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PubMedDate not supplied

Preferred method for insertion of the Toronto Stentless Porcine Valve.

The Toronto Stentless Porcine Valve has been extensively used for aortic valve replacement. A standardized, detailed description of a preferred operative technique has been absent from the literature. A method is described that stresses (a) proper position and orientation of the aortotomy, (b) debridement of the diseased native valve, (C) proper sizing of the aortic root and choice of prosthesis and (d) implantation of the valve. Using this technique, the prosthesis can be reproducibly implanted with relative ease, without valvular insufficiency or coronary obstruction.

Aortic Valve↗
PubMed2003

Diagnostic and technical approach to esthetic rehabilitations.

The success of an esthetic rehabilitation depends on the understanding of the patient's needs and on effective communication among the entire dental team. The involvement of the dental technician since the beginning of the treatment plan is one of the keys for success. This article describes a systematic approach to oral rehabilitations involving esthetic areas. Technical suggestions for the construction of the diagnostic wax-up, the provisional, and the final ceramic restorations are illustrated in a logical sequence.

Crowns↗
PubMed2000

Orofacial prosthesis design and fabrication using stereolithography.

The use of stereolithography for the manufacture of implantable prostheses is relatively new. Until now, its use with regard to mandibular resection has been to produce pre-operative models that allow more sophisticated planning of the contour and better preparation of the metallic framework to be implanted. This framework rejoins the sections of the mandible, returning some function, but providing no soft tissue support. Hence, the aesthetic results are not optimal. The aim of this study was to investigate the accuracy with which a stereolithographic model could be made to completely reunite both surfaces of the resected mandible and restore full contour. The design and fabrication of a mandibular prosthesis utilizing CAD/CAM technology and stereolithography is still in the early stages, but initial results indicate that with further research and better tools this could provide a new approach to mandibular resections, providing better aesthetic results.

Computer-Aided Design↗
PubMed2000

Optimization of design and surgical positioning of inflatable penile prostheses.

The interaction between the cylinders of an inflatable penile prosthesis (IPP) and the surrounding tissues during IPP-aided erection may result in local elevated stresses. These stresses may reach values that can obstruct penile blood vessels and cause ischemia and/or stimulate nerves around the operation site, thereby inducing sensations of pain. A new numerical model was used to analyze penile stresses postimplantation of different IPP types, in order to optimize prosthesis design and surgical positioning by enabling minimal stress transfer to dorsal blood vessels and nerves. The results suggest that intraluminal pressures should be maintained at low levels (about 80 kPa) while cylinder thickness and stiffness should be kept just high enough (approximately 15% of the radius and 1000 MPa, respectively) to eliminate deleterious cylinder-tissue contact stresses. Smaller prosthetic cylinders, i.e., occupying about 45% of the cavernosal space, may be advantageous in terms of reducing dorsal stresses, but lower penile rigidity should be expected. A significant decrease of dorsal stresses can also be achieved by encouraging the surgeon to position the cylinders toward the lower part of the corpora. The numerical simulations indicate that circular cylinders may allow greater biomechanical compatibility of the IPP with the penis structure than elliptic ones, and this should be a subject for clinical investigations.

Biomechanical Phenomena↗
PubMed2006

Acetabular cup geometry and bone-implant interference have more influence on initial periprosthetic joint space than joint loading and surgical cup insertion.

Environmental variations in patient-dependent and surgical factors were modeled using robust optimization with a finite element acetabular cup-pelvis model. A previously developed statistical optimization scheme was used to: (1) determine the cup geometry and the optimal cup-bone interference that maximized bone-implant contact areas and minimized changes in the gap volume between the implant and bone surface during gait loading and unloading; and (2) determine the relative contributions of design, patient-dependent, and surgical factors to variations in bone-implant contact areas and a change in gap volume. The statistical analyses indicated that the design variables, namely the equatorial diameter and eccentricity, explained most of the variations in the performance measures. Further, the hemispherical designs performed better than the nonhemispherical designs. The 58 mm hemispherical cup, with 2 mm diametral interferences, minimized the change in gap volume and attained 82% and 81% of the maximum predicted total and rim contact areas, respectively. The equatorial diameter and eccentricity, not the patient-dependent and surgical factors, explained most of the variations in the performance measures. Perfect surface apposition was not attained with any of the cup designs.

Acetabulum↗
PubMed2005

Digital correction of magnification in pelvic x rays for preoperative planning of hip joint replacements: theoretical development and clinical results of a new protocol.

The introduction of digital radiological facilities leads to the necessity of digital preoperative planning, which is an essential part of joint replacement surgery. To avoid errors in the preparation and execution of hip surgery, reliable correction of the magnification of the projected hip is a prerequisite. So far, no validated method exists to accomplish this. We present validated geometrical models of the x-ray projection of spheres, relevant for the calibration procedure to correct for the radiographic magnification. With help of these models a new calibration protocol was developed. The validity and precision of this procedure was determined in clinical practice. Magnification factors could be predicted with a maximal margin of error of 1.5%. The new calibration protocol is valid and reliable. The clinical tests revealed that correction of magnification has a 95% margin of error of -3% to +3%. Future research might clarify if a strict calibration protocol, as presented in this study, results in more accurate preoperative planning of hip joint replacements.

Algorithms↗
PubMed2001

Psychophysical recovery from single-pulse forward masking in electric hearing.

Psychophysical single-pulse forward-masking (SPFM) recovery functions were measured for three electrodes in each of eight subjects with the nucleus mini-22 cochlear implant. Masker and probe stimuli were single 200-micros/phase biphasic current pulses. Recovery functions were measured at several masker levels spanning the electric dynamic range of electrodes chosen from the apical, middle, and basal regions of each subject's electrode array. Recovery functions were described by an exponential process in which threshold shift (in microA) decreased exponentially with increasing time delay between the masker and probe pulses. Two recovery processes were observed: An initial, rapid-recovery process with an average time constant of 5.5 ms was complete by about 10 ms. A second, slow-recovery process involved less masking than the rapid-recovery process but encompassed much longer time delays, sometimes as long as several hundred milliseconds. Growth-of-masking slopes for the rapid process depended upon time delay, as expected in an exponential recovery process. Unity slopes were observed at a time delay of 0 ms, whereas progressively shallower slopes were observed at time delays of 2 ms and 5 ms. Many recovery functions demonstrated nonmonotonicities or "facilitation" at very short masker-probe delays (1-2 ms). Such nonmonotonicities were usually most pronounced at low masker levels. Time constants for the rapid-recovery process did not vary systematically with masker level or with electrode location along the implanted array. Most subjects demonstrated rapid-recovery time constants less than 7 ms; however, the subject with the longest duration of deafness prior to implantation exhibited clearly prolonged time constants (9-24 ms). Time constants obtained on basal electrodes were inversely related to word recognition scores.

Adult↗
PubMed2004

Effect of handset proximity on hearing aid feedback.

The increased sensitivity of hearing aids to feedback as a telephone handset is brought near has been studied experimentally and numerically. For the measurements, three different hearing aids were modified so that the open-loop transfer function could be measured. They were mounted in the pinna of a mannikin and the change in open-loop transfer function determined as a function of handset proximity. Increases of over 20 dB were observed, most of this change occurring within the first 10 mm of separation between pinna and handset. Numerical calculations performed using a boundary element technique were in good agreement with the measurements.

Acoustics↗
PubMed2004

Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds.

Interactions among the multiple channels of a cochlear prosthesis limit the number of channels of information that can be transmitted to the brain. This study explored the influence on channel interactions of electrical pulse rates and temporal offsets between channels. Anesthetized guinea pigs were implanted with 2-channel scala-tympani electrode arrays, and spike activity was recorded from the auditory cortex. Channel interactions were quantified as the reduction of the threshold for pulse-train stimulation of the apical channel by sub-threshold stimulation of the basal channel. Pulse rates were 254 or 4069 pulses per second (pps) per channel. Maximum threshold reductions averaged 9.6 dB when channels were stimulated simultaneously. Among nonsimultaneous conditions, threshold reductions at the 254-pps rate were entirely eliminated by a 1966-micros inter-channel offset. When offsets were only 41 to 123 micros, however, maximum threshold shifts averaged 3.1 dB, which was comparable to the dynamic ranges of cortical neurons in this experimental preparation. Threshold reductions at 4069 pps averaged up to 1.3 dB greater than at 254 pps, which raises some concern in regard to high-pulse-rate speech processors. Thresholds for various paired-pulse stimuli, pulse rates, and pulse-train durations were measured to test possible mechanisms of temporal integration.

Analysis of Variance↗
PubMed2005

Surgical coverage of exposed hydroxyapatite implant with retroauricular myoperiosteal graft.

BACKGROUND: With the increasing use of hydroxyapatite orbital implants, the complication of exposure has become apparent to oculoplastic surgeons. Many kinds of patch grafts, such as sclera, dermis, and hard palate mucosa, have been used to cover exposed hydroxyapatite implants with inconsistent results. In this study, the authors use a newly developed technique, autogenous retroauricular myoperiosteal graft, and the results are reported. METHODS: A piece of retroauricular muscle together with its underlying periosteum was carefully harvested. This myoperiosteal graft was patched to the debrided hydroxyapatite exposure area with the periosteal surface facing outward. The margin of periosteal surface was secured with conjunctiva and left uncovered for the surrounding conjunctiva to epithelialise. RESULTS: Nine eyes with hydroxyapatite exposure more than 3 mm were managed with autogenous retroauricular myoperiosteal grafts. Seven cases were successfully treated with single graft surgery. The other two cases needed an additional graft surgery, and there was no re-exposure noted thereafter. Five patients received a successful insertion of the motility peg. All nine patients have been fitted with prosthesis with reasonable motility. There were no complication noted during more than 1 year of follow up. CONCLUSION: The thick composite nature of the myoperiosteal graft provides a durable and vascularised coverage for exposed hydroxyapatite implants. This technique offers an encouraging alternative for the management of exposed hydroxyapatite implants.

Adult↗
PubMed1998

Clinical results of implantation of the Chirila keratoprosthesis in rabbits.

AIMS/BACKGROUND: An ideal keratoprosthesis (KPro) would closely resemble a donor corneal button in terms of its surgical handling, optics, and capacity to heal with host tissue in order to avoid many of the complications associated with the KPros which are currently in clinical use. This study was carried out to assess the long term clinical outcomes on implantation of the core and skirt poly(2-hydroxyethyl methacrylate) KPro in animals. METHODS: 20 KPros were made and implanted as full thickness corneal replacements into rabbits and followed for up to 21 months to date. RESULTS: 80% of the prostheses have been retained, with a low incidence of complications such as cataract, glaucoma, and retroprosthetic membrane formation which are frequently associated with KPro surgery. CONCLUSIONS: KPros of this type may offer promise in the treatment of patients for whom penetrating keratoplasty with donor material carries a poor prognosis. Refinement of the KPro and further animal trials, including implantation into abnormal corneas, are however mandatory before human implantation could be planned.

Animals↗
PubMed2005

Prosthesis-patient mismatch: definition, clinical impact, and prevention.

Prosthesis-patient mismatch (PPM) is present when the effective orifice area of the inserted prosthetic valve is too small in relation to body size. Its main haemodynamic consequence is to generate higher than expected gradients through normally functioning prosthetic valves. This review updates the present knowledge about the impact of PPM on clinical outcomes. PPM is common (20-70% of aortic valve replacements) and has been shown to be associated with worse haemodynamic function, less regression of left ventricular hypertrophy, more cardiac events, and lower survival. Moreover, as opposed to most other risk factors, PPM can largely be prevented by using a prospective strategy at the time of operation.

Aortic Valve↗
PubMed2006

Prediction of valve prosthesis-patient mismatch prior to aortic valve replacement: which is the best method?

BACKGROUND: To predict the occurrence of valve prosthesis-patient mismatch (VP-PM) after aortic valve replacement (AVR), the surgeon needs to estimate the postoperative effective orifice area index (EOAI). AIM: To compare different methods of predicting VP-PM. METHODS: The effective orifice area (EOA) of 383 patients who had undergone AVR between July 2000 and January 2005 with various aortic valve prostheses was obtained echocardiographically 6 months after the operation. We tested the efficacy of (1) EOAI calculated from the echo data obtained in our own laboratory, (2) indexed geometric orifice area, (3) EOAI estimated from charts provided by prosthesis manufacturers (which are based either on in vitro or on echo data) and (4) EOAI estimated from reference echo data published in the literature to predict VP-PM. RESULTS: Sensitivity and specificity to predict VP-PM were 53% and 83% (method 1), 80% and 53% (charts based on echo data, parts of method 3) and 71% and 67% (method 4) using reference data derived from echocardiographic examinations. The sensitivity of method 2 and of charts based on in vitro data (parts of method 3) to predict VP-PM was 0-17%. The incidence of severe VP-PM could be reduced from 8.7% to 0.8% after the introduction of the systematic estimation of the EOAI at the time of operation (p = 0.003, method 1). CONCLUSIONS: The best method of predicting VP-PM is the use of mean (SD) EOAs derived from echocardiographic examinations, whereas the use of in vitro data or the geometric orifice area is unreliable. After the surgeon's anticipation of VP-PM prior to AVR, the incidence of VP-PM could be reduced.

Aged↗
PubMed1995

Patient satisfaction: an indicator of quality in disablement services centres.

OBJECTIVES: To develop a patient satisfaction system for disablement services centres and to report on how the initial findings have been used in audit to improve their quality of care and services. DESIGN: Interview survey of randomly selected users attending in three centres: Birmingham (centre X), Oxford (centre Y), and Cambridge (centre Z) to establish core topics for developing a patient satisfaction questionnaire with incorporation into a computer patient satisfaction system (PATSAT) to enable collation of responses to the questionnaire. A pilot of the questionnaire was undertaken in the centres to assess the sensitivity of the questionnaire, which was subsequently used as part of clinical audit process during June 1991 and April 1992 in centre X and the patient satisfaction system used to monitor changes in routine practice. PATIENTS: 123 amputees in the development phase, selected by cluster sampling, and 1103 amputees in the pilot study. MAIN MEASURES: Satisfaction scores for components of the service. RESULTS: The questionnaire included 16 core topics contributing to quality of care and services, including comfort of limbs, appointments, interpersonal aspects of care, a system of support and counselling, and organisation. The pilot survey demonstrated high satisfaction scores for aspects of interpersonal care, organisation, and physical surroundings of the centres and lower satisfaction for counselling services, comfort of the limb and the number of alterations made before the limb was considered acceptable. During the audit in centre X these results prompted changes to care and services which produced significant improvements in satisfaction. CONCLUSIONS: The early results suggest that the questionnaire, coupled with PATSAT software system, enable users' views to be expressed, collated, and fed back to staff; the information provided has already prompted change, and the system is sufficiently sensitive to measure changes in satisfaction with the service.

Adolescent↗
PubMedDate not supplied

Electric-acoustic stimulation of the auditory system. New technology for severe hearing loss.

Various devices have been developed to overcome the widespread phenomenon of different degrees of hearing deficits between mild and profound hearing loss. Basically, we differentiate between acoustic stimulation (hearing aids), restricted to cases with a partially functioning cochlear receptor, and electrical stimulation (cochlear implants), stimulating the auditory nerve directly in cases with profound or total hearing loss. For the first time, animal data have been collected that indicate the possibility of nearly interference-free use of both stimulation types simultaneously. In addition, we have gathered the first clinical patient experience, which confirms the encouraging results. Future implications for patients with severe high-frequency hearing loss are discussed.

Acoustic Stimulation↗
PubMed1999

Postoperative lens position preoperatively determined by Scheimpflug photography.

The position of the artificial lens has an important influence on refractive power calculation. We compared the position of the crystalline lens with that of the artificial lens after cataract surgery by means of Scheimpflug photography. A difference in position of approximately 0.8 mm in the anterior direction could be determined.

Cataract Extraction↗