Acute Thermal Damage Research Articles

Comparative healing of swine skin following incisions with different surgical devices.

BackgroundElectrosurgical technology is widely used in surgical dissection and hemostasis, but the generated heat creates thermal injury to adjacent tissues and delays wound healing. The plasma blade (PB) applies pulsed radiofrequency (RF) to generate electrical plasma along the edge of a thin, flat, insulated electrode, minimizing collateral tissue damage. This study aimed to evaluate wound healing in swine skin following incision with a new surgical system that applies low-temperature plasma (NTS-100), a foreign PB, conventional electrosurgery (ES), and a scalpel blade.MethodsIn vitro porcine skin and an in vivo porcine skin model were used in this study. Full-thickness skin incisions 3 cm in length were made on the dorsum of each animal for each of the 5 surgical procedures at 0, 21, 28, 35, and 42 days. The timing of the surgical procedures allowed for wound-healing data points at 1, 2, 3, and 6 weeks accordingly. Local operating temperature and blood loss were quantified. Wounds were harvested at designated time points, tested for wound tensile strength, and examined histologically for scar formation and tissue damage.ResultsLocal operating temperature was reduced significantly with NTS-100 (cut mode 83.12±23.55 °C; coagulation mode 90.07±10.6 °C) compared with PB (cut mode 94.46±11.48 °C; coagulation mode 100.23±6.58 °C, P<0.05) and ES (cut mode 208.99±34.33 °C, P<0.01; coagulation mode 233.37±28.69 °C, P<0.01) in vitro. Acute thermal damage from NTS-100 was significantly less than ES incisions (cut mode: 247.345±42.274 versus 495.295±103.525 µm, P<0.01; coagulation mode: 351.419±127.948 versus 584.516±31.708 µm, P<0.05). Bleeding, histological scoring of injury, and wound strength were equivalent for the NTS-100 and PB incisions.ConclusionsThe local operating temperature of NTS-100 was lower than PB, and NTS-100 had similarly reliable safety and efficacy.

Thermal coagulum formation and hemostasis during repeated multipulse Nd:YAG laser treatment of cutaneous vascular lesions: animal experiment study.

Laser therapy has been widely used to treat port-wine stain (PWS) and other cutaneous vascular lesions via selective photothermolysis. High incident laser fluence is always prohibited in clinic to prevent the thermal damage in normal skin tissue, leading to insufficient energy deposition on the target blood vessel and incomplete clearance of PWS lesion. In this study, repeated multipulse laser (RMPL) irradiation was proposed to induce acute thermal damage to target blood vessels with low incident fluence (40J/cm2 for 1064-nm Nd:YAG laser). The feasibility of the method was investigated using animal models. Repeated multipulse irradiation cycles with 10-min intervals were performed in RMPL. A hamster dorsal skin chamber model with a visualization system was constructed to investigate the instant generation of thermal coagulum and relevant hemostasis by thrombus formation during and after irradiation under 1064nm Nd:YAGsinglemultipulse laser (SMPL) and RMPLirradiation. The diameter of the target blood vessel and the size of thermal coagula were measured before and after laser irradiation. The reflectance spectra of the dorsal skin were measured by a reflectance spectrometer during RMPL. Stasis thermal coagula that clogged the vessel lumen were generated during SMPL irradiation with low incident fluence. However, there was no acute thermal damage of blood vessels. Reflectance spectra measurement showed that the generation of thermal coagula and subsequent thrombus formation increases blood absorption by more than 10% within the first 10min after laser irradiation. Acute vessel thermal damage could be induced in the target blood vessel by RMPL with low incident fluence of 40J/cm2. Compared with our previous SMPL study, nearly 30% reduction in incident laser fluence was achieved by RMPL. Low fluence RMPL may be a promising approach to improve the therapeutic outcome for patients with cutaneous vascular lesions by improving energy deposition on the target blood vessel.

Assessment of acute thermal damage volumes in muscle using magnetization-prepared 3D T2 -weighted imaging following MRI-guided high-intensity focused ultrasound therapy.

To evaluate magnetization-prepared 3D T2 -weighted magnetic resonance imaging (MRI) measurements of acute tissue changes produced during ablative MR high-intensity focused ultrasound (MR-HIFU) exposures. A clinical MR-HIFU system (3T) was used to generate thermal lesions (n = 24) in the skeletal muscles of three pigs. T1 -weighted, 2D T2 -weighted, and magnetization-prepared 3D T2 -weighted sequences were acquired before and after therapy to evaluate tissue changes following ablation. Tissues were harvested shortly after imaging, fixed in formalin, and gross-sectioned. Select lesions were processed into whole-mount sections. Lesion dimensions for each imaging sequence (length, width) and for gross sections (diameter of lesion core and rim) were assessed by three physicists. Contrast-to-background ratio between lesions and surrounding muscle was compared. Lesion dimensions on T1 and 2D T2 -weighted imaging sequences were well correlated (R2 ∼0.7). The contrast-to-background ratio between lesion and surrounding muscle was 7.4 ± 2.4 for the magnetization-prepared sequence versus 1.7 ± 0.5 for a conventional 2D T2 -weighted acquisition, and 7.0 ± 2.9 for a contrast-enhanced T1 -weighted sequence. Compared with diameter measured on gross pathology, all imaging sequences overestimated the lesion core by 22-33%, and underestimated the lesion rim by 6-13%. After MR-HIFU exposures, measurements of the acute thermal damage patterns in muscle using a magnetization-prepared 3D T2 -weighted imaging sequence correlate with 2D T2 -weighted and contrast-enhanced T1 -weighted imaging, and all agree well with histology. The magnetization-prepared sequence offers positive tissue contrast and does not require IV contrast agents, and may provide a noninvasive imaging evaluation of the region of acute thermal injury at multiple times during HIFU procedures. 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:354-364.

Experimental investigation and histopathological identification of acute thermal damage in skeletal porcine muscle in relation to whole-body SAR, maximum temperature, and CEM43 °C due to RF irradiation in an MR body coil of birdcage type at 123 MHz

Purpose: This study is an investigation of the relationship between several characteristic parameters and acute thermal damage in porcine skeletal muscle. Material and methods: Fourteen pigs under injection anaesthesia were placed into a magnetic resonance body coil and exposed for different time durations to different specific energy absorption rate (SAR) levels at 123 MHz. Local temperatures were measured using four temperature sensors. Sensors 1–3 were placed in skeletal muscle and one sensor was placed in the rectum. Sensors 1 and 2 were placed in hot-spot areas and sensor 3 was placed at the periphery of the animals. The pigs were exposed to whole-body SAR (SAR-wb) between 2.5 W/kg and 5.2 W/kg for 30 or 60 min. Three animals received no SAR. After each experiment, muscle samples adjacent to the positions of sensors 1–3 were taken for frozen section analysis. Three characteristic parameters were chosen for investigation: SAR-wb, maximum sensor temperature (T-max), and cumulative equivalent minutes at 43 °C (CEM43 °C). Results: Histopathological criteria were established to detect acute thermal tissue damage in frozen sections such as widening of intercellular space between the muscle fibres and loss of glycogen. Clear tissue damage thresholds were found for T-max and CEM43 °C, though not for SAR-wb. For all animals with high thermal exposure, damage was also found for muscle samples adjacent to the peripheral sensor 3. Conclusions: Both T-max and CEM43, are able to predict thermal damage in porcine muscle. However, CEM43 is the less ambiguous parameter. The reasons for the occurrence of the aforementioned damage at low local temperatures at the animals’ periphery remain unclear and further investigations are needed.

Comparative Healing of Surgical Incisions Created by the PEAK PlasmaBlade, Conventional Electrosurgery, and a Scalpel

The PEAK PlasmaBlade is a new electrosurgical device that uses pulsed radiofrequency to generate a plasma-mediated discharge along the exposed rim of an insulated blade, creating an effective cutting edge while the blade stays near body temperature. Full-thickness incisions were made on the dorsums of pigs with the PlasmaBlade, a conventional electrosurgical device, and a scalpel, and blood loss was quantified. Wounds were harvested at designated time points, tested for wound tensile strength, and examined histologically for scar formation and tissue damage. Bleeding was reduced significantly (59 percent) in PlasmaBlade incisions compared with scalpel incisions, and acute thermal damage from the PlasmaBlade (66 +/- 5 microm) was significantly less than both cut and coagulation mode electrosurgical incisions (456 +/- 35 microm and 615 +/- 22 microm, respectively). Histologic scoring for injury and wound strength was equivalent between the PlasmaBlade and scalpel incisions. By 6 weeks, the healed PlasmaBlade and scalpel incisions were approximately three times stronger, and scar cosmetic appearance was significantly better compared with electrosurgical incisions. The PlasmaBlade is a promising new surgical instrument that provides atraumatic, scalpel-like cutting precision and electrosurgical-like hemostasis, resulting in minimal bleeding, tissue injury, and scar formation.

Histopathologic Studies of the Below-the-Knee Great Saphenous Vein after Endovenous Laser Ablation

There has been hesitation to use endovenous laser ablation (EVLA) for the treatment of incompetence of the below-the-knee great saphenous vein (GSV). To assess early pathologic changes in the below-the-knee nonvaricose GSV and adjacent tissue after EVLA in legs scheduled for below-the-knee amputation. The below-the-knee GSV in five patients was exposed to EVLA using 14-, 12-, and 10-watt laser power with continuous or intermittent laser exposure using a 600-nm core, bare tip fiber. Six segments (3 x 3 cm) of GSV with adjacent tissue were excised, examined histologically, and compared with non-laser-exposed parts of the vessel. Histologic evaluation revealed thermal damage of the intima and the internal part of the media. At the site of the laser tip, carbonization and necrosis was observed. Vascular perforation with subsequent perivascular bleeding was occasionally (<10%) seen in cases treated with 40 to 80 J/cm and in all cases treated with 110 to 200 J/cm. The saphenous nerve was not damaged. Based on this histopathologic study, acute thermal damage of the below-the-knee GSV after EVLA was limited to the intima and the inner third of the media. No acute damage of perivascular nerve tissue was observed.

Selective brain cooling seems to be a mechanism leading to human craniofacial diversity observed in different geographical regions

Selective brain cooling (SBC) can occur in hyperthermic humans despite the fact that humans have no carotid rete, a vascular structure that facilitates countercurrent heat exchange located at the base of the skull in some mammals. Emissary and angular veins, upper respiratory tract, tympanic cavity and cerebrospinal fluid are major components of SBC system in humans. The efficiency of SBC is increased by evaporation of sweat on the head and by ventilation through the nose, but it is surprising to find out that mammals do not display SBC during exercise hyperthermia. What is the explanation then for the SBC at high body temperatures? Our hypothesis is that selective brain cooling protects the brain from thermal damage in a long-standing manner by allowing adaptive mechanisms to change the craniofacial morphology appropriate for different environmental conditions. Since the brain can only be as big that can cool, it is not surprising to find a lower (below 1300 cm 3) cranial volume in Australian Aborigines with respect to the one (over 1450 cm 3) in Eskimos. In addition to lower brain volume, other craniofacial features such as thick everted lips, broader nasal cavity and bigger paranasal sinuses that provide more evaporating surfaces seem to be anatomical variations developed in time for an effective SBC in hot climates. It was reported previously that these biological adaptations result from the tissues of neural crest origin. Among the crest derivatives, leptomeninges (pia and arachnoid mater), skeletal and connective tissues of the face and much of the skull seem to be structures upon which environment operates to produce more convenient craniofacial morphology for an effective SBC. In conclusion, selective brain cooling seems to be a mechanism leading to adaptive craniofacial diversity observed in different geographical regions. Thus, SBC is necessary for long-term biological adaptation, not for protecting the brain from acute thermal damage.

Combination of transurethral and interstitial ultrasound applicators for high-temperature prostate thermal therapy

The purpose of this study was to determine the feasibility of using a transurethral ultrasound applicator in combination with implantable ultrasound applicators for inducing thermal coagulation and necrosis of localized cancer lesions or benign disease within the prostate gland. The potential to treat target zones in the anterior and lateral portions of the prostate with the angularly directive transurethral applicator, while simultaneously treating regions of extracapsular extension and zones in the posterior prostate with the directive implantable applicators in combination with a rectal cooling bolus, is evaluated. Biothermal computer simulations, acoustic characterizations, and in vivo thermal dosimetry experiments with canine prostates were used to evaluate the performance of each applicator type and combinations thereof. Simulations have demonstrated that transurethral applicators with 180-270° acoustic active zones can direct therapeutic heating patterns to the anterior and lateral prostate, implantable needles can isolate heating to the posterior gland while avoiding rectal tissue, and that the combination of applicators can be used to produce conformal heating to the whole gland. Single implantable applicators (1.8mm ODx10mm long, ∼180° active sector, ∼7MHz, direct-coupled type) produced directional thermal lesions within in vivo prostate, with temperatures >50°C extending more than 10mm radially after 10-15min. Combination of interstitial applicators (1-2) and a transurethral applicator (3-2.5mm ODx6 mm long, 180° active sector, 6.8MHz, 6 mm OD delivery catheter) produced conforming temperature distributions (48-85°C) and zones of acute thermal damage within 15min. The preliminary results of this investigation demonstrate that implantable directional ultrasound applicators, in combination with a transurethral ultrasound applicator, have the potential to provide thermal coagulation and necrosis of small or large regions within the prostate gland, while sparing thermally sensitive rectal tissue.

Acute and chronic effects of transmyocardial laser revascularization in the nonischemic pig myocardium by using three laser systems.

Transmyocardial laser revascularization (TMLR) improves symptoms in patients with coronary heart disease. It is based on the hypothesis of direct perfusion of ischemic myocardium by means of laser-created channels. Three different lasers were used to study alternative effects on myocardium. The present study was conducted to evaluate comprehensively and compare the short and long-term tissue effects and the basic interaction mechanisms of CO2, Ho:YAG, and Er:YAG laser radiation with myocardium. The dynamics of laser-induced impacts in gel used as tissue phantom was visualized by time-resolved flash photography. Pressure measurements performed during perforation of myocardium in vitro revealed the explosive character of the ablation process. Channels made into the left ventricle of normal pig hearts were examined immediately and 6 weeks after creation. Regardless of laser source, all channels became occluded within 6 weeks by scar. Minimal acute thermal damage by Er:YAG laser corresponded to smaller scars. Pulsed Ho:YAG caused stronger tissue tearing than continuous wave CO2 irradiation. An increased volume density of intramyocardial vessels was found about the scars 6 weeks after treatment with all lasers. The laser sources permitted to study outcome of pressure effects and thermal damage in vivo. There were only minor differences between the three laser systems used. Rapid channel occlusion suggests that rather than revascularization, subsidiary physiologic tissue effects elicited by the thermal, oxidative, or mechanical action of the laser impact may contribute to the beneficial clinical effects of TMLR.

High-intensity focused ultrasound ablation of the kidney in a large animal model.

The purpose of this study was to establish the feasibility of noninvasive treatment of small renal tumors with high-intensity focused ultrasound (HIFU). A 1.69-MHz extracorporeal HIFU transducer of 150-mm focal length was used. In vitro experiments with excised porcine kidneys allowed determination of suitable exposure parameters to be tested in vivo. For short exposure times (< 2 seconds), the minimum energy required to produce acute thermal damage was 500 +/- 100 Wcm-2 per second. Porcine kidneys (N = 18) were treated in vivo at a depth of 40 mm from the skin surface, with acute damage detected in 13. Damage was macroscopically and histologically discrete and confined to the target area within the kidney. Skin induration was observed after treatment in nine cases, and there was one skin burn. Transducer developments to prevent this morbidity and to improve energy deposition within the target are discussed.

The photodynamic occlusion of choroidal vessels using benzoporphyrin derivative.

We used benzoporphyrin derivative-monoacid (BPD-MA), a new photosensitizing agent, in photodynamic therapy (PDT) to occlude choroidal vessels in the rabbit. Using BPD-MA, seven dutch-belted rabbit eyes were photodynamically treated to achieve acute choroidal vessel closure. Fundoscopy, fluorescein angiography (FA), and histology were performed 1 hour, 1 day, 3 days, 7 days, 14 days, 21 days, and 28 days after PDT. On FA, PDT-treated spots remained nonperfused until day 3 when gradual reperfusion from the periphery began to appear. By day 28 the area of PDT appeared completely reperfused. Histology of lesions showed acute damage to choroidal vascular endothelial cells and retinal pigment epithelial (RPE) cells. Over subsequent days, recovery of RPE cells and regeneration of large choroidal vascular endothelial cells occurred. In addition, retinal degeneration occurred gradually over the 28 days of follow-up. Since current argon laser therapy of retinal neovascularization causes immediate retinal damage, the ability to occlude choroidal vessels without inducing acute thermal damage holds promise for treating clinical pathologic conditions that feature abnormal neovascularization, such as age-related macular degeneration and diabetic retinopathy.

A comparison of thermal injury, healing patterns, and postoperative adhesion formation following CO2 laser and electromicrosurgery

To further define the role of CO2 laser in infertility surgery, the authors compared the immediate tissue damage and the subsequent healing patterns that followed the randomized use of CO2 laser and electrocautery on opposite sides of the reproductive tracts of 20 mature, female rabbits. Blind histopathologic evaluations were performed on the ovarian and uterine tissues immediately to compare the extent of the acute thermal damage, and 4 weeks postoperatively to compare the healing patterns. There were no differences in the depth of thermal damage, extent of collagen deposition, or in postoperative adhesion formation between CO2 laser and electrocautery. However, the mean depth of the acute thermal damage was significantly less on the ovary than on the uterus, and the area of fibrosis was significantly less when the incised uterine surfaces were approximated.