Scanning electron microscopy of corneal incisions using steel, diamond, and sapphire blades

In order to compare the wound morphology they produce, we used steel (Myocure), diamond (CILCO DK 121), and sapphire (Katena K2-6500) blades, to make parallel linear incisions, 500 microns deep, in 12 fresh enucleated porcine eyes. There was no discernible difference among the blades in terms of either the morphology of the collagen lamellae of the sides or the depth of the incisions produced. The major differences in the cuts produced were attributable primarily to the differences in the footplates.     

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.     

Comparative gross and histological study of the effects of scalpel, electric knife, and carbon dioxide laser on skin and uterine incisions in dogs

This study concerns the gross histological effects of scalpel, electric knife, and carbon dioxide laser incisions on skin and uterine tissue in dogs. Tissue studies comparing the carbon dioxide laser with the scalpel and electric knife have frequented the literature. However, a gross and histological comparison specifically involving uterine tissue is not presently known to have been reported. The evaluation on this series of animals considers both the skin and the uterus in an abdominal approach to evaluate the carbon dioxide laser for potential intrauterine surgery. Tissue sampling of both skin and uterus at 2, 6, and 8 weeks postoperatively were histologically examined to evaluate healing rates and degree of scar formation.     

Dynamic skin cooling with an environmentally compatible alternative cryogen during laser surgery

BACKGROUND AND OBJECTIVES: Cryogen spray cooling with tetrafluoroethane (R134a) has been used to enhance epidermal protection during dermatologic laser surgery. However, R134a has a very high global warming potential (GWP = 1300). Our objective was to evaluate the cooling effectiveness of an alternative cryogen with a much lower GWP, namely liquid carbon dioxide (CO(2), GWP = 1). STUDY DESIGN/MATERIALS AND METHODS: A thin-film thermocouple deposited on an epoxy skin phantom was used to measure surface temperature (T(s)) variations induced by R134a or CO(2) sprays. The temperature distribution in the skin phantom was estimated using T(s) and Duhamel's method. Impact pressure and noise level of both cryogen sprays were measured with a dynamic sensor and sound meter, respectively. Consumption of both cryogens was also evaluated. RESULTS: For R134a sprays, T(s) was kept almost constant after 15 milliseconds. For CO(2) sprays, T(s) decreased continuously during the entire spurt of 50 milliseconds. The minimum T(s) induced by the CO(2) sprays was lower than that induced by R134a when the spurt duration was longer than 35 milliseconds. Numerical simulation shows that CO(2) sprays were able to induce very similar temperature reductions in the skin phantom as compared to R134a sprays when the spurt duration and delay time were selected appropriately. R134a sprays induced an impact pressure of 3.6 kPa, as compared to 43.1 kPa for CO(2) sprays. The maximum noise level for R134a sprays was 109 dBA as compared to 135 dBA for the CO(2) sprays. The R134a consumption for a 50 milliseconds spurt is 67 mg as compared to 225 mg for a CO(2) spurt of the same duration. CONCLUSIONS: CO(2) sprays are expected to have similar skin cooling efficacy as R134a sprays. Although the CO(2) consumption is higher than R134a, its contribution to global warming is still much less than R134a. The effects of varying spurt durations on in vivo human skin and the impact on cutaneous blood flow require further investigation.     

A comparison of mass removal, thermal injury, and crater morphology of cortical bone ablation using wavelengths 2.79, 2.9, 6.1, and 6.45 microm

BACKGROUND AND OBJECTIVE: Previous investigations have reported evidence of wavelength dependence on cortical bone ablation. This study used mid-infrared laser wavelengths generated by a free electron laser (FEL) and mass removal measurements to further examine the ablation efficiency of a wavelength (2.79 microm) not previously reported and three wavelengths (2.9, 6.1, and 6.45 microm) previously demonstrated by crater morphology alone to be efficient for cortical bone removal. STUDY DESIGN/MATERIALS AND METHODS: The wavelengths examined were provided by an FEL emitting 4 microseconds macropulses consisting of 1-2 picoseconds duration micropulses delivered at 350 picoseconds intervals. The mass removal measurements were conducted by a microbalance, and the collateral thermal injury and crater morphology of cortical bone were examined by light microscopy following standard histologic processing. RESULTS: The study demonstrated that the highest mass removal was achieved at lambda = 6.1 microm followed by, in order, lambda = 2.9, 6.45, and 2.79 microm. The zones of thermal injury and crater morphology created in cortical bone at the selected wavelengths were examined at the radiant exposure of 28.3 J/cm2. Ablation using lambda = 6.1 microm provided the largest crater size and the least collateral thermal injury. The greatest amount of collateral thermal injury was produced by lambda = 2.79 microm at both the sides and base of the ablation crater. CONCLUSIONS: The mass removal of cortical bone produced by FEL ablation at selected mid-IR wavelengths was measured as a function of incident radiant exposure. The ablation efficiency was found to be dependent upon wavelength. The lambda = 2.79 microm did not offer any improvement over the other wavelengths evaluated, suggesting that a potential shift in the dynamic optical properties of water during tissue irradiance with the FEL does not present an advantage to the cutting of cortical bone. The lambda = 6.1 microm provided the highest ablation efficiency with deepest crater and the least amount of collateral thermal injury.     

The low-output carbon dioxide laser for cutaneous wound closure of scalpel incisions: comparative tensile strength studies of the laser to the suture and staple for wound closure

The low-output carbon dioxide (CO2) laser was used for cutaneous wound closure of scalpel incisions. Cutaneous scalpel incisions were placed over the dorsum of three minipigs and were then closed by either the laser, sutures, or staples. At multiple time points after wound closure, up to day 90, the tensile strengths of these wounds were comparatively evaluated. All wounds, including those closed with the laser, clinically appeared to heal similarly with no evidence of wound dehiscence or infection. Tensile strength studies revealed similar sigmoid curves for all wound closure modalities with low initial tensile strengths up to days 14 to 21, which afterwards increased rapidly, with a plateau toward day 90. From our study, it appears that the CO2 laser, in the low-output mode, can be used for cutaneous wound closure and that similar clinical healing and tensile strength measurements are obtained relative to the conventional cutaneous wound closure modalities of the suture or staple.     

Effect of steroids or tissue preceding on edema and tissue thermal coagulation after CO2 laser impact

The carbon dioxide laser is frequently used in laryngeal microsurgery. Some surgeons have empirically used preoperative steroids or precooling with ice prior to laser impact to limit the resultant tissue thermal coagulation and/or edema. An animal model was designed to quantitatively test these effects. Depillated areas of rat skin were exposed to a CO₂ beam of 1 mm diameter at 15 W for 0.1 sec after either administration of Decadron (0.25 mg/kg) immediately prior to impact or precooling more than 10^oC below basal body temperature. Measurement of edema was quantitated as extravasation of Evan's blue dye that had been injected intravenously. Tissue thermal coagulation was measured on hematoxylin and eosin stained histologic sections. In comparison to controls, statistically significant reduction in edema was seen only at the 24 hour time period after laser exposure for the steroid group (P<.002) but not for the precooling group. Tissue thermal coagulation was significantly smaller for both the steroid and the ice group (P < .006 and P < .001, respectively) when compared to controls. © 1992 Wiley-Liss, Inc.     

Peripheral thermal and mechanical damage to dentin with microsecond and sub-microsecond 9.6 microm, 2.79 microm, and 0.355 microm laser pulses

BACKGROUND AND OBJECTIVES: It is desirable to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. There were two primary objectives of this study. The first objective was to measure the degree of thermal damage peripheral to incisions in dentin produced with lasers resonant to the specific absorption bands of water, collagen, and hydroxyapatite with varying pulse duration using polarized-light microscopy (PLM). The second objective was to use synchrotron radiation infrared spectromicroscopy (SR-FTIR) to identify the specific chemical nature of the optical changes observed under PLM in the respective zones of thermal damage peripheral to the laser incisions. STUDY DESIGN/MATERIALS AND METHODS: Precise incisions were produced in 3 x 3 mm2 blocks of human dentin using CO2 (9.6 microm), Er:YSGG (2.79 microm), and Nd:YAG (355 nm) lasers with and without a computer controlled water-spray. Optical coherence tomography (OCT) was used to obtain optical cross-sections of each incision to determine the rate of ablation. The peripheral thermal damage zone around each incision was analyzed using PLM and SR-FTIR. RESULTS: Thermally induced chemical changes to both mineral and the collagen matrix were observed with SR-FTIR with a 10 microm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10 microm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr) of the deposited laser energy, with and without applied water at 9.6 microm and with only applied water at 2.79 microm. For pulse durations greater than Tr, greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water-spray. There was minimal thermal damage for 355 nm laser pulses less than Tr with and without applied water; however, extensive mechanical damage (cracks) was observed. CONCLUSIONS: High resolution SR-FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub-microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone.     

Mid-IR laser ablation of articular and fibro-cartilage: a wavelength dependence study of thermal injury and crater morphology

BACKGROUND AND OBJECTIVE: The aim of this study was to evaluate areas of collateral thermal injury and crater morphology for evidence of wavelength-dependent effects on the ablation of articular cartilage and fibro-cartilage (meniscus) using selected mid-IR wavelengths produced by a free electron laser. STUDY DESIGN/MATERIALS AND METHODS: Two types of cartilage, articular cartilage and fibro-cartilage were used in the study. The wavelengths (lambda) evaluated were 2.79, 2.9, 6.1, and 6.45 microm generated by a free electron laser (FEL) using a 4 microseconds macropulse configuration. The zone of thermal injury and crater morphology produced by laser ablation were examined by light microscopy following standard histologic processing. RESULTS: The zone of thermal injury and crater morphology created in cartilage by the FEL at selected mid-IR wavelengths were examined as a function of incident radiant exposure. Ablation using lambda = 6.1 microm provided the largest crater size for both articular and fibro-cartilage at all radiant exposures. For the zones of collateral thermal injury in articular cartilage, lambda = 6.1 microm produced the least thermal injury at the radiant exposure of 7.6 J/cm2. When the radiant exposure is increased to 20.4 J/cm2, both lambda = 6.1 and 6.45 microm produced less thermal injury than the ablation using lambda = 2.79 and 2.9 microm. The greatest amount of collateral thermal injury was produced by lambda = 2.79 microm for both tissue types. CONCLUSIONS: The results demonstrate that crater depth and collateral thermal injury produced in articular cartilage and fibro-cartilage are wavelength-dependent with 6.1 microm providing the largest craters at all radiant exposures. The least amount of thermal injury was created in articular cartilage using lambda = 6.1 microm at the radiant exposure of 7.6 J/cm2. Both 6.1 and 6.45 microm wavelengths demonstrated similar amount of thermal injury at 20 J/cm2 that was less than lambda = 2.79 and 2.9 microm at similar fluences. These observations are explained based on the absorption by water and protein in the tissue types studied. It is further observed that the use of crater dimensions may not provide a reliable estimate for the amount of tissue removal provided by an ablation procedure.     

Selective targeting of protein, water, and mineral in dentin using UV and IR pulse lasers: the effect on the bond strength to composite restorative materials

BACKGROUND AND OBJECTIVES: Previous studies have shown that during the laser irradiation of dentin and bone, thermal damage can be minimized by using a highly absorbed laser wavelength, laser pulses shorter than the thermal relaxation time of the deposited laser energy at that wavelength, and the addition of a layer of water to the tissue surface before ablation. The objective of this study was to investigate the influence of laser pulse duration and wavelength with and without the added water layer on the bond strength of composite to laser prepared dentin surfaces. The specific hypothesis that was tested was that thermal damage to the collagen matrix in dentin compromises the bond strength to composite restorative materials. STUDY DESIGN/MATERIALS AND METHODS: Three laser systems were employed that were tuned to water, collagen, and mineral absorption with pulse durations less than the thermal relaxation time of the deposited energy. The surfaces of human dentin were irradiated by laser irradiation from free-running and Q-switched Er:YSGG lasers, pulsed CO(2) lasers operating at 9.6-microm, and a Q-switched Nd:YAG laser operating at 355-nm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to access the suitability of laser treated surfaces for bonding. Bonded interfaces were examined by SEM. RESULTS: All the laser groups had significantly lower bond strengths than the positive acid etch control group. The highest bond strengths were for the short pulse (< 5-microsecond) Er:YSGG and CO(2) laser groups with water. Laser groups without water had significantly reduced bond strengths and thicker layers of thermally damaged dentin. CONCLUSIONS: Thermal damage to the collagen matrix profoundly influences the bond strength to composite restorations.     

An experimental pathologic study of gingivectomy using dual-wavelength laser equipment with OPO

BACKGROUND AND OBJECTIVES: This study was conducted to evaluate how soft tissues respond to treatment by a tunable laser with an optical parametric oscillating (OPO) mechanism capable of simultaneously emitting two wavelengths. MATERIALS AND METHODS: Marginal gingiva of dogs was incised by a prototype laser oscillator. The oscillator was set at two wavelengths known to effectively incise tissue and arrest hemorrhage with minimal invasiveness. Four laser irradiation conditions were set based on different combinations of the 1.67 and 2.94 microm wavelengths. The animals were sacrificed immediately after surgery, 7 days after surgery, and 28 days after surgery for histological examination. RESULTS: When irradiation at 1.67 and 2.94 microm wavelengths was simultaneously applied, the former conferred an observable hemostatic effect and the latter incised the tissue. Wound healing was similar to that in conventional methods and no serious inflammation was observed. CONCLUSION: Simultaneous irradiation at wavelengths of 1.67 and 2.94 microm can be an effective method in soft tissue surgery.     

Free electron laser ablation of articular and fibro-cartilage at 2.79, 2.9, 6.1, and 6.45 microm: mass removal studies

BACKGROUND AND OBJECTIVE: The wavelength and tissue-composition dependence of cartilage ablation was examined using selected mid-infrared laser wavelengths. STUDY DESIGN/MATERIALS AND METHODS: The mass removal produced by pulsed laser ablation of articular and fibro-cartilage (meniscus) were measured. The wavelengths examined were 2.79, 2.9, 6.1, and 6.45 microm and provided by a free electron laser (FEL) emitting 4 microsecond macropulses consisting of 1-2 picoseconds duration micropulses delivered at 350 picosecond intervals. The measurement of tissue mass removal was conducted using a microbalance during laser ablation. RESULTS: These studies demonstrated that for articular cartilage the highest mass removal was achieved at lambda = 6.1 microm followed by, in order, lambda = 2.79, 2.9, and 6.45 microm. In comparison, the maximum mass removal for fibro-cartilage was achieved using lambda = 6.1 microm radiation with no statistically significant differences in mass removal provided by the other wavelengths. In evaluation of the comparative influence of each wavelength on tissue type, there was no difference in ablation efficiency between articular and fibro-cartilage at lambda = 6.1 microm. However, the ablation efficiency of articular cartilage was higher than that of fibro-cartilage at both lambda = 2.79 and 2.9 microm. By contrast, lambda = 6.45 microm radiation ablated fibro-cartilage more efficiently than articular cartilage at radiant exposures greater than 12 J/cm2. CONCLUSIONS: The mass removal of articular and fibro-cartilage produced by FEL ablation at selected mid-IR wavelengths was measured as a function of incident radiant exposure. The ablation efficiency was found to depend on both wavelength and tissue type. The 6.1 microm wavelength was found to provide the highest ablation efficiency for both articular and fibro-cartilage.     

The in vitro performance of carbon dioxide absorbents with and without strong alkali

We report the in vitro longevity of a conventional soda lime carbon dioxide absorbent and an absorbent free from strong alkali (Amsorb). Although the times taken to breakthrough of carbon dioxide (> 0.5%) within an in vitro low flow breathing system were shorter with the alkali-free absorbent, we found that the size and shape of the absorbent container was the major factor in determining the efficiency of the carbon dioxide absorbents.     

The Efficacy and Safety of Epidermal Growth Factor Combined with Fractional Carbon Dioxide Laser for Acne Scar Treatment: A Split-Face Trial

BackgroundEpidermal growth factor (EGF) stimulates collagen production and supports the wound healing process. However, there are no studies on fractional carbon dioxide (CO₂) laser combined with EGF for acne scar treatment.ObjectiveWe sought to evaluate the efficacy and safety of fractional CO₂ laser combined with topical EGF versus fractional CO₂ laser alone in the treatment of acne scars.MethodsTwenty-three patients with atrophic acne scars underwent three monthly sessions of randomized split-face application of fractional CO₂ laser combined with topical EGF or placebo twice daily for seven days following each laser session. Scar improvement was evaluated at one month and three months posttreatment by two blinded dermatologists and the Antera 3D^® skin analysis system. Wound healing response and adverse events were also evaluated.ResultsTwenty-one patients completed the trial. According to dermatologist grading and skin analysis system, EGF showed significant superiority at three months posttreatment compared to placebo. The wound healing response did not differ between the groups. Surprisingly, the melanin index on the EGF side showed a significant decrease at three months posttreatment, compared to placebo. There was no allergic reaction to the topical EGF.ConclusionTreatment with topical EGF after ablative fractional CO₂ laser improves the clinical appearance of atrophic acne scars, and EGF may help decrease skin pigmentation after laser treatment. The use of topical EGF is safe when applied to post-laser ablation.     

先天性心脏病患儿P_(ET)CO_2、TcPCO_2与PaCO_2监测的相关性

目的评估先天性心脏病患儿P_(ET)CO_2、经皮二氧化碳分压(TcPCO_2)与PaCO_2值的相关性。方法选择拟在体外循环下行先天性心脏病手术患儿80例,男42例,女38例,年龄1月~5岁,ASAⅡ~Ⅳ级,分为四组:紫绀型伴严重肺动脉高压组(N1组)、紫绀型不伴肺动脉高压组(N2组)、非紫绀型伴严重肺动脉高压或肺血流增加组(N3组)和非紫绀型伴轻度肺动脉高压或肺动脉压力正常组(N4组),每组20例。统一选取相同的麻醉方案,在手术开始前记录患儿的P_(ET)CO_2、TcPCO_2与PaCO_2值,计算P_(ET)CO_2、TcPCO_2与PaCO_2的差值,并进行相关性分析。结果 N1、N2、N3组P_(ET)CO_2与PaCO_2差值较大,N4组中相对较小;四组患儿TcPCO_2与PaCO_2差值都相对较小;N1、N2、N3组中TcPCO_2-PaCO_2值明显低于P_(ET)CO_2-PaCO_2值,N4组中TcPCO_2-PaCO_2值明显高于P_(ET)CO_2-PaCO_2值。P_(ET)CO_2与PaCO_2的相关性分析中,N1、N2、N3、N4组的R2分别为0.028、0.197、0.390、0.711(P0.05、0.02P0.05、P0.01、P0.01),在N1、N2组相关性较低,N3、N4组相关性较高;TcPCO_2与PaCO_2的相关性分析中,R2在N1、N2、N3、N4组分别为0.750、0.827、0.835、0.691(P0.01),各组均表现良好的相关性。结论小儿先天性心脏病无论是肺血流增加还是右向左分流均可使P_(ET)CO_2与PaCO_2的相关性较差,P_(ET)CO_2与PaCO_2仅在左向右分流的先天性心脏病患儿中表现较好的相关性;TcPCO_2与PaCO_2在小儿先天性心脏病监测中有良好的相关性,更适合为小儿先天性心脏病无创监测CO_2提供依据。