The main cause of arrhythmias is the reentry phenomenon. Spiral wave reentry, a phenomenon of abnormal circulating excitation wave propagation, is speculated to be the cause of ventricular tachycardia (VT) and ventricular fibrillation (VF) . The “spiral wave shift” hypothesis was proposed in a previous simulation study. A spiral wave shift is a phenomenon in which the position of the center of the spiral wave reentry [referred to as phase singularity (PS)] is shifted when electrical stimulation is applied near PS with appropriate position and timing. Since a spiral wave shift can be induced with stimulation energy lower than defibrillation energy, a new defibrillation method has been proposed. This technique involves arbitrarily applying an anatomical block line to collide with PS, thereby stopping VT or VF. However, understanding of the mechanism of a spiral wave shift in biological specimens remains limited. Thus, this study aimed to clarify the mechanism of the spiral wave shift using biological specimens. Spiral wave reentry was induced in perfused rabbit hearts (n=8) stained with a fluorescent dye sensitive to membrane potential. Monophasic stimulation was applied to the surface of each specimen using a multi-electrode array. The timing and position of the electrical stimulation for inducing a spiral wave shift were varied. The optimal conditions for inducing a spiral wave shift were identified as those that minimized the displacement of the PS position after electric stimulation. The results revealed that three conditions must be satisfied to induce a spiral wave shift: (a)the PS and electrode should be located in close proximity to each other, (b)they should be positioned along the cardiac fiber orientation, and (c)electric stimulation should be applied in the repolarization phase of an action potential.
Several studies have reported on maze tasks for humans. From the results of these maze tasks, human brain function has been elucidated. However, few studies have verified the level of difficulty of maze tasks. Therefore, the validity of these studies is questionable. The purpose of this study was to investigate factors influencing the level of difficulty of maze task for humans. We conducted an experiment in which subjects search for a goal in mazes generated on a computer. Subjects explore the mazes on two different days. In making the mazes, we set the number of steps required to reach the goal position and the number of T-junctions from the start position to the goal position. We called such mazes “continuous-T mazes.” When a subject reached the goal position three consecutive times without extra steps, the subject moved on to the next maze. The number of trials before moving on to the next maze was recorded as the score. We established new parameters;“maze cost” and “weighted maze cost,” to estimate the level of difficulty of mazes, and compared the score with these parameters. The score correlated with both the “maze cost” and the “number of T-junctions from the start position to the goal position.” These results suggest that both parameters indicate factors influencing the difficulty of mazes.
Finger manipulation plays an important role in daily life, and the importance of its analysis is increasing in a variety of research fields. Applications in humanoid robots, artificial hands, and improvement of rehabilitation technology could be aided by a quantitative understanding of finger manipulation, which requires the measurement of natural operations. Although many previous studies examined finger manipulation, the experiments tested only a limited range of objects manipulated by the fingers or the sensation of the fingertip was inhibited by attaching sensors. The current study focused on hold and pick manipulations, exploring dynamic features of the thumb and index fingers. To measure natural operation, we used a haptic wearable sensor that measured finger pressure and 3-axis direction acceleration without inhibiting the operator's sense of touch. We conducted user experiments in seven subjects while they manipulated a cylindrical urethane object. We defined 10 features determined uniquely from the measured values, then calculated the recognition rate of pick and hold movements when various dimensions and sets of features were used. We identified common features among subjects which characterized hold and pick manipulations.
Digital signal processing is one of the fundamental technologies utilized in the field of biomedical engineering. Typical purposes of digital signal processing are acquisition and analysis of biological signals, noise reduction and extraction of the required signals, and identification of biological systems. This introductory article provides some basic ideas and techniques of digital signal processing in biomedical engineering:biosignal sampling, spectrum analysis, and filter design.