Nozomu Hoshimiya

A multichannel FES system for the restoration of motor functions in high spinal cord injury patients: a respiration-controlled system for multijoint upper extremity

A multichannel functional electrical stimulation (FES) system for the restoration of quadriplegic upper extremity function is described. The system is composed of a personal computer, peripheral electronic circuits, CRT display and respiratory sensors for volitional control by the patient, and percutaneous electrodes. In this system, versatile volitional control is realized by controlling the memory allocation of the stored stimulation data by voluntary respiratory signals, and sophisticated fine control of the fingers, wrists, and elbow is realized by creating multichannel stimulation data from recorded myoelectric activities of normal subjects during movements of the upper limb.<<ETX>>

Telemedicine using mobile satellite communication

With a view to providing paramedical care within moving vehicles, a telemedicine technique using mobile satellite communication was proposed. With this technique, the diagnosis from a specialist and the emergency care under his/her instructions would be available on the spot without unnecessary delay. The characteristic problems of this technique were identified as: channel capacity, size of the system, reliability of vital sign transmission, real-time operation and electromagnetic interference. Measures against these problems were devised, and their effectiveness was analyzed. A data format was designed and an experimental system was developed. The system can simultaneously transmit a color image, an audio signal, 3 channels ECG and blood pressures from a mobile station to a ground station. It can transmit an audio signal and error control signals from a ground station to a mobile station in a full duplex mode. Fundamental transmission characteristics were measured in a fixed station. Finally, experiments of medical data transmission were conducted with a navigating ship and an aircraft flying an international route. The measured threshold values of C/N/sub o/ to guarantee satisfactory data reception were well below the lower boundary of C/N/sub o/ of the communication link. Consequently, the feasibility of this technique was verified.<<ETX>>

TheApteronotus EOD field: Waveform and EOD field simulation

Summary1.Electric organ discharges (EOD) were measured in a wave-type electric fish,Apteronotus, with an array of electrodes.2.The EOD waveform observed in the transient area (area where the equipotential lines converged) was a triphasic one in comparison to a biphasic one in the rest of the area. Electronic circuit simulation suggested that the triphasic waveform resulted from incomplete electrocyte synchronization within the electric organ.3.The EOD field was obtained by computer simulation using the finite-element-method. The simulated results were used for calculation of the transepidermal potential difference distribution. This distribution is discussed with respect to sensitivity differences of electroreceptors in various parts of the fish.

An approach to a muscle model with a stimulus frequency-force relationship for FES applications

A simplified model of electrically stimulated muscle for use in applications of functional electrical stimulation (FES) is discussed in this paper. The muscle model was required to have both stimulus frequency and stimulus intensity (amplitude/width) inputs. The stimulus frequency versus force relationship of rabbit muscle was modeled first with a small number of model parameters that could be identified by simple experiments in a short time. The model identified was found to be applicable to human muscles. The frequency-force relationships of electrically stimulated fast and slow type muscles were also predicted by the model. The frequency-force model and a simplified model of muscle activation dynamics were used to construct a muscle model that described the summation of muscle contraction. The use of this model decreased the time burden on patients during parameter identification at the clinical site. The clinical applicability of these new model descriptions was suggested through computer simulations.

Evaluating the regional elastic modulus of a cylindrical shell with nonuniform wall thickness.

PurposeFor noninvasive diagnosis of atherosclerosis, we attempted to evaluate the elasticity of the arterial wall by measuring small changes in thickness caused by the heartbeat. The elasticity of the arterial wall has been evaluated noninvasively by measuring the change in diameter of the artery or the pulse-wave velocity; however, there is no method for noninvasively evaluating the elasticity of the arterial wall from changes in its thickness.MethodsEmploying the phased tracking method that we developed, changes in thickness of less than 100 µm were measured in each regional area, which corresponded to the diameter of the ultrasonic beam.ResultsThe elasticity of the arterial wall could be evaluated with better spatial resolution from the change in thickness than from the change in diameter of the artery or pulse-wave velocity. We therefore propose a method for evaluating the elastic modulus of an arterial wall of nonuniform wall thickness.ConclusionsIn basic experiments employing silicone rubber tubes with nonuniform wall thickness as arterial models, the elastic moduli of silicone rubber tubes were evaluated by measuring changes in wall thickness. These results confirm the value of the proposed method.

Accuracy Evaluation in the Measurement of a Small Change in the Thickness of Arterial Walls and the Measurement of Elasticity of the Human Carotid Artery

For the diagnosis of the early stages of atherosclerosis, it is important to evaluate the local acoustic characteristics of the arterial wall. For this purpose, it is necessary to increase the spatial resolution in the axial direction to several millimeters, which corresponds to the size of the macular lesion on the surface of the wall. We have proposed a method for measuring small velocity signals on the intima and adventitia of the arterial wall from the skin surface using pulsive ultrasonic waves. The small change in thickness of the arterial wall is obtained by integrating the difference between the two velocity signals on the intima and adventitia. The elastic property of the arterial wall is noninvasively evaluated from the change in thickness and the arterial inner pressure. In this paper, we evaluate the accuracy of the proposed method for measuring the small displacement. Moreover, we applied this method to evaluate the elastic property of the arterial wall of 50 patients and 8 healthy subjects.

Electromyogram analysis and electrical stimulation control of paralysed wrist and hand

Restoring paralysed hand functions with functional electrical stimulation (FES) essentially requires control of joint angles in their functional positions as well as control of speed and power for grasping. In this study, standard FES patterns were created from the electromyogram (EMG) analysis of 15 healthy subjects in order to restore hand and wrist joint functions in C4 and C5 quadriplegics. Stimulating the hand muscles with the standard patterns produced both wrist joint fixation in a functional position and grasping movement similar to that of healthy subjects. To control the joint angle, certain stimulation voltages were read at the same memory address. Similarly, motion speed was adjusted by changing the reading speed at the stimulation data memory address. Since stimulation patterns created from the EMG analysis of healthy subjects restored the hand and wrist joint functions in C4 and C5 quadriplegics, this method was found to be successful in allowing some normal daily activity for quadriplegics.

Two-terminal electronic circuit neuron model with excitable membrane V-I-t characteristics

Two-terminal electronic circuit neuron model is described. The model has time-variant voltagecurrent characteristics of an excitable membrane. Corresponding equivalent circuit is shown by the use of time-invariant elements as a voltage-controlled oscillator. The design principle of the model is outlined. Two application examples are demonstrated: (1) Simulator of the excitable membrane for the investigation of a voltage-clamp instrument, which works in the low current and low voltage region. (2) Circuit model for an electric organ of a weakly electric fish, Apteronotus.

Stimulus adjustment protocol for FES-induced standing in paraplegia using percutaneous intramuscular electrodes

The desirable upright posture for standing via functional electrical stimulation (FES) is defined based on simulation results using a link model in the sagittal plane. The criterion for the posture selection is the minimization of the sum of the squared joint flexion moments caused by gravity. The stimulus intensities are adjusted systematically to attain the defined upright posture. Controlled standing was achieved in a Th7 and a Th8-level spinal-cord-injured paraplegic individuals without joint contracture, by using the stimulus adjustment protocol. A practical standing without any bracing devices was obtained, with the vertical upper extremity support of less than four percent of the body weight, and with single-hand-support attainable. The maximal durations of standing were 30 minutes in both cases.

A method of multichannel PID control of two‐degree‐of‐freedom wrist joint movements by functional electrical stimulation

In restoring motor functions of paralyzed extremities by functional electrical stimulation (FES), determination of stimulus intensities of many muscles in multichannel control is an ill-posed problem because of redundancy in the input (stimulus intensity)-output (joint angle) relationship of the musculoskeletal system. In this paper, we use a multi-input and multi-output PID controller and propose a parameter determination method for the controller, which can solve the ill-posed problem in closed-loop control. In the parameter determination process, the stimulus intensity-joint angle characteristics of all muscles controlled were measured first. The elements of the matrix that transforms stimulus intensities into joint angles were determined by linear approximation of the measured characteristics. Then a generalized inverse matrix of the transformation matrix was calculated. The generalized inverse matrix and an expanded CHR method were used to determine the parameters of the PID controller. The PID controller was examined in tracking control on several trajectories of two-degree-of-freedom movement of the wrist joint with neurologically intact subjects. Electrical stimulation was applied to four muscles relating to the wrist joint movements through surface electrodes. The tracking control was achieved generally with good performance under different conditions of the gravitational effect. The new method proposed in this paper was found to provide a solution of the ill-posed problem. Multichannel closed-loop FES control of the wrist joint could be realized with this method.