PubMed Health⌕ Search

Biomedical subjects

W Yamanashi

Publications and source records attributed to W Yamanashi.

11 recordsLinked to original sources
PubMed2002

Functional analysis of the effect of the posterior stabilising cam in two total knee replacements. A comparison of the Insall/Burstein and Bisurface prostheses.

The Bisurface knee prosthesis (BP) has a posterior stabilising cam (ball-and-socket joint) in the mid-posterior region of the femorotibial joint in an attempt to improve the range of movement. Based on an in vitro weight-bearing study contact areas of the Insall/Burstein 2 (IB2) and the BP knee were compared using pressure-sensitive films. The stability afforded by the cam was evaluated by means of dislocation distances in the vertical and horizontal planes. Significant adverse anterior translation in mid-flexion was not observed with the BP knee since the cam was effective above 60 degrees of flexion. At flexion of 60 degrees or more, the total contact areas were larger, as the cam represented a weight-bearing surface. The dislocation distances for the BP knee compared favourably with those for the IB2 knee. We conclude that the cam of the BP knee allows good movement, stability and wear.

Arthroplasty, Replacement, Knee↗
PubMed2000

Endovascular neural stimulation via a novel basket electrode catheter: comparison of electrode configurations.

We previously showed that parasympathetic stimulation by a basket electrode catheter (BEC) positioned in the superior vena cava (SVC) can slow sinus rate (SR) or ventricular response (VR) during atrial fibrillation (AF). In 11 dogs, anesthetized with Na-pentobarbital, standard ECG leads II and aVR, blood pressure and right atrial electrograms were continuously monitored. Two different BEC configurations (B1, B2) were tested in the SVC. B1 consisted of five metal splines, each 3 cm in length. Stimulation was applied between adjacent splines. B2 consisted of 2 electrodes at opposite ends of each of 5 splines and a larger electrode at the middle of each spline. Stimulation was delivered between the two end electrodes and the middle electrode on the same arm. Stimulation consisted of square wave stimuli, each 0.1 msec duration, frequency 20 Hz at voltages from 1-40 V. Six dogs were studied with B1 and five were studied with the B2 configuration. The average voltage required to produce a 50% decrease in heart rate was 22+/- 12 V when stimulating between adjacent splines (B1) compared to 10+/- 5 V when stimulating along a single spline (B2), a 55% decrease (p</=0.05). During AF, the voltage required to reduce the average ventricular rate to 100 beats/min was 19+/- 13 V for B1 and 8+/- 5 V for B2, a 58% reduction (p</=0.05). Thus, the significant difference between B1 and B2 and in slowing SR or VR during AF was probably due to a greater current density delivered with B2 to the endovascular wall and adjacent neural elements.

Animals↗
PubMed1994

Electromagnetic field focusing instrument augments resection of meningiomas.

The electromagnetic field focusing (EFF) surgical instrument creates an oscillating electromagnetic field that induces eddy currents in the tissue, which converge at the point of contact. This energy creates a focal spark capable of vaporizing tissue. The EFF instrument was used to resect 17 meningiomas in 14 patients. The effectiveness of the EFF probe in resecting tumor tissue was compared with that of the Cavetron ultrasonic surgical aspirator (Model 100) in 11 patients. The EFF system was superior to the Cavetron ultrasonic surgical aspirator in tumor excision in all but two cases, in which the EFF grounding tip was poorly tuned. Surgical time and blood loss were reduced by subjective analysis in all but these two cases, especially in the rubbery or calcified meningiomas resistant to aspiration. No complications were directly attributable to use of the EFF. Drawbacks encountered with the EFF system include buildup of "char" on the tip, requiring scraping, and intense heat at the tip, which occasionally melted the insulating sheath, requiring replacement.

Adult↗
PubMed1994

Electroconvergent cautery.

A new cautery system known as the electroconvergent cautery system is described. This cautery system uses a radiofrequency current of 13.56 MHz. The current is passed through an amplifier, an impedance matching system, and a loading and tuning coil into a probe. After the probe tip is touched to the tissue, the mismatch of impedance between the probe tip and the generator is minimized to almost zero, resulting in high-current density at the probe tip, which causes pinpoint heating of the tissue at the point where it is touched by the probe without spread of heat to the surrounding tissue. This heat can cut and vaporize tissue and coagulate vessels. The probe can also be used to coagulate vessels with standard surgical forceps. Because convergence of energy is used for tissue heating, a grounding pad is not needed. The system can also be used under cerebrospinal fluid or saline.

Astrocytoma↗
PubMed1992

Bacteriophage phi X-174 as an aerobiological marker for surgical plume generated by the electromagnetic field focusing system.

The aerosol of surgical plume could be measured effectively with the use of bacteriophage phi X-174 as a biological marker, in contrast to previous methodologies reported by others. Recovery of virus plaque-forming units was highest from hydrophobic polytetrafluoro-ethylene membranes compared to hydrophobic polycarbonate screen filters or polyvinylidene difluoride depth filters, indicating that the method of virus recovery strongly affects the utility of a virus as an aerobiological marker. With this new method, surgical plume was indeed found in significant amounts when cutting tissue phantoms made with agar containing virus. The Electromagnetic Field Focusing System was used, which is a new thermal surgical device. The nominal power setting did not appear to be a factor in the amount of virus recovered. However, when pulse modulating the power by adjusting the crest factor from 1.4 to 4.3, a measure of the duty cycle for power delivery which adjusted the device from its cutting to haemostatic mode, a nearly five-fold increase in surgical plume, as evidence by the recovery of phi X-174 plaque forming units, was seen. The data indicate that bacteriophage phi X-174 can be used effectively as an aerobiological marker for aerosols generated during clinical procedures, and reinforce the need to use a safety vacuum during aerosol generating procedures. The availability of a safe and economical biological marker for aerosols from clinical procedures, which may lead to acquired infections in hospital personnel, makes evaluation of procedures and containment systems markedly easier. The data also indicates that surgical plume biohazard may be present in other techniques that employ pulse modulation including surgical lasers and electrocauteries.

Aerosols↗
PubMed1992

Stereotactic microsurgical resection of intracranial tumors using the electromagnetic field focusing system.

The intense heat produced at the tip of the electromagnetic field focusing (EFF) probe at its point of contact with tissue can cut and vaporize tissue and coagulate blood vessels. As the probe is shaped like a bayonet and has a diameter of 0.3 mm at its tip, it can be used on deep structures through narrow openings, making it ideal for stereotactic craniotomy. Thirteen stereotactic craniotomy procedures using the EFF system were performed. Locations of the lesions were deep in the cerebrum, cerebellum and in the lateral ventricle. The system proved efficient with reduced blood loss and unobstructed view of deep structures. No complications resulted from the use of the system.

Brain Neoplasms↗
PubMed1990

Electromagnetic field focusing system in clinical neurosurgery--preliminary report.

The electromagnetic field focusing system is capable of sharply focusing induced current resulting in pinpoint heating of tissue. This heat can cut and vaporize tissue while simultaneously coagulating vessels. This is a report on the first 15 consecutive neurosurgical cases where this system was used for tumor excision. The system was found to be an effective and safe surgical tool. It functioned effectively, even under saline and cerebrospinal fluid and through narrow openings during stereotactic microsurgical procedures.

Adult↗
PubMed1988

Electromagnetic field focusing (EFF) probe for intravascular endarterectomy. Preliminary feasibility study.

Vaporization of atheromas in 10 human aorta segments immersed under flowing blood in vitro were done using the EFF probe. No increase in packed cells of the flowing blood following atheroma vaporization were noted suggesting absence of post vaporization debris. No damage to the aorta underlying the vaporized atheroma was noted on light microscopy suggesting well localized vaporization process. This study suggests that EFF probe might be a safe tool for intravascular endarterectomy.

Aortic Diseases↗
PubMed1986

Electromagnetic field focusing (EFF) probe in aneurysm thrombosis. Preliminary report.

Due to its capability of producing a well localized intense heat field of predictable dimensions, the electromagnetic field focusing probe was evaluated experimentally as a surgical tool in aneurysm thrombosis. Aneurysm models were created by anastomosing a segment of vein to the abdominal aorta. Seventy-five such aneurysms were created in seventy-five animals. The aneurysms were then placed under the solenoidal radiofrequency coil and the tip of the field focusing probe was inserted into them. Intense heat was delivered with well defined, effective and quick thrombosis and shrinkage of the aneurysm. Nineteen of the aneurysms were followed for up to one week. Histological studies were conducted showing complete thrombosis of the aneurysm with good preservation of the aorta. With further refinement of this technique, it is hoped that stereotaxic aneurysm thrombosis might be possible.

Aneurysm↗
PubMed1985

Focal heating of V-2 tumors with a hybrid radiofrequency applicator.

A hybrid radiofrequency heating system previously reported to produce highly focused heating patterns at less than or equal to 10 cm depth in phantom models was utilized to selectively heat hypervascular, heat resistant rabbit V-2 tumors implanted in the left hindlimb. Spheroidal heating patterns 3 to 4 cm in diameter with minimal temperatures of 43 degrees C to 46 degrees C in two non-field perturbing probes at opposing edges of the tumor were consistently produced; however, temperature maxima 0.5 +/- 0.4 to 8.6 +/- 5.9 degrees C above minimum target temperatures of 43 degrees C and 46 degrees C, respectively, were observed. This led to both tumor regressions and adjacent normal tissue damage in some animals. These findings suggest this system may have application to selective heating of deep seated tumors, but that problems related to accurate thermal mapping and to intratumor temperature distribution must first be resolved.

Animals↗