Effect of low intensity laser (830 nm) irradiation on skin temperature and antidromic conduction latencies in the human median nerve: Relevance of radiant exposure

The effects of low intensity near-infrared laser radiation (830 nm; 1.5–12 J/cm²; continuous wave) on peripheral neurophysiology and skin temperature were investigated using antidromic conduction studies in the human median nerve in vivo. Healthy human volunteers (n = 80) were recruited and randomly allocated to one of two control (n = 30) or five laser groups (1.5, 3.0, 6.0, 9.0, and 12 J/cm²; n = 10 per group). Analysis of variance (ANOVA) in negative peak latency difference scores (NPLDs) and skin temperature over a 20 min period post-irradiation demonstrated a significant decrease in skin temperature following irradiation at the lowest radiant exposure (1.5 J/cm²) coupled with a significant increase in NPLDs (P < 0.05). While no such (significant) changes were found in the other laser groups, it was found that observed changes (increases and decreases) in NPLDs were inversely related to changes in skin temperature. These findings demonstrate measurable peripheral neurophysiological effects of laser radiation concomitant with changes in skin temperature; however, further studies are indicated to establish the precise relationship between the observed effects on skin temperature and nerve Conduction. © 1994 Wiley-Liss, Inc.     

ArF-excimer laser–induced secondary radiation in photoablation of biological tissue

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200–800 nm. The intensity of secondary radiation in the range of 200–315 nm (UVC and UVB) is ∼20% of the total intensity at high laser fluences (>2 J/cm²), and ∼50% at moderate laser fluences (<500 mJ/cm²); 10 μJ/cm² in the UVC and UVB were measured at the sample surface, at fluences (<1J/cm²) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (>5 J/cm²) are required. As a consequence, laser–induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field. © 1994 Wiley-Liss, Inc.     

An experimental study of the healing effect of the HeNe laser and the infrared laser

Changes in the macroscopic appearance and in the histological features of full-thickness, excised, circular wounds treated with either an infrared (IR) or a helium-neon (HeNe) laser were compared with those occurring in control wounds over a period of 15 days. The wounds were produced in the skin of the backs of anaesthetized adult female rats, and were initially 1 cm in diameter. The control and the two experimental laser-treated groups each consisted of ten wounds, one per rat. In the experimental groups either the IR laser was applied at 2.1 J/cm², 904 nm, 3500 Hz, for four min each day, or the HeNe laser was applied at 3.6J/cm², 632.8 nm, continuous, for eight min. The laser-treated wounds decreased in size and re-epithelialized more rapidly than did the controls. Qualitative histological examination indicated that periodic acid-Schiff-positive material decreased more rapidly in the laser-treated groups than in the controls. No significant differences in the effects of the two forms of laser treatment were found. The clinical significance of these observations is discussed.     

Effect of photodynamic therapy on urinary bladder function: an experimental study with rats

Photodynamic therapy (PDT) produces localized necrosis with light after prior administration of a photosensitizing drug. The problems with laser light dosimetry and complications relating to bladder function appear to be important limiting factors of PDT in urology. Photodynamic therapy on urinary bladder with normal epithelium of rats was performed using an argon ion laser as an energy source, with aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) photosensitizer. Four hours after ALA intravenous administration, the bladders were intravesically radiated with light doses 20, 40, or 80 J/cm². Animals in the control group did not receive ALA and were radiated with 20 J/cm² light dose. Three weeks prior to PDT, the bladder capacity and pressure changes during filling cystometry were assessed. Cystometrics were repeated 1, 3, 7, or 21 days after laser therapy. The light dose 20 J/cm² and 40 J/cm² together with the used ALA dose caused no reduction in bladder capacity, whereas 80 J/cm² light dose produced up to 50% reduction in the capacity at 3 weeks postoperatively. In control group without ALA, the animals did not regain more than 34% of the capacity of their control values at 3 weeks. The light dose of 20 J/cm² and 40 J/cm² with ALA induced functional changes that subsided after day 1. Our results indicate that with proper dosing of photosensitizing drug and light energy, the functional impairment of urinary bladder may be reduced as transient. These findings support the use of PDT as safe therapy of superficial bladder cancer. Received: 10 April 2000 / Accepted: 16 November 2000     

Low intensity laser irradiation inhibits tritiated thymidine incorporation in the hemopoietic cell lines HL-60 and U937

The purpose of this study was to determine the effect of low intensity laser irradiation (660 nm, 12 mW, 5 kHz) on tritiated thymidine incorporation in two hemopoietic cell lines, HL-60 and U937. Cells were suspended at a concentration of 1 × 10⁶/ml in their respective serum-free media and irradiated at energy densities from 1.0 to 11.5 J/cm². Twenty-four hours after irradiation the cells were assayed for their ability to incorporate tritiated thymidine (³H-TdR) in comparison with nonirradiated cells. Analysis by two-way analysis of variance (ANOVA) for unrelated groups showed that laser irradiation at all energy densities ? 5.8 J/cm produced a significant decrease in ³H-TdR incorporation (P < 0.05) into HL-60 cells. In U937 cells, irradiation at energy densities of 5.8, 7.2, and 11.5 J/cm² caused a similar reduction in ³H-TdR incorporation (P < 0.01), although not at 8.6 and 9.6 J/cm². The temperature of each cell suspension was recorded both during and immediately postirradiation, and no significant thermal changes were observed. These findings demonstrate a direct photobiological effect of laser irradiation on these two cell lines. The precise mechanism for this effect is unknown but may have significance in understanding the biological action of laser's known therapeutic effectiveness in promoting wound repair. © 1994 Wiley-Liss, Inc.     

Pulsed carbon dioxide laser ablation of burned skin: In vitro and in vivo analysis

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

The effect of He-Ne and Ga-Al-As laser light on the healing of hard palate mucosa of mice

Low-level laser therapy (LLLT) has been used to accelerate wound healing, yet questions remain concerning its therapeutic applications. This study aimed to compare the healing efficacy of helium-neon (He-Ne) red light (laser) and gallium aluminum arsenide (Ga-Al-As) infrared lasers at two different doses on hard palate wounds. In a randomized controlled study, 75 adult male mice were divided into five groups of 15 each, after undergoing identical surgical procedures; a control group, with no laser irradiation; HD1 and HD2 groups, treated with He-Ne laser (wavelengths 632.8 nm, power 5 mW, and spot size 0.02 cm²) at doses of 4 J/cm² and 7.5 J/cm² respectively; and GD1 and GD2 groups, treated with Ga-Al-As laser (wavelengths 830 nm, peak power 25 mW, and spot size 0.10 cm²) at the doses of 4 J/cm² and 7.5 J/cm², respectively. Five animals from each group were killed on the third, seventh, and 14 days after surgery, and biopsies were made for histological analysis. On the 3rd and 7th day after the surgery, the number of polymorphonuclear cells (PMN) in HD1, HD2, GD1, and GD2 groups was significantly lower than that of the control group. On the 7th and 14th day, the fibroblasts and new blood vessels counts and collagen density fibers in HD1, HD2, GD1, and GD2 groups were also significantly higher than that of the control groups, and the fibroblast counts and collagen density fibers in HD1 and HD2 groups were higher than that of the GD1 and GD2 groups. LLLT with He-Ne laser compared to Ga-Al-As laser has a positive healing effect on hard palate gingival wounds in mice regardless of the radiation dose.     

Effect of Helium-Neon (He-Ne) Laser Irradiation on Dog Neoplasm Cells in Culture

The effects of laser light on the cellular proliferation have been extensively characterised. Low-power laser sources, such as the helium–neon (He-Ne) laser irradiation with a wavelength of 632.8 nm, have been found to produce photobiological and photodamaging effects with evidence of interference with cell proliferation functions. The present study has investigated the in vitro effect of He-Ne laser irradiation on the proliferative action of dog tumour cells in culture. Dose–response studies showed that repeated He-Ne irradiation (irradiance 12.8 mW/cm²) once a day for 4 consecutive days in a dose range between 0.13 and 2.08 J/cm² significantly increased with increasing energy density up to a laser dose of 0.26 J/cm², whereas at >1.04 J/cm², the cell proliferation decreased with increasing energy densities. It is concluded that the application of He-Ne laser irradiation at energy densities ranging from 0.13 J/cm² to 2.08 J/cm² produced different effects on cell proliferation in dog tumour cells in culture. Paper received for publication 27 June 1997; accepted following revision 6 February 1998.     

Fluoride uptake and acid resistance of enamel irradiated with Er:YAG laser

This study evaluated the resistance to demineralization and fluoride incorporation of enamel irradiated with Er:YAG. A total of 110 bovine teeth were selected and divided into eight groups: unlased, 37% phosphoric acid, and samples irradiated with the Er:YAG laser at several fluences (31.84 J/cm², 25.47 J/cm², 19.10 J/cm², 2.08 J/cm², 1.8 J/cm², and 0.9 J/cm²). The application of acidulated phosphate fluoride was performed after treatments. All samples were immersed in 2 ml of 2.0 M acetic–acetate acid solution at pH 4.5 for 8 h, and fluoride, calcium, and phosphorus ions dissolved were analyzed by atomic absorption spectrometry and spectrophotometry. The phosphoric acid and 31.84 J/cm² groups presented the lowest dissolution of calcium and phosphorus ions. Higher fluoride incorporation was observed on 1.8 J/cm² and 0.9 J/cm² groups. Based on these results, Er:YAG laser was able to decrease acid dissolution and increase fluoride uptake and can be a promissory alternative for preventive dentistry.     

The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro

Summary The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin ether (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50–100 mW/cm² and exposure times (2–15 s), representing incident pulse energy fluences of 2.5–5 mJ/cm² and energy densities of 0.1–1.5 J/cm². The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm² (LD₉₀=0.54 J/cm²). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm²).     

Effects of the helium-neon laser on rat kidney epithelial cells in culture

The cellular mechanisms of action of low power lasers are only partially understood. Therefore, we have studied effects of helium-neon (He−Ne) laser irradiation in a cell culture model. The studies were performed with the permanent rat kidney cell line RK-L. By electron microscopy, significant ultrastructural changes of the cells were seen after He−Ne irradiation at 40 mW/cm² for 4h (569 J/cm²), including detritus-like formations of the cell organelles close to the nucleus. While such changes were not observed after 1 h irradiation (142 J/cm²), the number of cells in mitosis increased under this condition. In addition, the rate of incorporation of³H-thymidine into DNA decreased transiently 6–9 h after 1 h He−Ne irradiation of the cells. The consumption of glucose was also lowered for 10 h after irradiation, while the production of lactate increased. Finally, the synthesis of prostaglandin E₂ was reduced following irradiation. These results show that the He−Ne laser induces significant effects at the cellular level. In addition, our findings support the concept that the biological effects of low power laser treatment involve changes in the cell cycle.     

Effects of low-level laser therapy on mitochondrial respiration and nitrosyl complex content

Among the photochemical reactions responsible for therapeutic effects of low-power laser radiation, the photolysis of nitrosyl iron complexes of iron-containing proteins is of primary importance. The purpose of the present study was to compare the effects of blue laser radiation on the respiration rate and photolysis of nitrosyl complexes of iron-sulfur clusters (NO-FeS) in mitochondria, subjected to NO as well as the possibility of NO transfer from NO-FeS to hemoglobin. It was shown that mitochondrial respiration in State 3 (V₃) and State 4 (V₄), according to Chance, dramatically decreased in the presence of 3 mM NO, but laser radiation (λ?=?442 nm, 30 J/cm²) restored the respiration rates virtually to the initial level. At the same time, electron paramagnetic resonance (EPR) spectra showed that laser irradiation decomposed nitrosyl complexes produced by the addition of NO to mitochondria. EPR signal of nitrosyl complexes of FeS-clusters, formed in the presence of 3 mM NO, was maximal in hypoxic mitochondria, and disappeared in a dose-dependent manner, almost completely at the irradiation dose 120 J/cm². EPR measurements showed that the addition of lysed erythrocytes to mitochondria decreased the amount of nitrosyl complexes in iron-sulfur clusters and produced the accumulation of NO-hemoglobin. On the other hand, the addition of lysed erythrocytes to mitochondria, preincubated with nitric oxide, restored mitochondrial respiration rates V₃ and V₄ to initial levels. We may conclude that there are two possible ways to destroy FeS nitrosyl complexes in mitochondria and recover mitochondrial respiration inhibited by NO: laser irradiation and ample supply of the compounds with high affinity to nitric oxide, including hemoglobin.     

Effect of low-level laser irradiation and epidermal growth factor on adult human adipose-derived stem cells

The study investigated the effects of low-level laser radiation and epidermal growth factor (EGF) on adult adipose-derived stem cells (ADSCs) isolated from human adipose tissue. Isolated cells were cultured to semi-confluence, and the monolayers of ADSCs were exposed to low-level laser at 5 J/cm² using 636 nm diode laser. Cell viability and proliferation were monitored using adenosine triphosphate (ATP) luminescence and optical density at 0 h, 24 h and 48 h after irradiation. Application of low-level laser irradiation at 5 J/cm² on human ADSCs cultured with EGF increased the viability and proliferation of these cells. The results indicate that low-level laser irradiation in combination with EGF enhances the proliferation and maintenance of ADSCs in vitro.     

Biological Effect of Helium-Neon (He-Ne) Laser Irradiation on Mouse Myeloma (Sp2-Ag14) Cell Line In Vitro

We examined the effect of helium-neon (He-Ne) laser irradiation with a wavelength of 632.8 nm on cell cycle synchronisation of monolayer growing mouse myeloma (Sp2-Ag14) cell line. The monolayer cultures were exposed to repeated doses of different energy densities (4–64 J/cm²). The nuclear DNA content has been studied by flow cytometry to obtain the cell percentage in each cell cycle phase. Results showed that the He-Ne laser irradiation at energy densities of 8–64 J/cm² produced a significative and different effect on the G0–G1 and S phases of cell cycle over control. In contrast, no significant effect in G2–M phase was produced by He-Ne laser irradiation at any energy density compared with non-treated control. These results support previous observations suggesting that He-Ne laser irradiation of low energy density interferes with cell cycling and may inhibit cell proliferation when irradiation is performed at doses of 8 J/cm² or more. Received for publication 22 July 1997; accepted following revision 6 February 1998.     

Scanning electron microscopy and thermal characteristics of dentin ablated by a short-pulse XeCl excimer laser

The interaction of a short pulse XeCl excimer laser radiation with human dentin was investigated. The dependence of surface temperatures and temperature gradients into the treated teeth on laser parameters such as fluence (0.5J/cm²-7J/cm²), pulse repetition rate (1Hz-35Hz), and spot size (0.004cm²-0.12cm²) was studied. Additionally, the effect of fluence and pulse repetition rate on dentin microstructure was studied using scanning electron microscopy (SEM). It is demonstrated that this “cold ablation” excimer laser can result in significant thermal modification in the dentin surfaces. Changes include the formation of melted dentin grains, which uniformly cover the surface and the exposed dentin tubules. Maximum temperatures of the ablated surfaces, however, remained relatively low at most laser parameters used. Also, the immediate neighborhood of the root canal was essentially undisturbed at most laser parameters. These observations suggest that with the appropriate choice of parameters XeCl lasers can be effective in producing surface structures that may prove useful in enhancing bond strength or other applications in dentistry, without exposing tooth pulp to significant temperature elevation. © 1993 Wiley-Liss, Inc.     

Helium-Neon laser irradiation inhibits the growth of kidney epithelial cells in culture

We have investigated the in vitro action of helium-neon (He-Ne) laser light on the cell cycle and the growth of rat kidney epithelial cell cultures. Dose-response studies showed that repeated He-Ne irradiation (dose rate 40 mW/cm²) once a day in a dose range between 11.9 and 142 J/cm² significantly inhibited cell growth, while daily irradiation with 4.7 J/cm² had no effect. Microscopic examination of nuclear spreads revealed an increased number of cells in mitosis after a single irradiation with 142 J/cm². These results support previous observations suggesting that laser light of low thermal energy interferes with cell cycling and may inhibit cell growth when irradiation is performed at doses of 11.9 J/cm² or more.     

Erythrocyte sedimentation rate of human blood exposed to low-level laser

This study is designed to investigate in vitro low-level laser (LLL) effects on rheological parameter, erythrocyte sedimentation rate (ESR), of human blood. The interaction mechanism between LLL radiation and blood is unclear. Therefore, research addresses the effects of LLL irradiation on human blood and this is essential to understanding how laser radiation interacts with biological cells and tissues. The blood samples were collected through venipuncture into EDTA-containing tubes as an anticoagulant. Each sample was divided into two equal aliquots to be used as a non-irradiated sample (control) and an irradiated sample. The aliquot was subjected to doses of 36, 54, 72 and 90 J/cm² with wavelengths of 405, 589 and 780 nm, with a radiation source at a fixed power density of 30 mW/cm². The ESR and red blood cell count and volume are measured after laser irradiation and compared with the non-irradiated samples. The maximum reduction in ESR is observed with radiation dose 72 J/cm² delivered with a 405-nm wavelength laser beam. Moreover, no hemolysis is observed under these irradiation conditions. In a separate protocol, ESR of separated RBCs re-suspended in irradiated plasma (7.6?±?2.3 mm/h) is found to be significantly lower (by 51 %) than their counterpart re-suspended in non-irradiated plasma (15.0?±?3.7 mm/h). These results indicate that ESR reduction is mainly due to the effects of LLL on the plasma composition that ultimately affect whole blood ESR.     

Ultrastructural changes in normal rat colon induced by photodynamic therapy

Despite the fact that photodynamic therapy (PDT) is a promising new technique for the treatment of gastrointestinal tumours, its effect on normal mucosa has so far received little attention. With a view to understanding the changes that occur in normal colon mucosa, we have examined the ultrastructure of normal rat colon mucosa after PDT. Female Wistar rats were treated with dihaematoporphyrin derivative (Photofrin^®) administered i.v. at a concentration of 5 mg kg^?1 body weight. Twenty-four hours after injection lesions were produced using a special device and irradiation was carried out with an argon-ion pumped-dye laser system (λ=630 nm, energy density 150 J cm^?2 and 30 J cm^?2; power density 100 mW cm^?2). At different points of time animals were sacrificed, tissues specimens were removed and a light and ultrastructural examination was carried out. At 90 min after treatment with 30 J cm^?2, superficial epithelial cells showed vacuoles in the basal part and were separating from the basement membrane. Capillaries were engored with erythrocytes and 24h after treatment there was destruction of capillaries and massive haemorrhage into the lamina propria. Immediately after treatment with 150 J cm^?2 there was sloughing of superficial epithelial cells from the basement membrane and crypt cells contained numerous vacuoles. After 24h there was complete necrosis of the mucosa. The action of PDT applied to normal rat colon mucosa is time- and energy-density-dependent and manifests as primary cytotoxic effects on superficial epithelial and crypt cells. Secondarily, there is destruction of the capillary system in the lamina propria, which leads to haemorrhagic necrosis of the mucosa.     

Biological effect of He-Ne laser: Investigations on functional and micromorphological alterations of cell membranes,in vitro

A 1-J/cm² dose of single laser-irradiation applied on primary human embryo fibroblast culture was not followed either by functional or micromorphological alterations of cell surfaces. This dose, however, applied four times with 24-hour intervals changed the functional conditions as well as surface charges of cell membranes. As detection methods, radioactive glucosamine uptake, lectin, and cationized ferritin-binding techniques were applied. At the same time, the scanning and transmission electron microscopy of laser-irradiated cells did not reveal any micromorphological or ultrastructural alterations. The effect of a 5-J/cm²dose did not differ from that of 1 J/cm². It is suggested that laser radiation-induced circumstances on cell surfaces can contribute to the strength of cell-to-cell contacts, i.e., to the stimulation of epithelization experienced in the clinical gynecol- ogic practice.     

Low-level laser therapy improves repair following complete resection of the sciatic nerve in rats

The aim of this study is to analyze the effects of low-level laser therapy (LLLT) on the regeneration of the sciatic nerve in rats following a complete nerve resection. Male Wistar rats were divided into a control injury group, injury groups irradiated with a 660-nm laser at 10 or 50 J/cm², and injury groups irradiated with an 808-nm laser at 10 or 50 J/cm². Treatment began 24 h following nerve resection and continued for 15 days. Using the sciatic functional index (SFI), we show that the injured animals treated with 660 nm at 10 and 50 J/cm² had better SFI values compared with the control injury and the 808-nm groups. Animals irradiated with the 808-nm laser at 50 J/cm² show higher values for fiber density than do control animals. In addition, axon and fiber diameters were larger in animals irradiated with 660 nm at 50 J/cm² compared to the control group. These findings indicate that 660-nm LLLT is able to provide functional gait recovery and leads to increases in fiber diameter following sciatic nerve resection.