When two spatially separated stimuli are given on the human skin sequentially under appropriate conditions, a continuous stimulus moving sensation, called a “tactile apparent mevement”, can be perceived. This study focuses on spatiotemporal properties of somatosensory evoked potentials associated with perception of tactile apparent movement. To induce the perception of an apparent movement, a pair of electrical stimuli of 0.2ms square pulses with 120ms of interstimulus onset interval (ISOI) were given at two different points located at 80mm apart on the wrist (apparent stimulation). For comparison, two sequential stimuli with the same ISOI were given at a single fixed point (control stimulation). Evoked potentials responded to these stimuli were recorded from 16 scalp sites in the 10-20 system to obtain topographic potential maps. Topographic patterns of evoked potentials obtained by subtracting the responses to the control stimulation from those to the apparent stimulation were obtained. P 300-like positive components were observed at central and frontal scalp regions at the latencies 300-500ms. The peak latencies measured from the onset of the second stimulus can be considered to depend on the time required to recognize and evaluate the apparent movement.

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This paper describes a fundus reflection densitometer and its application to measurement of the foveal cone pigment regeneration of healthy subjects. A 500W xenon lamp provides bleaching, measuring and reference light beams. A PC9801 personal computer is used for control shutters of three beams, on-line calculation and display of cone pigment regeneration. When the bleaching light is on, the fundus can be viewed. The measuring field is fixed at 3.5deg. Using it, we have measured the two-way density and regeneration time of 5 healthy subjects (3 male and 2 female), with clear optical media and good visual acuity, ranging in age from 27 to 28 years. The two-way densities and regeneration times of 5 subjects show mean values of 0.426±0.038 SD and 152.5±21.1 SD s, respectively.

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This study focused on the properties of nerve excitation responded to series of pulsed electric fields induced by time-varying magnetic fields. We observed a phenomenon that the amplitudes of EMG responses to magnetic stimulation changed with the direction of stimulating eddy currents. We introduced a model to explain this phenomenon. A computer simulation shows that the excitability of nerve fiber is changed with the angle between a coil and a nerve fiber. We also carried out magnetic stimulation of the human plexus brachialis by a sequence of rectangular electric fields induced by trapezoidal magnetic fields. Nerve excitation processes were studied, changing the duration of plateau of the trapezoid. The results show that nerve excitation is suppressed when plateau is short. This inhibitory effect was simulated well based on a neurophysiological model.

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It has been reported that the accuracy of measuring the point of force application with force plate is affected by the position and magnitude of the force vector. The purpose of the present report is to evaluate the accuracy in determining the point of force application for investigating body sway, and to improve this accuracy by proposing a correction procedure. In the experiment with calibrated masses the measured points of force application were shifted parallel to X- and Y-axes in addition to being reduced comparing with the actual point. The error tended to be greater in the smaller magnitude of the masses. The root mean square of error (RMS error) at the smallest mass of 10kg was found to be 10mm X-coordinate and 6mm in Y-coordinate. The errors in the measured point of force application seem to be caused by 1) nonlinearity of load cells, 2) deformity of the top platform of the force plate and 3) differences in the gain and offset voltage among each load cell. The experimental results showed that the nonlinearity of the load cells was less than 2% even at the light loading of 2.8kg. A concave bending of the top platform due to force application makes a force act within the load cell rectangle. As a consequence, the measured value of force application tends to be greater than the actual point. Our results demonstrated the opposite, namely underestimation of the actual point. The greater deformity of force plate due to extreme force application like landing during running and jumping may become a significant factor. Thus, nonlinearity of the load cell and deformity of the top plate were ruled out as factors of the errors in investigation of body sway. A mathematical model of the force plate including load cells with different gain and offset voltage provided a satisfactory explanation of the errors in the measured point. Based on the observed error distribution and the model, a correction procedure independent of the magnitude of the force application was proposed. The correction algorithm improved the accuracy to the RMS error of less than 1mm at the calibrated mass of 10kg. It was confirmed that the correction procedure could provide more accurate and reliable information for investigating body sway.

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Several techniques for measuring tissue hardness have been proposed which might provide effective means for the screening of disease. However, no practical measurement technique has been established yet. We have proposed a new measurement technique of tissue hardness in which the radiation force is employed to deform the tissue. And the deformation is measured by a conventional pulse-echo method. The merit of this technique is the feasibility of evaluating tissue hardness only from the time dependance of relative force or displacement. By using both viscoelastic model and Hertz's contact theory, the characteristic value of hardness is derived from the force-relaxation curve. After proving that Hertz's theory is valid for visco-elastic material if the deformation is small, hardness measurement of several specimens including human organs has been carried out to obtain diagrams of correlation between elasticity and viscosity. These diagrams show typical correlation for each organ. This result suggests that hardness measurement is possible without measuring the absolute value of deformation and/or stress and that this proposed measurement technique can be used in vivo measurement.

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A flexible ultrasonic lithotriptor was newly developed in 1988. This new device is made of stainless steel, 94cm in length and 0.5mm or 0.8mm in diameter, which is covered with a teflon sheath. Experimental studies were performed using this new device and urinary stones and model stones were easily fragmented. It took less than three minutes to destruct a 10×5×5mm model stone completely. This device was specially effective in a patient of middle ureteral stone. It is expected that the device will be emnployed widely in PNL technique.

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In order to make an effective use of closed-loop artificial pancreas, it is necessary to monitor the glucose content in blood continuously. Mostly an enzyme electrode has been used for measuring the glucose content in blood because of its high selectivity and sensitivity. The glucose is diffused within the immobilized enzyme accompanied with chemical reaction and the process of glucose transport in detail in the immobilized enzyme has not been revealed yet. Particularly the optimal design of enzyme electrode requires the quantitative information of permeability of glucose and H₂O₂ in the enzyme membrane. In this study the effective diffusivities of glucose and H₂O₂ in the immobilized enzyme membrane were measured to find the design feature of implanted glucose electrode for long term use. Albumin-linked glucose oxidase sandwiched by two sheets of Polyacrylonitrile (PAN) membrane was attached to the tip of the platinum anode. The transfer rate of glucose transformed into H₂O₂ in the membrane was determined by the amount of H₂O₂ detected in the electrode. Thereby the effective diffusivity of glucose and H₂O₂ in the immobilized membrane was determined. Based on the feature of mass transport process obtained in this study, the design of various type of electrode such as an implantable one becomes feasible.

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