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Objective: To compare the long-term clinical and histologic outcome of immediate autografting of full-thickness burn wounds ablated with a high-power continuous-wave CO2 laser to sharply débrided wounds in a porcine model., Summary Background Data: Continuous-wave CO2 lasers have performed poorly as tools for burn excision because the large amount of thermal damage to viable subeschar tissues precluded successful autografting. However, a new technique, in which a high-power laser is rapidly scanned over the eschar, results in eschar vaporization without significant damage to underlying viable tissues, allowing successful immediate autografting., Methods: Full-thickness paravertebral burn wounds measuring 36 cm2 were created on 11 farm swine. Wounds were ablated to adipose tissue 48 hours later using either a surgical blade or a 150-Watt continuous-wave CO2 laser deflected by an x-y galvanometric scanner that translated the beam over the tissue surface, removing 200 microm of tissue per scan. Both sites were immediately autografted and serially evaluated clinically and histologically for 180 days., Results: The laser-treated sites were nearly bloodless. The mean residual thermal damage was 0.18+/-0.05 mm. The mean graft take was 96+/-11% in manual sites and 93+/-8% in laser sites. On postoperative day 7, the thickness of granulation tissue at the graft-wound bed interface was greater in laser-debrided sites. By postoperative day 180, the manual and laser sites were histologically identical. Vancouver scar assessment revealed no differences in scarring at postoperative day 180., Conclusions: Long-term scarring, based on Vancouver scar assessments and histologic evaluation, was equivalent at 6 months in laser-ablated and sharply excised sites. Should this technology become practical, the potential clinical implications include a reduction in surgical blood loss without sacrifice of immediate engraftment rates or long-term outcome.

Background and Objective: The pulsed CO2 laser has received attention because of its successful application to dermatologic surgery and burn debridement surgery. Despite impressive results, tissue removal using pulsed CO2 laser irradiation has not been optimized. We examined the ablation processes by performing mass removal and thermal injury experiments at wavelengths where tissue water is the primary absorber (10.6 microm), and where water and collagen have comparable absorption (9.5 microm)., Study Design/materials and Methods: Samples of porcine reticular dermis were irradiated with 180-ns laser pulses at either wavelength. Tissue removal was measured using a digital balance. Thermal injury was assessed using a microscope with a calibrated reticle after hematoxylin and eosin staining., Results: Tissue removal using 10.6-microm radiation resulted in a heat of ablation of 3,740 J/g, an ablation threshold of 1.15 J/cm2, and a zone of thermal injury of 53 microm. By contrast, tissue removal using 9.5-microm radiation resulted in a heat of ablation of 3,330 J/g, an ablation threshold of 1.47 J/cm2, and a zone of thermal injury of 34 microm. The differences in ablation threshold and thermal injury were statistically significant., Conclusion: Pulsed CO2 laser irradiation at 9.5 microm removes tissue more efficiently and with a smaller zone of thermal injury than at 10.6 microm.

The physical mechanisms that achieve tissue removal through the delivery of short pulses of high-intensity infrared laser radiation, in a process known as laser ablation, remain obscure. The thermodynamic response of biological tissue to pulsed infrared laser irradiation was investigated by measuring and analyzing the stress transients generated by Q-sw Er:YSGG (lambda = 2.79 microns) and TEA CO2 (lambda = 10.6 microns) laser irradiation of porcine dermis using thin-film piezoelectric transducers. For radiant exposures that do not produce material removal, the stress transients are consistent with thermal expansion of the tissue samples. The temporal structure of the stress transients generated at the threshold radiant exposure for ablation indicates that the onset of material removal is delayed with respect to irradiation. Once material removal is achieved, the magnitude of the peak compressive stress and its variation with radiant exposure are consistent with a model that considers this process as an explosive event occurring after the laser pulse. This mechanism is different from ArF- and KrF-excimer laser ablation where absorption of ultraviolet radiation by the collagenous tissue matrix leads to tissue decomposition during irradiation and results in material removal via rapid surface vaporization. It appears that under the conditions examined in this study, explosive boiling of tissue water is the process that mediates the ablation event. This study provides evidence that the dynamics and mechanism of tissue ablation processes can be altered by targeting tissue water rather than the tissue structural matrix.

The use of surgical lasers has been shown to decrease adhesion formation as compared with scalpel control groups in various surgical procedures. The potential benefits of laser technology have not been assessed in the treatment of adherent tendons. The current study was designed to first develop a reliable and reproducible model for consistent adhesion formation following flexor tendon trauma. The second goal was to compare the effects of laser tenolysis procedures on tendon gliding with those of traditional scalpel tenolysis. In phase I, the adhesion-induction model utilized bilateral standardized crush- abrasion injuries to the hind limb digital flexor tendons of New Zealand White rabbits. Following 4 weeks of immobilization, the animals were sacrificed, and peritendoneal adhesions were assessed biomechanically. A significantly higher maximal force was required to extract the adherent tendons from the foot as compared with nontraumatized control tendons. In phase II, six groups of animals underwent the same standardized tendon trauma. Four weeks later the rabbits were randomly assigned to undergo either CO2 laser or holmium:YAG laser tenolysis on one foot. Scalpel lysis was used on the contralateral foot and served as an intraindividual control. Biomechanical assessment was performed at 1, 2, and 4 weeks following tenolysis. Significantly less force was required to extract the treated tendons at 1 and 2 weeks following holmium:YAG laser tenolysis when compared with scalpel or CO2 laser tenolysis. After 4 weeks, differences between holmium:YAG and CO2 laser and scalpel treatment were no longer significant. Extracted tendons were pulled apart to failure, and no difference in breaking strength was noted between groups. We conclude that holmium:YAG laser tenolysis results in easier tendon gliding as compared with scalpel or CO2 laser tenolysis at early time points. Laser tenolysis does not affect intrinsic tendon strength.

Background and Objective: The pulsed holmium laser is a promising tool for tissue ablation but possesses some limitations. For example, it is capable of producing significant mechanical damage in certain tissues in the form of fissures and fractures. Because longer pulse durations should reduce mechanical damage, this study examined the tissue effects produced by a prototype continuous wave holmium laser., Study Design/materials and Methods: A prototype liquid nitrogen cooled holmium operating at 2.12 microns was used. The heat of ablation and ablation threshold were determined using a mass loss technique. Fresh pig skin was irradiated in air or under saline, and prepared for histologic analysis. Hemostasis was qualitatively assessed in vivo during incisions made in the skin, liver, and small intestine., Results: Threshold radiant exposure and heat of ablation were calculated from the mass loss measurements to be 191 J/cm2 with a 95% confidence interval of -80-440 J/cm2. Residual thermal damage in skin ranged from 390 to 690 microns in saline and from 390 to 490 microns in air. Excellent hemostasis was achieved in all incisions., Conclusion: Using appropriate irradiation parameters, the continuous wave holmium laser produces tissue effects suitable for a general use surgical instrument. In addition, the laser source could become compact and inexpensive when diode-pumped and direct diode devices become available.

In this article the clinical uses of lasers in gastroenterology are reviewed. The endoscopic delivery of light for therapeutic as well as diagnostic purposes is discussed. Current research directions in the field are also indicated where appropriate.

A Ho:YAG (holmium-yttrium-aluminum-garnet) laser system operating at a wavelength of 2.1 microns has been introduced recently for use in arthroscopic surgery. The acceptability of this new tool will be determined not only by its ability to resect tissue, but also by its long-term effects on articular surfaces. Two studies were performed to evaluate the acute and chronic effects of the laser on cartilaginous tissue. The acute in vitro effects of 2.1-micron laser irradiation were evaluated, including measurement of ablation efficiency, ablation threshold, and thermal damage in meniscal and articular cartilage. To document the chronic effects on articular cartilage in vivo, a 10-week healing study was performed. Eight sheep weighing 30 to 40 kg underwent bilateral arthrotomy procedures. Multiple full-thickness and partial-thickness defects were created. Animals were euthanized at 0, 2, 4, and 10 weeks. The results of the healing study showed (1) no healing of full- or partial-thickness defects in hyaline cartilage at 10 weeks; (2) fibrocartilaginous granulation tissue filling full-thickness defects at 2 and 4 weeks that was no longer evident at 10 weeks; (3) chondrocyte necrosis extending to > 900 microns distal to ablation craters at 4 weeks, with no evidence of repair at later dates; (4) chondrocyte hyperplasia at the borders of the damage zone at 2 weeks but not at euthanization occurring at later periods.

A thermal model to predict the effect of laser parameters on the zone of thermal injury produced by laser ablation of biological tissue is presented. The model suggests that the Péclèt number based on the optical penetration depth of laser radiation is the key parameter in determining the resulting zone of thermal injury. We show that the zone of thermal injury is minimized for Péclèt numbers greater than one since the transport of energy via conduction beyond the ablation front is minimized. We also show that for Péclèt numbers less than one, larger zones of thermal damage are unavoidable regardless of the laser pulse duration. The predictions of the model are compared with data available in the literature. Deviations between the model predictions and published data are discussed and the potential effects of the model assumptions, optical scattering, pyrolysis, temporal pulse shape, pulse duration, irradiance and pulse repetition rate are explored.

Background: Ablative lasers have been used for cutaneous surgery for greater than two decades since they can remove skin and skin lesions bloodlessly and efficiently. Because full-thickness skin wounds created after thermal laser ablation may require skin grafting in order to heal, we have examined the effect of the residual laser-induced thermal damage in the wound bed on subsequent skin graft take and healing. In a pig model, four different pulsed and continuous-wave lasers with varying wavelengths and radiant energy exposures were used to create uniform fascial graft bed thermal damage of approximately 25, 160, 470, and 1100 microns. Meshed split-thickness skin graft take and healing on the thermally damaged fascial graft beds were examined on a gross and microscopic level on days 3 and 7, and then weekly up to 42 days., Results: Laser-induced thermal damage on the graft bed measuring greater than 160 +/- 60 microns in depth significantly decreased skin graft take. Other deleterious effects included delayed graft revascularization, increased inflammatory cell infiltrate at the graft-wound bed interface, and accelerated formation of hypertrophied fibrous tissue within the graft bed and underlying muscle., Conclusions: Ablative lasers developed for cutaneous surgery should create less than 160 +/- 60 microns of residual thermal damage to permit optimal skin graft take and healing. Pulsed carbon dioxide and 193-nm excimer lasers may be valuable instruments for the removal of full-thickness skin, skin lesions, and necrotic tissue, since they create wound beds with minimal thermal damage permitting graft take comparable to that achieved with standard surgical techniques.

Background: Continuous-wave carbon dioxide lasers are not widely used for the surgical removal of most skin lesions because it is difficult to control laser ablation and the extensive laser-induced thermal damage slows healing. Pulsed lasers provide means to reduce thermal damage produced during laser ablation and permit precise control of tissue removed during ablation. Using a swine model, we compared on a gross and microscopic level the healing of middermal wounds of similar depth and area created by a dermatome and a focused pulsed CO2 laser., Results: Pulsed CO2 laser ablation removed skin precisely and bloodlessly with 85 +/- 15 microns (mean +/- SD) of residual thermal damage covering the surface of the wound. Compared with the dermatome, tissue reepithelialization was delayed in the laser wounds at day 3. By day 7, epithelial coverage of the laser-created wounds was not significantly different from the dermatome-created wounds. No significant difference in the appearance of the two wounds was noted at 42 days., Conclusions: We conclude that the focused pulsed CO2 laser is capable of precisely and bloodlessly ablating skin with conservation of residual subjacent adnexal elements, minimal early interference with epibolic epithelial outgrowth, and no pathologic effects on the wound healing process. Pulsed CO2 lasers may be a valuable instrument for the conservative ablation of skin and skin lesions.

We used a pulsed tunable dye laser (operating at 60 mJ per pulse, 504-nm wavelength) to fragment large (0.8-4.5 cm) stones retained in the hepatic ducts or common bile duct in 12 patients after cholecystectomy. Attempts to extract stones via a T-tube or endoscope had been unsuccessful in all patients. In nine of 12 patients, all stone fragments were successfully eliminated during the initial treatment. In one patient, fragmentation occurred but debris remained, requiring endoscopic stenting. Pseudomonas sepsis developed in this patient 30 days after the procedure and was treated by extraction of the stone fragments. Fragments remaining after lithotripsy were cleared at the same sitting by using saline flushing or endoscopic or percutaneous basket extraction. In two of 12 patients, the treatment was unsuccessful because of laser malfunction. The treatment was performed without complications, except for clinically insignificant hyperamylasemia, which occurred in two patients. Our experience suggests that laser lithotripsy offers a safe alternative for nonsurgical treatment of large retained biliary stones for patients in whom traditional treatments have failed.

The ablation rate and thermal damage in skin produced by a superpulsed CO2 laser operating at pulse repetition rates between 1 and 900 Hz was measured. When delivering a fixed number of pulses (20 or 30) of equal energy, a 55-60% increase in the amount of tissue ablated was observed when the pulse repetition rate rose from 10 to 200 Hz. At pulse repetition rates greater than 200 Hz no further increase was seen. Under identical conditions, an 80% increase in the zone of thermal damage was observed when the pulse repetition rate was increased from 1 to 60 Hz. The large increases in tissue ablation and tissue damage may indicate the existence of a layer of mixed-phase (i.e., liquid and vapor) or metastable liquid which can store significant amounts of thermal energy between pulses. The data suggest that CO2 lasers should be operated at relatively low repetition rates for optimal performance.

Experimental work has established that the Candela (Candela Laser Corporation, Wayland, MA) flashlamp excited dye laser (wavelength, 504 nm) is a highly effective method for fragmenting biliary stones and has minimal potential for injuring the bile duct wall. This technique was evaluated in 25 complex patients whose stones, usually because of large size, did not respond to standard nonoperative treatment. The laser imaging was applied through a quartz fiber and aimed either under direct vision with choledochoscopes passed percutaneously or through a special "mother" duodenoscope or under fluoroscopic guidance at standard duodenoscopy. Laser treatment resulted in some fragmentation of stones in 23 cases. Subsequently, it proved that it was possible to clear the bile duct of stones in 20 patients, 12 of them receiving successful treatment during the same endoscopic procedure. There were no significant complications. This endoscopic technique seems to be a useful new alternative to surgery in patients with large and difficult bile duct stones.

A new, near-infrared, pulsed holmium laser (wavelength, 2.1 microns; pulse duration, 400 microseconds) was used to ablate bovine articular cartilage and meniscal fibrocartilage. Microscopic examination revealed zones of thermal damage extending 550 microns from ablation sites. Ablation rates were measured with a mass loss technique. Above threshold, mass removal rates were proportional to laser radiant exposure. Threshold radiant exposure for ablation was 50 J/cm2 for articular cartilage and 11 J/cm2 for meniscal fibrocartilage. Because the holmium laser can precisely and rapidly resect cartilaginous tissues with only moderate necrosis, function in a saline environment in direct contact with tissue, and be transmitted through conventional optical fibers, it has the potential to become a useful tool for the precise arthroscopic removal of intraarticular tissue.

Pulsed lasers produce efficient and precise tissue ablation with limited residual thermal damage. In this study, the efficiency of pulsed CO2 laser ablation of burned and normal swine skin was studied in vitro with a mass loss technique. The heats of ablation for normal and burned skin were 2,706 and 2,416 J/cm3 of tissue ablated, respectively. The mean threshold radiant exposures for ablating normal skin and eschar were 2.6 J/cm2 and 3.0 J/cm2, respectively. Radiant exposures greater than 19 J/cm2 produced a plasma, which decreased the efficiency of laser ablation. Thus the radiant exposures for efficient ablation range from 4 to 19 J/cm2, and within this radiant exposure range 20-40 microns of tissue are ablated per pulse. We also examined, on a gross and histopathologic basis, in vivo burn eschar excision with a pulsed CO2 laser. The laser allowed bloodless excisions of full thickness burns on the backs of male hairless rats. The zone of thermal damage was approximately 85 microns over the subjacent fascia. The pulsed CO2 laser can ablate burn eschar efficiently, precisely, and bloodlessly and may prove valuable for the excision of burned and necrotic tissue.

A pulsed holmium laser transmitted through a quartz fiber was used to create osteotomies in the facial bones and sinuses of rabbits. The ablation process was quantified and residual thermal injury was assessed by light microscopy. Adjacent thermal damage was determined to vary between 130 and 220 microns and was independent of radiant exposure and pulse repetition rate. In other studies, large osteotomies were made to examine the biological response and to assess the technical feasibility of using fiber-delivered laser pulses in an operative setting. The animals tolerated the procedure without obvious problems and postoperative follow-up revealed a vigorous healing response. Because it can ablate both bone and soft tissue and can be transmitted through readily available, flexible quartz fibers, the holmium laser may prove to be a useful adjunct to endoscopic sinus surgical procedures.

High-speed flash photographs of laser-induced fragmentation of biliary and renal calculi under water were obtained using one-microsecond-long dye-laser pulses for both illumination and ablation. The photographs show the presence of a bubble with irregularities on the surface that suggest the early presence of debris or microbubbles. Fragmentation occurs before the bubble collapses, suggesting that fragmentation is due to laser-induced acoustic transients rather than to collapse of a laser-induced cavitation bubble.

Although generally ignored in considerations of laser ablation of tissue, reflectance of laser light from tissue during laser-induced ablation is a potentially important factor in determining ablation efficiency because it determines the amount of laser light coupled into the target. To determine the significance of reflectance changes induced by laser irradiation, we examined the reflectance of liver samples during pulsed holmium laser ablation by placing the target at one focus of an ellipsoidal reflector and a detector at the other focus. The temporal behavior, total reflectance, and effect of multiple pulses were examined. Tissue reflectance as large as 50% was observed during holmium laser irradiation but depended upon laser radiant exposure and number of laser pulses. These measurements suggest that changes in the optical properties of the target during ablation are important and should be considered in detailed modeling of the ablation process.

Transscleral photocoagulation of the ciliary body was achieved in pigmented rabbits using a sapphire probe delivery system coupled to a commercial surgical continuous-wave Nd:YAG laser. This contact technique was found to be effective in reducing intraocular pressure (IOP); greater treatment energies were associated with a more prolonged reduction in IOP, and also correlated with a greater degree of histologic damage to the ciliary body. Treatment energies of 0.8-1.0 Joules produced substantial disruption of the ciliary body. This technique is easy to learn and offers ease in control and placement of the coagulation spots.

The safety and efficacy of pulsed tunable dye laser fragmentation of common bile duct stones was assessed in pigs. Laser pulses were conducted through a flexible quartz fiber that was in direct contact with stones that had been surgically implanted into the common bile duct. All calculi were rapidly fragmented into small pieces without significant damage to the common bile duct. The immediate and delayed effects of pulsed lasers on the common bile duct were also evaluated. The common bile duct demonstrated a high tolerance to laser-induced damage even when the laser was discharged directly into the bile duct wall. These results suggest that laser lithotripsy can be performed in humans with a high degree of safety and efficacy.

The use of pulsed laser radiation to recanalize occluded biliary endoprostheses was examined. In vitro measurements demonstrated that a repetitively pulsed organic dye laser transmitted through a small diameter quartz fiber can recanalize an occluded stent in less than 10 sec without causing visible damage to the stent. The laser parameters required for recanalization do not result in significant damage to the common bile duct of a pig even when the laser energy is delivered directly into the tissue, indicating that biliary endoprostheses can be cleared with a large margin of safety. Although the duration of this effect is unknown, pulsed laser radiation is a simple, safe, and effective means of recanalizing occluded biliary endoprostheses and may be an alternative to stent replacement.

The pulsed dye laser (wavelength 504 nm, pulse duration 1 microsecond) is widely used for fragmenting urinary and biliary calculi. In this study, the performance of this laser was compared with pulsed dye lasers producing pulse durations of 8 and 20 microseconds. Fragmentation thresholds and fragmentation rates were measured using a variety of urinary and biliary calculi. Effective fragmentation of urinary and biliary calculi was obtained with 1-microsecond and 8-microseconds pulse durations, but satisfactory fragmentation could not be achieved at 20 microseconds.

A pulsed holmium laser (wavelength 2.1 microns, pulse duration 250 microseconds) was used to ablate rabbit liver, stomach, and colon in vivo. Microscopic examination of the tissues revealed zones of thermal damage extending 0.5-1.0 mm from ablation sites. In addition, ablation rates were measured using a mass loss technique and found to increase linearly with delivered radiant exposure. The threshold radiant exposure for ablation was calculated to be 50 J/cm2 with a heat of ablation of 7000 J/cm3. Because the holmium laser produces less thermal necrosis than current endoscopic laser systems, such as the continuous-wave neodymium:YAG laser, and because the ablation rate can be precisely controlled, the holmium laser shows promise as an alternative method for endoscopic removal of tissue.

The feasibility of using lasers to fragment biliary calculi was examined in vitro. Flashlamp-pumped tunable dye lasers were coupled to small-diameter flexible quartz fibers that were placed in direct contact with biliary calculi. The minimum laser energy necessary to damage a calculus was measured for wavelengths between 450 and 700 nm and for pulse durations between 0.8 and 360 microseconds. This threshold energy increased with increasing wavelength but was not significantly affected by pulse duration. Cholesterol stones had uniformly higher thresholds than pigmented ones. When a repetitively pulsed laser was used, complete fragmentation required fewer than 500 pulses and fragments were predominantly less than 2 mm. The pulsed dye laser can effectively fragment biliary calculi when transmitted through a small-diameter quartz fiber and may be useful as a tool for fragmenting retained common duct stones.