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Biomedical subjects

G J Verkerke

Publications and source records attributed to G J Verkerke.

At least 19 recordsLinked to original sources
PubMed2003

Precision, comfort and mechanical performance of the Quadriso-tester, a quadriceps force measuring device.

The mechanical performance, repeatability and comfort of the Quadriso-tester, which assesses isometric knee extensor muscle strength, were examined. Twenty healthy subjects and 20 patients treated for unilateral anterior ligamenta cruciata insufficiency were tested. Intra-rater repeatability was determined by the testing and retesting of subjects and calculation of the intra-class correlation coefficient and the mean difference between test and retest values. The comfort level was determined a questionnaire. Measuring time was recorded, and the relationship between knee angle and extension moment was plotted. Strength and stiffness were determined using the finite element method. Intra-rater repeatability was high; the intra-class correlation coefficient of the right and left leg was 0.90 and 0.91, respectively; the coefficient of variation was 6.4 and 6.0%, respectively. The median comfort score of the healthy subjects was 7, and that of the patients was 9. Measuring time remained within 30 min. Misalignment of the knee and sidebar axis disturbed the relationship between knee angle and extension moment Strength and stiffness were higher than required. In conclusion, the Quadriso-tester is a comfortable and fast device to determine quadriceps force with a high repeatability. The knee and sidebar axis should be well aligned.

Adult↗
PubMed2003

Change of required foot impact position during running to exhaustion on a treadmill.

In healthy human subjects running on a treadmill, measurements were made to determine how rapidly and precisely they were able to adjust the impact position of their feet using visual clues. Foot impact position was measured with force transducers at each corner of the treadmill. Required longitudinal positions were indicated by three lines of light ("target-lines"), projected transversely across the treadmill plate. Test runs were conducted until exhaustion at speeds exceeding the aerobic threshold (mean endurance time about 9 min; mean belt speed 12 km/h, mean inclination 6.9 %). During running, required foot positions were, at irregular intervals and during periods of 7 steps each, temporarily switched from the most posterior target-line (TL3) to one of the two more anterior ones (TL2 or TL1). The first change of foot impact position took place within about 175 - 225 ms after a switch from TL3 to TL2/TL1; this initial small change was in a direction opposite to that required. The total adjustment of foot impact position, as seen during 7 consecutive test steps, took place during at least 2 - 3 steps (0.8 - 1.2 s). Towards the end of the test run, with exhaustion approaching, the adjustment process became somewhat slower and showed an increasing lengthwise deficit. Our results demonstrate the existence of prolonged multi-step processes of motor adjustment during treadmill running plus a sensitivity of the foot placement process to time-on-task (when approaching exhaustion?).

Adult↗
PubMed2002

Groningen temporomandibular joint prosthesis. Development and first clinical application.

Patients with a severely degenerated temporomandibular joint (TMJ) may benefit from an alloplastic TMJ replacement. The aim of the study was to develop a safe and properly functioning TMJ prosthesis. The design was based on imitation of anterior condylar translation by an inferiorly located centre of rotation, unrestricted mandibular movements by a double articulation, correct fit to the skull by a self-adjusting skull part consisting of two connected parts, and stable fixation by bone screws that are rigidly connected to the prosthesis parts. The prosthesis consists of a titanium skull part with ceramic inlay, a titanium mandibular part with a ceramic spherical head, and an intervening polyethylene disc. Titanium-alloy bone screws are used for fixation. All parts are available in a number of different shapes. In vitro laboratory and in vivo animal tests showed a low wear rate, the possibility of a close fit to the skull, a stable fixation, sufficient mechanical strength, appropriate choice of materials and proper functioning. Thereafter the step to first patient application was made. First patient application was carried out without adverse events. In conclusion, the presented TMJ prosthesis passed the pre-clinical tests and has progressed to clinical application. The fit to the skull, the expected lifetime of the device and the reliability of the implantation procedure require further evaluation in well-designed clinical trials.

Adult↗
PubMed2002

On the determination of the angular orientation of a vertebra.

In this paper we consider the spatial orientation of vertebrae. We take the view that, in determining their rotation angles from X-rays, the procedure applied by Drerup yields the most reliable empirical results, viz. the three angles through which a vertebra rotates about its own symmetry axes in a specific sequence. With a view to the further use of this information to analyze deformations or the motion of a spine we recommend that the Drerup angles be converted into the well-known Eulerian angles. How this can be done is the subject of this report.

Algorithms↗
PubMed2002

Glottal flow through a two-mass model: comparison of Navier-Stokes solutions with simplified models.

A new numerical model of the vocal folds is presented based on the well-known two-mass models of the vocal folds. The two-mass model is coupled to a model of glottal airflow based on the incompressible Navier-Stokes equations. Glottal waves are produced using different initial glottal gaps and different subglottal pressures. Fundamental frequency, glottal peak flow, and closed phase of the glottal waves have been compared with values known from the literature. The phonation threshold pressure was determined for different initial glottal gaps. The phonation threshold pressure obtained using the flow model with Navier-Stokes equations corresponds better to values determined in normal phonation than the phonation threshold pressure obtained using the flow model based on the Bernoulli equation. Using the Navier-Stokes equations, an increase of the subglottal pressure causes the fundamental frequency and the glottal peak flow to increase, whereas the fundamental frequency in the Bernoulli-based model does not change with increasing pressure.

Air Pressure↗
PubMed2002

Improving the fixation of an artificial intervertebral disc.

The fixation of an artificial intervertebral disc has been studied especially with respect to the dimensions, the convexity of the endplates and the size of the fixation elements. From literature and cadaveric vertebrae, the dimensions and shape of the lumbar vertebral endplates were determined and the dimensions of fixation ribs for the artificial intervertebral disc were calculated. To withstand shear forces and prevent dislocation, two sagittal ribs, each 3.5 mm in height and at least 20 mm in length and four transversal ribs, each 1.5 mm in height and with a total length of 60 mm are sufficient. A range of five different sagittal diameters was selected as sufficient for all patients. At least 72.6 % of the endplate of the vertebrae is covered. A convexity with a radius of 140 mm limits the gap to 0.62 mm.

Biomechanical Phenomena↗
PubMed2001

A novel tracheal tissue connector for fixation of laryngeal prostheses.

A tissue connector (TC), basically consisting of a ring that will be integrated into the trachea, is under development to study the fixation of laryngeal prostheses. Two experiments have been performed to test the TC in goats. In experiment 1, a polypropylene mesh was implanted around the trachea. The meshes were explanted after 6 and 12 weeks. In experiment 2, the actual TC consisted of two titanium rings (inner ring and outer ring) executed as quarter rings, fixed on each other, and a polypropylene mesh like a sandwich in between. The titanium inner ring was implanted between two tracheal rings thus penetrating the trachea with the mesh around the trachea and the fixed titanium outer ring on the outside of the trachea. The TCs were removed after 12 weeks. Experiment 1 showed that the mesh was entirely infiltrated by host tissue. Inflammatory cells and high vascularisation were observed in 3 of 4 implants. However, in experiment 2, the mesh was completely incorporated by mature connective tissue without inflammation reaction. At some areas, deposition of cartilage tissue was observed. In conclusion, the TC was firmly embedded in the trachea thus being appropriate for its intended use.

Animals↗
PubMed2001

[Tracheostomy valve with integrated cough flap for improving hands-free speech in laryngectomized patients--development and clinical applications].

BACKGROUND: Following successful voice restoration after laryngectomy either by a voice prosthesis, a surgical shunt or microvascular laryngoplasty, a further goal in rehabilitation is the insertion of a tracheostoma valve, which enables the patient to speak without using his fingers for closure of the tracheostoma. One important disadvantage of the tracheostoma valves, which are available today, is the necessity of removal of the valve in case of coughing, because the valve could be thrown from the stoma by the strong air flow during coughing. As many laryngectomies suffer from chronic bronchitis, this coughing problem is one of the reasons why only few patients could be provided with this useful aid. METHOD: At the department of biomedical engineering of the faculty of medicine at the university of Groningen, the Netherlands, 1994 two prototypes of a tracheostoma valve with an integrated cough lid were developed. These devices contain two separate valve systems: the normal speaking valve and a special coughing valve, which opens at a certain air flow and closes automatically after the coughing attack. Thus no manipulations are necessary during coughing, the patient can speak undisturbed. The ADEVA company (Lübeck, Germany) undertook the industrial production of this new type of tracheostoma valve creating different modifications of the prototype #2. PATIENTS: In four series with 6-8 patients per group the modified tracheostoma valves were tested clinically and the occurring faults or lack of correct function eliminated by small changes in the production. RESULTS: Meanwhile a suitable model for routine use is available, which was tested in 30 patients so far. This suitability was achieved by improvements in the valve mechanism, the valve seal and the adjustment mechanisms for the individual pressure level of the speaking and the coughing valve. CONCLUSION: The newly developed tracheostoma valve with integrated coughing lid (Window, ADEVA-medical Company, Lübeck, Germany) provides further improvement in speech rehabilitation of laryngectomies. The low acceptance of tracheostoma valves, which enable the patient to speak without using his fingers for closure of the tracheostoma, possibly may be raised by this new aid.

Bronchitis↗
PubMed2001

Airflow resistance of airflow-regulating devices described by independent coefficients.

Rehabilitation after laryngectomy includes more and more the use of airflow-regulating devices such as shunt valves (SVs), tracheostoma valves (TSVs), and heat and moisture exchange (HME) filters. In determining the quality of those devices, airflow resistance is a very important factor. It is currently defined as pressure drop divided by airflow. However, for most applications, this definition does not result in a pressure- and airflow-independent parameter. Therefore, a new set of parameters is defined and applied to pressure-airflow curves of airflow-regulating devices. Pressure drop over TSVs and HME filters appears to have a squared relationship with flow. In SVs, it has a linear relationship. The new set of parameters describes the pressure-airflow relationship properly for all considered devices. In conclusion, theoretical predictions of flow mechanics appear to be valid for SVs, TSVs, and HME filters. Only 2 coefficients are necessary to describe the pressure-flow characteristics of these airflow-regulating devices, independent of pressure drop over and flow through the device.

Airway Resistance↗
PubMed2001

Design and analysis of coupling methods for modular endoprosthetic systems as an alternative to the conical coupling.

Modular endoprostheses are often used in bone tumor management. However, the conical coupling that connects the various modules has several shortcomings. As an alternative, four new couplings have been developed. To find out if they have sufficient strength and show no movement during loading, each coupling was analysed using the finite element method. Bolt force and friction coefficient was varied to examine their influence. From the analysis it was concluded that coupling B, a dovetail coupling, meets all requirements and is the best alternative to the conical coupling. Sensitivity to bolt force and friction coefficient is very limited.

Biomechanical Phenomena↗
PubMed2001

Requirements for an artificial intervertebral disc.

Intervertebral disc degeneration is an important social and economic problem. Presently available artificial intervertebral discs (AIDs) are insufficient and the main surgical intervention is still spinal fusion. The objective of the present study is to present a list of requirements for the development of an AID which could replace the human lumbar intervertebral disc and restore its function. The list addresses geometry, stiffness, range of motion, strength, facet joint function, center of rotation, fixation, failsafety and implantation technique. Date are obtained from the literature, quantified where possible and checked for consistency. Existing AIDs are evaluated according to the presented list of requirements. Endplate size is a weak point in existing AIDs. These should be large and fit vertebral bodies to prevent migration. Disc height and wedge angle should be restored, unless this would overstretch ligaments. Finally, stiffness and range of motion in all directions should equal those of the healthy disc, except for the axial rotation to relieve the facet joints.

Biomechanical Phenomena↗
PubMed2001

Flow analysis in vascular shunts that bypass the carotid artery.

When blood flow through a carotid artery is impaired and vascular surgery is necessary to restore adequate circulation a vascular shunt can be applied to maintain cerebral blood flow. Several vascular shunts are commercially available, but there is only limited test data on their flow capacity. The purpose of this study is to determine the flow capacity of three vascular shunt systems. A theoretical model has been developed for this purpose. To validate the model, in vitro flow measurements were taken. Application of the model showed that all shunts cause a decrease in blood flow. The amount of flow decrease varied widely from 13% (Javid shunt) to 55% (Pruitt-Inahara). In vitro measurements confirmed the validity of the model. In conclusion, it is important for the vascular surgeon to realise that vascular shunts show large differences in flow capacity. Of the three investigated shunts, the Javid has the highest flow capacity.

Arteriovenous Shunt, Surgical↗
PubMed2000

Assessing medical technologies in development. A new paradigm of medical technology assessment.

OBJECTIVE: Our study aims to provide a practical contribution to the field of medical technology assessment within a new paradigm. This paradigm indicates the need for more comprehensive technology assessments in the development stage of a new technology. METHOD: We introduce a method, based on Saaty's Analytic Hierarchy Process, which quantitatively supports discussions between the various actors that shape the technology's development and diffusion. These discussions focus on technical, medical, social, and economical requirements relevant to the design and diffusion of the new technology. DISCUSSION: In contrast to more traditional technology assessments, our method encompasses the perspectives of the diverse actors in the social context of technology development and diffusion. It influences their decision making on technology design and diffusion in order to improve this technology's later clinical as well as social effectiveness.

Decision Support Techniques↗
PubMed2000

A short-term study in sheep with the Groningen temporomandibular joint prosthesis.

As part of the pre-clinical testing process of a newly developed temporomandibular joint (TMJ) prosthesis, animal experiments were performed. In 14 sheep, the right TMJ was replaced by the developed TMJ prosthesis. The prosthesis consisted of a skull part, a mandibular part and an intervening polyethylene disc. In the first series (6 sheep), three designs were tested, differing in the applied metal (stainless steel or titanium) and in the fitting method of the skull part (a fitting member or bone cement). The sheep were sacrificed after 8-16 weeks. In the second series (8 sheep), the preferred titanium fitting member design was applied, and the sheep were sacrificed after 2-10 weeks. One sheep was excluded because no correct position of the prosthesis parts could be achieved. At sacrifice, the removal torque of the screws was measured, and the surrounding tissues were harvested for histologic examination. The sheep recovered well and functioned until the end of the scheduled sacrifice date. Encountered problems were two disc dislocations, one fistula formation, and one screw failure. All mandibular parts were clinically stable, as were most skull parts with a fitting member, and one of both skull parts fitted with bone cement. The clinically observed stability was confirmed by the removal torque values, which indicated well-integrated screws. It is concluded that the TMJ prosthesis could remain stable and functional over the initial healing period. The main restriction of the sheep model is the much larger translatory capacity compared with patients, which adversely influences tissue healing.

Animals↗
PubMed2000

Fitting a temporomandibular joint prosthesis to the skull.

Fitting a temporomandibular joint (TMJ) prosthesis to the skull by using stock prostheses seems to be an appropriate method. However, fitting the skull with one stock part requires many differently shaped parts. Therefore, we fitted the skull with two connected stock parts. The aim of the study was to test whether it is possible to achieve a close fit to the skull with this design, with a maximum of 10 different parts. The articular eminence was fitted with a gully-shaped fitting member, which was rotationally connected to a basic part that fitted to the lateral side of the TMJ. The relevant dimensions of 20 dry skulls were measured and the results were used to derive the optimal dimensions of the prosthesis parts. Prototypes were subsequently fabricated. The fit of the prototypes was tested by measuring the maximum gap between fitting member and skull. All skulls could be fit with a set of four different basic parts and three different fitting members. The average maximum gap between fitting member and skull was 0.20 mm (range 0.11-0.43 mm). It was concluded that a close fit to the skull can be achieved with two connected stock parts and with a total number of seven parts.

Feasibility Studies↗
PubMed2000

Design and test of a vascular access device.

Transarterial left ventricular assist devices (LVADs), such as the Hemopump, IABP, and PUCA-pump, are meant to be introduced into the body via the femoral or axillary artery without major surgery. For certain applications, introduction is performed directly into the aorta via an open thorax procedure. A prototype of a vascular access device has been realized that allows direct access into the aorta as an alternative for the common surgical graft anastomosis suturing technique. The device consists of a metal tube acting as a circular knife to cut a hole in the aortic wall, a screw to store the removed part of the aortic wall, and a plastic tube that is introduced through the hole and tightly connected to the aortic wall. The device could be placed without aortic clamping. The device has been tested on a slaughterhouse porcine aorta. A low-pressurized aorta appeared to be the worst case; thus, two animal experiments in the low-pressurized pulmonary artery were performed. No leakage occurred for pressures between 40 and 300 mm Hg.

Anastomosis, Surgical↗
PubMed2000

Comparison of two systems for rigidly connecting 2.0-mm bone screws to an implantable device: in vitro stability testing.

The stability of a screw-fixed implantable device can be improved by eliminating the freedom of movement between the screws and the device. Two systems have been developed for rigidly connecting 2. 0-mm bone screws to an implantable device, and the aim of this study was to test and compare the stability of the two systems. In system A, a fixing disc locked the screw-head. In system B, the thread of the screw locked directly into the device. The stability of the connection was tested by measuring the resistance against a torque on the screw, against shear loading, against push-out loading, and against dynamic shear loading (70 N) for 5 million cycles. Both systems met the required minimum values for the resistance against a torque, shear loading and push-out loading, and dynamic shear loading did not cause movements between the screw and the device. We conclude that both systems are stable, but prefer system B because it is easier to make and implant than system A.

Bone Plates↗