Influence of laser wavelength and pulse duration on gas bubble formation in blood filled glass capillaries.
OBJECTIVE
Hypervascular skin lesions (HVSL) are treated with medical lasers characterized by a variety of parameters such as wavelength lambda, pulse duration t(p), and radiant exposure E that can be adjusted for different pathology and blood vessel size. Treatment parameters have been optimized assuming constant optical properties of blood during laser photocoagulation. However, recent studies suggest that this assumption may not always be true. Our objective was to quantify thermally induced changes in blood that occur during irradiation using standard laser parameters.


METHODS
Glass capillary tubes (diameter D = 100, 200, and 337 microm) filled with fresh or hemolyzed rabbit blood were irradiated once at lambda = 585, 595, or 600 nm, t(p) = 1.5 milliseconds; and also at lambda = 585 nm, t(p) = 0.45 milliseconds. E was increased until blood ablation caused formation of permanent gas bubbles. In a corroborative study, human blood was heated at 50 degrees C and absorbance spectra were measured as a function of time.


RESULTS
Threshold radiant exposure, E(thresh), for gas bubble formation was found not to depend on lambda, which might be surprising in view of the 10-fold lower absorption coefficient at 600 nm as compared to 585 nm. The spectroscopic study revealed heat-induced changes in blood constituent composition of hemoglobins (Hb) from initially 100% oxyhemoglobin (HbO2) to deoxyhemoglobin (HHb) and, ultimately, methemoglobin (metHb) as the major constituent. Model calculations of E(thresh)(lambda,D) based on changing constituent blood composition during heating with milliseconds lasers were found to correlate with experimental results.


CONCLUSIONS
For laser treatment of HVSL it appears that lambda is of secondary importance and that the choice of t(p) is a more important factor.
Kimel
Sol
S
Beckman Laser Institute, University of California, Irvine, California 92612, USA.
Choi
Bernard
B
Svaasand
Lars O
LO
Lotfi
Justin
J
Viator
John A
JA
Nelson
J Stuart
JS
D000818:Animals; D001769:Blood / Q000528:radiation effects*; D001774:Blood Chemical Analysis; D004307:Dose-Response Relationship, Radiation; D004864:Equipment and Supplies; D005740:Gases / Q000528:radiation effects*; D005898:Glass; D006454:Hemoglobins / Q000032:analysis; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D066298:In Vitro Techniques; D017075:Laser Coagulation / Q000009:adverse effects; D007834:Lasers / Q000009:adverse effects*; D028022:Low-Level Light Therapy / Q000009:adverse effects; D008297:Male; D008706:Methemoglobin / Q000032:analysis*; D010108:Oxyhemoglobins / Q000032:analysis; D011817:Rabbits
D005740:Gases; D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D008706:Methemoglobin