XeCl laser action at medium fluences on biological tissues: fluorescence study and simulation with a chemical solution.

A rat heart, isolated and perfused, was irradiated with a XeCl excimer laser at 308 nm. The evolution of the fluorescence spectrum was measured. For an incident energy E greater than 4 kJ m-2 per pulse the fluorescence changed with time in a complex and spectrally non-uniform way. The proposed interpretation is that the radiation acts on the cellular respiratory chain. Buffered solutions of NADH, cytochrome c and FAD, which play a role in the respiratory chain, were irradiated in order to simulate the in vivo findings. The conclusion of this study is that XeCl radiation introduces a modification in the functioning of the respiratory chain: it accelerates electron transfer, but this quickly leads to an interruption of the respiratory chain.

[Contribution of excimer laser to coronary angioplasty]. / Apport des lasers à excimères à l'angioplastie coronaire.

Reports on the problems encountered with thermal laser system in angioplasty have prompted us to test an excimer Xe-Cl laser of 308 nm wavelength and 20 ns impulses on preparations of healthy and atheromatous coronary arteries, the purpose of the study being to quantify the adequate parameters required for angioplasty. We effectively used optic fibres of different diameters--a method which has not yet been reported in medical literature. Our choice of an ultraviolet laser was justified on theoretical grounds: essentially its mode of photo-ablation devoid of thermal effects and proportional to the number of inter- and intramolecular bonds destroyed. The photo-ablation threshold we measured being 1.40 J/cm2, we micrometrically determined the volume of matter removed by various combinations of energy intensities and numbers of impulses, as well as the undesirable effects of such combinations. We found that with an energy surface density of 4.23 J/cm2 the depth of ablation was directly proportional to the number of impulses (between 20 and 100). Under these experimental conditions, the ablation produced by the Xe-Cl laser system was 14 microns per impulse in depth, and of the same diameter as that of the optic fibre used. Virtually identical data were obtained in healthy, fibrotic, atheromatous and calcified tissues. Undesirable effects, i.e. coagulation necrosis, only appeared with high-intensity energies irrelevant to the study. No lesion of the parietal cells was observed, even in the vicinity of the ablation plane. Finally, the question of oncogenic effects raised with 193 nm laser beams does not seem to apply to the 308 nm wavelength.(ABSTRACT TRUNCATED AT 250 WORDS)

In situ double-beam NADH laser fluorimetry: choice of a reference wavelength.

A double-beam laser fluorimeter, using a single optical fiber to guide the lights, was constructed for in situ and on-line monitoring of NADH concentration [( NADH]) from normally blood-perfused living tissues. The device was tested on an isolated blood-perfused rat heart system to determine the most efficient reference wavelength for the compensation of the hemodynamic artifact induced by blood circulation in the tissues on the fluorescence measure; 586 nm was found to be an accurate reference wavelength, and a mathematical relationship was established that allowed the digital treatment of the measured fluorescence to give a signal (compensated fluorescence) that varied only with [NADH] in the volume of tissue investigated.

Comparative study of the effects of argon and neodymium YAG laser beams on the normal fundic wall in the beagle dog.

A study was performed to compare the lesions induced by argon and neodymium YAG laser beams in the normal fundic wall of the same beagle dogs and to follow their healing over a 21-day period. The total energy per application was 21 joules for the argon laser and 53 joules for the neodymium YAG laser. Both laser beams were emitted from the same distance, directed at right angles to the tissue surface, and with the same flow rate of coaxial gas. Thirty-nine shots were performed with each type of laser. Differences between the two lasers were observed in the appearance of the impacts, the volume of tissue affected, and the rate of healing, but all the lesions healed without any perforation. The differences observed were probably due to differences between the two lasers in the radial distribution of luminous energy and its absorption and transformation within the tissue into heat. It was concluded, however, that under the experimental conditions chosen, both kinds of laser could be used to penetrate the mucosal and submucosal tissue without risk of damage either to the longitudinal or to the serosal layers of the fundic wall.