Biomedical subjects

W S Yamanashi

Publications and source records attributed to W S Yamanashi.

At least 19 recordsLinked to original sources

PubMed2001

Radiofrequency catheter ablation with the split-tip electrode in the temperature-controlled mode.

The 7 Fr "split-tip electrode" (2.5-mm tip electrode divided longitudinally into four electrodes with an adjacent 2-mm ring electrode) improves mapping resolution due to its small recording electrodes and narrow interelectrode distances (0.1 mm). The purpose of this study was to examine the temperature-controlled ablation properties of this electrode. In seven anesthetized dogs, the thigh muscles were exposed and superfused with canine blood. A split-tip catheter electrode (with a thermocouple in each of the five electrodes) and a conventional 4-mm catheter electrode were positioned at constant pressure perpendicular or parallel to the surface of the thigh muscle. Impedance measured between each split electrode and a skin patch correlated with the degree of contact with blood and tissue. In the parallel catheter to tissue orientation, split electrodes not in contact with tissue had a low impedance (mean 210-224 ohms), and the split electrode almost entirely in contact with tissue had the highest impedance (380 +/- 56 ohms). In the perpendicular catheter to tissue orientation all split electrodes had a similar impedance (mean 279-286 ohms). A total of 75 radiofrequency (RF) lesions were produced in the temperature-controlled mode with the 4-mm electrode (target 60 degrees C) or the split-tip electrode (power limited by the hottest electrode reaching 70 degrees C) with current delivered to all five electrodes simultaneously, or only to electrodes in contact with tissue. Lesion depth was not significantly different between electrodes in the parallel orientation (5.2 +/- 0.9 vs 5.1 +/- 1.4 vs 5.3 +/- 1.1 mm), but significantly deeper with the conventional 4-mm tip electrode in the perpendicular orientation (6.7 +/- 1.2 vs 5.3 +/- 1.3 vs 5.6 +/- 0.9 mm, P < 0.05). This was due to higher power delivered to the conventional 4-mm electrode (27 +/- 9 vs 17 +/- 7 vs 15 +/- 7 W, P < 0.05) because convective cooling by the blood flow was less effective for the split-tip electrode due to a reduced heat conduction across the interelectrode space from the hottest electrode to cooler areas of the group of five electrodes (mean temperature difference between the hottest split electrodes and the ring electrode: 24 degrees C). Electrode cooling or heat conduction was not effected by the elimination of current delivery to non-contact electrodes. Steam pops occurred in 36% of applications with the conventional 4-mm electrode in the perpendicular orientation but never with the split-tip electrode in spite of the higher target temperature. Measurement of impedance from the split electrodes allow the determination of electrode tissue contact and RF lesions produced with the split-tip electrode in the temperature-controlled mode using a target of 70 degrees C were of reasonable size and not associated with steam pops.

Animals↗

PubMed1998

Inverse relationship between electrode size and lesion size during radiofrequency ablation with active electrode cooling.

BACKGROUND: Clinical efficacy has driven the use of larger electrodes (7F, length > or =4 mm) for radiofrequency ablation, which reduces electrogram resolution and causes variability in tissue contact depending on electrode orientation. With active cooling, ablation electrode size may be reduced. The purpose of this study was to examine the effect of electrode length on tissue temperature and lesion size with saline irrigation used for active cooling. METHODS AND RESULTS: In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood. A 7F ablation catheter with a 2- or 5-mm irrigated tip electrode was positioned perpendicular or parallel to the thigh muscle. Radiofrequency current was delivered at constant voltage (50 V) for 30 seconds during saline irrigation (20 mL/min) to 148 sites. Tissue temperature at depths of 3.5 and 7 mm and lesion size were measured. In the perpendicular electrode-tissue orientation, radiofrequency applications at 50 V with the 2-mm electrode compared with the 5-mm electrode resulted in lower power at 50 V (26 versus 36 W) but higher tissue temperatures, larger lesion depth (8.0 versus 5.4 mm), and greater diameter (12.4 mm versus 8.4 mm). Also, in the parallel orientation, overall power was lower with the 2-mm electrode (25 versus 33 W), but tissue temperatures were higher and lesions were deeper (7.3 versus 6.9 mm). Lesion diameter was similar (11.1 versus 11.3 mm) for both electrodes. CONCLUSIONS: The smaller electrode resulted in transmission of a greater fraction of the radiofrequency power to the tissue and resulted in higher tissue temperature, larger lesions, and lower dependency of lesion size on the electrode orientation.

Animals↗

PubMed1998

Why a large tip electrode makes a deeper radiofrequency lesion: effects of increase in electrode cooling and electrode-tissue interface area.

INTRODUCTION: Increasing electrode size allows an increase in radiofrequency lesion depth. The purpose of this study was to examine the roles of added electrode cooling and electrode-tissue interface area in producing deeper lesions. METHODS AND RESULTS: In 10 dogs, the thigh muscle was exposed and superfused with heparinized blood. An 8-French catheter with 4- or 8-mm tip electrode was positioned against the muscle with a blood flow of 350 mL/min directed around the electrode. Radiofrequency current was delivered using four methods: (1) electrode perpendicular to the muscle, using variable voltage to maintain the electrode-tissue interface temperature at 60 degrees C; (2) same except the surrounding blood was stationary; (3) perpendicular electrode position, maintaining tissue temperature (3.5-mm depth) at 90 degrees C; and (4) electrode parallel to the muscle, maintaining tissue temperature at 90 degrees C. Electrode-tissue interface temperature, tissue temperature (3.5- and 7.0-mm depths), and lesion size were compared between the 4- and 8-mm electrodes in each method. In Methods 1 and 2, the tissue temperatures and lesion depth were greater with the 8-mm electrode. These differences were smaller without blood flow, suggesting the improved convective cooling of the larger electrode resulted in greater power delivered to the tissue at the same electrode-tissue interface temperature. In Method 3 (same tissue current density), the electrode-tissue interface temperature was significantly lower with the 8-mm electrode. With parallel orientation and same tissue temperature at 3.5-mm depth (Method 4), the tissue temperature at 7.0-mm depth and lesion depth were greater with the 8-mm electrode, suggesting increased conductive heating due to larger volume of resistive heating because of the larger electrode-tissue interface area. CONCLUSION: With a larger electrode, both increased cooling and increased electrode-tissue interface area increase volume of resistive heating and lesion depth.

Animals↗

PubMed1996

Thermal latency in radiofrequency ablation.

BACKGROUND: Progression of unintentionally induced atrioventricular delay is occasionally observed directly after termination of radiofrequency delivery in the vicinity of the atrioventricular node. We postulated that the application of a radiofrequency pulse may result in a tissue temperature rise that continues after the pulse. METHODS AND RESULTS: Using the thigh muscle preparation, 5-, 10-, 20-, and 30-second pulses were applied as 30 to 40 W via a standard 4-mm tip electrode with 10-g contact pressure. Forty-one undisturbed pulses were delivered while recording intramural temperatures at 2-, 4-, and 7-mm depth. Maximal "thermal latency" was observed with the shortest pulse duration and at greatest depth. With 5-second applications, tissue temperature at 7-mm depth peaked 11.6 seconds after termination of radiofrequency delivery and stayed above end-of-pulse value as long as 34.5 seconds after the pulse. The additional rise in tissue temperature was 2.9 degrees C. If only recording within the lesion border zone were considered, the duration of latency was maximal with 10-second pulses: an additional gain in tissue temperature of 3.4 degrees C was observed 6.4 seconds after the pulse while tissue temperature stayed above end-of-pulse value during 18.3 seconds. CONCLUSIONS: With relatively short applications, tissue temperature continues to rise after termination of radiofrequency delivery. This "thermal latency" may result in lesion growth after the pulse and may so explain the incidentally observed progression of conduction block after short pulses in the vicinity of the atrioventricular node. It also may explain the apparent discrepancy between lesion growth rate and intramural temperature rise studies.

Animals↗

PubMed1995

Comparison of in vivo tissue temperature profile and lesion geometry for radiofrequency ablation with a saline-irrigated electrode versus temperature control in a canine thigh muscle preparation.

BACKGROUND: It is thought that only a thin layer of tissue adjacent to the electrode is heated directly by electrical current (resistive heating) during radiofrequency ablation. Most of the thermal injury is thought to result from conduction of heat from the surface layer. The purpose of this study was to determine whether lesion depth could be increased by producing direct resistive heating deeper in the tissue with higher radiofrequency power, allowed by cooling the ablation electrode with saline irrigation to prevent the rise in impedance that occurs when the electrode-tissue interface temperature reaches 100 degrees C. METHODS AND RESULTS: In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood (36 degrees C to 37 degrees C). A 7F catheter, with a central lumen, a 5-mm tip electrode with six irrigation holes, and an internal thermistor, was positioned perpendicular to the thigh muscle and held at a constant contact weight of 10 g. Radiofrequency current was delivered to 145 sites (1) at high constant voltage (66 V) without irrigation (CV group, n = 31), (2) at variable voltage (20 to 66 V) to maintain tip-electrode temperature at 80 degrees C to 90 degrees C without irrigation (temperature-control group, n = 39), and (3) at high CV (66 V) with saline irrigation through the catheter lumen and ablation electrode at 20 mL/min (CV irrigation group, n = 75). Radiofrequency current was applied for 60 seconds but was terminated immediately in the event of an impedance rise > or = 10 omega. Tip-electrode temperature and tissue temperature at depths of 3.5 and 7.0 mm were measured in all three groups (n = 145). In 33 CV irrigation group applications, temperature was also measured with a separate probe at the center (n = 18) or edge (n = 15) of the electrode-tissue interface. In all 31 CV group applications, radiofrequency energy delivery was terminated prematurely (at 11.6 +/- 4.8 seconds) owing to an impedance rise associated with an electrode temperature of 98.8 +/- 2.1 degrees C. All 39 temperature-control applications were delivered for 60 seconds without an impedance rise, but voltage had to be reduced to 38.4 +/- 6.1 V to avoid temperatures > 90 degrees C (mean tip-electrode temperature, 84.5 +/- 1.4 degrees C). In CV irrigation applications, the tip-electrode temperature was not > 48 degrees C (mean, 38.4 +/- 5.1 degrees C) and the electrode-tissue interface temperature was not > 80 degrees C (mean, 69.4 +/- 5.7 degrees C). An abrupt impedance rise with an audible pop and without coagulum occurred in 6 of 75 CV irrigation group applications at 30 to 51 seconds, probably owing to release of steam from below the surface. In the CV and temperature-control group applications, the temperatures at depths of 3.5 (62.1 +/- 15.1 degrees C and 67.9 +/- 7.5 degrees C) and 7.0 mm (40.3 +/- 5.3 degrees C and 48.3 +/- 4.8 degrees C) were always lower than the electrode temperature. Conversely, in CV irrigation group applications, electrode and electrode-tissue interface temperatures were consistently exceeded by the tissue temperature at depths of 3.5 mm (94.7 +/- 9.1 degrees C) and occasionally 7.0 mm (65.1 +/- 9.7 degrees C). Lesion dimensions were smallest in CV group applications (depth, 4.7 +/- 0.6 mm; maximal diameter, 9.8 +/- 0.8 mm; volume, 135 +/- 33 mm3), intermediate in temperature-control group applications (depth, 6.1 +/- 0.5 mm; maximal diameter, 11.3 +/- 0.9 mm; volume, 275 +/- 55 mm3), and largest in CV irrigation group applications (depth, 9.9 +/- 1.1 mm; maximal diameter, 14.3 +/- 1.5 mm; volume, 700 +/- 217 mm3; P < .01, respectively). CONCLUSIONS: Saline irrigation maintains a low electrode-tissue interface temperature during radiofrequency application at high power, which prevents an impedance rise and produces deeper and larger lesions. A higher temperature in the tissue (3.5 mm deep) than at the electrode-tissue interface indicates that direct resistive heating occurred deeper

Animals↗

PubMed1995

An initial physical mechanism in the treatment of neurologic disorders with externally applied pico Tesla magnetic fields.

The recent clinical studies describing the treatment of some neurological disorders with an externally applied pico Tesla (10(-12) Tesla, or 10(-8) gauss) magnetic field are considered from a physical view point. An equation relating the intrinsic (or rest) energy of a charged particle of mass m with its energy of interaction in an externally applied magnetic field B is presented. The equation represents an initial basic physical interaction as a part of a more complex biological mechanism to explain the therapeutic effects of externally applied magnetic fields in these and other neurologic disorders.

Brain Diseases↗

PubMed1995

A physical mechanism in the treatment of neurologic disorders with externally applied pico Tesla magnetic fields.

The clinical studies describing the treatment of some neurological disorders with an externally applied pico Tesla (10R Tesla, or 10(-8) gauss) magnetic field are considered from a physical view point. An equation relating the intrinsic or "rest" energy of a charged particle of mass with its energy of interaction in an externally applied magnetic field B is presented. The equation is proposed to represent an initial basic physical interaction as a part of a more complex biological mechanism to explain the therapeutic effects of externally applied magnetic fields in these and other neurologic disorders.

Humans↗

PubMed1994

Five-year survival in breast cancer treated with adjuvant immunotherapy.

In this follow-up report of the treatment of primary breast cancer with adjuvant immunotherapy, a total of 95 patients were studied: 46 patients with stage I breast cancer and 49 patients with stage II breast cancer. All patients underwent standard surgical treatment and received immunotherapy as adjuvant treatment. Patients received a primary series of eight doses (1 mL of tumor-associated antigen preparation given as 0.2 mL intradermally and 0.8 mL subcutaneously) given over 8 weeks, and then booster injections every 3 months for at least 2 years. The 5-year survival with adjuvant immunotherapy was 83% for those with negative axillary nodes and 53% for those with positive nodes; this compares favorably with national 5-year survival statistics from two other studies (node-negative, 72% and 83%; node-positive, 51% and 59%). Based on these data, the addition of immunotherapy to other adjuvant therapies in randomized prospective trials seems both reasonable and justified.

Actuarial Analysis↗

PubMed1994

A possible, physical mechanism in the treatment of neurologic disorders with externally applied pico Tesla magnetic fields.

The clinical studies describing the treatment of some neurological disorders with an externally applied pico Tesla (10(-12) Tesla, or 10(-8) gauss) magnetic field are considered from a physical view point. An equation relating the intrinsic (or "rest") energy of a charted particle of mass m with its energy of interaction in an externally applied magnetic field B is presented. The equation is proposed to represent an initial basic physical interaction as a part of a more complex biological mechanism to explain the therapeutic effects of externally applied magnetic fields in these and other neurologic disorders.

Electromagnetic Fields↗

PubMed1992

Laparoscopic cholecystectomy: an initial community experience.

The initial 950 consecutive laparoscopic cholecystectomies performed in one city at four hospitals by 30 general surgeons are reported, covering a period from April 4, 1990 to April 3, 1991. There were two operative deaths (0.2%), three common bile duct lacerations (0.3%), two subhepatic abscesses, two bowel perforations, and three bile leaks, two requiring laparotomy. Seven episodes of bleeding occurred, of which five required laparotomy, but none involved a major vessel. Sixty-five procedures were converted to open (6.7%). The mean operative time was 85.4 min. Intraoperative cholangiography was adequately completed in 49.8% and not attempted in 30.3%. Thirteen patients (2.7%) were found to have common duct stones. The pathologic diagnoses were chronic cholecystitis in 784 patients (82.5%), acute cholecystitis in 145 (15.3%), and cancer of the gallbladder in one (0.1%). Hospital stays ranged from 4 h to 31 days (mean 49.5 h). This procedure can be learned and performed safely in a community setting.

Age Factors↗

PubMed1991

Intervascular occlusion of canine renal, splenic, and vertebral arteries using electromagnetic field focusing (EFF) probe.

Electromagnetic field-focusing (EFF) probe is a precision surgical and interventional tool. Use of the device produces maximum temperature in excess of 1800 degrees C by convergence of radio-frequency (RF) induced eddy currents in biological tissues. Applications of the EFF probe in angioplasty, aneurysm thrombosis, and neurosurgery have been previously reported. In the present work, the EFF probe was guided under fluoroscopic control and used to occlude renal, splenic, and vertebral arteries in dogs. The occlusion was typically accomplished with about one minute of RF power application. Histology of the treated vessel three to six weeks posttreatment showed total occlusion consisting of intimal and subintimal changes and organized thrombus in the lumen. This suggests that the EFF probe in comparison with other procedures is an inexpensive, relatively safe precision interventional tool for performing an occlusion for experimental and therapeutic purposes.

Animals↗

PubMed1991

Effects of cocaine on canines' coronary arteries.

Nine canines were anesthetized with pentobarbital and studied by both selective and semiselective coronary artery angiography following intravenous bolus doses of 1,3,5,8, or 10 mg/kg of cocaine. Catheterization was accomplished with a 5 Fr catheter over a 0.035 inch guidewire under fluoroscopic control, and angiograms were obtained by injection of a diatrizoate solution. Digital subtraction angiography (DSA) was performed prior to cocaine administration and at minutes 0.5, 1, 1.5, 3, 5, and, in some cases, minutes 10 and 15 after cocaine administration. The 1 and 3 mg/kg doses of cocaine had no effect on the coronary arteries. The 5 mg/kg dose significantly dilated the coronary arteries. The 8 mg/kg dose produced significant dilation at 30 seconds after cocaine but nonsignificant dilation of the coronary arteries at all other times. The 10 mg/kg dose produced significant dilation at 30 seconds, nonsignificant dilation at 60 seconds followed by significant constriction at 90 seconds after cocaine, which led to immediate death in most animals. The coronary dilation and constriction produced by 10 mg/kg of cocaine could be prevented by either preadministration or postadministration of naloxone, but this did not prevent subsequent death.

Angiography, Digital Subtraction↗

PubMed1988

Properties of electromagnetic field focusing probe.

The electromagnetic field focusing (EFF) apparatus consists of a radio frequency generator, solenoidal coil, and a hand-held or catheter probe. Applications such as aneurysm treatment, angioplasty, and neurosurgery in various models have been reported. The probe is operated in the near field (within one wavelength of an electromagnetic field source) of a coil inducing eddy currents in biological tissues, producing maximal convergence of the induced current at the probe tip. The probe produces very high temperatures depending on the wattage selected for the given radio frequency of output power. The high temperature can be used in cutting, cauterizing, or vaporizing. The EFF probe is comparable to different types of lasers and to bipolar and monopolar cautery. The EFF probe can be used with catheters or endoscopes. Objectives of this study were to determine what the thermal properties of the EFF probe are and how instrument parameters can be varied to obtain different temperatures in the tissue near the probe tip. In this study an F2 catheter was used as an insulated sheath and the tip of the guide wire was used as the probe tip. Different powers, wave forms, coil-to-probe distances, and probe-tip lengths were tested on a phantom that simulates tissue electrical properties. Some of the experiments were conducted under normal saline to simulate treatment of tissue with body fluids such as blood vessels or brain tissue under normal physiologic conditions. It is concluded that the EFF probe has the advantages of easy manipulation, relative safety, cost effectiveness, and a high degree of spatial control.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocoagulation↗

PubMed1988

Electromagnetic field focusing probe (EFFP)--a new angioplasty tool.

An electromagnetic field focusing probe (EFFP) consists of a radiofrequency generator, solenoidal coil, and a hand-held or catheter probe. The probe is operated in the near field (distance within one wave length of an electromagnetic field source) of a coil, which induces eddy current in a biological tissue. The induced eddy current is converged maximally at the tip of the probe upon contact of the tip with the tissue. The probe produces very high temperatures depending on the wattage selected. In this study, the EFFP was used to evaporate atheromatous plaques in human cadaver abdominal aorta specimens, which were then studied histologically. Gas produced by this technique was analyzed and the volume found to be related to power delivered, but in such small amounts as to be of no embolic significance. While temperature varied with wattage and time of application, it was maximal at the probe tip and easily controlled, resulting in clean obliteration of plaque.

Angioplasty, Balloon↗

PubMed1988

Electromagnetic field focusing system in the treatment of brain tumors.

The electromagnetic field focusing (EFF) probe, which is based on the principle of eddy current convergence, produces intense pinpoint heat at its point of contact with tissue. This allows cutting and vaporization of tissue and coagulation of vessels. The present experiments were conducted to study heat distribution to the surrounding tissue in brain and phantom and the effect on the brain of vaporization of intracerebral tumors in 19 rabbits. The follow-up period was as long as 47 days. The heating pattern showed a rise of temperature up to 250 degrees C at the probe tip, with minimal or no temperature increase at 2 mm and beyond. Minimal or no change was noted in the surrounding brain after tumor vaporization, indicating that this system would be safe in the vaporization of brain tumors in clinical neurosurgery.

Animals↗

PubMed1988

Precision surgery with an electromagnetically induced current convergence probe application in aneurysm treatment, angioplasty, and brain tumor resection in in vivo and in vitro models.

A hand-held probe, or one introduced through a catheter, rapidly produces an extremely high, tissue-vaporizing temperature in a precisely defined manner enabling surgeons or interventional radiologists to perform angioplasty, thrombose aneurysms, and vaporize tumors. The probe is operated in a near field of an inductive coil, and the current induced in the biologic tissue is converged maximally at the tip of the probe at the resonance frequency of both the inductor and the probe, producing a maximum temperature in excess of 1400 degrees C. Radio-frequency power controls the probe-tip temperature. The operation of the probe is comparable to that of a CO2 or YAG laser and is complementary to laser-surgical techniques. The low cost relative to lasers and simplicity of the device including its disposable components make the prospect of commercialization of this device promising.

Aneurysm↗

PubMed1987

Proton NMR of human breast tumors: correlation with clinical prognostic parameters.

Proton NMR spectroscopy and imaging of human breast tissue have provided new methods in studying breast carcinomas. Continuous wave proton NMR spectroscopy in this study is able to discriminate breast carcinomas from normal breast tissue on the basis of the integrated area under the water and lipid peaks, width at half height of the water peak, and chemical shift of the lipid peak. In addition, the NMR parameters were correlated with the following clinical and pathologic prognostic indices: TNM tumor stage, nuclear grade, and estrogen receptor status (ER). Width at half height of the lipid peak (1/2 delta lipid) correlated with tumor content and ER. Studies using higher resolution proton or phosphorus NMR spectra may separate signals that can correlate with biological information on breast neoplasms useful to the clinician. Chemical shift of the lipid peak may be used to sharpen contrast on MRI of breast tumors.

Adenofibroma↗

PubMed1987

Electromagnetic field focusing (EFF) probe--a new neurosurgical tool.

The electromagnetic field focusing (EFF) probe is capable of producing well circumscribed, intense heat at the point of contact with the tissue. Experimental studies were carried out to assess this probe as a neurosurgical tool using 38 rats and 4 mice with mammary carcinoma. The study on the rats included study of the cutting, coagulating and vaporizing effect on brain tissue including study of blood brain barrier disruption and heat dissipation. The study on the mice included the study of vaporizing property of the probe on solid tumours. The probe proved to be an excellent tool for cutting, coagulating and vaporizing purposes with very minimal disruption of blood brain barrier and demonstrated well circumscribed heating pattern. The study indicates that this tool combines the beneficial effect of both the YAG and CO2 laser.

Animals↗