Effects of Nd:YAG and CO2 lasers on cerebral microvasculature. Study in normal rabbit brain

The effect of Nd:YAG and CO2 laser beams on cerebral microvasculature was examined in experimental animals. Soft x-ray microangiography and histological examination of the brain after Nd:YAG laser exposure revealed broad avascular or oligovascular zones in the irradiated and the surrounding edematous tissue, in which the surviving vessels were narrowed and tapered without significant leakage of blood. After CO2 laser exposure, a wedge-shaped tissue defect surrounded by layers of charring, coagulation, and edema was observed. The main finding in the surrounding coagulation and edematous layers was dilatation of the vessels. Hemorrhage was sometimes observed, mainly in the edematous layer. These findings seem to explain the effective hemostatic capability of the Nd:YAG laser and the occasional hemorrhage following CO2 laser exposure, especially at high energy output.     

Experimental study of brain lesions after combined coaxial exposure to high-peaked pulse wave form CO2 and Nd: YAG lasers on the brain

The CO2 laser is useful for cutting and vaporization but not for coagulation and hemostasis. On the contrary, YAG laser is effective for coagulation and hemostasis but not for cutting. The purpose of this study is to examine the effect of the exposure of combined, coaxial CO2 and YAG laser on the animal brain to supplement the advantages and draw-backs of each other. To compare these results, each of non-combined pulse wave form CO2 and YAG lasers was employed separately. Materials and Methods: The lasers in this study were pulse wave form CO2 and YAG lasers, employed separately or simultaneously using 130 YZ of Nihon Infrared Industries Company. Japanese white rabbits were anesthetized with pentobarbital. Fronto-parietal burr holes were made, the dura was removed and then Evans blue solution was injected intravenously. The lasers were employed to the cerebral cortex without great vessels using a micromanipulator attached to the operative microscope with a distance of 30 cm. The spot size was 700 mu for CO2 laser and 1200 mu for YAG laser. The first experiment was to see the effect of nine combinations of simultaneous coaxial CO2 of 2, 4 and 8 watts and YAG lasers of 10, 20 and 40 watts, 1 sec on the brain. In the second experiment, also combining two lasers, the exposure time of YAG laser was elongated from 1 or 2 seconds into 2 or 4 seconds and the arrangement of powers was the same as that of the first experiment. The lesions were thus made in 18 different conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of argon, dye, and Nd:YAG lasers on epidermis, dermis, and venous vessels

The aim of the present study, which was performed at the dorsal aspects of the ears of guinea pigs, was to compare effects of different lasers on epidermis, dermis, and small venous vessels. Irradiations were performed with argon, dye, and Nd:YAG lasers. In the first series tissue repair processes were studied after argon laser application. Laser defects were excised after 1, 4, 8, and 14 days and were prepared for routine histological examination. The breadth of epidermal defect and extent of dermal coagulation and occlusion of vessels by thrombus formation were examined histologically. In a second series parameters of irradiation (ie, exposure time, laser power) of the three different lasers were changed systematically. Laser-induced morphological tissue changes could be best observed 24 hours after irradiation. Each of the lasers led to occlusion of vessels by thrombus formation and also coagulated epidermis and dermis. The extent of dermal and epidermal coagulation was less pronounced after dye laser application. Using short exposure times it was possible to reduce the extent of epidermal damage caused by argon and Nd:YAG lasers. Only 50-msec dye laser pulses led to intravascular thrombus formation without epidermal and dermal damage.     

Effects at the periphery of the laser lesion in human brain and its tumors after CO2, Nd:YAG, and CO2 high-peak pulsed radiation

The histological changes in various tissues irradiated with lasers are well known. Our own previous observations with the optical microscope confirm those already reported in the laser literature. If tissue is treated with various laser sources, the results are similar, with the characteristic three layers from the outside toward the inside of carbonization, coagulative necrosis, and edema. Otherwise, only the shapes and sizes of the lesions differ, with craters of different depths. In this paper, we report an ultrastructural study of the changes occurring in the periphery of the laser lesions in both normal human brain and neoplastic tissues (gliomas and meningiomas). Continuous-wave CO2 and Nd:YAG lasers were used at different exposure times and powers and the effects of high-peak pulsed CO2 laser radiation has also been investigated. The study, performed during neurosurgical procedures was mostly focused on microcirculation at 1.5-3 mm outside the area of coagulative necrosis, at the level of the edema zone. Only lesions of the blood brain barrier are produced in normal brain by CO2 radiation (power ranging from 40 to 80 W; exposure time from 3 to 10 seconds). The same results were achieved by Nd:YAG radiation of short duration (3 seconds) regardless of the power used (40 and 80 W). Long-duration Nd:YAG radiation (10 sec; power: 40-80 W) produces endoluminal phenomena leading to the complete occlusion of the capillaries. In neoplastic brain tissues, microcirculation does not seem to be impaired by CO2 radiation. More marked lesions are produced in tumors even after Nd:YAG short-time radiation. Endoluminal obliteration is observed in meningiomas and perivascular hemorrhage occurs in highly vascularized gliomas. According to these results, the risk of delayed post-operative hemorrhages, noticed in some patients with glioblastoma operated on by Nd:YAG lasers, suggests that residual tumor in the cavity should be treated by CO2 laser because of its minimal damage of microcirculation.     

Comparison of surgical lasers and conventional methods in skin incisions

Steel scalpel, electrocautery, CO2 laser used in a continuous wave mode (CW) and rapid superpulse mode (RSP), and contact Nd: YAG laser were tested on pig skin incisions. Speed of incision and histological changes near the wounds were examined. Light microscopical observations were made on postoperative day 0 using standard Van Gieson stain. Width of the scar on postoperative day 14 was also measured. Steel scalpel produced the least pathological changes in the skin, followed by RSP. Electrocautery did not differ significantly from the CO2 lasers in this respect on postoperative day 0. The damage was larger after contact Nd:YAG laser. The situation was essentially similar on postoperative day 14. The width of the scar was narrowest after steel scalpel and widest after contact Nd:YAG laser (p less than 0.01; Nd:YAG vs. other methods). Electrocautery and the two CO2 lasers produced equal scarring. However, electrocautery was significantly faster than any of the lasers (p less than 0.001).     

Application of pulsed and continuous wave 1.32 and 1.06 microns wavelengths of the Nd:YAG laser in the canine tracheobronchial tree: a comparative study

Previous investigations have shown good clinical potential for the use of the 1.32 microns wavelength Nd:YAG laser because its soft tissue absorption is better than that of the 1.06 microns wavelength Nd:YAG laser. The 1.32 microns wavelength Nd:YAG laser has an absorption coefficient in water that is 10 times higher than the 1.06 microns wavelength Nd:YAG laser. A comparative in vivo study of laser soft tissue effects was performed by using the 1.32 microns wavelength and the 1.06 microns wavelength Nd:YAG lasers in a pulsed wave (PW) mode and continuous wave (CW) mode using a non-contact endoscopic delivery system. A standard 5 mm mucosal lesion was made in the canine tracheobronchial tree down to the level of the perichondrium. Soft tissue and cartilage effects were examined by light and scanning electron microscopy, acutely, 1 week and 2 weeks after operation, and a comparison was made between the different laser modalities. To create similar lesions, higher energy was required when using the 1.06 microns wavelength Nd:YAG laser. Soft tissue injury was greater with the 1.06 microns wavelength in CW mode, and no cartilage damage occurred in the PW mode. Soft tissue and cartilage repair after 1 and 2 weeks was better with the 1.32 microns wavelength laser. In comparison, the CO2 laser and the contact Nd:YAG laser proved to be more precise cutting tools than the 1.32 microns wavelength or the 1.06 microns wavelength Nd:YAG lasers. Both Nd:YAG laser wavelengths were useful for coagulation and vaporization of tissues and blood vessels. More studies are needed to determine the effect of the new 1.32 microns wavelengths on endotracheal tumors.     

Lasers in medicine

Since its discovery, the laser has been intensively investigated and used in medicine, first in ophthalmology then in ear, nose and throat surgery, gynaecology, neurosurgery etc. Development spans from the ruby and argon lasers in outpatient eye surgery to the carbon dioxide and Nd:YAG lasers in the operating theatres and further on to the PDT-dye lasers, excimer and solid state angioplasty lasers or flash lamp pumped "gallstone cracker" lasers. The CO2-Nd: YAG laser combination will be described as the state-of-art surgical laser. This simultaneous, coaxial and coherent combination laser offers a new possibility to cut and coagulate effectively at the same time. Operating times are shortened and bleeding volumes minimised. The CO2-Nd: YAG laser represents a new type of interaction between laser and tissue, laser enhanced tissue absorption, which will be described.     

Sutureless microvascular anastomosis using the THC:YAG laser: a preliminary report

Laser anastomosis of the rat carotid artery was performed using a new mid-infrared laser, the pulsed thulium-holmium-chromium: YAG (THC:YAG) laser (2.15 microns). Solid silicone stents made stay sutures unnecessary for coaptation of vessel edges during laser bonding. Grossly, the laser anastomoses displayed minimal thermal distortion of the vessel contour and no tissue carbonization. Of the 30 anastomoses performed, 27 were patent and 3 had separation of the weld shortly after the approximator clamp was released. Mean anastomotic time was 4 min 48 sec. Mean bursting pressure for the 9 vessels tested was 400 mm Hg. Thrombosis did not occur at any time during our examination of these anastomoses. Fusion of collagen fibers in the media was confirmed histologically. Unlike the CO2 laser, the THC:YAG is transmissible through flexible silica fibers, which greatly facilitates delivery of the laser in a microsurgical operative field. The THC:YAG provides shallower absorption depth than Nd:YAG and argon lasers but somewhat deeper tissue penetration than CO2. For microvessels, this intermediate absorption results in full-thickness fusion of the media, with minimal thermal damage to vascular tissue adjacent to the anastomosis.     

Acute effect of the Nd:YAG laser on the cerebral arteriovenous malformation: a histological study

The acute effect of Nd:YAG laser beam on cerebral arteriovenous malformations (AVMs) was examined. Histological examination of the specimens after treatment with the Nd:YAG laser revealed that the most prominent effect of the laser was shrinkage of the collagen of the vessels of the AVM, which led to laser-induced narrowing of blood vessels. The brain tissue confined to the resected AVM did not contain any histological evidence of acute damage. The resection of 10 cases of AVMs was safely accomplished with no morbidity or increased neurological deficits attributable to the laser technique.     

An experimental study of the effects of electrocautery and various lasers on gastrointestinal tissue

It is possible that in the future, lasers will replace electrocautery in gastrointestinal surgical procedures. Few studies exist that compare the tissue effects of electrocautery with newer laser modalities. In this study, the tissue effects of electrocautery, noncontact Nd:YAG, contact Nd:YAG, and CO2 lasers were studied in the stomach, small bowel, colon, liver, and pancreas in 24 rats. At light microscopic examination, all tissue damage was thermal in nature, irrespective of the modality used. Furthermore, an independent observer was unable to distinguish which method has been used in most tissues. Tissue effects were similar in the stomach, small intestine, and colon after use of all the modalities. The CO2 laser caused slightly less damage than the other methods (p less than 0.05), but with use of this modality, hemostasis could not be achieved in the liver and pancreas. The contact Nd:YAG laser caused moderate damage with excellent hemostasis in all tissue. The noncontact Nd:YAG caused significantly more tissue damage than all other methods (p less than 0.01), especially in the liver and pancreas. The results suggest that the new contact laser system provides an effective method of performing gastrointestinal surgery with especially good hemostatic effects on liver and pancreatic resections.     

Biological effects of laser welding on vascular healing

The feasibility of welding thin-walled microvessels by laser has been established. This report summarizes our experience using laser welding to repair thick-walled, high-pressure, 4 to 8-mm canine arteries using CO2, Nd:YAG, and argon lasers. The CO2 laser did not produce seals that could withstand arterial pressure. Nd:YAG laser welds were initially successful, but the majority failed within 20 to 40 minutes. The argon laser uniformly sealed 2-cm-length arteriotomies that healed rapidly within 4 to 6 weeks and had less foreign body response compared to sutured controls. Laser welding may represent an alternative for repair of small- and large-diameter vessels with several advantages compared to conventional suture techniques.     

Experimental study of partial liver resection with a combined CO2 and Nd:YAG laser

The use of the CO₂ laser in liver surgery is mainly limited by the lack of coagulation of the larger vessels. In an experimental study, partial liver resections were performed on pigs with a Nd:YAG as well as with a combined CO₂ and Nd: YAG laser. The best cutting efficiency was obtained with the CO₂ laser. On the other hand, the Nd:YAG laser and the combined laser sources showed excellent hemostasis at the cutting edge corresponding with a width of necrosis at about 5 mm in histomorphometric examination and zones with histologically different characteristics. Rebleedings from the resection lines were avoided in all cases using the combined CO₂ and Nd:YAG laser.     

Vasovasostomy in the murine vas deferens: comparison of the Nd:YAG laser at 1.06 microns and 1.318 microns to the CO2 laser

A comparison is made of laser anastomoses of the murine vas deferens at different energies with the neodymium (Nd):YAG laser at 1.06 micron and 1.318 micron and with the CO2 laser. A total of 28 welds were performed with a free-hand technique employing a 600-micron silicon fiber with the Nd:YAG and a hand piece with a 500-micron spot size for the CO2. After 6 weeks, all animals were sacrificed and the vasa evaluated for patency. Fifteen out of 28 controls repaired with microsurgical techniques were found to be patent; 4/10 vasa were patent with use of the Nd:YAG at 1.318 micron at laser energies of 300 mW and 500 mW. At 1.06 micron, only 1/4 anastomoses was patent at a power setting of 1 W. None of the anastomoses performed with the CO2 laser was patent. Histologic study revealed intense fibrosis in all the lasered vasa, with sperm granuloma formation associated with most anastomoses. Although this is a preliminary study, it appears that the Nd:YAG laser at 1.318 micron and a power setting of 300-500 mW provides patency rates superior to the Nd:YAG at 1.06 micron and to the CO2 lasers and is equivalent to standard micro-surgical techniques in the murine vas deferens.     

Thermal effects in tissues from combined simultaneous coaxial CO2 and Nd:YAG laser beams.

This study examines the depth of thermal coagulation and charring in swine liver, kidney cortex, tongue (inferior surface), skeletal muscle, inflated lung, and skin resulting from in vivo incision with simultaneous coaxial CO2 and Nd:YAG (1.064 microM) laser beams. At values of 20 w and 40 w, respectively, and at values of 30 w and 60 w, respectively, of combined CO2 and Nd:YAG laser radiation, coagulation depths determined histologically in liver were significantly greater (P less than 0.01) than in the other tissues and were significantly less in inflated lung (P less than 0.05) than in other tissues for the larger laser power settings employed. Coagulation depths achieved at 10 w and 20 w, respectively, and at 20 w and 40 w, respectively, of CO2 and Nd:YAG laser power were comparable to those obtained by other workers in liver and other relatively vascular tissues using a contact Nd:YAG laser tip. Charring depths obtained at power settings of 30 w (CO2) and 60 w (Nd:YAG) were greater in liver (P less than 0.001) than in all other tissues examined. Hemostasis during incision was achieved only for values of the ratio of CO2 to Nd:YAG laser power in the range 2-3 in the more vascular tissues, liver and kidney cortex, whereas hemostasis was achieved also in the lesser vascular tissues at higher values. These results strongly suggest the usefulness of combined simultaneous CO2 and Nd:YAG laser beams in surgery of the more vascular organs and tissues.     

Laser-Assisted Hair Transplantation: Histologic Comparison Between CO2 and Ho:YAG Lasers

BACKGROUND: Various laser wavelengths and devices have been advocated for use in the creation of recipient channels during hair transplant surgery, including flash-scanned CO2, Ho:YAG (lambda = 2.12 microm), and Er:YAG (lambda = 2.94 microm). OBJECTIVE: To determine the tissue injury caused by flash-scanned CO2 and pulsed Ho:YAG lasers during the creation of hair transplant recipient channels and to assess the efficacy of the Ho:YAG laser. METHODS: Recipient channels were created in vivo in human scalp tissue using both lasers, and were excised and prepared for histologic examination. Optical micrometry of tissue sections was used to assess thermal injury. RESULTS: The Ho:YAG laser created jagged, irregular-shaped channels with larger zones of thermal injury (superficial deepithelialization, thermal necrosis, and thermal damage). In contrast, the CO2 laser produced well-defined cylindrically shaped channels free of cellular debris with minimal epithelial disruption and significantly less lateral thermal injury. CONCLUSION: Given that the Ho:YAG produced larger regions of thermal injury and recipient channels that were unacceptable for graft, the CO2 laser remains the better choice for the creation of recipient channels during hair transplant surgery. However, ongoing research will be necessary to determine the optimal laser wavelength and/or devices for this procedure.     

Laser therapy for the treatment of brain tumors.

The author examine the specific cases where laser therapy may be indicated for the treatment of brain tumors. The different types of lasers currently available are described and the effects on the tissue, at different powers and with different modalities of use, are reported. On the basis of experience reported in literature, the Author describes the characteristics and the fields of application of the 1.32 nm Nd:YAG laser, the superpulse CO2 and the Nd:YAG with sapphire tips for contact laser surgery. The advantages of laser surgery as opposed to the traditional techniques in the most frequently observed tumors, are also described.     

三种红外波长激光治疗面部草莓状血管瘤的疗效

目的对比观察3种红外波长激光治疗小儿面部草莓状血管瘤（strawberry hemangiogila．SH）的疗效及容貌结果。方法5～12岁面部SH患儿300例．随机分为半导体激光组,Nd：YAG激光组和CO2激光组,每组100例。3组治疗参数相同（功率10W、光斑直径0．2cm、功率密度318W／cm2）,根据皮损面积大小,半导体激光组和Nd：YAG激光组分别行非接触式扫描凝固术．CO2激光组行气化术。治疗后6个月复查评定疗效及容貌结果。结果治愈率半导体激光组89％,Nd：YAG激光组83％。CO2激光组69％（P〈0．05）;容貌优良率CO2激光组87．0％,半导体激光组86．5％,Nd：YAG激光组57．8％（P〈0．01）;平均治疗次数、治疗时间和治疗中出血量半导体激光组均少于Nd：YAG激光组和CO2激光组（P〈0．01）。结论波长830nm的半导体激光（功率密度318W／cm2）,治疗小儿面部SH具有1次治愈率高、治疗时间短、治疗中出血少和容貌结果好等优点,为治疗小儿面部SH的首选方法。     

In vitro effects of Nd:YAG laser radiation on blood: A quantitative and morphologic analysis

Use of the Neodymium: yttrium -aluminum -garnet (Nd:YAG) laser to recanalize stenosed arteries may require delivery of the beam through blood. To assess the degree of hemolysis and debris formation, 54 samples of citrated whole blood were exposed to Nd:YAG laser radiation of varying powers (10, 20 and 30 watts) and duration (1, 2.5 and 5 seconds). Compared to control samples which were not subjected to laser light, there was no significant decrease in hematocrit (41 to 40.5 +/- 5%), hemoglobin concentration (13.8 to 13.8 +/- .06 g/1OO ml), or increase in "free" hemoglobin concentration. Debris weight (from .45 +/- .002 to .45 +/- .002 mg), as well as the white blood cell count, was also not significantly changed (from 5,400 to 5,200 +/- 240 WBC/cm). Light microscopy examination of debris from samples of whole blood, washed erythrocytes, and platelet-rich plasma subjected to the laser at 30 watts for five seconds failed to demonstrate the presence of membrane denaturation of blood elements, as compared with the morphologic changes observed in whole blood samples exposed to a "hot tip" rather than Nd:YAG laser radiation. Nd:YAG laser can be used intravascularly without fear of hemolysis or debris "micro-embolization" up to a power of 30 watts for five seconds.     

Ablation of polymethylmethacrylate by Ho:YAG,Nd:YAG,and Erb:YAG lasers

Ho:YAG, Nd:YAG, and Erb:YAG laser ablation of Polymethylmethacrylate (PMMA) was investigated under in vitro and simulated clinical conditions. Ablation rates were measured for all lasers and after ablation, macroscopic and microscopic appearance of the ablation site was investigated. The mean ablation rates of the Erb:YAG, Ho:YAG, and Nd:YAG laser increased from 8 μm per pulse at 100 mJ to 44 μm per pulse at 300 mJ from 100 μm per pulse at 200 mJ to 222 μm per pulse at 800 mJ and from 28 μm per pulse at 100 mJ to 189 μm per pulse at 800 mJ, respectively. Macroscopic investigation exhibited melting of bone cement for the Ho:YAG and Nd:YAG lasers and pulse-to-pulse vaporization for the Erb:YAG laser. The width of thermal alteration, however, was comparable for all lasers used. Removal of cement from bone specimens under simulated clinical conditions showed good detachment of cement when the fiber was used parallel; in case of perpendicular use, remainders of cement and carbonization of bone could be observed upon histological investigation. © 1993 Wiley-Liss, Inc.     

Laser skin resurfacing using a frequency doubled Nd:YAG laser after topical application of an exogenous chromophore.

BACKGROUND AND OBJECTIVES: Although laser skin resurfacing performed with CO(2) or Er:YAG lasers is efficient, side effects such as prolonged postoperative erythema, delayed healing, scarring, and pigmentation, have been reported. These side effects are due to skin characteristics but also to variations of the thermal effects associated with laser skin resurfacing. The study aimed to evaluate a new laser resurfacing method based on a previous topical application of an exogenous chromophore in order to have reproducible thermal effects. MATERIALS AND METHODS: Exogenous chromophore consisted in carbon dispersed and mixed with film-forming polymers and water. The resultant solution was applied to the skin surface using an airbrush. Experimental evaluation was performed in vivo on hairless rat skin using the following parameters (532 nm, 2.7 W, 1 mm, 50-200 ms, 17.2-68.8 J/cm(2), single pass). Skin biopsies were taken to evaluate histological changes and to quantify epidermis ablation and dermal coagulation depth. Wound healing was followed up during 10 days. RESULTS: Total epidermis ablation was achieved with all pulse durations used. Dermal coagulation depth increased as a function of exposure time. Scar formation was correlated with dermal coagulation depth. CONCLUSION: The concept of applying a carbon-based solution onto skin in order to obtain laser light conversion into heat followed by heat transfer to the tissue is valid for laser skin resurfacing. By selecting exposure time, the thermal effects are predictable and dermal coagulation depth can be either that observed with a Er:YAG laser or that obtained with a CO(2) laser. Moreover, frequency doubled Nd:YAG laser, already used in dermatology for angiodysplasias treatment, could be easily used for resurfacing of periorbital or perioral zones.