Gj Verkerke

Design of a Lengthening Element for a Modular Femur Endoprosthetic System

A malignant tumour may develop around the knee joint of a child. In the majority of cases it will then be necessary to resect the involved bone with adjacent tissue. A joint team of Groningen University Hospital and University of Twente is currently working on the project of developing a modular endoprosthetic system to bridge the defect resulting from the resection. Since the other, normal, leg continues to grow, the endoprosthetic system will have to include an element the length of which can be adjusted non-invasively. The main conditions to be met by the lengthening element are non-invasive continuous adjustability and a maximum total lengthening of 114 mm. This was achieved by using an external magnetic field. Animal experiments showed that the lengthening element worked well, although moisture infiltrated the telescopic tubes and the lengthening element was covered by proliferating bone at an early stage. Also, the necessary magnetic field proved to be larger than calculated. In a revised design, these problems are resolved. In vitro tests show that the new lengthening element meets all requirements.

Numerical modelling of blood flow behaviour in the valved catheter of the PUCA-pump, a LVAD.

Mechanical heart assistance, performed by the PUIsatile CAtheter (PUCA) pump, chronologically takes place by sucking blood from the left ventricle and ejecting it into the ascending aorta. Within the pump activity the problem of hemolysis and clotting is encountered. In this study the influence of valve geometry on blood cell damage and stagnant zones has been investigated. A variable valve length coupled to a catheter ejection gap and a variable valve angle have been studied. In case of the studied valve, optimal parameter values have been determined. Compared to small catheter ejection gaps with a corresponding valve length, blood damage is found to be less for large ejection gaps with corresponding valve dimensions. In systole a valve positioned in a 0° angle proves to be best, whereas in diastole a +20° angle is preferable. Because the system is operating in both systole and diastole, a 0° angle valve is applied.

Determination of parameters for lumped parameter models of the vocal folds using a finite-element method approach

To study the mechanical behavior of the vocal folds, lumped parameter models of the vocal folds have been developed in the past. Coupling with a model of the aerodynamics in the glottis provides the possibility of simulating glottal waves. A new method is presented to obtain values for the masses and springs of the lumped parameter models by using a finite-element method model of the vocal folds. This finite-element method model is based on geometry and material data from the literature, resulting in a model that describes the vocal fold in a realistic way. Requiring the dynamic behavior of the lumped parameter model of the vocal fold to be equal to the dynamic behavior of the finite-element method model of the vocal fold, parameter values are obtained that are purely based on dynamic considerations. Therefore, the behavior of the vocal folds is described in a realistic way by these parameters. These values are compared with the values used by previous authors and are implemented in lumped parameter models. Self-sustained oscillation is achieved with the new values for masses and springs.

Design and in vitro testing of a voice-producing element for laryngectomized patients.

A voice-producing element has been developed to improve speech quality after laryngectomy. The design process started with the formulation of a list of requirements. The lip principle has the best potential for fulfilling the requirements. A numerical model was made to find the optimal geometry of an element based on the lip principle. Extensive in vitro tests were performed to check all requirements. For this a test set-up with realistic acoustic and aerodynamic properties was developed. Results show that the protruding lip length dominates fundamental frequency, cross-sectional area dominates flow resistance and relation between flow and fundamental frequency. Most requirements have been fullfilled; both for males and females a potentially good functioning prototype could be selected. Clinical experiments will be performed to confirm the quality of the voice-producing prosthesis.

Design and test of a hands-free tracheostoma valve to improve the rehabilitation process after laryngectomy.

The surgical treatment of throat cancer often requires total laryngectomy. The necessary tracheostoma attracts attention, especially during speech, when one must close it manually to force air into the esophagus. To avoid this manual control, several devices have been developed. These must be placed in or around the tracheostoma and possess a valve which closes with a large air flow value. Most devices have a major drawback; coughing calls for manual adaptation, which again attracts attention. A new hands-free tracheostoma valve has been developed. The device consists of two magnetic valves, one which closes the outflow to allow speech, and one which opens to cough. Prototypes were tested in a physical model. Air flow resistance and closing pressures of the speech valve proved to be comparable to those of existing devices. Patients were enthusiastic about the new approach, even though air leakage sometimes occurred.

Development and test of an extendable endoprosthesis for bone reconstruction in the leg

A malignant bone tumour may develop in the femur of a child. In the majority of cases it will be necessary to resect the bone involved, growth plate and adjacent tissues. A modular endoprosthetic system has been developed which can be extended non-invasively to bridge the defect resulting from such a resection. Elongation is achieved by using an external magnetic field. In vitro tests with a prototype showed that the lengthening element met all requirements. Six animal experiments showed that the lengthening element also functioned in vivo.

In Vivo Aerodynamic Characteristics of the Nijdam Voice Prosthesis

The Nijdam voice prosthesis is an indwelling valveless voice prosthesis for postlaryngectomy voice rehabilitation. The in vitro aerodynamic characteristics are reported to be comparable to that of the low-resistance Groningen voice prosthesis. Owing to the design of the prosthesis the airflow resistance depends on the shaft length of the voice prosthesis in relation to the thickness of the tracheo-oesophageal wall. As tissue characteristics of the patients oesophageal mucosa could also be of importance, an in vivo study was found necessary. To assess in vivo characteristics the following parameters were recorded in 10 patients: intratracheal pressure, intraoesophageal pressure and airflow during phonation. At an airflow of 0.15 1/sec the transdevice pressure loss varied from 0.5 up to 7 kPa (mean 3.9 kPa). With an artificial increase of the tracheo-oesophageal wall thickness, transdevice pressure losses up to 13 kPa were found. Significant interindividual as well as intraindividual differences were noted. The airflow resistance of the Nijdam voice prosthesis in relation to the thickness of the tracheo-oesophageal wall was compared with the airflow resistance reported for various other voice prostheses. The in vivo aerodynamic characteristics of the Nijdam voice prosthesis found in this study indicate the need to modify the present design in order to improve its airflow resistance and to eliminate the influence of the thickness and tissue characteristics of the tracheo-oesophageal wall.

A critique of techniques for reconstruction after internal hemipelvectomy for osteosarcoma

Osteosarcoma may affect any bone but is mainly encountered in long bones like the femur and is rarely observed in flat bones [1]. According to Schajowicz

In vivo and in vitro experience with the PUCA-II, a single-valved pulsatile catheter-pump

The Pulsatile Catheter (PUCA) pump is a trans-arterial pulsatile ventricular assist device that can be used for short-term left ventricular support. The separate inflow and outflow valves in the first version of the device (PUCA-I) were replaced by a single inflow/outflow valve in the latest PUCA pump version (PUCA-II). The new combined valve was tested during in vitro (mock circulation) and in vivo experiments for valve leakage, flow resistance, and thrombus formation. During the in vitro experiments a maximum valve leakage of 6% during ejection and 21% during aspiration was found. The maximum flow resistance coefficient (K) was 4. The animal experiments demonstrated that the PUCA-II could be positioned within a few minutes into the left ventricle without X-ray guidance and without using a vascular graft. Thrombi were not found in the combined valve after total pump time of 3 hours, which proved the good washout of the valve. Initial experiments to position the pump in the right ventricle through the pulmonary artery were successful and contributed to the development of a new application for the device.

Design of a Load Cell for the Wagner Distractor

A leg length inequality can be treated by using a Wagner distractor. With this apparatus, it is possible to extend the upper or lower leg slowly. By analysing the measurements of the axial force acting on the femur or tibia the treatment can be optimized and soft tissue damage prevented. To measure the axial force, a load cell has been designed and constructed. This load cell is built into a Wagner distractor and connected with a specially designed measuring amplifier. The load cell and amplifier do not interfere with the lengthening procedure. They are safe for the patient and have an acceptable error of 7 per cent.