Effect of CO2 and blood media on laser probe temperature

Carbon Dioxide in Vascular Imaging and Intervention

Angiography with iodinated contrast agents is bound up with the risks of contrast-induced nephrotoxicity and hypersensitivity, which led to the idea of using carbon dioxide (CO2) gas as a negative contrast medium to eliminate these drawbacks. During the last decade, refinements and experiences have proved carbon dioxide digital subtraction angiography (CO2-DSA) to be an accurate, safe, and clinically promising vascular imaging modality, with the advantages of no hypersensitivity and no nephrotoxicity as well as minimal patient discomfort. In this article, we have reviewed the history, physical and chemical aspects, techniques, and pathophysiologic changes with the use of CO2-DSA as well as some clinical trials. Applications of CO2 gas in vascular interventions and other imagings, and the advantages and limitations of using CO2 gas in DSA are also discussed.

Percutaneous Transluminal Laser Angioplasty

The progress in percutaneous transluminal laser angioplasty (PTLA) over the past two years is presented. The technical development includes the application of new equipments to laser sources, delivery systems and monitors. We review new experimental research in rapidly establishing animal models and human postmortem specimens, as well as efforts to select adequate wave length and irradiation time for laser energy with suitable infusion media. A summary of clinical trials is given on expanding usage, complication rates and long-term patency of PTLA. The current trends in PTLA respecting guide wire assisted balloon angioplasty and other recanalization methods are described.

Angioscopy: a new light on peripheral vascular disease

Although fibre-optic imaging has been used in a number of medical specialties for several years, it has only recently begun to develop in the area of peripheral vascular disease. This review considers the historical development of angioscopy, its current role in peripheral vascular surgery and, finally, its potential for the future.

CO2 gas perfusion: improved efficiency and safety with sapphire-probe laser ablation of human artery

CO2 gas has been proposed as a new perfusion medium for laser angioplasty. To compare CO2 gas with conventional saline perfusion, 146 fresh specimens of normal and atheromatous human artery were irradiated with a neodymium: yttrium-aluminum-garnet laser with a sapphire probe in flowing whole blood in an experimental circulation-occlusion model. The dimensions of the ablation crater and the extent of the surrounding tissue damage were measured microscopically. Significantly better ablation of atheromatous plaque was achieved with CO2 perfusion than with saline perfusion: mean ablation areas were 5.0 mm2 versus 2.8 mm2, respectively (P = .001, Student t test). In contrast, the ablation areas on normal vessel wall were identical (mean, 3.4 mm2) with the two perfusion media. Moreover, CO2 gas functioned as a negative contrast agent and facilitated direct monitoring of the laser recanalization procedure. On an experimental basis, CO2 gas perfusion seems to improve the efficiency and safety of laser ablation in human arteries.

Temperature along the surface of modified fiber tips for Nd:YAG laser angioplasty

For laser angioplasty probes, the thermal properties of the probes will primarily determine their mechanism of action. We examined the absorption, temperature increase, and probe degradation of transparent contact probes (hemispherical contact probe and ball-shaped fibers) and metal laser probes coupled to a continuous-wave Nd-YAG laser. Temperature was recorded by means of thermocouples and the measurements were corrected for direct light absorption by the thermocouple. During 15 W, 1 s exposure, the peak temperature rise of the hemispherical contact probe in contact with tissue dropped from approximately 1,000 degrees C at the front end to below 45 degrees C (95% drop) at the lateral side. In contrast, during continuous exposure the peak temperature rise of metal laser probes in contact with tissue dropped from 560 degrees C at the front end to near 400 degrees C (30% drop) at the 5.5 mm proximal rear end. During exposure in blood or tissue, the transparent contact probes became contaminated. Their absorption increased from 5 to 33% and the probe deteriorated. Repeated use of metal laser probes in blood resulted in a higher temperature at the rear than at the front end due to backburing of the fiber. Owing to the large temperature drop along the surface of transparent contact probes, the area of thermal destruction is limited to the tissue in front of the probe, whereas along the entire surface of metal laser probes the tissue will be affected. The large difference between these temperature distributions should be respected during clinical application of the transparent contact probe and the metal laser probe.

Temperature monitoring during peripheral thermo-optical laser recanalization in humans

To determine probe temperature required to achieve laser thermal recanalization of human peripheral arteries, temperature was monitored at the probe tip using a K-type thermocouple and displayed on a computer screen in real-time in 21 procedures. Recanalization was performed using a Spectraprobe-PLR delivering both laser light and heat in patients with prolonged ischemic limb symptoms. Laser recanalization of totally occluded peripheral arteries (occlusion length = 5.3 +/- 3.8 cm) was done percutaneously (17 procedures) or intraoperatively (4 procedures), after unsuccessful attempts of recanalization using standard guide wire and balloon angioplasty techniques. Probes were activated using argon laser irradiation starting at 5 W and increased by 1-W increments until successful recanalization, or up to a maximum of 12 W. Laser recanalization was achieved in 16/21 (76%) procedures at a mean temperature of 178 +/- 120 degrees C (range 64-503 degrees C) and a mean time of 12.4 +/- 14.1 s. Eleven of the 16 (69%) recanalizations occurred at probe temperature lower than 160 degrees C. Recanalization was achieved at a mean power of 7 +/- 2 W. Perforation occurred in 6 arteries at peak probe temperatures ranging from 73 to 502 degrees C. Perforations occurred in 4 of 6 densely calcific vessels which required high probe temperatures (greater than 250 degrees C). An important feature of temperature monitoring was the immediate detection of probe dysfunction. Although recanalization temperature had a wide range, the majority of recanalizations occurred at probe temperature below 160 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon dioxide gas as a perfusion medium for the sapphire probe in laser ablation of human atheromatous plaques: comparison study with saline

The effectiveness of CO2 gas as a perfusion medium was compared to that of saline in laser ablation of human atheromatous plaque. In an experimental circulation-occlusion model using flowing whole blood, human cadaveric arterial samples were irradiated by a sapphire probe with the Nd-YAG laser. The following experiments were performed: 1) lasing without perfusion, 2) lasing with saline perfusion of the probe, and 3) lasing with CO2 perfusion. Different perfusion flow rates of saline and CO2 were used. Results showed that the mean ablation area was 1.6-fold larger with CO2 than with saline perfusion (P less than 0.05, Student's t test). The mean lateral injury at the site adjacent to the ablation crater and at the area directly facing the probe was not significantly different with either perfusion medium. The larger ablation area with CO2 was probably due to the fact that CO2 is a good insulator for maintaining a higher probe temperature and keeps the probe free of blood debris. In conclusion, our results show that CO2 perfusion facilitates more effective laser ablation of atheromatous plaque than saline perfusion by the sapphire probe with the continuous wave Nd-YAG laser.