Arterial response to excimer and argon laser irradiation in the atherosclerotic swine

Injury associated with laser-induced tissue ablation may be reduced by using pulsed energy delivery at low repetition rates, as opposed to using continuous wave energy delivery. This study was designed to examine the similarities and differences between these two systems as regards the healing process, and to examine whether one is superior to the other. In order to test this postulate, the healing response of normal and atherosclerotic aorta were examined after exposure in vivo to argon and excimer (XeCl 308 nm) laser radiation in hypercholesterolemic swine. Swine were fed hyperlipidemic diets for eight months following balloon denudation of the descending aorta. Following general anaesthetic, the descending aorta was isolated and laser burns were made on both normal and atherosclerotic intima using a continuous wave argon laser delivered through a 50 diameter quartz fibre, and a XeCl excimer laser carried through a 1 mm diameter fibre. Energy levels of 3 to 5 J were applied with the argon laser. The pulse duration for the excimer laser was 30 ns and craters were produced using 10 to 60 pulses at a repetition rate of 20 Hz and an energy density of 2 J cm^–2.Forty-eight hours after laser application, craters created by both lasers were filled with thrombus material. Argon burns were surrounded by thermal and acoustic injury which was not seen with excimer burns. Three weeks after laser application all crater surfaces were reconstituted. Unlike the excimer burns, argon craters demonstrated necrosis well beyond the crater margins and were characterized by multinucleate giant-cell reaction surrounding char debris. By nine weeks both excimer and argon laser burns were covered by fibrous tissue but could be distinguished by the fact that char debris and subjacent tissue injury arose with the argon burns.The results suggest that both lasers can be used to remove focal atherosclerotic plaque from arteries without inducing excessive thrombogenicity. Rapid healing is observed with both; however, damage to surrounding tissue is significantly greater with a continuous energy delivery laser as opposed to pulsed energy delivery.Work supported in part by: Heart and Stroke Foundation of Ontario, Grant-in-Aid No. 5-17     

Retinal burns from experimental laser iridotomy

Simulated argon laser iridotomy was performed in 12 cynomolgus monkey eyes to evaluate the effectiveness of the Abraham iridectomy lens in preventing inadvertent retinal burns. At 600 milliwatts, only two of the three eyes developed small retinal burns using the Abraham lens, whereas three eyes developed larger retinal burns without the Abraham lens. At 1000 milliwatts, retinal burns occurred with or without the Abraham lens, but the size and intensity of the burns were reduced with the lens.     

Low-power laser light in the healing of burns: a comparison between two different wavelengths (635 nm and 690 nm) and a placebo group

BACKGROUND AND OBJECTIVE: Studies on the influence of low-power laser light on wound healing have shown inconsistent results, or, as in the case of burns, are very scarce. We have studied the effects of two different low-power diode laser lights on the healing of burns in rats. STUDY DESIGN/MATERIALS AND METHODS: Thirty rats were burned on both flanks and randomly allocated to one of three study groups. In group A, both wounds remained untreated; in groups B and C, one wound each was irradiated with 635 nm or 690 nm laser light (1.5 J/cm(2)), whereas the other wound remained untreated. Diameter, redness, and edema of the wounds were examined daily. RESULTS: Between and within groups, diameter, redness, and edema of the wounds were similar throughout the entire observation period. Irradiation of the burns did not accelerate wound healing when compared with control wounds. CONCLUSION: We conclude that neither 690 nm nor 635 nm low-power laser light produced any beneficial effects on the healing processes of burns in rats.     

Early laser excision of thermal burns in the white rat and miniature pig

To find a technique which will permit a quick bloodless primary excision of an acute burn, through hyperaemic tissues, experiments have been conducted in the laser excision of thermal burns of the white rat and the miniature pig.The animals were burned, excised by carbon dioxide laser, argon laser, cold-knife scalpel or Bovie electric scalpel, and grafted. Burns were successfully excised with minimal blood loss using the lasers, but there was no significant difference in haematocrit, WBC, total protein or weight values between the laser-excised rats and those excised by Bovie or cold-knife scalpel. There was little difference between take and survival of grafts in the Bovie, cold-knife and laser series, but there were marked differences between the thermally excised and cold-knife excised burns in the ability of epithelial islands of the burn area to grow out and cover the lost-graft areas.Differences were found in the coverage of burns between the white rat and the miniature pig.     

The treatment of sulphur mustard burns with laser debridement.

The chemical warfare agent, sulphur mustard (SM), is a potent blistering agent in man. Skin exposure can produce partial-thickness burns which take up to three months to heal. The aim of this study was to investigate the use of early laser ablation as a means of accelerating this exceptionally slow rate of healing. Four circular partial-thickness SM burns were induced on the dorsum of nine large white pigs (under general anaesthesia). At 72 h post-exposure, three burns per animal were ablated with a single pass of an UltraPulse 5000C CO(2) laser, at a fluence of 5-6 J cm(-2). All the burns were dressed with silver sulphadiazine and a semi-occlusive dressing. At one, two and three weeks post-surgery three animals were culled and all lesions excised for histological analysis. Burn depth was confirmed and measurements of the radii of regenerative epithelium were performed allowing the area of the zone of re-epithelialisation in each lesion to be calculated. Laser-treated lesions showed a significant increase (350%) in healing rates compared to controls (p<0.005). At two weeks, the laser-treated sites were 95% healed in comparison with control sites (28% healed). These data suggest that laser ablation may be effective in the treatment of partial-thickness SM-induced skin injury.     

Efficacy of laser debridement with autologous split-thickness skin grafting in promoting improved healing of deep cutaneous sulfur mustard burns

The consequences of receiving a cutaneous sulfur mustard (SM) burn are prolonged wound healing and secondary infection. This study was undertaken to find a treatment that promotes quick healing with few complications and minimal disfigurement. Multiple deep SM burns (4 cm diameter) were generated on the ventrum of weanling pigs and treated at 48 h. Four treatments were compared: (1) full-thickness CO₂ laser debridement followed by skin grafting; (2) full-thickness sharp surgical tangential excision followed by skin grafting, the “Gold Standard” used in deep thermal burns management; (3) partial-thickness laser ablation with no grafting; and (4) partial-thickness sharp excision with no grafting. A computer controlled, raster scanned, high-powered continuous wave (cw) CO₂ laser was utilized. Ulceration, wound geometry, and wound contraction were evaluated during a 36-day healing period. Histopathological evaluations were conducted at the end of the healing period. Engraftment rates were similar between both methods of debridement. Laser debridement followed by skin grafting was as efficacious in improving the wound healing of deep SM burns as the “Gold Standard.” Full-thickness laser debridement of these small total body surface area (TBSA) burns was time efficient and provided adequate beds for split-thickness skin grafting. Laser debridement offered additional benefits that included hemostatic control during surgery and minimal debridement of normal perilesional skin. Mid-dermal debridement by sharp excision or laser ablation without grafting produced less desirable results but was better than no treatment.     

Semiconductor diode laser endophotocoagulation

We successfully used a semiconductor diode laser to deliver endophotocoagulation burns to the retina of a rabbit. The diode laser employed emits light at a wavelength of 817 nm (near infrared). It has a power output of up to 1.0 W in the continuous-wave mode, equivalent to the capability of current argon laser endophotocoagulators. A standard, commercially available fiberoptic endophotocoagulation probe was used to deliver the laser burns. We used power settings ranging from 300 mW to 400 mW and exposure times of 0.1 to 0.2 seconds to produce chorioretinal burns that appeared clinically and histopathologically indistinguishable from those induced with conventional wavelengths. This new laser system has the decided advantages over traditional endophotocoagulators of being much smaller, less costly, and requiring no water cooling, without sacrificing power output or ease of delivery.     

The LDI Enigma Part II: Indeterminate depth burns,man or machine?

IntroductionLaser Doppler imaging is universally considered the most evidence-based method for objective burn depth assessment by accurately predicting burn wound healing potential. This study has analyzed how exactly laser Doppler imaging measurements can be useful in the early therapeutic decision making for patients with clinically indeterminate depth burns.Material and methodsAn extensive survey, by questionnaire and in-depth interviews, was conducted among 51 burn centers worldwide to gain insight on the practical use of laser Doppler imaging.ResultsTwenty-seven (53%) of the 51 burn centers contacted almost completely answered the 32 questions. Fifty-two percent of these centers (14/27) had at least 10 years of laser Doppler imaging experience. laser Doppler imaging was considered to be mainly or almost completely accurate by 89%. In case of discrepancy between clinical assessment and LDI, 41% relied more on clinical diagnosis, 25% delayed decision to operate, while 16% re-scanned the next day. The centers most experienced with laser Doppler imaging (13%) relied on it more. Final decisions for treatment were based on the combination of laser Doppler imaging and clinical assessment by 74%. Seventy percent of the centers almost never operated burns with laser Doppler imaging-red and would almost always operate burns with LDI-blue. Treatment decisions for intermediate laser Doppler imaging colors (pink, yellow and green) varied, with 76% basing decisions on other factors: % Total Body Surface Area (TBSA), general health, age, location of the burn, potential for colonization/infection, patient preference, compliance with aftercare, logistics, and socio-economic factors.ConclusionLaser Doppler imaging reduces the number of clinical indeterminate depth burns. For these intermediate depth burns on laser Doppler imaging, treatment decisions are based on a combination of interpretation (‘man’) and laser Doppler imaging measurements (‘machine’). Thorough knowledge of confounding factors and validated laser Doppler imaging color code, consideration of surrounding laser Doppler imaging colors, the use of mean flux values, and not directly burn related factors are essential. Burn centers with most laser Doppler imaging experience considered laser Doppler imaging an indispensable diagnostic tool.     

Temperature controlled burn generation system based on a CO2 laser and a silver halide fiber optic radiometer

BACKGROUND AND OBJECTIVES: Experimental animal study of burns is dependent on a reliable burn generation system. Most of the experimental systems used today are unable to produce precise partial thickness burns. This limits the ability to study minor changes associated with burn care. The aim of the study was to develop a method for generating burns with a fixed depth using a CO2 laser burn generation system. MATERIALS AND METHODS: The burn generation system was composed of two components: a burn generation device and a temperature sensing and control system. These components were designed to operate together in order to keep a constant, predetermined skin surface temperature during prolonged burn generation. One hundred thirty-eight spot burns were generated on the back of five shaved 450 g male Wistar rats. The rat skin was exposed to a 70 degrees C for 5-60 seconds. The burned areas were excised and underwent evaluation by hematoxylin-eosin-stained slide microscopy. RESULTS: A linear correlation was found between the duration of exposure and the average burn depth (r = 0.93). This correlation is represented by the equation: burn depth in millimeters = 0.012x (duration in seconds of skin exposure at 70 degrees C). CONCLUSIONS: The fiber-optic-controlled laser burn generation system studied is a reliable tool for creating partial thickness as well as full thickness skin burns in rats.     

Comparisons of wound healing among excisional, laser-created, and standard thermal burns in porcine wounds of equal depth.

The present study was designed to characterize similarities and differences among three wounding modalities in partial-thickness porcine wounds. We hypothesized that inherent differences, such as endogenous cytokine delivery into excisional wounds or ablation of eschar during laser vaporization, should accelerate the magnitude and sequence of reparative events above the delayed repair that is frequently observed in patients with burns. A constant mid-dermal depth of injury was created by a Padgett dermatome, a computer-controlled pulsed CO(2) laser, or a temperature-controlled metal template. Wounds were harvested after 5, 10, or 15 days. After 5 days, significant resurfacing differences were apparent with values of 54% in excisions, 29% in lasers, and 12% in standard thermal burns. Sequences of fibroblastic proliferation were measurably different among the three wound modalities. At day 5 the bromodeoxyuridine labeling index for fibroblasts showed laser wound levels greater than excision wound levels, which were greater than burn wound levels; but by day 10, the proliferative profiles indicated that burn wound levels were greater than excision wound levels, which were greater than laser wound levels. Capillary areas (an assessment of angiogenesis) differed among the three wound types throughout the study. Peak values were observed at day 5 in both excisional and laser injuries; however, standard thermal burns did not peak until day 10. Both the magnitude and sequence of expression of three matrix metalloproteinases (-1, -2, and -9) differed among the three types of injuries. Laser wounds showed the earliest peak in matrix metalloproteinase-1 expression, whereas burns showed the least expression at day 5. In conclusion, although the three types of wounds undergo similar reparative processes such as reepithelialization, fibroblastic proliferation, angiogenesis, and expression of matrix metalloproteinases, the magnitude and temporal sequences are measurably altered among the three wound modalities. A greater understanding of specific differences within wound environments may lead to more insightful design of interventional wound therapies.     

The effect of triglycyl-lysine-vasopressin (terlipressin INN, Glypressin) on skin blood flow, measured with laser Doppler flowmetry, thermography and plethysmography. A dose-response study

Triglycyl-lysine-vasopressin (TGLVP) has been shown to reduce blood loss in connection with early excision of experimentally induced burns in pigs. In order to determine an appropriate dosage of TGLVP in patients with burns, a dose-response study was undertaken. TGLVP was administered intravenously in various doses to healthy volunteers, and skin blood flow was measured with laser Doppler flowmetry, thermography and plethysmography. Blood pressure, heart rate and electrocardiac activity were monitored as well as serum and urine changes. The doses of 5, 10 and 20 micrograms TGLVP/kg b.wt. caused statistically significant reduction of skin blood flow; minimal values were 35, 26 and 25% of predrug values for the three doses, respectively. Thermography and plethysmography were less sensitive for detecting effects of TGLVP than laser Doppler flowmetry. Minor effects on blood pressure and heart rate were recorded after TGLVP, but no disturbances in electrocardiac activity. Urinalyses revealed an antidiuretic action of TGLVP. The study supports earlier findings and suggests a dose level of TGLVP for the use in excision of burns.     

Effect of low-level laser therapy on mast cells in second-degree burns in rats

OBJECTIVE: This study sought to investigate whether low-level laser therapy (LLLT) with a helium-neon (He-Ne) laser would affect mast cell number and degranulation in second-degree burns in rats. Background Data: LLLT has been recently applied to stimulate the wound healing process. MATERIALS AND METHODS: Sixty-five rats were randomly allocated to one of five groups. A deep second-degree burn was inflicted on all rats except those in the control group. In the sham-exposed group burns remained untreated. In the two laser-treated groups, the burns were irradiated every day by LLLT, with energy densities of 1.2 and 2.4 J/cm(2). In the fifth group the burns were treated topically with 0.2% nitrofurazone cream every day. The unburned skin of the rats in the control group were used for baseline study. The effects on mast cell number and degranulation were assessed by counting the number of intact and degranulated mast cells in sections fixed in formalin and stained with toluidine blue. RESULTS: On the seventh and 16th days post-burn, the type 1 mast cell count in the 2.4-J/cm(2) laser-treated group was significantly higher than that of the control group. On the 30th day, the total numbers of mast cells in the laser-treated groups were lower than those in the control and sham-exposed groups. CONCLUSION: LLLT of deep second-degree cutaneous burns in rats significantly increased the number of intact mast cells during the inflammatory and proliferative phases of healing, and decreased the total number of mast cells during the remodeling phase.     

Experimental full-thickness burns induced by CO2 laser

Many studies have been conducted on the treatment of burns because they are important in morbidity and mortality. These studies are mainly focused on improving care and quality of life of patients. The aim of this study is the induction of standardized full-thickness burns of the skin of rats using the CO₂ laser. The results show that non-contact technique using the CO₂ laser is effective to induce such standardization of burning and is an important step in determining the efficiency of different therapies used in treating burns.     

Should we use platelet‐rich plasma as an adjunct therapy to treat “acute wounds,” “burns,” and “laser therapies”: A review and a proposal of a quality criteria checklist for further studies

Platelet‐rich plasma seems to help wound healing. The goal of this review is to determine if the adjunction of platelet‐rich plasma enhances the clinical outcome of acute wounds, burns, and laser therapies. A PubMed and Cochrane library search was performed by two reviewers with the senior author as a consultant. Medical Subject Headings search terms used were the following: [“Platelet‐rich plasma” OR “Platelet gel” OR “Platelet growth factor”] AND [“Acute wound” OR “Wound” OR “Burn” OR “Laser”]. We included controlled studies assessing the clinical outcome of acute wounds, burns, and laser therapies treated by platelet‐rich plasma. Nine randomized controlled studies, six prospective controlled studies, and two retrospective controlled studies were included. Regarding acute wounds, three randomized controlled trials found a statistical benefit regarding either the healing time, the return back to work time, the quality of life, or the pain and three prospective controlled studies found a statistical difference regarding the velocity of healing. Platelet‐rich plasma decreased the intensity or duration of erythema after laser therapy in four randomized studies. Regarding the long‐term outcome of laser therapies, two studies found a statistical benefit and two others did not. Platelet‐rich plasma accelerates acute wound healing and decreases erythema after laser therapies. Its use on burns has not been enough studied.     

Effect of laser rays on wound healing

Low doses of laser were found to stimulate the regeneration not only of mechanically induced wounds but also of burns. The wound-healing stimulated by laser radiation involves an increased rate of epithelial growth, which may eventually be the starting point of neoplastic growth.     

Inadvertent corneal burn by using indirect wide-field contact lenses and different laser beam delivery systems during experimental fundus photocoagulation

BACKGROUND AND OBJECTIVE: At fundus photocoagulation by using a wide-field indirect contact lens, the laser radiant exposure may be increased at the anterior segment of the eye. We examined the likelihood of producing inadvertent corneal burn by using parfocal and sharped edge defocus laser delivery systems with various indirect contact lenses. STUDY DESIGN/MATERIALS AND METHODS: The two laser delivery systems were used with four lenses of different viewing angles during fundus photocoagulation in a total 44 eyes of rabbits. RESULTS: By using the lenses, the parfocal system increased corneal radiant exposure more than did the sharped edge defocus system. By using the Widefield PRP 165 lens of the widest viewing angle, there was no difference between the two systems in the corneal burns produced. CONCLUSION: Some indirect contact lenses used in combination with the parfocal system caused inadvertent corneal burns more readily than did the same lenses in combination with the sharped edge defocus system.     

Utilization of laser Doppler flowmetry and tissue spectrophotometry for burn depth assessment using a miniature swine model

Currently, the diagnosis of burn depth is primarily based on a visual assessment and can be dependent on the surgeons' experience. The goal of this study was to determine the ability of laser Doppler flowmeter combined with a tissue spectrophotometer to discriminate burn depth in a miniature swine burn model. Burn injuries of varying depth, including superficial‐partial, deep‐partial, and full thickness, were created in seven Göttingen minipigs using an aluminium bar (100 °C), which was applied to the abdominal skin for periods of 1, 3, 6, 12, 30, and 60 seconds with gravity alone. The depth of injury was evaluated histologically using hematoxylin and eosin staining. All burns were assessed 3 hours after injury using a device that combines a laser light and a white light to determine blood flow, hemoglobin oxygenation, and relative amount of hemoglobin. The blood flow (41 vs. 124 arbitrary units [AU]) and relative amount of hemoglobin (32 vs. 52 AU) were significantly lower in full thickness compared with superficial‐partial thickness burns. However, no significant differences in hemoglobin oxygenation were observed between these depths of burns (61 vs. 60%). These results show the ability of laser Doppler flowmeter and tissue spectrophotometer in combination to discriminate between various depths of injury in the minipig model, suggesting that this device may offer a valuable tool for burn depth assessment influencing burn management.     

Effects of laser irradiation (670-nm InGaP and 830-nm GaAlAs) on burn of second-degree in rats

This study investigated the effects of 670-nm indium gallium phosphide (InGaP) and 830-nm gallium aluminum arsenide (GaAlAs) laser therapy on second-degree burns induced on the back of Wistar rats. Sixty-three male Wistar rats were anesthetized, and second-degree burns were made on their back. The animals were then divided randomly into three groups: control (C), animals treated with 670-nm InGaP laser (LIn), and animals treated with 830-nm GaAlAs laser (LGa). The wound areas were removed after 2, 6, 10, 14, and 18 days of treatment and submitted to structural and morphometric analysis. The following parameters were studied: total number of granulocytes and fibroblasts, number of newly formed blood vessels, and percentage of birefringent collagen fibers in the repair area. Morphometric analysis showed that different lasers 670-nm InGaP and 830-nm GaAlAs reduced the number of granulocytes and an increase of newly formed vessels in radiated lesions. The 670-nm InGaP laser therapy was more effective in increasing the number of fibroblasts. The different treatments modified the expression of VEGF and TGF-β1, when compared with lesions not irradiated. The different types of light sources showed similar effects, improved the healing of second-degree burns and can help for treating this type of injury. Despite the large number of studies with LLTI application in second-degree burns, there is still divergence about the best irradiation parameters to be used. Further studies are needed for developing a protocol effective in treating this type of injury.     

Diagnosis of burn depth using laser-induced indocyanine green fluorescence: a preliminary clinical trial

Clinical assessment of burn depth is frequently inaccurate. In order to effectively plan the treatment of burn wounds, an accurate diagnosis of burn depth is desirable. A new method for evaluating the depth of burns by imaging the blood flow through the burned tissue using fluorescence from intravenously injected indocyanine green (ICG) dye illuminated with a 785-nm, near-infrared diode laser array was evaluated. Nine patients and 15 individual burn sites were studied. Five sites were classified by the ICG study as superficial second degree, four were deep-dermal second degree, and six were third degree. Etiology of the injuries included flame, contact burns, and scalds. The date postburn of the study ranged from 1 to 11 days. In all cases, the relative fluorescence levels (e.g. superficial second-degree burns yielded relatively bright fluorescence, third-degree burns appeared much darker than surrounding normal skin) were found to correlate well with actual burn depth as determined by histologic examination of biopsies and intraoperative clinical assessment.     

Ultrasound assessed thickness of burn scars in association with laser Doppler imaging determined depth of burns in paediatric patients

This study describes the ultrasound assessment of burn scars in paediatric patients and the association of these scar thickness with laser Doppler imaging (LDI) determined burn depth. A total of 60 ultrasound scar assessments were conducted on 33 scars from 21 paediatric burn patients at 3, 6 and 9 months after-burn. The mean of peak scar thickness was 0.39 ± 0.032 cm, with the thickest at 6 months (0.40 ± 0.036 cm). There were 17 scald burn scars (0.34 ± 0.045 cm), 4 contact burn scars (0.61 ± 0.092 cm), and 10 flame burn scars (0.42 ± 0.058 cm). Each group of scars followed normal distributions. Twenty-three scars had original burns successfully scanned by LDI and various depths of burns were presented by different colours according to blood perfusion units (PU), with dark blue <125, light blue 125–250, and green 250–440 PU. The thickness of these scars was significantly different between the predominant colours of burns, with the thinnest scars for green coloured burns and the thickest for dark blue coloured burns. Within light blue burns, grafted burns healed with significantly thinner scars than non-grafted burns. This study indicates that LDI can be used for predicting the risk of hypertrophic scarring and for guiding burn care. To our knowledge, this is the first study to correlate the thickness of burns scars by ultrasound scan with burn depth determined by LDI.