Biomedical subjects

T Papaioannou

Publications and source records attributed to T Papaioannou.

At least 19 recordsLinked to original sources

PubMed2001

Excimer laser (308 nm) based transmyocardial laser revascularization: effects of the lasing parameters on myocardial histology.

BACKGROUND AND OBJECTIVE: The effect of the excimer laser (308 nm) parameters on transmyocardial revascularization (TMR) channels is not well defined. This study investigates the influence of the pulse repetition rate, the size of the delivery catheter and its advancement speed on the morphology of TMR channels in vivo. STUDY DESIGN/MATERIALS AND METHODS: Myocardial ablation was performed in a porcine model (N = 27) using multifiber catheters of 1.0 and 1.4 mm in diameter. The catheters were advanced into the myocardium at different speeds (1.27 and 2.54 mm/sec) while ablating at various repetition rates (10-80 Hz). The radiant exposure was kept at 35 mJ/mm(2) throughout the experiments. The channel histology was quantified by digital microscopy. RESULTS: The channel cross-sectional area and the extent of the thermal damage decrease as the catheter advancement speed exceeds the ablation speed and vice versa. Within the parameters tested, advancement speed of about 1.3 mm/sec and pulse repetition rates of 40 Hz produce channels of size comparable to the catheter's diameter with moderate thermomechanical damage. CONCLUSIONS: The repetition rate, catheter size, and catheter advancement speed are closely intertwined and crucial to the histological outcome of excimer laser based TMR.

Animals↗

PubMed2001

Excimer laser (308 nm) recanalisation of in-stent restenosis: thermal considerations.

Excimer laser recanalisation of in-stent restenosis may be a viable modality for improving coronary patency. However, the presence of arterial stents modifies the thermal properties of the irradiated area and may alter temperature patterns generated during ablation. The goal of this study was to evaluate, in vitro, temperature changes during excimer laser ablation of stented vessels and compare them with those obtained from unstented (control) vessels. Six different stent types (AVE Microstent-II, AVE-GFX, ACS Multi-link, JJ Palmaz-Schatz, JJ Crown, and NIR) were deployed in freshly excised porcine coronary vessels. Three control unstented samples were also measured. Blood or saline was infused through the vessels, while the tissue environment was kept at approximately 37 degrees C. A 308 nm excimer laser (Spectranetics, CVX300) with an eccentric 2.0 mm laser catheter (Spectranetics, EII) delivered two trains of 200 pulses each, 10 s apart, at 60 mJ/mm2, and 40 Hz, simulating maximum clinical exposure. The catheter was positioned midway in the stent, first coaxially parallel to the vessel wall, and then at an angle against the stent and vessel wall. Temperature measurements (n= 168 for blood, n=96 for saline) were performed with a approximately 210 microm diameter, fast-response thermocouple with 0.1 degrees C resolution. The probe was positioned to within approximately 250 microm from the inner surface of the vessels. Tissue temperature was measured at the catheter tip and at the distal and proximal edges of the stents. Maximum recorded temperatures for coaxial and angular alignment, did not exceed 42.2 degrees C (approximately 6 degrees C above baseline) and 54.2 degrees C (approximately 18.1 degrees C above baseline) respectively, for all stents types tested, controls, and all probe locations. Both stented and unstented vessels exhibited comparable temperature gradients. The observed maximum temperatures, obtained under extreme lasing conditions, indicated that 308 nm ablation, in the presence of stents under blood or saline infusion, produces clinically acceptable temperatures.

Angioplasty, Laser↗

PubMed1996

Safety evaluation of laparoscopically applied clips.

We have evaluated in vitro, the security of laparoscopically applied clips, through two commercially available clip appliers: the Endo Clip II (US Surgical) and the Ligaclip (Ethicon). The clip performance was tested with respect to dislodgment and leakage. Dislodgment was attempted both transversely and at 45 degrees with respect to the main axis of the tubular structures tested. The mean maximum force (N = 24) necessary to dislodge a clip applied to silicone tubing (2.1, 2.4, 3.2 mm o.d.) and porcine vascular tissue was measured. The maximum force needed to transversely dislodge a clip applied to silicone tubing, ranged from 262 +/- 9 g (2.1 mm) to 315 +/- 11 g (3.2 mm) for the Endo Clip II applier, while the values for the Ligaclip were 220 +/- 28 g (2.1 mm) and 273 +/- 11 g (3.2 mm), respectively. To achieve dislodgment at 45 degrees pull, corresponding forces of 294 +/- 8 g (2.1 mm) and 369 +/- 14 g (3.2 mm) for the Endo Clip II, and 254 +/- 14 g (2.1 mm) and 297 +/- 13 g (3.2 mm) for the Ligaclip (N = 24) were required. Transverse dislodgment forces, for clips applied to tissue, were 556 +/- 146 g for the Endo Clip II and 356 +/- 170 for the Ligaclip (N = 6). Leakage tests were also performed under pulsatile blood circulation at mean pressure of approximately 800 mm Hg. No tested clips applied to either silicone tubing or tissue allowed for any blood leakage. The dislodgment test showed that the Endo Clip II exhibits superior performance compared to the Ligaclip, based on the fact that it requires more force for transverse and semiaxial dislodgment. In the leakage test, both clip appliers performed equivalently.

Animals↗

PubMed1994

Results of excimer laser photorefractive keratectomy for the correction of myopia.

PURPOSE: This report summarizes the authors' 3-year experience with excimer laser photorefractive keratectomy on 240 eyes of 161 patients. METHODS: With constant laser emission parameters, nitrogen flow across the cornea was used on 79 eyes, whereas 161 eyes had no nitrogen flow. Of the 240 eyes, 74 were operated on without suction ring fixation. Postoperative pain management included patching and oral analgesics in 77 eyes and the use of topical diclofenac or ketorolac and a therapeutic soft contact lens in 163 eyes. Follow-up ranged from 1 month (206 eyes) to 36 months (10 eyes). RESULTS: At 3 months, 88% (144 eyes) had uncorrected visual acuity of 20/40 or better; 86% (151 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 10% (17 eyes) lost two or more lines of best-corrected visual acuity. At 12 months, 89% (122 eyes) achieved uncorrected visual acuity of 20/40 or better, 79% (115 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 4% (6 eyes) lost two or more lines of best-corrected visual acuity. At 24 months, 92% (44 of 48 eyes) had uncorrected visual acuity of 20/40 or better, 86% (44 of 51 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 5% (2 eyes) lost two or more lines of best-corrected visual acuity. At 36 months, 90% (9 eyes) achieved an uncorrected visual acuity of 20/40 or better, 90% (9 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and no eyes lost two or more lines of best-corrected visual acuity. CONCLUSIONS: The results obtained with one procedure are within accepted standards of accuracy for refractive surgery, and there is the potential for refinement of the final optical correction. Complication rates are low and are not vision threatening. They included increased intraocular pressure, epithelial "map dot" changes, and recurrent corneal erosion syndrome, "central islands," and others. Photorefractive keratectomy appears to be a safe procedure over the short and medium term.

Adult↗

PubMed1994

Photodynamic therapy for the treatment of squamous cell carcinoma using benzoporphyrin derivative.

BACKGROUND: Photodynamic therapy (PDT) involves laser light excitation of a tumor-localizing photosensitizer to destroy neoplasms. Benzoporphyrin derivative (BPD) is a new photosensitizer with several favorable characteristics. OBJECTIVE: Studies were designed to: 1) assess the efficacy of BPD-mediated PDT in treating in vivo squamous cell carcinomas (SCC); 2) obtain dosimetry data for BPD and laser parameters; and 3) establish clinical and histologic correlates of BPD-induced tumor regression. METHODS: Human SCC was implanted into nude mice. One group received BPD followed by laser light of 150 J/cm2 from an argon-pumped dye laser at 690 nm. Three control groups included laser energy alone, BPD alone, and no treatment. RESULTS: At day 21 posttreatment only PDT-treated tumors showed a statistically significant decrease in tumor volume and complete cure rate. Clinical resolution (scar) correlated perfectly with histologic resolution (scar). CONCLUSION: Human SCC in a nude mouse model responds to BPD-mediated PDT.

Anaplasia↗

PubMed1993

A two-year experience with excimer laser photorefractive keratectomy for myopia.

PURPOSE: This report summarizes the authors' 2-year experience with excimer laser photorefractive keratectomy (PRK) on 160 eyes of 128 patients. METHODS: All eyes were treated with an excimer laser: fluence, 160 mJ/cm2; frequency, 5 Hz; ablation zone diameter, 5.0 to 5.5 mm; and depth per pulse, 0.21 to 0.27 microns. A suction fixation ring was used in all eyes either with nitrogen flow (79 eyes) or without nitrogen flow (81 eyes) across the cornea. Follow-up ranged from 1 month (152 eyes) to 24 months (12 eyes). RESULTS: At 3 months, 82% (139) of eyes achieved an uncorrected visual acuity of 20/40 or better; 83% were corrected to within +/- 1 diopter (D) of intended correction and 30% lost one line of best-corrected visual acuity. At 6 months, 88% (124) of eyes achieved an uncorrected visual acuity of 20/40 or better; 84% were corrected to within +/- 1 D of intended correction and 15% lost one line of best-corrected visual acuity. At 12 months, 91% (71) of eyes achieved an uncorrected visual acuity of 20/40 or better; 84% were corrected to within +/- 1 D of intended correction and 17% lost one line of best-corrected visual acuity. At 24 months, 100% (12) of eyes achieved an uncorrected visual acuity of 20/40 or better; 91.6% were within +/- 1 D of intended correction and 0% lost one line of best-corrected visual acuity. CONCLUSIONS: In eyes with a follow-up of 6 to 24 months, 77% to 100% achieved an uncorrected visual acuity of 20/40 or better and 84% to 92% were corrected to within +/- 1 D of the intended correction. The authors conclude that excimer laser PRK appears to be a safe procedure capable of correcting the eyes of patients with low to moderate myopia with approximately the same degree of accuracy as radial keratotomy.

Adult↗

PubMed1992

Endoscopy of the lacrimal outflow system.

Management of obstructions in the lacrimal drainage system would be greatly aided by improvements in the ability to visualize the blockages. We describe a new method of observation using miniature fiberoptics to view the entire lacrimal excretory system. We employed flexible endoscopes of fiberoptic bundles with outside diameters of from 0.5 to 0.7 mm. These endoscopes were inserted through the puncta and canaliculi. Sixteen patients were examined. A range of pathologic conditions were found, including slightly stenosed passages and severely destroyed canalicular mucosal lining. Our results indicate that this technique is feasible and useful in the diagnosis of lacrimal excretory disease.

Endoscopes↗

PubMed1992

Carpal canal stenosis in men with idiopathic carpal tunnel syndrome.

The carpal canal and carpal bones of 14 male patients with idiopathic carpal tunnel syndrome and 26 normal male controls were examined by computed tomography. When compared with the controls, there was significant stenosis of the proximal part but not of the distal part of the carpal canal. Carpal canal stenosis is an important etiologic factor in the development of idiopathic carpal tunnel syndrome in males.

Adult↗

PubMed1991

Excimer laser ablation of fibrocartilage: an in vitro and in vivo study.

To date, lasers have found only limited applications in orthopedics. We employed a 308 nm XeCl excimer laser for ablation of fibrocartilage, in order to investigate the feasibility of excimer laser assisted meniscectomy. Experiments were conducted both in vitro and in vivo. For the in vitro study, human menisci, obtained during surgery and autopsy, were irradiated via a 600 microns core fiber at radiant exposures ranging between 20 mj/mm2 and 80 mj/mm2, at 20 Hz. Ablation rate measurements and histological analysis of the samples were performed. The ablation rates were found to range from 3 microns/pulse to 100 microns/pulse depending on the radiant exposure and/or the applied pressure on the fiber delivery system. Thermographic analysis was also performed during pulsed excimer as well as CW Nd:Yag and CW CO2 laser irradiation. Temperatures were lower for excimer laser (Tmax less than 65 degrees) than CW ND: Yag (Tmax less than 210 degrees) or CW CO2 (Tmax less than 202 degrees) laser. For the in vitro study, medial meniscectomy was performed in 15 rabbits with the excimer laser and a CW Nd:Yag laser in the right and left knee respectively. Excimer laser irradiation was performed at 70 mj/mm2. Nd:Yag irradiation was performed via a 600 microns core fiber at power outputs between 20 to 40 W for 10 and 20 seconds duration. The healing response to injury was investigated by histological analysis of the menisci after 1 day, 1, 2, 4, and 8 weeks following the laser procedure. Excimer laser treated menisci showed less inflammatory reaction and noticeable repair with minimal inflammatory response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Biliary calculi fragmentation by a 308 nm excimer laser: a preliminary study.

The use of a 308-nm XeCl excimer laser for biliary stone fragmentation is reported. The 130-nsec laser pulses are delivered via UV grade fused silica fibers to the target stones immersed in normal saline solution and placed in direct contact with the fiber. Sixty biliary calculi, 20 cholesterol and 40 pigment, were fragmented in vitro. The energy delivered per unit mass of the stone is kept constant at 50 mJ/mg. The effect of laser repetition rate, energy fluence, and fiber core size on stone fragmentation was studied. Fragmentation thresholds for a variety of biliary calculi of known composition were measured. It was found that higher fragmentation efficiency was obtained with larger fluence, lower repetition rate, and fiber of larger core. Our study indicates that the 308-nm excimer laser may be effective as a laser lithotriptor with low threshold and good efficiency for biliary stone fragmentation.

Evaluation Studies as Topic↗

PubMed1991

XeCl excimer laser-induced fluorescence for selective ablation of atheromatous tissue.

In order to develop a reliable laser-induced fluorescence (LIF) guided laser angioplasty system, real time, pulse-by-pulse fluorescence spectra were recorded and the same fiberoptic was used for both detection of the fluorescence and for atheromatous tissue ablation. A 308 nm XeCl excimer laser served as the laser source for both the induction of fluorescence and the ablation. The fluorescence signal was induced at high laser energies during ablation without any serious change in the fluorescence pattern. A new characteristic fluorescence peak at 540 nm for atheromatous tissue was observed after treatment with chlortetracycline hydrochloride (CTC). This allowed the development of an algorithm and a subsequent index to discriminate the atheromatous tissue from the normal tissue. During atheromatous tissue ablation, this index changed as normal tissue was approached, thereby avoiding vessel perforation. Our results suggest that monitoring of this index through the catheter delivering the laser energy enhances selective ablation while simultaneously reducing the risk of vessel perforation.

Arteriosclerosis↗

PubMed1990

Fragmentation of biliary stones with a 308 nm excimer laser.

The use of a XeCl excimer laser (308 nm) for biliary stone fragmentation is reported. Laser energy is delivered via UV grade fused silica fibers to the target stones immersed in normal saline solution. Sixty biliary calculi--pigment (n = 40), and cholesterol (n = 20)--were fragmented in vitro. The total energy delivered per unit mass of the stone is kept constant. Two energy fluences (80 and 110 mJ/mm2) at two repetition rates (5 and 20 Hz) delivered through fibers of two core sizes (300 and 600 microns) are utilized to study the effect of different laser parameters on the fragmentation process. Although both pigment and cholesterol stones are susceptible to excimer laser fragmentation, higher fragmentation efficiency is obtained for the pigment stones than for the cholesterol stones. Our study suggests that higher energy fluence and larger fiber core size result in higher fragmentation efficiency for pigment stones. Fragmentation thresholds at stone surface for a variety of biliary calculi of known composition were measured. The threshold energy fluence is approximately 3 mJ/mm2 and 17 mJ/mm2 for pigment and cholesterol stones, respectively. Our study indicates that the 308 nm excimer laser may be effective as a laser lithotriptor with low threshold and good efficiency for biliary stone fragmentation.

Cholelithiasis↗

PubMed1990

Photodynamic therapy of choriocarcinoma transplanted to the hamster cheek pouch. I. Intraperitoneal photosensitization.

Human choriocarcinoma (JEG-3) cells were transplanted into the cheek pouch of hamsters and treated with photodynamic therapy. Twenty-four hours after intraperitoneal injection of the photosensitizer dihematoporphyrin ether (DHE), 20 tumors were illuminated with 100 J/cm2 of 630-nm light from an argon pumped dye laser. Contralateral tumors served as controls. Dihematoporphyrin ether alone had no effect on tumor growth, while laser light in the absence of DHE resulted in complete regression in 3 tumors (17%), and partial regression in 4 of 18 tumors (22%), possibly due to hyperthermia, P greater than 0.10. Using the combination of DHE plus light (photodynamic therapy) complete tumor regression was noted after a single treatment in 11 of 20 tumors (55%, mean tumor volume 279 mm3) and in 7 of 7 tumors (100%) after a second treatment. Two of 20 tumors were not retreated. Therefore, 18 of 20 tumors (90%) were grossly destroyed by one or two photodynamic treatments. Contralateral control tumors continued to grow to a median volume of 990 mm3 (chi 2 = 26.30, P less than 0.0001). Choriocarcinoma transplanted into the hamster cheek pouch is highly responsive to photodynamic therapy.

Animals↗

PubMed1989

Excimer ablation of human intervertebral disc at 308 nanometers.

Excimer laser energy, which has been shown to photoablate tissue at a precisely controllable rate with minimal thermal damage, was applied to human intervertebral disc in an effort to develop a technique for percutaneous discectomy. Cadaveric samples of human disc were used. Excimer laser energy was produced by a XeCl, magnetically switched, long-pulse laser working at 308 nm, 20 Hz. Annulus tissue of approximately 1 mm thickness was placed in contact with the output tip of a 400 microns core diameter quartz fiber, and measurements of ablation rate were made at different radiant exposures. Ablation rates were found to vary linearly with radiant exposure, from 0.7 micron/pulse at 10 mJ/mm2 to 11.0 microns/pulse at 55 mJ/mm2, with a correlation coefficient of 0.984. Threshold radiant exposure, calculated by extrapolation, was found to be about 7 mJ/mm2. Histologic analysis showed a minimum of thermal damage in these specimens, and when ablated with modification to maintain constant fiber-tissue contact, thermal injury was nearly absent, as compared to samples ablated with Nd:YAG through a contact probe. Thermographic analysis, performed using the AGA 782 Digital Thermography system, showed increasing temperature with increasing radiant exposure, with a maximum temperature of 47.2 degrees C at 55 mJ/mm2. In that precise tissue ablation was demonstrated with minimal generated heat, and excimer energy at 308 nm is transmissible through fiber optics, excimer holds great promise for the development of a percutaneous discectomy technique.

Humans↗

PubMed1989

Excimer laser ablation of the human lens at 308 nm with a fiber delivery system.

A 308 nm excimer laser has been used with a fiber delivery system to perform ablation of the human lens. Preliminary results demonstrate the system's ability to ablate lens nucleus and cortex selectively, preserving the anterior and posterior capsules. The total delivered energy necessary to ablate a human lens ranged from 35 to 63 joules. Laser tissue interaction and ablation rates were computed for the different components of the human lens (capsule, cortex, nucleus) for the operatively useful energy densities (fluences). Operative experience suggests that cortex and nucleus can be ablated while preserving the capsule if an adequate irrigation and aspiration system is developed. These results also suggest that this modality may be adequate for performing endocapsular cataract extraction. Laser tissue interactions were also computed at variable distances between the fiber tip and tissue. As this distance increased, the spread of the beam increased and a significant increase in energy was necessary to induce tissue ablation. This was due to the decrease in fluence with increasing distance to the target tissue and/or the absorption and scattering of the delivered energy within a short distance from the fiber tip by the ablated material. Evidence of a sonic effect was also present.

Aged↗

PubMed1988

Role of laser and thermal ablation devices in the treatment of vascular diseases.

Since the first coronary angioplasty in 1977, both the number and complexity of interventional procedures have grown dramatically. Continuous-wave and pulsed lasers may further extend the capabilities of balloon angioplasty. Fiberoptic catheters may be used to transmit continuous-wave laser energy to ablate plaque via thermal mechanisms. Pulsed laser systems (such as the excimer) are technologically more complex than the continuous-wave systems, but may prove superior in small vessels given their ability to ablate plaque with minimal associated effects. On the other hand, modifications of the fiber-optic tip, such as the placement of a metal cap, have yielded even better results than current bare fiber systems. Such laser thermal techniques have proved a useful adjunct to balloon dilatation in peripheral vessels, but further research is necessary to determine their effect on coronary arteries. New, nonlaser technologies, however, may provide simpler power sources for thermal angioplasty. Although balloon angioplasty remains the cornerstone of interventional vascular therapy, new technologies should help to further expand the indications for nonsurgical interventions.

Angioplasty, Balloon↗

PubMed1988

[Evaluation of clinical symptoms and laboratory data as diagnostic criteria for Sjögren's syndrome].

In this study the authors evaluated the sensitivity, specificity and misclassification error rate of the following parameters: subjective xerophthalmia (questionnaire), positive Schirmer's I test less than or equal to 5 mm/5 min, positive rose-bengal staining on slit lamp examination, subjective xerostomia (questionnaire), abnormal stimulated parotid flow rate less than or equal to 0.5 ml/5 min and recurrent parotid gland enlargement. Thirty-two patients with primary SS (pSS), 40 patients with some of the criteria for pSS, 20 patients with SS in association with RA (sSS), 45 patients with RA and some of SS criteria and 29 RA patients without any clinical or histological manifestations of SS participated in this study. The minor salivary gland histopathology (focal lymphocytic infiltrates greater than or equal to 2+ (T. M. Tarpley et al., 1972) was taken as prerequisite for the diagnosis of SS and the absence of any clinical or serological manifestations of other autoimmune disease for the diagnosis of pSS. Based on this analysis the authors suggested that definite pSS can be diagnosed in the absence of any other autoimmune disease, positive labial biopsy and the presence of subjective xerostomia or parotid gland enlargement or positive rose-bengal staining, and definite sSS if a patient has RA, positive labial biopsy and subjective xerophthalmia or positive rose-bengal staining.

Diagnosis, Differential↗

PubMed1986

Preliminary diagnostic criteria for Sjögren's syndrome.

Although Sjögren's syndrome (SS) is a very common autoimmune disease there are no uniformally accepted diagnostic criteria. In this study we evaluated various clinical parameters as criteria for this disorder. Fifty-two patients with sicca complaints but no evidence of other autoimmune rheumatic disorders were studied. These patients were further subdivided into definite primary SS (primSS) (n = 19) and possible primary SS (n = 33). The patients of the definite group fulfilled 2/3 of the following criteria: xerophthalmia defined by subjective complaints, Schirmer's test less than or equal to 5 mm/5 min or positive rose-bengal staining on slit lamp examination, xerostomia defined by subjective complaints and parotid flow rate less than or equal to 1 cc/5 mm/gland and, presence or history of parotid gland enlargement. In all patients the histology of labial minor salivary glands showed round cell infiltrates greater than or equal to 2+ (Tarpley's classification). The clinical manifestations of definite primary SS were compared to those of patients with possible primary SS. In addition, 49 patients with rheumatoid arthritis (RA) and suspected secondary SS were evaluated. Eleven patients were initially classified as definite secondary SS in association with RA (lip biopsy greater than or equal to 2+ and 1/2 of the criteria: xerophthalmia and xerostomia) and the remaining 38 as possible secondary SS with RA.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗