Argon laser photocoagulation in the dog stomach.

Laser photocoagulation is one of a number of methods currently under investigation for the endoscopic treatment of gastrointestinal haemorrhage. The Argon ion and Neodymium Yttrium Aluminium Garnet (Nd YAG) lasers are theoretically suitable as the beam from each may be transmitted via a flexible fibre. Argon laser photocoagulation has been shown to be effective and we have elucidated which factors determine its safety and efficacy. Studies on normal canine gastric mucosa showed that the depth of tissue damage depended chiefly on the total incident laser energy on any one spot, and that below 50 J the risk of perforation was extremely low. The energy density was much less important. The haemostatic effect depended more on the laser power. In artificial bleeding gastric ulcers in heparinised dogs the most effective level was 7--9 W, at which 22 out of 23 ulcers (96%) stopped bleeding completely, compared with one out of 12 controls. Photocoagulation was achieved in these cases with energies well within the safe limits. The procedure was effective endoscopically, and these results justify early clinical studies in man.     

Safety and efficacy of Neodymium-Yag laser photocoagulation: an experimental study in dogs.

Acute and chronic experiments were carried out in 26 beagle dogs to study the safety and efficacy of Neodymium-Yag laser photocoagulation in the treatment of bleeding gastric lesions. Continuous high power (50-60 W) Neodymium-Yag laser photocoagulation applied to the exposed stomach of the dog produced evaporation lesions that reached the muscle layer after six to 10 seconds and caused free perforation after 10 to 12 seconds. The tissue damage caused by these long lasting exposures was closely related to the working distance. Moreover, long pulses of high power photocoagulation were not always effective in stopping experimentally induced gastric bleedings. Short pulses (1/2-1 s) of very high power (60-70 W) caused less tissue evaporation, which reached the muscle layers only after 14 to 18 pulses and caused free perforation after 22 to 24 pulses. The tissue damage was not related to the working distance when short pulses were used. Repeated shots of high power Yag laser radiation always resulted in stopping the experimental bleedings without deep injury. It is concluded that high power Neodymium-Yag laser photocoagulation is safe and may be used with success in the treatment of bleeding gastric lesions if the radiation is performed in shots of short duration (1 s or less). Clinical studies in man are warranted and indicated.     

Laser-induced vascular lesions by cw-NdYAG or pulsed UV lasers during angioplastic procedures

Conventional (NdYAG, Argon and CO2 lasers) laser and pulsed far ultraviolet laser radiation are able to remove arteriosclerotic tissue of the arterial wall. However, there is a striking difference between both systems: The continuous wave of conventional wave-length laser-radiation produces considerable thermal injury to the surrounding tissue, whereas the effect of pulsed far ultraviolet radiation induces less or no thermal damage despite an easily assessable tissue-removing effect. In the following study the potential of far UV laser-radiation for recanalization of occluded vessels is demonstrated in in-vitro experiments on fresh and well preserved atherosclerotic human vessels.     

Successful control of bleeding from gastric antral vascular ectasia (watermelon stomach) by laser photocoagulation.

We report a case of gastric antral vascular ectasia in a patient with primary biliary cirrhosis in whom chronic blood loss was a major problem. She required repeated blood transfusions that were complicated by reactions and still had persistent anaemia. She was treated with laser phototherapy in the form of quadrantic photocoagulation with a neodynium yttrium-aluminium-garnet laser. This greatly improved the endoscopic appearance of the gastric lesions and effectively controlled blood loss. She required no further transfusions. Bleeding recurred after 11 months which was controlled by further laser photocoagulation.     

Current Status of Lasers for Arrhythmia Ablation

Current Status of Lasers for Arrhythmia Ablation. Wavelength specific effects and mode of laser operation allow either photocoagulation or tissue removal as a means of approaching arrhythmia ablation. Successful intraoperative ablation of ventricular tachycardias has been performed with the Nd: YAG laser (photocoagulation) and argon laser (tissue vaporization). The argon laser has been used intraoperatively for transection of accessory pathways. Experimental studies indicate a strong theoretical potential for Nd:YAG laser catheter ablation of ventricular tachycardia. Laser energy has been used experimentally to evaluate the possibility of AV junctional ablation/modification and accessory pathway ablation. Adaption of laser energy to effective catheter systems for arrhythmia ablation requires solutions to problems inherent in all catheter systems and some unique to laser energy. (J Cardiovasc Electrophysiol, Vol. 3, pp. 345–353, August 1992)     

Nature and extent of histological changes induced by argon laser photocoagulation in canine gastric mucosa.

The tissue changes in canine gastric mucosa caused by exposure to an argon laser beam vary from mild mucosal oedema to complete cell destruction. Intermediate degrees of damage cause an inflammatory cell response with the formation of granulation tissue, particularly in the submucosa. The rate of healing is similar to that after other forms of injury to the gastric mucosa. Cell destruction at the surface of the mucosa starts with energies greater than 8 Joules on any one spot, and occurs at greater depths as the energy is increased but, unless cells are actually destroyed, the extent of histological damage is limited to a zone 1 mm lateral to, or below, the area exposed to the laser beam. Haemostasis is achieved by thermal contraction of bleeding vessels and of the surrounding tissue, thrombosis only occurring as a secondary effect.     

Histological changes following Nd YAG laser photocoagulation of canine gastric mucosa.

Tissue changes produced in the dog stomach by exposure to a Nd YAG laser varied from mild mucosal oedema to cell vaporisation. Intermediate degrees of damage caused a marked inflammatory response leading to extensive fibrosis in the submucosa and muscularis propria. The true extent of tissue damage was not apparent immediately, and treated mucosa that initially appeared intact sometimes sloughed several days later to leave an ulcer. The extent of damage and the rate of healing depended on the amount of laser energy used. With pulses at optimum laser power (75 w) and exposure time (0.4 sec), however, haemostasis was achieved in induced ulcers with total energy concentrations that did not produce full thickness tissue damage nor alter the healing rate from that observed in untreated ulcers. Thermal contraction was the primary haemostatic mechanism, thrombosis only occurring as a secondary effect.     

Treatment of diabetic retinopathy with laser photocoagulation (author's transl)]

Laser photocoagulation has changed the visual prognosis of diabetic patients affected by retinopathy. It aims to lower the risk of blindness of diabetic patients. The goal of photocoagulation is to reduce the tissue damage of microangiopathic origin expressed by nonperfusion areas and permeability abnormalities that are responsible for retinal ischemia and oedema respectively. Loss of visual acuity in the diabetic is due mainly to two causes : first, vitreous hemorrhage with its dramatic loss of vision; secondly, macular cystoid oedema, occuring more commonly and with progressive loss of central vision. The efficiency of pan-retinal photocoagulation in reducing the risk of vitreous hemorrhage and consequent blindness in patients with disc or preretinal newly formed vessels, has been ascertained by American and British randomised studies. The indications, technics and results of photocoagulation in non-proliferative diabetic retinopathy are the subject of many studies. Only photocoagulation for macular oedema due to intra-retinal microvascular abnormality has shown to be of benefit.     

Endoscopic therapy for upper-GI vascular ectasias

BACKGROUND: Upper-GI vascular ectasias, including angiodysplasia and gastric antral vascular ectasia may present with either acute or chronic bleeding. Endoscopic thermal modalities have been used to control acute bleeding and reduce transfusion requirements. METHODS: Endoscopic experience was reviewed for a 6-year period during which 32 patients requiring blood transfusions for upper-GI angiodysplasia or gastric antral vascular ectasia were evaluated. Patients seen during the first 5 years were treated with either Nd:YAG laser photocoagulation or multipolar electrocoagulation. During the most recent 12 months, all patients were treated by argon plasma coagulation. Response to therapy was assessed by change in mean Hb and transfusion requirements. RESULTS: Overall, 16 patients were treated by laser photoablation alone; 9, argon plasma coagulation with or without laser; and 7, multipolar electrocoagulation with or without laser. Mean follow-up for all patients was 19 months. After therapy, mean Hb concentration rose from 76 to 114 g/L for patients with gastric antral vascular ectasia and from 85 to 118 g/L for those with angiodysplasia. Endoscopic therapy abolished or reduced transfusion requirements in 93% of patients with gastric antral vascular ectasia and 76% with angiodysplasia. Patients with gastric antral vascular ectasia required a mean of 6 treatment sessions, while those with angiodysplasia required one to two sessions. CONCLUSIONS: Endoscopic thermal ablation effectively controls acute bleeding and reduces transfusion requirements in most patients with upper-GI vascular ectasias. Patients with gastric antral vascular ectasia require significantly more treatment sessions to achieve this effect.     

The development of laser angioplasty

Recent developments in technology have stimulated interest in the use of catheter-directed laser energy for removal of atherosclerotic plaques. Over the past three years, intensive research efforts by a number of investigators have defined the potential therapeutic benefit of laser angioplasty, as well as its limitations. Unlike balloon angioplasty, the laser has the capacity to remove totally atheromatous plaque or thrombus by photovaporization. Unique properties of the laser allow light energy to be concentrated for plaque removal. Arterial damage adjacent to the plaque is prevented by certain lasers, while others produce thermal injury to the arterial wall. Chemical pretreatment with vital dyes or drugs has been shown to enhance absorption of laser radiation by plaque and may enable selective destruction of the arterial plaque. Fiberoptic catheters have been designed to transmit laser energy to remote intravascular targets; however, precise guidance systems for catheter delivery have not been developed sufficiently for safe intracoronary application. Complete arterial healing by endothelial cell migration has been demonstrated after laser ablation of plaque in animal studies. Among the first four clinical trials of laser angioplasty, relief of atherosclerotic obstruction was successful using argon, neodymium-YAG, and carbon dioxide lasers. Despite the satisfactory initial appearance of laser-treated arteries, the long-term effects and risk of atherogenesis are undetermined. A potential risk of thrombosis has been identified after laser application, especially with the argon and NdYAG lasers. Further basic and clinical research are needed to establish the role of this promising new technology in the treatment of cardiovascular disease.     

Amyloid tumour resected by laser therapy

We report a patient presenting with dyspnoea, cough and fever with a middle lobe atelectasis. Amyloid deposits in the bronchial wall caused almost complete obstruction of the middle lobe bronchus. The patient was treated with neodymium yttrium aluminium garnet (NdYAG) laser photoresection resulting in complete clearance of the middle lobe bronchus. Laser therapy has to be considered as first-line therapy for patients with endobronchial amyloidosis.     

Use of the thermal laser effect of laser irradiation for cardiovascular applications exemplified by the Nd:YAG laser

Techniques of percutaneous transluminal application of laser energy for vessel recanalization have been used clinically since 1983. The commonly used Nd:YAG and argon lasers achieve ablation of atherosclerotic plaques by thermal action (vaporization). In order to reduce undesirable thermal damage in the neighborhood of the target tissue and to avoid vessel perforation, optimal irradiation parameters, modified (atraumatic) fiber tips (hot tips, sapphires), and steerable catheter systems needed to be implemented. Favorable results from peripheral application have encouraged use in the coronary circulation. More recently, coagulative tissue effects of circumferential irradiation of the vessel wall during balloon dilatation have been used for stabilization of acute and late results after mechanical balloon angioplasty. Enhancement of the differential light absorption of atherosclerotic plaque by use of biological dyes may further improve selective intravascular laser application. Intraoperative ECG-guided laser coagulation of arrhythmogenic areas of myocardium is a method for treatment of malignant arrhythmias. Transluminal non-operative application of myocardial laser photocoagulation has now been tested experimentally and shown to be safe and effective. There was no arrhythmogenicity or thermal damage of coronary arteries associated with this method. Innovative techniques such as nanosecond pulsed excimer lasers (athermal action) and development of "intelligent" lasers--which are equipped with spectroscopy-guided feedback systems for plaque recognition--have opened new perspectives and will further improve safety and efficacy of clinical laser application. However, according to current experience, the thermally acting Nd:YAG laser is an effective and versatile mode of laser therapy for selected cardiovascular indications.     

Laser photocoagulation for gastrointestinal bleeding.

Endoscopic laser photocoagulation is one of the exciting developments in the field of gastrointestinal endoscopic therapy. However, much work needs to be done before these techniques should be allowed to proliferate into widespread use. There are few controlled randomized clinical studies evaluating any endoscopic treatment of bleeding, including argon laser and Nd:YAG laser photocoagulation. Despite this, uncontrolled clinical trials of both argon and Nd:YAG laser photocoagulation have begun. Laser photocoagulation of bleeding upper gastrointestinal lesions should be considered a procedure in an experimental stage of development, to be performed only under protocol studies at endoscopic research centres. Only after this or any other haemostatic technique has been proven effective and safe in thorough animal trials and then in controlled clinical trial should it be considered ready for general clinical use.     

The influence of 15(R)-15 methyl PGE2, methyl ester, on Nd:YAG laser-induced gastric ulcers

The effect of 15(R)-15 methyl PGE2 on the evolution of gastric ulcers induced by endoscopic Nd:YAG laser photocoagulation was studied. By continuous application of 50 to 70 watt power for 4 sec at a distance of 15 mm from the gastric mucosa, reproducible ulcers can be induced. The effect of the drug in nonantisecretory doses (10 micrograms/kg) on the acute ulcer formation and on the healing rate was evaluated in mongrel dogs by light microscopy. Local administration or oral pretreatment did not influence the size or depth of acute ulcers (7.4 mm in diameter) as compared to a control series (7.2 mm). Pretreatment for several days, however, had a marked beneficial effect on the healing rate of the ulcers (1.71 mm after 7 days compared to 2.76 mm for the control series). From these data it may be concluded that 15(R)-15 methyl PGE2 has a beneficial effect on ulcer healing, even in nonantisecretory doses.     

Argon vs. neodymium YAG laser photocoagulation of experimental canine gastric ulcers

A neodymium YAG (Nd:YAG) laser was evaluated in a dog ulcer model used in the same manner as is recommended for bleeding patients (power 55 W, divergence angle 4 degrees, with CO2 gas-jet assistance). The experiments were performed during sterile laparotomy in heparinized dogs. Bleeding gastric ulcers were photocoagulated until bleeding stopped and then examined histologically 7 days later when depth of tissue injury was maximal. In the first series of experiments, the Nd:YAG laser was compared with the 7-W argon laser in the same dogs. Both lasers stopped bleeding from all experimental ulcers. The 55-W Nd:YAG laser caused full-thickness injury to the gastric wall beneath 11 of the 14 treated ulcers, whereas the 7-W argon laser caused no full-thickness injury beneath 14 treated ulcers. In a second series of experiments, we tried to determine whether varying exposure times with the 55-W Nd:YAG laser would make it less injurious; it did not. In a third series of experiments, the 55-W Nd:YAG laser was tested with and without CO2 gas-jet assistance in order to determine if this would affect the depth of injury; it did not. In the final series of experiments, the wattage of the Nd:YAG laser was varied to see if this would reduce depth of injury; lower wattage did not stop bleeding, and intermediate and higher wattages did stop bleeding but did not reduce depth of injury. We conclude that the 55-W Nd:YAG laser as it is currently used clinically produces deeper tissue damage than the argon laser in our animal model. This damage is not reduced by changes in power, duration of exposure, or the presence of gas-jet assistance.     

The tissue effect of argon plasma coagulation on esophageal and gastric mucosa

BACKGROUND: Argon plasma coagulation is a diathermy-based non-contact therapeutic endoscopic modality that may have a lower risk of perforation than other tissue ablation techniques. METHODS: Its effect was studied on three fresh esophageal and three fresh gastric resection specimens using power settings from 40 to 99 Watts at 90 degrees, with 1 mm separation using pulse durations of 1 and 3 seconds. A scoring system for depth of tissue damage was created and samples were analyzed blindly by a gastrointestinal histopathologist. RESULTS: There was significantly greater damage to gastric tissue using a 3-second (compared with 1-second) pulse (p = 0.003) and marginally significantly greater damage to esophageal tissue using the 3-second pulse (p = 0.053). Tissue damage was related to power setting for gastric (p = 0.031) but not for esophageal tissue (p = 0. 065). Only 1 of 42 esophageal samples and 2 of 42 gastric samples examined showed damage extending into the muscularis propria. CONCLUSIONS: Deep tissue damage that could lead to perforation was rare with argon plasma coagulation. The depth of gastric mucosal damage increased with increased pulse duration and increasing power settings, and, although the depth of esophageal mucosal damage was marginally related to pulse duration, it was not related to the power setting. (Gastrointest Endosc 2000;52:342-5).     

Salicylate effects on a monolayer culture of gastric mucous cells from adult rats.

Aspirin, acetyl salicylic acid, damages gastric mucosal cells. This effect is considered related to its inhibition of prostaglandin synthesis. On the other hand, sodium salicylate has been reported to be cytoprotective against drug damage to gastric mucosa in vivo. One reason for this difference is that salicylic acid, unlike acetyl salicylic acid does not inhibit prostaglandin synthesis by gastric mucosa in vivo. Previous studies on tissue culture cells from our laboratory have required gastric mucosa from fetal rats; this was time consuming and expensive. The purpose of this study was to develop a primary cell culture of adult rat fundic epithelial cells and to test the effect of sodium salicylate on: (1) prostaglandin (PGE2) production, (2) cell viability, (3) reducing cell damage by sodium taurocholate. Gastric epithelial cells were isolated from adult rat stomachs and cultured on collagen gel. Cells reached confluency on day 4 at which stage fibroblasts were rarely seen (less than 1%). Autoradiographic study showed that cultured cells incorporated [3-H] thymidine into nuclei. In histochemical studies, 94% of the cells contained PAS positive granules (mucous cells). Mucous granules were observed in the cytoplasm of the majority of cells by electronmicroscopy. These cells synthesised prostaglandin E2 as determined by radioimmunoassay. Indomethacin 10(-4) M strongly suppressed PGE2 production after 30 minutes while 10(-3) and 10(-4)M sodium salicylate had no effect. Pharmacologic concentrations of 10 mM sodium salicylate had no effect on PGE2 production at 30 minutes and only weakly inhibited production after one hour incubation. Sodium salicylate up to 30 mM had no effect on cell viability, a concentration of 50 mM being necessary to produce significant cell damage. Sodium salicylate 10 mM significantly protected cells against damage induced by 10 mM sodium taurocholate. We conclude: (i) adult rat gastric mucous epithelial cells can be successfully cultured in vitro; (ii) prostaglandin synthesis is inhibited by indomethacin but not by low doses of sodium salicylate; (iii) sodium salicylate does not damage gastric mucosal cells except at very high concentrations; (iv) sodium salicylate protects against damage to cells induced by sodium taurocholate.     

Endoscopic Nd:YAG laser treatment of severe radiation injury of the lower gastrointestinal tract: long-term follow-up

We report a series of patients with severe radiation injury treated with endoscopic laser photocoagulation. Eight patients with recurrent lower gastrointestinal bleeding secondary to procosigmoiditis were treated with endoscopic Nd:YAG laser therapy. Patients were followed for an average of 21.7 months after the first laser treatment. Average transfusion requirements and hospital admissions per patient-month were 0.93 and 0.27, respectively, in the prelaser period and 0.18 and 0.06, respectively, in the entire period following the first laser treatment. A total of 26 laser treatments were performed. There were three major (prolonged ileus) and one minor (pain) complication. We conclude that endoscopic Nd:YAG laser photocoagulation is a safe, effective, and lasting treatment in severe, symptomatic radiation injury of the lower gastrointestinal tract.     

Gastric mucosal lesions induced by hemorrhagic shock in baboons

In this study we sought to define the role of oxygen-derived free radicals during ischemia and reperfusion in the production of acute damage to the gastric mucosa of baboons. The protective effect of the xanthine oxidase inhibitor, allopurinol, the superoxide scavenger, superoxide dismutase (SOD), and a long-acting SOD-albumin was determined. Mucosal damage was evaluated using light and scanning electron microscopy. Evidence for oxidative insult to the gastric mucosa was sought by measuring tissue concentrations of reduced (GSH) and oxidized (GSSG) glutathione. Gastric mucosal blood flow was estimated using the microsphere technique. A similar pattern of tissue damage was found at the end of ischemia in all three groups. Thirty minutes after reperfusion, severe mucosal damage (grade 3) increased only in the untreated control. In the two treated groups, grade 3 damage remained unchanged during reperfusion and a decrease in the percentage of moderate damage (grade 2) was seen. Both GSH and GSSG tissue concentrations were lower in the untreated controls as compared to the scavenger-treated groups, making it questionable whether GSH/GSSG tissue levels adequately reflect oxidative stress. We conclude that in our ischemiareperfusion model the generation of oxygen-derived free radicals produces mucosal damage and prevents the restitution of moderate mucosal damage during reperfusion. In ischemia, factors other than free radicals seem to be responsible for mucosal damage. The protective effect of allopurinol and SOD was not mediated by changes in gastric mucosal blood flow.     

Evaluation of the laser-Doppler velocimetry method in the measurement of gastric blood flow in rats--spatial resolution

In this paper, gastric blood flow in rats was measured with the laser-Doppler velocimetry method (the LDV method) to study about the tissue locus where its flow signal arises (spatial resolution). In the measurement throughout some 1 mm thickness of another nonperfused gastric wall interposed between the laser probe and gastric mucosal surface, its laser flow signal was 17% of the flow signal in the usual measurement. In the blood flow measurement with the LDV prove on the mucosal and the serosal surface of gastric wall, the laser flow signal on the mucosal surface was higher (p less than 0.05) than that on the serosal surface. These results suggested that the laser flow signal mainly arose from the tissue right under the laser probe, reflecting the total gastric blood flow of the gastric wall. In the regional blood flow measurement at corpus and antrum, the ratio between antral and corpus flow signals by the LDV method was similar to that between gastric mucosal blood flows at both sites by the hydrogen gas clearance technique. In the blood flow measurement after the intravenous infusion of each pentagastrin, isoproterenol, and vasopressin, flow signal of the LDV method could detect the each effect of these drugs on gastric mucosal blood flow as well as well as the hydrogen gas clearance technique. These results showed that the laser flow signal and gastric mucosal blood flow were mutually correlated.(ABSTRACT TRUNCATED AT 250 WORDS)