BIOPHYSICAL STUDIES ON CO₂ LASER SURGERY (PART III)

Further Analysis of the Relationships among Incision Depth, Cutting Velocity, Laser Power and Power Density in CO₂ Laser Incision

Abstract

This series of reports entitled “Biophysical Studies on CO₂ Laser Surgery” is based upon the CO₂ laser surgical research which we performed from 1969 thru 1970 at the Laser Laboratory of the University of Cincinnati Medical Center.
Experiments were undertaken to quantitate depth of incision by CO₂ laser system as a function of laser output, power density and cutting velocity. An American Optical CO₂ laser with surgical manipulator was used for focal incision of liver and skin. Experimental data are shown in Figure 1, 3, 4, 5 & 6.
(1) Graphical analysis of the relationship among laser power (P), incision depth (X) and cutting speed (v) indicates functional relationship of the form: X=k√P/v, where k is a constant. (Hishimoto-Rockwell's formula)
(2) Further graphical analyses of the relationship of power density (H), cutting velocity (v) and incision depth (X) suggest a relationship of the form: H=Kv^NXⁿ, where K is a constant.
(3) Non-linear curve, suggestive of a functional relationship of H=Ae^bv, at higher cutting velocities for skin incisions in Figure 5 must be attributed to increases in focal spot size and quasi-CW nature of energy delivery of the CO₂ laser scalpel.
(4) A problem that arises in applying the above formulas for deeper incision depth is abrupt reduction of the power density beyond the focal waist of the laser beam as the beam diverges. This variation in power density in deeper layer of the tissue may lead to deviation in mathematically expected values from the true ones.