Wound healing and collagen thermal damage in 7.5-microsec pulsed CO(2) laser skin incisions

The Thermal Damage of Canine Vocal Fold by CO2 Laser Under Different Laser Emission Mode

OBJECTIVE

The purpose of this study is to review the differences between continuous wave (CW) and UltraPulse (UP) on thermal damage of the laser with different power.

METHODS

Four adult beagle dogs underwent transoral laser microsurgery (TLM) using CO₂ laser. The laser emission mode and power was CW (3 W, 5 W, and 8 W) and UP (3 W and 5 W), respectively. The tissue from 4 animals was evaluated histologically on postoperative days 1 and 3. The thermal damage of the laser was measured using slide scan system via SlideViewer version 1.5.5.2 software.

RESULTS

All dogs underwent TLM uneventfully. Under microscope examined, the laser damage area was composed of 2 parts: the vaporized zone (VPZ) and thermal damage area. The thermal damage area can be divided into thermal coagulative necrosis area (TCN) and hydropic degeneration area. The width of VPZ and TCN in UP mode was less than that in CW mode (P < .01). The data indicate that lower laser power created less thermal damage (P < .01). In addition, the width of VPZ on postoperative day 3 was less than that on postoperative day 1 (P < .01).

CONCLUSION

CO₂ laser with UP and lower power could decrease the laser thermal damage and may offer more prompt wound healing.

Treatment of plaque-like oral lichen planus with CO2 laser

Background:

Oral lichen planus (OLP) is a chronic autoimmune disease, which annoys the patients for several years. It presents with various clinical forms. Although plaque-like form of OLP is usually asymptomatic, it could transform to a malignant lesion. Therefore, treatment considerations are essential to reduce the development of oral cancer. Laser therapy is a newer modality for treatment of plaque-like lesions.

Aims:

This study aimed to perform laser therapy for plaque-like lesions of OLP.

Methods:

We described some plaque-like OLP lesions evaporated with CO2 laser. The power of 4–7 watt as continuous wave (CW) and defocused mode was employed for evaporation. The complications and recurrence were evaluated in the follow-up sessions.

Results:

In some patients, mild keratotic lesions were observed in the follow-up sessions. Most patients were satisfied with treatment process and reported mild burning after treatment. No complication was observed in the patients.

Conclusion:

CO2 laser could be employed for OLP lesions; however, some degrees of recurrence may occur.

Retrospective Matched Case-Control Study on the Use of CO2 Laser for the Treatment of Nonhealing Diabetic Foot Ulcers: The DULCIS-2 (Diabetic ULcer, CO2 Laser, and Infections) Study

PURPOSE

Infection, which is one of the possible complications of diabetic foot ulcers (DFUs), makes the treatment of ulcers challenging because of its negative impact on healing processes and the high prevalence of multiresistant germs. This study is aimed at verifying the effect of a surgical CO₂ laser (which reduces the bacterial load and allows a more accurate debridement), as compared with the traditional lancets, on the healing rate of DFU.

METHODS

The present case-control retrospective analysis was performed on patients with chronic (>6 months) DFU with Texas grade >1, treated with 80 W surgical CO₂ laser (DEKA SmartXide2 C80, El.En. Group) and compared with a matched sample of patients with similar characteristics, who were treated with a traditional surgical approach. The debridement was performed trying to achieve the complete removal of nonviable tissues. The principal endpoint was the proportion of patients healed at 6 months. All analyses were carried out with SPSS 25.0. The study protocol was approved by the local ethical committee.

RESULTS

This study included 118 patients (59 cases and 59 controls). At 6 months, the proportion of healing patients was 35% and 18% in cases and controls, respectively (P = .034). The corresponding figure at 1 year was 62% and 38% (P = .009), whereas no difference was observed at 1, 2, and 3 months. No serious adverse event was observed.

CONCLUSIONS

In this article, we show for the first time that CO₂ laser treatment, in comparison with traditional surgical approaches, can be associated with an increased healing rate in patients with DFU.

Quantitative analysis of collagen and capillaries of 3.8-μm laser-induced cutaneous thermal injury and wound healing

The biological effects of cutaneous thermal injury and wound healing after 3.8-μm laser radiation were investigated by observing the effects of different radiation doses on in vivo cutaneous tissue. A 3.8-μm laser with a radiation dose that changes from small (5.07) to large (15.74 J/cm²) was used to irradiate mouse skin with the 2 × 4 grid array method. The healing progress of laser-injured spots, pathological morphology (H&E staining), and collagen structure changes (Sirius Red staining) were dynamically observed from one hour to 21 days after laser radiation, and the capillary count and collagen content were quantitatively and comparatively analyzed. When the radiation doses were 5.07, 6.77, 8.21, and 9.42 J/cm², a white coagulation spot predominantly occurred, and when the radiation doses were 11.09 12.23, 14.13, 15.74 J/cm², a small injured spot predominantly occurred. One hour after radiation, the collagen structure was obviously damaged. Three to fourteen days after radiation, the hyperplasia and morphology of the collagen in the 5.07 J/cm² group were significantly better than those in the other dose groups. The number of capillaries in the 5.07 J/cm² and 6.77 J/cm² groups was significantly higher than that in the normal group (P < 0.01 or P < 0.05). Twenty-one days after radiation, only the collagen in the 5.07 J/cm² group was densely arranged, and it was basically close to the normal group level. The collagen content in the 5.07 J/cm² group was approximately 10.7%, but it was still lower than that in the normal group (with a collagen content of approximately 14.1%). The collagen in the other dose groups was diminished and had not returned to the normal group level. As the dose of the 3.8-μm laser increased, skin thermal injury gradually increased, the full-thickness skin increased, and the collagen content decreased, showing better dose-dependent and time-dependent effect relationships. The increase in capillaries in the early stage of laser radiation and the significant increase in collagen content in the middle and late stages of laser radiation were two important factors that promoted wound healing.

Technological Advances in Surgical Equipment in Exotic Pet Medicine

Surgery can be challenging in exotic pets owing to their small size and blood volume, and their increased anesthetic risk compared with small animals. Various devices are available to facilitate suturing, cutting, and hemostasis in the human and veterinary fields. These surgical equipment improve the simplicity, rapidity, and effectiveness of surgery. Vessel-sealing devices, radiosurgery, lasers, and ultrasound devices are commonly used because of their ease of use and increase in surgical efficiency. Other surgical devices are available (eg, stapling devices) but are not discussed in this article.

A randomized, open-label, controlled trial to evaluate the antimicrobial and surgical effect of CO2 laser treatment in diabetic infected foot ulcers: DULCIS (diabetic ulcer, CO2 laser, and infections) study

AIM

Debridement of fibrin and necrotic tissue from the ulcer surface is an important component of the treatment of diabetic ulcers. A possible alternative to standard lancets is represented by CO₂ laser, which vaporizes necrotic tissues together with any pathogen. The present trial is aimed at verifying the effect of a CO₂ laser on bacterial load in the debridement of infected diabetic foot ulcers.

METHODS

In this open-label randomized controlled trial (NCT02677779), patients with diabetes and an infected foot ulcers were randomized to either CO₂ laser or traditional debridement.

RESULTS

The reduction (%) of bacterial load with CO₂ laser was significantly greater than in control group [-99.9 (-100.0; -90.0) vs. -50.0 (-96.0; -75.0), p = 0.049]. Similarly, a significantly greater reduction (%) of the fraction of ulcer area covered by fibrin was obtained in the intervention group [-84.1 (-95.0; -72.2) vs. -46.9 (-69.5; -40.8), p = 0.038].

CONCLUSIONS

Debridement of ulcers with CO₂ laser significantly reduces bacterial load and fibrin-covered areas, and could be of help in the treatment of diabetic foot ulcer.

Relationship between CO2 laser-induced artifact and glottic cancer surgical margins at variable power doses

BACKGROUND

The carbon dioxide laser can induce thermal cytologic artifacts at the margin of early glottic squamous cell carcinoma histologic specimens, which makes assessment of the margin difficult. This study assesses and correlates the depth of laser-induced thermal artifact with laser power rating.

METHODS

The surgical margins of 30 patients with early glottic squamous cell carcinomas who underwent laser resection were reanalyzed retrospectively.

RESULTS

Thermal damage consisted of collagen denaturation within the vocal cord lamina propria and vocalis muscle, and epithelial structural changes. There was a decrease in depth of tissue artifact with increased power rating (p > .05). The average depth of thermal damage was 380.83 ± 178.79 μm.

CONCLUSION

The laser causes less thermal damage at higher power, presumably because of the increased speed of cutting and reduced contact time with surrounding cells. Knowledge of the depth of thermal artifact is important surgically when ensuring the cancer is excised with sufficient oncologic margin. © 2015 Wiley Periodicals, Inc. Head Neck 38: E712-E716, 2016.

Pulsed versus continuous wave CO2 laser excisions of 100 oral fibrous hyperplasias: a randomized controlled clinical and histopathological study

BACKGROUND

In experimental animal studies, pulsing the CO2 laser beam has been shown to reduce the thermal damage zone of excised oral mucosal tissue. However, there is still controversy over whether this is borne out under clinical conditions.

OBJECTIVE

To compare the outcome following excisional biopsies of fibrous hyperplasias using a pulsed (cf) versus a continuous wave (cw) CO2 laser mode regarding the thermal damage zone, duration of surgeries, intra- and postoperative complications, postoperative pain sensation, scarring and/or relapse during the initial 6 months.

MATERIALS AND METHODS

One hundred Swiss-resident patients with a fibrous hyperplasia in their buccal mucosa were randomly assigned to the cw mode (5 W) or the cf mode (140 Hz, 400 microseconds, 33 mJ, 4.62 W) group. All excisions were performed by one single oral surgeon. Postoperative pain (2 weeks) was recorded by visual analogue scale (VAS; ranging from 0 to 100). Intake of analgesics and postoperative complications were recorded in a standardized study form. The maximum width of the collateral thermal damage zone was measured (µm) in excision specimens by one pathologist. Intraoral photographs at 6-month follow-up examinations were evaluated regarding scarring (yes/no).

RESULTS

Median duration of the excision was 65 seconds in the cw and 81 seconds in the cf group (P = 0.13). Intraoperative bleeding occurred in 16.3% of the patients in the cw and 17.7% of the cf group. The median value of the thermal damage zone was 161(±228) μm in the cw and 152(± 105) μm in the cf group (P = 0.68). The reported postoperative complications included swelling in 19% and minor bleeding in 6% without significant differences between the two laser modes. When comparing each day separately or the combined mean VAS scores of both groups between Days 1-3, 1-7, and 1-15, there were no significant differences. However, more patients of the cw group (25%) took analgesics than patients of the cf group (9.8%) resulting in a borderline significance (P = 0.04). Scarring at the excision site was found in 50.6% of 77 patients after 6 months, and more scars were identified in cases treated with the cf mode (P = 0.03).

CONCLUSIONS

Excision of fibrous hyperplasias performed with a CO2 laser demonstrated a good clinical outcome and long-term predictability with a low risk of recurrence regardless of the laser mode (cf or cw) used. Scarring after 6 months was only seen in 50.6% of the cases and was slightly more frequent in the cf mode group. Based on the findings of the present study, a safety border of 1 mm appears sufficient for both laser modes especially when performing a biopsy of a suspicious soft tissue lesion to ensure a proper histopathological examination.

CO(2) laser versus cold steel margin analysis following endoscopic excision of glottic cancer

Objective

To compare the suitability of CO₂ laser with steel instruments for margin excision in transoral laser microsurgery.

Methods

Prospective randomized blinded study. Patients with glottic cancer undergoing laser resection were randomized to margin excision by either steel instruments or CO₂ laser. Margins were analyzed for size, interpretability and degree of artifact by a pathologist who was blinded to technique.

Results

45 patients were enrolled in the study with 226 total margins taken. 39 margins taken by laser had marked artifact and 0 were uninterpretable. 20 margins taken by steel instruments had marked artifact, and 2 were uninterpretable. Controlling for margin size, the laser technique was associated with increasing degrees of margin artifact (p = 0.210), but there was no difference in crude rates of uninterpretability (p = 0.24).

Conclusion

Laser margin excision is associated with a greater degree of artifact than steel instrument excision, but was not associated with higher rate of uninterpretability.

The effect of laser diode irradiation on wound healing of rat skin

BACKGROUND

Light amplification by stimulated emission of radiation (LASER) diode irradiation (LDI) has some beneficial effects on the wound healing. However, little is known about the biochemical effect of LDI on wound healing. We have performed animal study to clarify the effect of LDI on wound healing based on microscopic findings.

METHODS

Eight-month-old male rats (NTacSam:SD, SamtakoBioKorea), weighting 250-300 g, were used. Round blade, of 1 cm diameter, was penetrated through the skin and subcutaneous level after elevating the skin just above the thoracic spine of the rats. Laser diode of 655, 785, and 850 nm wavelengths were irradiated to the skin wound for 9 days, 20 min a day. Eight rats were used in each four groups including non-irradiated group. Immunochemical staining was carried out to evaluate pan-cytokeratin and actin, and Masson's trichrome staining was carried to evaluate the cellular and protein components relating to wound healing. Wound size was measured on 9th postoperative day with computer system.

RESULT

Collagen formation was graded as 2+, 3+, and 4 + in the order of non-radiation group, 655, 785, and 850 nm irradiation groups, respectively. Myofibroblast was formed more abundantly in LDI group than in non-irradiated group. The mean values of proliferating cell nuclear antigen (PCNA) were 67.8 ± 5.0, 84.0 ± 4.6, 78.0 ± 6.8, and 74.2 ± 4.0 nm in the order of non-radiation group, 655, 785, and 850 nm irradiation groups, respectively. Mean values of defect size were 2,840 ± 124 um, 1,689 ± 125 um, 1,254 ± 94 um, and 1,423 ± 113 in the order of non-radiation group, 65, 785, and 850 nm groups, respectively.

CONCLUSION

LDI has beneficial effects on the formation of fibroblast and collagen, and results in better wound healing.

Comparison of lateral thermal injury and healing of porcine skin incisions performed by CO2-laser, monopolar electrosurgery and radiosurgery: a preliminary study based on histological and immunohistochemical results

BACKGROUND

Despite the wide application of lasers and electrosurgery in dermatology, the pertinent literature provides conflicting data regarding the lateral thermal injury (LTI) associated with these instruments and its effects on wound healing. This study aims to quantitate the LTI produced by CO(2)-laser, monopolar electrosurgery (MES), and radiosurgery (MRS) and determine its effects on the healing process (re-epithelialization and inflammatory response) of incisional wounds.

METHODS

Five adult swine of similar weight (22.8-25 kg) were submitted to standardized full-thickness incisions on the lateral abdominal skin by the above instruments (at settings similar to those used in clinical practice) and scalpel (control group). Full-thickness specimens from the surgical site were harvested immediately afterwards and 48 hours later (days 1 and 3). The animals were euthanized by intravenous administration of propofol and pentobarbital. All specimens were formalin fixed, paraffin embedded, cut, and stained with hematoxylin-eosin to quantitate the extent of LTI and inflammatory infiltration. Sections of day 3 were stained with the MIB-1 monoclonal antibody to detect Ki-67 as a marker of epithelial cell proliferation adjacently to the incisions.

RESULTS

LTI was most extensive in the CO(2)-laser-group but did not differ significantly between MES- and MRS-groups. Immunohistochemistry ascertained significantly greater epithelial cell proliferation in the CO(2)-laser-group. Inflammatory infiltration was significantly greater in the CO(2)-laser-group, when compared with the controls but did not differ significantly between the MES/MRS and control groups.

CONCLUSION

CO(2) laser incisions exhibit more extensive LTI, epithelial cell proliferation, and inflammatory response. Confirmation of these findings requires a greater sample.

Ultrafast mid-IR laser scalpel: protein signals of the fundamental limits to minimally invasive surgery

Lasers have in principle the capability to cut at the level of a single cell, the fundamental limit to minimally invasive procedures and restructuring biological tissues. To date, this limit has not been achieved due to collateral damage on the macroscale that arises from thermal and shock wave induced collateral damage of surrounding tissue. Here, we report on a novel concept using a specifically designed Picosecond IR Laser (PIRL) that selectively energizes water molecules in the tissue to drive ablation or cutting process faster than thermal exchange of energy and shock wave propagation, without plasma formation or ionizing radiation effects. The targeted laser process imparts the least amount of energy in the remaining tissue without any of the deleterious photochemical or photothermal effects that accompanies other laser wavelengths and pulse parameters. Full thickness incisional and excisional wounds were generated in CD1 mice using the Picosecond IR Laser, a conventional surgical laser (DELight Er:YAG) or mechanical surgical tools. Transmission and scanning electron microscopy showed that the PIRL laser produced minimal tissue ablation with less damage of surrounding tissues than wounds formed using the other modalities. The width of scars formed by wounds made by the PIRL laser were half that of the scars produced using either a conventional surgical laser or a scalpel. Aniline blue staining showed higher levels of collagen in the early stage of the wounds produced using the PIRL laser, suggesting that these wounds mature faster. There were more viable cells extracted from skin using the PIRL laser, suggesting less cellular damage. β-catenin and TGF-β signalling, which are activated during the proliferative phase of wound healing, and whose level of activation correlates with the size of wounds was lower in wounds generated by the PIRL system. Wounds created with the PIRL systsem also showed a lower rate of cell proliferation. Direct comparison of wound healing responses to a conventional surgical laser, and standard mechanical instruments shows far less damage and near absence of scar formation by using PIRL laser. This new laser source appears to have achieved the long held promise of lasers in minimally invasive surgery.

Remodeling of the rat gingiva induced by CO2 laser coagulation mode

BACKGROUND AND OBJECTIVES

This study was conducted to clarify the morphologic characteristics and subsequent repair process of coagulation necrosis produced by pulsed CO(2) laser irradiation with relatively low fluence, and thereby to evaluate the clinical efficacy of this irradiation mode.

STUDY DESIGN/MATERIALS AND METHODS

Wounding of rat gingiva to produce coagulation necrosis was done with a CO(2) laser with a fluence of 326 J/cm(2). The structural characteristics of the wound and subsequent repair process were examined by means of histology, immunohistochemistry, and electron microscopy.

RESULTS

At 6 hours after irradiation, the cells in the laser wound appeared histologically intact but had lost the immunoreactivity to antibodies against Hsp47 and exhibited various ultrastructural signs of cell death. This wound area was lined by Hsp70-positive cells. At 1-day post-irradiation, the uptake of BrdU rapidly increased in the adjacent epithelium and connective tissue. The re-epithelization commenced at 1 day and was completed by 7 days. The necrotic tissue gradually became integrated within the newly formed connective tissue and the original contour of the gingiva was retained during the repair process. The repair process of the laser-induced wound progressed more rapidly than that of a scalpel-made wound.

CONCLUSIONS

The present study suggests that the coagulation necrosis produced by the low fluence pulsed CO(2) laser does not disturb the repair process but promotes its steady progress and subsequent tissue remodeling. This laser mode will pave the way for more conservative and minimally invasive surgery for treating a wide variety of oral soft tissue disorders.

In-vivo optical imaging of hsp70 expression to assess collateral tissue damage associated with infrared laser ablation of skin

Laser surgical ablation is achieved by selecting laser parameters that remove confined volumes of target tissue and cause minimal collateral damage. Previous studies have measured the effects of wavelength on ablation, but neglected to measure the cellular impact of ablation on cells outside the lethal zone. In this study, we use optical imaging in addition to conventional assessment techniques to evaluate lethal and sublethal collateral damage after ablative surgery with a free-electron laser (FEL). Heat shock protein (HSP) expression is used as a sensitive quantitative marker of sublethal damage in a transgenic mouse strain, with the hsp70 promoter driving luciferase and green fluorescent protein (GFP) expression (hsp70A1-L2G). To examine the wavelength dependence in the mid-IR, laser surgery is conducted on the hsp70A1-L2G mouse using wavelengths targeting water (OH stretch mode, 2.94 microm), protein (amide-II band, 6.45 microm), and both water and protein (amide-I band, 6.10 microm). For all wavelengths tested, the magnitude of hsp70 expression is dose-dependent and maximal 5 to 12 h after surgery. Tissues treated at 6.45 microm have approximately 4x higher hsp70 expression than 6.10 microm. Histology shows that under comparable fluences, tissue injury at the 2.94-microm wavelength was 2x and 3x deeper than 6.45 and 6.10 microm, respectively. The 6.10-microm wavelength generates the least amount of epidermal hyperplasia. Taken together, this data suggests that the 6.10-microm wavelength is a superior wavelength for laser ablation of skin.

Submucosal glycerol injection-assisted laser surgical treatment of oral lesions

Recently, we modified laser surgery for superficial lesions in the oral cavity by using submucosal glycerol injection. This procedure was based on a technique for endoscopic mucosal resection (EMR) in the gastrointestinal tract. The aim of this study was to evaluate the effectiveness of the modified laser surgery assisted by a submucosal glycerol injection. Eleven superficial oral lesions in ten patients were treated with diode laser (continuous wave mode, 3 W) after a submucosal injection of glycerol solution. Injection of glycerol solution created mucosal expansion, which enabled the procedures to be done without bleeding, over cutting, over coagulation and unintended irradiation. The surface of the wounds showed little carbonization, resulting in good healing. Submucosal glycerol injection for laser treatment in the oral cavity is a promising technique for treating superficial oral lesions by virtue of less invasion and good results.

Controlling thermal damage of incisions using diamond, copper, and sapphire heat-conducting templates with and without cooling

INTRODUCTION

We investigated the reduction of thermal damage to the surrounding tissue when laser incisions were made with and without using thermal conducting templates at room temperature and cooled to 5 degrees C.

STUDY DESIGN/MATERIALS AND METHODS

We used the Vanderbilt free-electron laser (FEL) at 5.4, 6.1, 6.45, and 7.7 microns. We also used a conventional continuous wave (CW) carbon dioxide laser at 10.6 microns. Incisions were made on 5x10 mm pieces of human breast skin (in vitro) and analyzed with histology. Computer morphometrics were used to measure the amount of thermal damage.

RESULTS

All templates produced a statistically significant reduction in the thermal damage. Additionally, we showed that cooling the templates made a statistically significant greater reduction in the thermal damage. The cooled diamond template reduced the thermal damage from the FEL to 28% of the damage observed without a template. The same cooled template reduced the thermal damage from the CO(2) laser to 56% of the damage observed without a template. Lesser reductions were observed with the copper template and even less with the sapphire template. The sapphire template reduced the thermal damage to 39 and 67% of the damage observed without a template for the FEL and the CO(2) laser, respectively.

CONCLUSION

These results indicate that unwanted lateral thermal damage from laser incisions can be reduced with cooled thermally conductive templates with the best results obtained with the diamond template, which is also the best thermal conductor.

Histologic comparison of skin biopsy specimens collected by use of carbon dioxide or 810-nm diode lasers from dogs

OBJECTIVE

To compare histologic artifacts caused by carbon dioxide (CO2) or 810-nm diode surgical lasers used to obtain small biopsy specimens of skin from healthy dogs.

DESIGN

Prospective study.

ANIMALS

4 dogs.

PROCEDURE

21 skin biopsy specimens were collected from each dog. Three biopsy specimens were obtained with a CO2 or an 810-nm diode laser at 3 operating settings each, and 3 biopsy specimens were obtained with a 6-mm biopsy punch instrument (controls). After processing, biopsy specimens were examined for artifacts related to laser-tissue interactions. Microscopically visible char was measured from the lateral edge of each specimen obtained with a laser.

RESULTS

There were no significant differences among mean char distances in biopsy specimens obtained with the CO2 laser at various settings. Mean char distance was significantly greater in all skin biopsy specimens obtained with the diode laser, compared with those obtained with the CO2 laser. Mean char distance was significantly greater in biopsy specimens obtained with the 810-nm diode laser at high power, compared with biopsy specimens obtained with the 810-nm diode laser at low power.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the CO2 laser caused less thermal injury at margins of skin biopsy specimens; therefore, if a surgical laser is used for removal of cutaneous masses or to obtain skin biopsy specimens, use of the CO2 laser is recommended. Veterinarians performing a biopsy by using a surgical laser should be aware that laser-induced artifacts may render small biopsy specimens useless for providing accurate histologic diagnosis.

Wound healing of 6.45-microm free electron laser skin incisions with heat-conducting templates

We have previously shown a reduction in lateral thermal damage with acute studies of skin incisions made in vitro using heat-conducting templates. Here we examined the wound-healing response to laser incisions with heat-conducting templates and explored the use of an optically transparent template with the free electron laser (FEL) at 6.45 microm. First we evaluated the effects of a sapphire heat-conducting template on the lateral thermal damage of FEL incisions using in vitro human skin samples. Next we compared wound tensile strength and histological scoring of the healing of incisions created on the dorsal pelts of live rats with the FEL utilizing metal and sapphire heat-conducting templates and scalpel incisions. The animals were euthanized and the wounds were analyzed at postoperative days 7, 14, and 21. The depth and lateral thermal damage of FEL incisions on in vitro human skin were significantly reduced with the sapphire heat-conducting template. Nonstatistically significant differences in wound tensile strengths and histological scoring of wound healing were noted at days 7 and 14. By day 21, all of the incisions appeared similar. When the data from days 7 and 14 were combined, statistically significant differences were found for each of the templates (except the histological evaluation with the aluminum template) and the scalpel compared with laser incisions made without using a template. The use of metal or sapphire heat-conducting templates reduced the wound-healing delay of laser incisions seen at postoperative days 7 and 14.

Comparison of Mouse Matrix Metalloproteinase 13 Expression in Free-Electron Laser and Scalpel Incisions During Wound Healing

Collagenase-3 (matrix metalloproteinase 13, MMP-13) was employed as a surrogate marker to compare the characteristics of incisional wound repair after surgery with the free-electron laser at 6.1 microm and the scalpel. Using a transgenic mouse strain with the MMP-13 or the COL1A2 promoter driving luciferase expression, we observed MMP-13 and COL1A2 expression, tensile strength, macrophage infiltration, and wound histology for up to 62 d. The scalpel incisions showed higher tensile strength than free-electron laser wounds from days 10 to 22 postwounding, despite minimal collateral thermal damage. After 45 d healing was similar. Trichrome staining confirmed that the scalpel incisions had more dense collagen deposition than free-electron laser incisions up to 36 d postinjury, but at day 45 they became similar. MMP-13 expression was biphasic, with peak activities at days 15 and 37 after injury, whereas free-electron laser wounds showed greater luciferase activity than scalpel wounds. Peak COL1A2 activity preceded the MMP-13 maximum. MMP-13 expression localized predominantly to dermal fibroblasts near the epidermis at day 15, and in the region of the deep dermis, muscle, and fascia at day 37 postwounding. Migrating muscle cells, but not all skeletal muscle cells, also expressed MMP-13. Free-electron laser incisions contained more macrophages than scalpel wounds at days 2 and 7 postinjury, suggesting that free-electron laser irradiation exacerbated the inflammatory response and thereby stimulated MMP-13 expression. These results revealed that MMP-13 was involved in a series of coordinated events during wound healing, not only the long-term remodeling of wound connective tissue, but also skeletal muscle repair. MMP-13 activity in vivo may correlate with the extent of tissue damage.

Reduction in lateral thermal damage using heat-conducting templates: a comparison of continuous wave and pulsed CO2 lasers

BACKGROUND AND OBJECTIVES

The advantages of the continuous wave (c.w.) CO(2) laser are offset by the delay in laser wound healing secondary to thermal damage. We have developed novel heat-conducting templates to reduce laser thermal damage. Because shortened pulse durations also decrease thermal damage, we tested the effectiveness of heat-conducting templates with a c.w. CO(2) clinical laser and a short-pulsed CO(2) laser to determine the best method and mechanism to minimize thermal damage.

STUDY DESIGN/MATERIALS AND METHODS

Comparison of 0.2-second shuttered c.w. and 5-microsecond pulsed CO(2) lasers were made by doing incisions on 150 tissue samples from reduction mammoplasties and abdominoplasties. Copper, aluminum, glass, and Plexiglass heat-conducting templates were tested against no template (air) with both lasers. Histological samples were evaluated using computerized morphometrics analysis.

RESULTS

Statistically significant reductions in lateral thermal damage were seen with the copper (50%) and aluminum (39%) templates used with the c.w. CO(2) laser. Only the copper template (39%) significantly reduced thermal damage when used with the pulsed CO(2) laser. Less thermal damage was seen using the pulsed CO(2) laser compared to the c.w. CO(2) laser with each template.

CONCLUSIONS

Heat-conducting templates significantly reduced the amount of lateral thermal damage when used with the c.w. CO(2) laser (copper and aluminum) and short-pulsed CO(2) laser (copper). The c.w. CO(2) laser with the copper template compared favorably to the short-pulsed CO(2) laser without a template. Therefore, both heat conductive templates and short-pulse structure provide successful methods for reducing lateral thermal damage, and a combination of the two appears to provide optimal results.

Scatter-limited phototherapy: a model for laser treatment of skin

BACKGROUND AND OBJECTIVES

To effectively deliver laser light into the skin for non-ablative resurfacing, hair removal, and other applications, one must account for scatter, absorption, and thermal diffusion. A novel method to control the penetration of laser light into tissue is proposed. This method uses the incident beam diameter, the pulse duration, and the intrinsic light scattering of tissues such as skin to limit the laser light penetration and thermal damage. We term this innovative laser delivery concept 'scatter-limited phototherapy'.

STUDY DESIGN/MATERIALS AND METHODS

This study demonstrates how the delivery mechanism simplifies the non-ablative treatment of sun-damaged skin. Calculations are based upon Gaussian scatter of light and isotropic thermal diffusion. Calculations of light distribution and profiles of temperature increase are created.

RESULTS

Using an optical fiber delivery system with the appropriate diameter, coupled with skin surface protection, one can create thermal damage at a given depth with preservation of the epidermis.

CONCLUSIONS

Scatter-limited phototherapy is a predictive model, allowing one to design better laser delivery systems. Scatter-limited phototherapy should also be applicable to other fields of dermatologic surgery, such as hair removal and the treatment of vascular lesions. Additionally, other medical specialties will be able to use the concept of scatter-limited phototherapy to predict and better understand laser-tissue interactions.

New-generation pulsed carbon dioxide laser: comparative effects on vocal fold wound healing

We investigated wound healing of vocal fold mucosal excisions using a canine model, comparing cold steel, the continuous wave (CW) carbon dioxide (CO2) laser, and a new, microsecond-pulsed CO2 laser. The thermal injury to the surrounding normal tissues produced by the laser increases the risk for scar formation and poor functional voice outcome. This injury may be reduced with a pulsed CO2 laser. Acute, 2-week, and 6-week studies of 15 dogs were made with blinded observers and nonparametric statistical analyses. Histologic comparison showed less thermal injury and scar formation in the vocal folds treated with the pulsed CO2 laser than with the CW CO2 laser. Functional outcomes as studied with laryngeal videostroboscopy revealed better vibratory characteristics with the pulsed CO2 laser as compared with the CW CO2 laser. No differences were seen on these measures between the pulsed laser and cold techniques. Pulsed CO2 lasers may offer the ease of laser laryngology and the superior wound healing of cold steel.