Application of virtual reality to the rehabilitation field to aid amputee rehabilitation: findings from a systematic review.

PURPOSE: To determine the scope and use of virtual reality (VR) applications in the gait rehabilitation field and to review and characterise VR approaches for application in amputee rehabilitation. METHOD: A state-of-the-art research analysis was completed to review different approaches of VR to the gait rehabilitation field. Systematic research using Medline, EBSCOhost and Science Direct (ISI Web of Knowledge) was conducted to analyse various VR rehabilitation methods, and we developed a framework to characterise different research findings. RESULTS: Framework for a research approach in the field of VR and rehabilitation was developed based on the literature review. On the basis of outcomes from gait rehabilitation using VR, trials for amputee rehabilitation using VR is warranted and an outline of this potential VR rehabilitation area was identified. CONCLUSIONS: Evidence supports the investigation of VR as applied to amputee rehabilitation based on general gait rehabilitation results. Research should be expanded to better understand the role and use of technology in community-based rehabilitation to enhance the quality of life of individuals.

Characterisation of a pneumatic muscle test station with two dynamic plants in cascade.

Pneumatic muscle actuators (PMAs) offer significant advantages over more traditional actuators, which make them prime candidates in rehabilitation devices. A dynamic test station (DTS) is modified to demonstrate the use of a PMA for this application. The DTS includes two dynamic systems: a PMA and a DC servomotor. An overall transfer function was developed utilising characterisation data for the PMA and DC servomotor. A Tustin (bilinear) transform was performed on the overall transfer function to obtain a discrete time system. Model parameters were optimised and used to generate input voltage profiles that achieve isokinetic (constant velocity) task specifications. Percent root mean square error values (PRMSE) between the actual and ideal profiles were used to evaluate the accuracy of this method in achieving isokinetic displacement. For PMA pressures (in kPa) of 150, 350 and 550 PRMSE were 7.80, 5.40 and 2.76, respectively.

Characterisation of a phenomenological model for commercial pneumatic muscle actuators.

This study focuses on the parameter characterisation of a three-element phenomenological model for commercially available pneumatic muscle actuators (PMAs). This model consists of a spring, damping and contractile element arranged in parallel. Data collected from static loading, contraction and relaxation experiments were fitted to theoretical solutions of the governing equation for the three-element model resulting in prediction profiles for the spring, damping and contractile force coefficient. For the spring coefficient, K N/mm, the following relationships were found: K = 32.7 - 0.0321P for 150 < or = P < or = 314 kPa and K = 17 + 0.0179P for 314 < or = P < or = 550 kPa. For the damping coefficient, B Ns/mm, the following relationship was found during contraction: B = 2.90 for 150 < or = P < or = 550 kPa. During relaxation, B = 1.57 for 150 < or = P < or = 372 kPa and B = 0.311 + 0.00338P for 372 < or = P < or = 550. The following relationship for the contractile force coefficient, F(ce) N, was also determined: F(ce) = 2.91P+44.6 for 150 < or = P < or = 550 kPa. The model was then validated by reasonably predicting the response of the PMA to a triangular wave input in pressure under a constant load on a dynamic test station.

Biomimetic model of skeletal muscle isometric contraction: I. an energetic-viscoelastic model for the skeletal muscle isometric force twitch.

This paper describes a revision of the Hill-type muscle model so that it will describe the chemo-mechanical energy conversion process (energetic) and the internal-element stiffness variation (viscoelastic) during a skeletal muscle isometric force twitch contraction. The derivation of this energetic-viscoelastic model is described by a first-order linear ordinary differential equation with constant energetic and viscoelastic coefficients. The model has been implemented as part of a biomimetic model, which describes the excitation-contraction coupling necessary to drive the energetic-viscoelastic model. Finally, the energetic-viscoelastic model is validated by comparing its isometric force-time profile with that of various muscles reported in the literature.

Biomimetic model of skeletal muscle isometric contraction: II. A phenomenological model of the skeletal muscle excitation-contraction coupling process.

This paper describes a new macroscopic, phenomenological model of the skeletal muscle excitation-contraction coupling process, as represented by four principal and consecutive compartments (biophysical, biochemical, and biomechanical phases) characteristic of isometric excitation-contraction coupling in mammalian skeletal muscle, and coupled by a system of simultaneous, first-order linear ordinary differential equations. The model is based upon biological compartmental transport kinetics and irreversible thermodynamic energy transformation, and represents a distinct improvement over other biomimetic models. The model was derived using physiological parameter data published in the literature, and validated using MATLAB R12.

Modeling the dynamic characteristics of pneumatic muscle.

A pneumatic muscle (PM) system was studied to determine whether a three-element model could describe its dynamics. As far as the authors are aware, this model has not been used to describe the dynamics of PM. A new phenomenological model consists of a contractile (force-generating) element, spring element, and damping element in parallel. The PM system was investigated using an apparatus that allowed precise and accurate actuation pressure (P) control by a linear servo-valve. Length change of the PM was measured by a linear potentiometer. Spring and damping element functions of P were determined by a static perturbation method at several constant P values. These results indicate that at constant P, PM behaves as a spring and damper in parallel. The contractile element function of P was determined by the response to a step input in P, using values of spring and damping elements from the perturbation study. The study showed that the resulting coefficient functions of the three-element model describe the dynamic response to the step input of P accurately, indicating that the static perturbation results can be applied to the dynamic case. This model is further validated by accurately predicting the contraction response to a triangular P waveform. All three elements have pressure-dependent coefficients for pressure P in the range 207 < or = P < or = 621 kPa (30 < or = P < or = 90 psi). Studies with a step decrease in P (relaxation of the PM) indicate that the damping element coefficient is smaller during relaxation than contraction.

In vitro characterization of a zinc based bioceramic.

Six different blends of zinc calcium phosphorous oxide ceramics (ZCAP) were prepared by mixing and calcining powders (ZnO:CaO:P2O5) of weight percent ratio: 50:30:20, 48:32:20, 44:20:26, 40:40:20, 30:40:30, and 30:30:40. ZCAP is a resorbable bioceramic and has been used to repair bone defects and deliver drugs in a continuous manner. The chemical composition, porosity, and elements released on exposure to buffered Tris HCl were measured for each blend of ZCAP. The products of mixing and thermal reaction were beta-Ca3(PO4)2, alpha-CaZn2(PO4)2, and 2CaO.P2O5. Free calcium and/or zinc oxide was present in several blends. The components of ZCAP and their volume percentages influenced the interconnected porosity of ZCAP bioceramics. The interconnected porosity for all blends of ZCAP ranged from 35 to 38%. Pore sizes from these six blends of ZCAP ranged from less 1 micron to greater than 100 microns. Results of the 12 hour dissolution study showed that more calcium was released than zinc or phosphorous from all blends of ZCAP. Zinc was released in trace amounts from all blends of ZCAP. Release of phosphorous from the different blends of ZCAP was not detected by the procedures used to detect phosphorous in this investigation. These blends of ZCAP have the potential to be used as bone substitutes and probably long term treatment of zinc deficiency in humans.

Controlled diffusional release of dispersed solute drugs from biodegradable implants of various geometries.

Chronic diseases and pathological medical conditions requiring the administration of longterm pharmaceutical dosages have in the past been treated by oral administrations of tablets, pills and capsules or through the use of creams and ointments, suppositories, aerosols, and injectables. Such forms of drug delivery, which are still currently used today, provide a prompt release of the drug, but with significant fluctuations in the drug levels within various regions of the body. Repeated administrations of the drug are often needed, at rather precise intervals of time, in order to maintain these levels within a relatively narrow therapeutic range as a means of assuring effectiveness at the low end and of minimizing adverse effects at the higher end of the fluctuation spectrum. Recent technical advances now permit one to control the rate of drug delivery. The required therapeutic levels may thus be maintained over long periods of months and years through implanted rate-controlled drug release capsules. Two such novel drug delivery systems currently employed are implanted erodible polymeric and ceramic capsules. Mathematical modeling and computer simulations can be very effective in improving and optimizing the performance of the self-regulating release of therapeutic drugs into specific regions of the body. Further development is needed for the optimal design of such capsules. It is in this area, in particular, that a review will be presented of the mathematical modeling techniques susceptible to refine the development of a reliable tool for designing and predicting the resulting pharmaceutical dosages as a function of time and space. Of primary importance in such models are the time-varying effective permeability of the capsule to the various molecules composing the drug, the effective solubility and diffusion coefficients of the drug and its metabolites in the surrounding tissues and fluids and, finally, the uptake of the drug at the target organ. Mathematical models are presented for the diffusional release of a solute from an erodible matrix in which the initial drug loading c0 is greater than the solubility limit cs. An inward moving diffusional front separates the reservoir (unextracted region) containing the undissolved drug from the partially extracted region. The mathematical formulation of such moving boundary problems has wide application to heat transfer with melting phase transitions and diffusion-controlled growth of particles, in addition to our topic of controlled-release drug delivery. In spite of this diversity of applications, only a very few mathematical descriptions have been published for the analysis of release kinetics of a dispersed solute from polymeric or ceramic matrices. In these rare instances, perfect sink conditions are assumed, while matrix swelling, concentration-dependence of the solute diffusion coefficient and the external mass transfer resistance have been largely neglected. The ultimate goal of such an investigation is to provide a reliable design tool for the fabrication of specialized implantable capsule/drug combinations which will deliver pre-specified and reproducible dosages over a wide spectrum of conditions and required durations of therapeutic treatment. Such a mathematical/computational tool can also prove effective in the prediction of suitable dosages for other drugs of differing chemical and molecular properties which have not been subjected to time-consuming animal laboratory testing. Finally, such models may permit more realistic scaling of the required dosages of therapeutic drug for variations in diverse factors such as body weight or organ size and capacity of the patient (clinical medicine) or animal (veterinary medicine for farm animals). Additional applications of controlled-release drug delivery for insecticide and pesticide use in agriculture, and the control of pollution in lakes, rivers, marshes, etc. in which a pre-programmed dose-time schedule is necessary, further

Preparation and characterization of ZCAP blends.

Six different blends of zinc oxide, calcium oxide, phosphorous pentoxide (ZCAP) were prepared by mixing zinc oxide (ZnO), calcium oxide (CaO), and phosphorous pentoxide (P2O5) powders. The blends were 50:30:20, 48:32:20, 44:26:30, 40:40:20, 30:40:30, and 30:30:40, ZnO:CaO:P2O5 by weight, respectively. The mixed powders were calcined at 800 degrees C for 12 hours. Each blend was then characterized using X-ray diffraction. The X-ray diffraction patterns indicated that in some cases the reaction between oxides may not have gone to completion. Compositions of beta-3CaO.P2O5 and alpha-CaZn2(PO4)2 were found in many of the blends.

Test apparatus and methods for performance evaluation of an artificial urinary sphincter.

We have designed, built and tested an experimental apparatus for in vitro performance testing of an artificial urinary sphincter. A simulated urinary tract delivered a simulated urine to either an excised porcine urethra or artificial urethra at a physiologically normal pressure range of 0-93 cm H2O (0-9.12 kPa) and flow rate range of 0-830 ml/min (0-1.38 x 10(-5) m3/s). Inlet urine pressure, sphincter temperatures at several locations, urine flow, differential pressure across the urethra, and linear motion of the sphincter were measured with appropriate transducers and recorded on a PC-based data acquisition system. We conclude that the simulated urinary tract is adequate for testing artificial sphincter performance and that the data acquisition system accurately measures, displays, and records the parameters which indicate system performance.

Electrical properties of ALCAP and ZCAP ceramics.

The electrical properties of implantable ceramics have been studied. The properties of resistivity, dielectric constant, magnetic permeability, and piezoelectric constant were measured using test methods developed to give reproducible results on common electrical instruments. The electrical properties of Aluminum Calcium Phosphorus Oxide (ALCAP) and Zinc Calcium Phosphorus Oxide (ZCAP) ceramics were measured with an ohmeter, impedance bridge, and oscilloscope in conjunction with special test fixtures. Both the ALCAP and ZCAP materials were characterized as insulating dielectrics with mean resistivities of 6.0E04 ohm.m and with mean dielectric constants of 5.3 for both ceramics. Neither the ALCAP nor the ZCAP exhibited magnetic or piezoelectric properties. The results indicate that these ceramics could be used as an insulative housing for a variety of medical devices.

Steady expiratory flow-pressure relationship in a model of the human bronchial tree.

Static pressure differences across a human bronchial tree model were obtained for steady expiratory flows of several gases producing Reynolds numbers (Re1) in the bronchus carrying the entire flow (first bronchus) between 150 and 50,000. The model was constructed from an air-dried lung and was complete to bronchi about 2 mm in diameter. Dimensionless static pressure plotted against Re1 consolidated the data on a single curve, phenomenologically described by an equation of the form: delta Ps/delta Pd1 = A + B Re1 where delta P d1 is a pressure drop for Poiseuille flow, Velocity profile measurements at two sites along the first bronchus for laminar and turbulent flows indicate a dependence on the latter and distance from the first junction. Loss in total pressure was computed and may result from both frictional dissipation and changes in momentum flux associated with development of velocity profiles near the junctions. An average loss in total pressure within a single bronchus was calculated after making several simplifying assumptions, and this result may be useful in modeling both the resistance of the entire bronchial tree and the more complex phenomenon of maximal expiratory flow.

Steady pressure-flow relationship of a model of the canine bronchial tree.

Static pressure differences (deltaP) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (V). The reproduction consists of a 10-cm length of trachea through bronchi of about 2 mm in diameter. The airflow was simulated by a water flow with tracheal Renolds number (Re0) in the range from 1,500 to 10,000. Loss in total pressure (deltaPt) was computed by summing deltaPt and V were well described (r greater than 0.98) by a dimensionless Rohrer equation deltaPt/deltaPd0 = A + B Re0 applicable to gas flow, in which deltaPd0 is a Poiseuille pressure drop. For expiratory deltaPt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer's equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.