Guilhem Godlewski

Applications and mechanisms of laser tissue welding in 1995: review

For several years laser tissue welding has appeared as a new alternative technique for tissue repair instead of manual sutures. It has been evaluated in different experimental models including blood vessels, skin, nerve, intestine, bile ducts, vas and fallopian tube. Different types of lasers with different sets of parameters have been used: carbon dioxide laser, Nd:YAG laser, argon and KTP laser and diode laser. Recent trends in tissue fusion promote near infrared lasers at low irradiance with intraoperative enhancement of light absorption by specific chromophores. As far as microvascular reconstruction is concerned, successful clinical applications are currently published. Although the molecular mechanism involved in welding is not completely understood, the tissular fusion is considered as a thermal phenomena. In laser assisted microvascular anastomosis, the best experimental model, the ultrastructural examination of arteries anastomosed with Nd:YAG, argon or diode laser revealed interdigitation of collagen fibers which appeared swollen, with modified striation and organized in irregular network. The mechanism of welding involving the formation of non covalent bands between collagen strands, is generally induced by a temperature of 60 - 63 degrees Celsius well adapted to collagen denaturation.

Microvascular carotid end-to-end anastomosis with a compact diode laser equipped with an auto-stop system: a preliminary study

Diode laser assisted microvascular anastomosis (LAMA) versus control ateral conventional suture microanastomosis (CMA) were performed in 50 rats. The laser source (830 nm) was included into a micromanipulator without optical fiber connection. The beam was directly focused on a deviating mirror giving a 200 micrometers spot size. The LAMA was performed on the left common carotid by means of 3 laser shots of 360 mW power and 8 s exposure time regulated by an auto-stop system, the irradiance being 1,146 W/cm2. CMA was performed on the right carotid by means of size 10.0 Ethilon stitches (BV 70, Ethnor, Neuilly, France). The anastomoses were evaluated by macroscopic controls and Doppler spectral analysis (D0 to D60). After LAMA, light and scanning electron microscopy visualized the rapid re-endothelialization of the anastomotic line with longitudinal migration of endothelial cells, while the media was repaired by collagen network due to tissular fusion. The procedure demonstrated the usefulness and the adaptability of our new laser system. The prototype, characterized by low weight (2,500 g), small size 30 X 10 X 6 cm), good laser transmission, equipped with a feed-back system is well adapted to microsurgery.

Morphological study of the healing process after diode laser-assisted end-to-end microanastomosis: comparison with conventional manual suture

A series of carotid end-to-end diode laser assisted microvascular anastomosis (LAMA) versus control ateral conventional suture microanastomosis (CMA) were performed in 120 Wistar rats (in the same animal, LAMA performed in the left side and CMA in the right). The optic and scanning electron microscopic examinations were assessed from day 0 to day 210. The results revealed that on day 0 LAMA gave rise to proteins deneturation and collagens fusion of the media and adventitia in the arterial wall. Re-endothelialization of anastomotic line began at day 3, as well as a large number of inflammatory aggregated in the adventitia. On day 10 the endothelial cells were restored on the anastomotic site and collagenous network developed in the media. On day 90 proliferation and disorientation of the elastic fibers appeared. A part of elastic laminae had been reconstructed on day 210. In the group CMA, the re- endothelialization developed later than LAMA, and the reconstruction of the elastic laminae failed to happen until day 210. These data suggest that the results of long term healing process after diode LAMA is better than that of CMA in normal artery repair.

Laser tissue welding: a new device controlled by reflectance

Laser tissue welding is used to close wounds or to anastomose conducts such as arteries. The welding effect is due to tissue denaturation which depends on the irradiation parameters. An excessive laser irradiation leads to irreversible thermal damage. In conventional welding procedures, laser irradiation is controlled by visual inspection of the welded zone. A new device based on an 800 nm diode laser allowing an automated welding procedure is described here. The device measures the variation of the diffuse reflectance on the treatment area and stops laser irradiation when a given optimal value is reached. This allows the user to increase the reproducibility of the treatment by avoiding the subjective aspect of welding completion assessment by visual criteria. The system has been tested by in vitro welding an egg yolk membrane on mesenteric bovine arteries. The results have shown that for a given laser power, there is a specific reflectance decrease threshold value leading to an optimal welding. Reproducible welds with minimal thermal damage could be obtained.

Diode laser and microvascular anastomosis-long term follow up

Direct diode laser assisted carotid end-to-end microanastomosis (LAMA) versus contralateral manual sutures microanastomosis (CMA) were performed in 70 Wistar rats. The laser beam- wavelength 830 nm, maximum power 3 W and continuous wave was transmitted through a micromanipulator and provided a focused spot of 300 micrometers in diameter. After placement of three 10.0 stitches for edge coaptation, LAMA was achieved on left common carotid (0.8 - 1.2 mm) using laser shots (average 3) of 500 mW power, 4.5 s duration and 700 W/cm2 irradiance each. CMA was performed on right carotid by means of six 10.0 stitches. Light and scanning electron microscopy (n equals 82) showed in LAMA that re-endothelialization was complete on day 10 while collagenous fusion of media and adventitia was evident. The patency rate was 93% after LAMA versus 93% after CMA. The intra operative advantages of LAMA versus CMA: shorter operating time minimizing organ ischemia (13 min versus 22 min) and reduced endothelial trauma were evidenced. The technical advantages of diode laser were pointed out: small size of device, absence of water cooling system, no maintenance and decreasing price of diodes.

Diode laser and interstitial hyperthermia against HT29 colonic cancer: effect of power settings on necrosis size

An experimental procedure of antitumoral interstitial diode laser hyperthermia was achieved in a series of 30 Swiss nu/nu mice (10 weeks old, 25 g weight). The tumor model was a subcutaneous HT29 colonic carcinoma. The diode laser (830 nm) was applied through a 300 micrometers optic fiber implanted in the tumor and delivered at different powers as follow: group 1 -- 0.2 W (n equals 5); group 2 -- 0.5 W (n equals 4); group 3 -- 0.8 W (n equals 4); group 4 -- 1.0 W (n equals 4); group 5 -- 1.2 W (n equals 4); group 6 -- 1.5 W (n equals 4); group 7 -- 1.8 W (n equals 5). The exposure time was 900 sec (360 to 1 620 J). According to the different laser applications the temperature range was 48.2 degree(s)C to 73.7 degree(s)C in the center of the tumor and 42.0 degree(s)C to 63.5 degree(s)C in its peripheral part. The tumor was removed 24 h after laser treatment. The largest necrosis diameter evaluated by macroscopic and histological sections were 8, 11, 13.25, 17.65, 18, 18.25 and 18.5 mm in the group 1, 2, 3, 4, 5, 6, 7, respectively. In the groups 6 and 7 (1.5 and 1.8 W) all animals died after treatment, the death being explained by extensive hyperthermia. Our results suggest that 1.0 W/900 sec might be the most effective condition for treating this tumor model in Swiss nu/nu mice.

Compliance of laser-assisted microvascular anastomosis: a comparative study with manual anastomosis (preliminary results)

The compliance of microvascular anastomosis is an important predictive factor for long term patency of graft or vascular reconstruction. This experimental study compare the compliance of manual suture and laser assisted end to end microvascular anastomosis. In nine New-Zealand white rabbits we performed manual end-to-end suture anastomosis on the left femoral artery and laser assisted anastomosis on the right femoral artery, with a diode laser (wavelength 988 nm, power output 500 mW). Compliance was obtained by echotracking (CBI 8000 sonomicrometry system with 20 MHz implantable microprobe from Crystal-Biotech, USA) on the anastomosis site as well as upstream, and downstream from the anastomosis. Vessel compliance was lower on the manual suture side compared to the laser assisted anastomosis side, especially downstream from the anastomosis.

Master oscillator power amplifier diode laser and microarterial anastomosis with chromophore

Feasibility of laser assisted micro-vascular anastomosis (LAMA) has already been proved for more than 15 years. But to our knowledge, equivalence between LAMA and conventional manual anastomosis (CMA) has never been demonstrated. With a Master Oscillator Power Amplifier diode laser (988 nm) and Fast Green FCF as chromophore, LAMA versus CMA were performed on the carotids of 92 Wistar rats. LAMA edge coaptation was achieved with three 10/0 stitches, irradiation with 3 shots of 500 mW in power and 800 nm in diameter. CMA was performed on the other side with six 10/0 stitches. At 2 months, 3 aneurysms were present on LAMA side and 3 on CMA side, the success rate was 96.7% on both sides. We established the equivalence of LAMA and CMA, in an interval of 5%, using a method of equivalence based on odds ratios and Chi-square test. Paired t-test comparing carotid flow, maximal Doppler frequencies, pulsatility and resistance index could not highlight any difference between the 2 methods. Histological analysis showed an earlier and better re-endothelialization on LAMA side. For the first time to our knowledge equivalent between LAMA and CMA has been demonstrated.

Mechanism of aneurysm formation after 830 nm diode laser assisted microarterial anastomosis

A series of 830 nm diode laser assisted longitudinal aortorrhophy with a condition of 400 to 500 J/mm2 for one cm length of anastomosis versus conventional manual anastomoses were performed in 90 Wistar rats. With comparing with normal media process, a histologic examination of aneurysm formation was conducted. The results show that there are two important factors to cause aneurysm formation after laser assisted anastomosis: (1) vessel wall is damaged by laser heating; (2) proliferation of collagen fiber at adventitia is absent when media reconstruction.

Diode laser thermotherapy in the treatment of hepatic tumors in rabbits

Laser induced thermotherapy (LITT) has been recently developed for treating deep seated tumors. Diode laser (830 nm) is suitable for LITT, because of its high penetration in tissue. The present animal experiment was conducted to evaluate the performance of a diode laser for treating liver tumors in rabbits. Fifty-two New Zealand rabbits were grafted in liver with a Vx2 tumor model. They were treated at a tumor size of 8 mm diameter. A laser energy of 1 350 J (power: 1.5 W; irradiation time 900 s) was delivered through a 300 micrometer fiber implanted in the center of the tumor. Our experiment was divided in two parts: (1) A survival study: we compared the medians survival between untreated tumors (Group A, n equals 21) and irradiated tumors (Group B, n equals 21), (2) An evaluation of LITT efficiency on day 7 (Group C, n equals 5) and at day 14 (Group D, n equals 5). We compared at day 7 and day 14 the radiologic data (ultrasonography and MRI realized before and after irradiation) to the microscopic examinations (haematoxylin eosine stain and picrosirius red F3BA). The results were a median survival not significantly different in group B (laser) than in group A (control) and an efficiency only at short time (on day 7). There was a good correlation between radiologic data and microscopic examinations in groups C and D. The picrosirius red F3BA estimated the extent of thermal damage. In conclusion, these disappointing results are due to an insufficient irradiation of peritumoral tissue and to the Vx2 aggressivity (undifferentiated). Using multiple optical fiber could improve the LITT efficiency. The correlation between radiological and microscopic findings would allow us to quantify the results of LITT.