser fiber with the lung parenchyma and the consistent mechanical forward feed of the fiber play a role.