PubMed Health⌕ Search

Biomedical subjects

R M Verdaasdonk

Publications and source records attributed to R M Verdaasdonk.

At least 19 recordsLinked to original sources
PubMed2003

Cerebral revascularization.

During the last 10 years, there has been a revival of interest in cerebral revascularization procedures. Not only have significant progressions in surgical techniques been published, the use of more advanced diagnostic methods has led to a widening of the indications for cerebral bypass surgery. The purpose of this review is to outline the current techniques for extracranial-to-intracranial (EC/IC) and intracranial-to-intracranial (IC/IC) bypass surgery, as well as to identify the current indications for revascularization procedures based on the available literature. The excimer laser-assisted non-occlusive anastomosis (ELANA) technique is described in more detail because we think that this technique almost completely eliminates the risk of cerebral ischemia due to the temporary vessel occlusion which is currently used in conventional anastomosis techniques.

Animals↗
PubMed2001

Contact laser-assisted neuroendoscopy can be performed safely by using pretreated 'black' fibre tips: experimental data.

BACKGROUND AND OBJECTIVE: Laser-assisted endoscopic neurosurgery by using conventional fibres requires the use of high-power laser light. Because this is potentially hazardous, we developed a pretreated fibre tip and evaluated tissue effects in vitro and in vivo. STUDY DESIGN/MATERIALS AND METHODS: By applying a highly absorbing coating to the front of the ball tip, almost all laser light is transformed into thermal energy, instantly producing ablative temperatures at the tip itself. The temperature distribution was examined by using an in vitro thermal imaging technique. The in vivo effect on rabbit cerebral tissue was examined macroscopically and histologically. RESULTS: By using a conventional fibre tip, ablation was not observed, despite the use of high energy and power (20 W for 10 seconds), whereas histology and thermal imaging demonstrated deleterious effects deeply into the cerebral tissue. By using the coated fibre tip, ablation was observed at low energy and power (1 W for 1 second) with thermal effects restricted to superficial structures. CONCLUSIONS: We show that laser-assisted neuroendoscopy can only be considered to be safe when pretreated "black" fibre tips are used, as laser light damages deep structures.

Animals↗
PubMed2001

Third ventriculostomy.

Since its description by Dandy in 1922, several techniques have been used to perform third ventriculostomy under endoscopic control. Except for the blunt technique, in which the endoscope is used by itself to create the opening in the floor of the third ventricle, the other techniques require more than one instrument to perforate the floor of the ventricle and enlarge the ventriculostomy. The new device described is a sterilizable modified forceps that allows both the opening of the floor and the enlargement of the ventriculostomy in a simple and effective way. The new device has the following characteristics: 1) the tip of the forceps is thin enough to allow the easy perforation of the floor of the ventricle; 2) the inner surface of the jaws is smooth to avoid catching vessels of the basal cistern; and 3) the outer surface of the jaws has indentations that catch the edges of the opening to prevent them from slipping along the instrument's jaws. The ventricle floor is opened by gentle pressure of the forceps, which is slowly opened so that the edges of the aperture are caught by the distal outer indentation of the jaws, leading to an approximately 4-mm opening of the floor. This device has been used successfully in 10 consecutive patients. This new device allows surgeons to perform third ventriculostomy under endoscopic control in a very simple, quick, and effective way, avoiding the need for additional single-use instruments.

Endoscopy↗
PubMed2000

Endoillumination during vitrectomy and phototoxicity thresholds.

AIM: To assess the retinal phototoxicity hazards of and to provide safety margins for endoillumination during vitrectomy. METHODS: The absolute power and spectral distribution from various light sources and filter combinations that are commercially available for vitreous surgery were measured. The maximal exposure times based on the ICNIRP safety guidelines for photochemical and thermal injury of the aphakic eye were calculated. Additionally, the effect of various measures that reduce the risk of phototoxicity was evaluated. RESULTS: Measurements of the spectrum and energy indicated that the ICNIRP safety guidelines for photochemical retinal damage are exceeded within 1 minute for nine out of 10 combinations tested. With an additional 475 nm long pass filter, light levels below 10 mW, and a distance from light probe to retina of at least 10 mm, the allowable exposure time can be increased up to 13 minutes. Thermal damage can be anticipated when the light probe touches the retina. CONCLUSION: Commercially available light sources for endoillumination during vitrectomy are not safe with respect to photochemical retinal damage. Even with maximal precautions macular phototoxic damage remains a factual danger during vitrectomy.

Hot Temperature↗
PubMed1999

Electrovaporization as a treatment modality for transurethral resection of the prostate: influence of generator type.

OBJECTIVES: To study the influence of the electrosurgical generator on the vaporization efficacy during electrovaporization (EVAP) using different vaporization elements. METHODS: Electrical properties of human prostatic (in vivo) and bovine myocardium (in vitro) tissue were measured under electroresection and electrovaporization conditions. The effective output power of four different generators ("old generation" Force 4 and Force 40 and "new generation" Force 300 and Force FX) was measured at different impedance loads. In vitro, the coagulation and vaporization capabilities of the electrosurgical generators in combination with resection and vaporization elements were studied on homogeneous tissue (bovine myocardium). RESULTS: The electrical impedance of human prostatic tissue and bovine myocardium increases from 400 to 1000 ohms when coagulated. The effective output power of the old generation electrosurgical devices depends strongly on tissue impedance. This implies that working on already coagulated tissue using such devices is not well controlled and not reproducible. By contrast, new generation electrosurgical devices correct for the higher impedance of coagulated tissue, thus delivering constant output power and corresponding tissue effects. CONCLUSIONS: For an effective application of the EVAP technique, the use of a new generation impedance independent electrosurgical unit is highly recommended.

Animals↗
PubMed1998

Influence of decay of laser fibers during laser prostatectomy on clinical results.

Three types of sidefiring laser fibers (34 Urolase, 20 Ultraline, and 114 Prolase II) were visually inspected after a laser prostatectomy, and transmission measurements were performed using a power meter (Aquarius). The results were correlated with the clinical outcome. Despite differences in the amount of loss in transmission for the fibers used, we could not establish any significant effect on clinical outcome measures, such as improvement in maximal flow rate or symptom score. The visual aspect of the Urolase fibers was significantly related to the amount of transmission loss, whereas no such relation was found for the other two types of fibers. Prostate size and the total amount of energy delivered by the laser source also did not correlate with the clinical outcome. To determine the relation between the energy absorbed by the prostate and clinical outcome, a large number of patients must be evaluated, and any factor that can be controlled needs to be monitored. For the latter, the power meter as presented here is a useful complementary tool.

Diuresis↗
PubMed1998

Laser-assisted neuroendoscopy using a neodymium-yttrium aluminum garnet or diode contact laser with pretreated fiber tips.

OBJECT: Although lasers have proved to be valuable in neuroendoscopy, surgeons are still not comfortable using high-energy laser endoscopic probes in proximity to vital structures such as the basilar artery in third ventriculostomy. The authors have developed a special laser catheter for use in neuroendoscopy; the object of this paper is to present their experimental and clinical experiences using the catheter. METHODS: This laser catheter is fitted with an atraumatic ball-shaped fiber tip that is pretreated with a layer of carbon particles. These carbon particles absorb approximately 90% of the energy emitted, which is very effectively converted into heat. As the heat is generated in this very thin layer of carbon coating, the temperature at the surface of the ball-shaped tip reaches ablative temperatures instantly at powers of only a few watts per second, which has enabled the authors to limit drastically the amount of laser light used and the length of exposure needed, thereby increasing safety even around critical structures. CONCLUSIONS: The authors present experimental data and their clinical experience using these pretreated fiber tips with a neodymium-yttrium aluminum garnet contact laser or a diode contact laser in 49 patients (22 males and 27 females) and a variety of procedures: third ventriculocistemostomy (33 patients), cyst fenestration (nine patients), colloid cyst resection (six patients), and fenestration of the septum pellucidum (one patient). There was no instance of mortality or increased morbidity. To date, the procedure success rate is 100% and the overall outcome success rate is 86%. The authors conclude that pretreated atraumatic ball-shaped fiber tips now make laser application safe and effective in a variety of neuroendoscopic procedures. Because of their low power range (only several watts), compact diode lasers will be the energy source of first choice.

Adolescent↗
PubMed1997

Nonocclusive excimer laser-assisted end-to-side anastomosis.

BACKGROUND: High-flow extraintracranial bypass operation on the brain is a risky procedure because of the temporary occlusion of the intracranial portion of the internal carotid artery. We therefore developed a nonocclusive anastomosis technique in the experimental animal laboratory in 100 chronic and acute experiments in rabbits. METHODS: In 40 patients we interposed a venous transplant between the external carotid artery or one of its branches and the intracranial portion of the internal carotid artery. During the construction of the distal anastomosis the recipient artery was not occluded. The donor vessel was stitched to the exterior of the recipient vessel and an Excimer laser catheter (Medolas GmbH, Amberg, Germany) was introduced by way of an artificial side branch. The tip of the laser catheter created a hole in the wall of the recipient artery just inside the anastomosis. The cut-out full-thickness portion of recipient vessel wall remained attached to the tip of the laser catheter by way of high vacuum suction and was removed together with the laser catheter. The artificial side branch was occluded with a hemostatic clip. No interruption of blood flow in the recipient artery was induced during the making of the anastomosis. RESULTS: The procedure was well tolerated by the patients and a high patency rate was observed. CONCLUSIONS: The nonocclusive Excimer laser-assisted anastomosis technique is safe and yields a high long-term patency rate in neurosurgical patients. It cannot be excluded that there are indications for this method in coronary bypass surgery.

Anastomosis, Surgical↗
PubMed1997

Laser light delivery systems for medical applications.

For medical applications, the choice of a delivery system will be governed by the characteristics of the laser system on the one hand and the tissue application on the other. The most important parts are the beam guide and the target optics. Most lasers have wavelengths in the visible and near-infrared and can be transported by silica fibres. For the mid- and far-IR other fibre materials or hollow waveguides are used. At the end of the waveguide or fibre, an optically active component is present to direct the beam and to control the power density on the target tissue. The laser beam can be delivered either by focusing handpieces and scanning devices to treat superficial areas or through microscopes, endoscopes and flexible fibres to treat areas almost anywhere inside the human body. The characteristics of the delivery systems can be determined looking at beam properties, transmission and thermal properties. The delivery of continuous wave or pulsed laser energy, contact or non-contact, will determine the contribution of optical, thermal and mechanical effects to the tissue. The practical use of laser delivery systems is illustrated by various clinical applications.

Diagnostic Imaging↗
PubMed1996

The modified excimer laser-assisted high-flow bypass operation.

BACKGROUND: To make high-flow revascularization of the brain possible, we developed an anastomosis technique that obviates temporary occlusion of the recipient artery. After connecting donor and recipient vessels, an Excimer laser catheter, introduced by way of an artificial side branch, creates a hole at the anastomosis site. Because of the inconsistency of the diameter of the hole produced by the closed laser tip, we developed an extensive modification of the procedure. METHODS: A new type of laser tip was developed, consisting of two layers of 60 mu laser fibers in a circular configuration with a diameter of 2.2 mm. The laser tip is fixed to the vessel wall at the anastomosis site by suction with a high-vacuum suction device, and a round piece of recipient vessel wall inside the anastomosis is cut out. RESULTS: Using the aorta as the recipient vessel in 30 rabbits, the modified technique was developed and, in the end, produced anastomoses with a high patency rate. In 25 patients, high-flow bypasses for different indications were made using a venous transplant interposed between the external carotid artery or one of its branches and the intracranial internal carotid artery, utilizing the modified Excimer laser technique for the intracranial anastomosis. Complications related to the new anastomosis technique were minimal, and a satisfactory patency rate was obtained. CONCLUSIONS: The modified Excimer laser-assisted anastomosis technique makes high-flow revascularization of the brain a safe procedure, since temporary occlusion of the recipient proximal brain artery during the making of the anastomosis is obviated.

Anastomosis, Surgical↗
PubMed1996

Variation in output power of laser prostatectomy fibers: a need for power measurements.

OBJECTIVES: The aim of this study was the assessment of the quality of side-firing fibers that are being used for laser prostatectomy, either by a laser light transmission measurement or by visual inspection. METHODS: A power meter (Aquarius) was developed to measure the actual power transmitted through a side-firing fiber and delivered to the prostatic tissue. The power measurements were performed under clinical conditions, that is, under water and at relatively high input power. Furthermore, a protocol was developed for visual inspection of the fibers. Eight types of side-firing fibers were measured before use. Before and after a procedure, three fiber types were measured: ProLase II (28 samples), UltraLine (23 samples), and UroLase (44 samples). All these fibers were used in standard treatment protocols. RESULTS: At 60 W the transmission of new fibers (not used) ranged between 49% and 83% when compared to a bare fiber. After use, a large variation was found in transmitted power between different samples of one device. A correlation with total transmitted power was not present. At higher power input, vapor bubbles are generated at the tip of the fibers. Depending on the fiber design, these bubbles have a major impact on the transmission. Only for the UroLase fiber was there a significant correlation between visual inspection and the transmission of used samples at 10, 20, and 40 W. CONCLUSIONS: The transmission strongly varies between fibers and between different samples of one fiber during clinical use. Moreover, the transmission does not correlate with visual inspection. A power measurement during a clinical treatment will contribute to a more controlled procedure and to a better comparison of clinical laser prostatectomy studies.

Biophysical Phenomena↗
PubMed1995

Side-firing devices for laser prostatectomy. An overview.

Transurethral laser coagulation of the prostate has become an accepted treatment for benign prostatic hyperplasia (BPH). The most common method is the use of a sideward-firing fiber that, once inserted in the prostatic area, irradiates the abundant prostatic tissue with Nd:YAG laser light. In this study, eight different side-firing fibers that are commercially available were evaluated. The devices can be characterized by the way laser light is deflected sideward and by their thermal behavior. Most of the eight devices differ with regard to the angle at which the laser beam is deflected, the spot size on the irradiated tissue surface, and the heating of the device itself. Implementation of the optical and thermal characteristics of each device in the treatment protocol will contribute to the optimal use of laser energy for prostatectomy.

Equipment Design↗
PubMed1995

Laser prostatectomy for patients with benign prostatic hyperplasia: a prospective randomized study comparing two different techniques using the Prolase-II fiber.

Laser prostatectomy for patients with complaints due to benign prostatic hyperplasia is a relatively new treatment option. The most effective procedure for coagulation and vaporization of the prostate is not yet known. In a prospective randomized study of 30 patients, 2 techniques for the delivery of laser energy were compared at 40 W for 90 s. The complications were minimal and antegrade ejaculation was preserved in 15 of 18 potent men. In 24 patients urodynamics evaluation was possible. In both groups a significant reduction in the symptom score was observed. The decrease in detrusor pressure at maximal flow and the increase in flow rate were, however, disappointing. No significant difference in the results was found between the two groups. The power setting needs to be changed in further studies.

Aged↗
PubMed1995

First clinical experience with Excimer assisted high flow bypass surgery of the brain.

A new type of revascularization of the brain is used in patients with brain ischaemia, caused by an occlusion of one or both internal carotid arteries, and in patients in whom the internal carotid artery has been deliberately occluded for the treatment of a giant aneurysm of the internal carotid artery. A so-called high flow extra-intracranial bypass operation is performed. An arterial or venous transplant is interposed between a branch of the external carotid artery or the external carotid artery itself and the intracranial portion of the internal carotid artery. The anastomosis with the intracranial portion of the internal carotid artery is made without temporary occlusion of the recipient artery and with the aid of the newly developed Excimer laser assisted anastomosis technique. The results of animal experiments and of a clinical series of 9 patients are reported.

Anastomosis, Surgical↗
PubMed1994

[Laser prostatectomy as alternative to transurethral prostate resection in benign prostatic hyperplasia].

OBJECTIVE: Assessment of the results of laser prostatectomy, as a treatment for benign prostatic hyperplasia (BPH). DESIGN: Prospective case control study. SETTING: University Hospital Utrecht, the Netherlands. METHOD: Between February 1992 and May 1993, 54 men with their micturition complaints due to BPH were treated with laser prostatectomy (TULIP system). Results were assessed using the international prostatic symptom score (IPSS), the maximal flow and urodynamic tests. The results were compared retrospectively with results of transurethral resection of the prostate (TURP; n = 40): both groups were urodynamically identical. RESULTS: Of the 54 patients, 10 could not be evaluated 6 months after treatment (5 of them underwent TURP or a second laser prostatectomy). In 40 patients complete evaluation including urodynamics before and six months after treatment was possible. A significant decrease in the symptom score from 19.3 (SD: 7.6) to 6.3 (SD: 5.4) and increase of the maximal flow during pressure-flow studies from 9.6 to 15.8 ml per second were observed. The decrease of the voiding pressure at 6 months after TURP in comparison with laser prostatectomy was close to significance (p = 0.05); the other improvements after urodynamics were comparable. CONCLUSION: Laser prostatectomy is a promising new therapy for BPH.

Aged↗
PubMed1994

Optimization of laser prostatectomy.

A recent development in the treatment of Benign Prostatic Hyperplasia (BPH) is the use of a side firing fiber device coupled with a Nd:YAG laser. In this study, a numerical and an in-vitro model were developed to calculate and visualize the temperature distribution and the associated tissue necrosis due to irradiation of the prostate with Nd:YAG laser light. Different irradiation modalities were included: a static beam, with the irradiating fiber remaining at one place and a moving beam, with the fiber scanning over the surface at different speeds. Also blood vessels were incorporated in the model and showed to have major influence on the resulting tissue necrosis.

Computer Simulation↗
PubMed1993

Use of the excimer laser in high-flow bypass surgery of the brain.

The technique of laser-assisted anastomosis for high-flow bypass surgery using the excimer laser is described in 15 rabbits and in one patient. The left common carotid artery of the rabbits was excised and, with two anastomoses, connected to the right common carotid artery. An end-to-side anastomosis technique was used that obviated the temporary occlusion of the recipient artery. The end of the donor artery was connected for its full circumference with the exterior of the recipient artery and, with the aid of an excimer laser catheter (introduced via an artificial side branch of the donor artery), the wall of the recipient artery was evaporated. In two animals only, occlusion of the anastomosis sites occurred. In the remaining 13 animals both anastomosis sites were proven to be patent by inspection at different times, followed by scanning electron microscopy in six animals. In a patient with hypoperfusion of the brain caused by bilateral internal carotid artery occlusion, revascularization of the right hemisphere was obtained by placing a shunt between the proximal superficial temporal artery and the intracranial portion of the internal carotid artery, using a free transplant of the right inferior epigastric artery. The anastomosis with the internal carotid artery was created using the excimer laser-assisted technique without occlusion of the recipient artery.

Animals↗