Application of wavelet analysis to the plethysmogram for the evaluation of mental stress

The present study proposes a new stress evaluation technique using the photoplethysmogram (PTG). Heart rate variability (HRV) is often used to evaluate mental stress. HRV can be measured from an electrocardiogram (ECG). The frequency variability of HRV and mental stress response are related. PTG also indicates changes in emotional response. PTG can easily be measured without body surface electrodes. This method is less invasive than ECG measurement. We attempt herein to evaluate mental stress by wavelet analysis of the PTG. PTG was measured in the resting and mental stress states, and wavelet transformed PTGs were compared. In nine out of ten subjects, the wavelet result for PTG revealed a decrease in the frequency band.

Basic study on a lower-energy defibrillation method using computer simulation and cultured myocardial cell models

Computer simulation and myocardial cell models were used to evaluate a low-energy defibrillation technique. A generated spiral wave, considered to be a mechanism of fibrillation, and fibrillation were investigated using two myocardial sheet models: a two-dimensional computer simulation model and a two-dimensional experimental model. A new defibrillation technique that has few side effects, which are induced by the current passing into the patient's body, on cardiac muscle is desired. The purpose of the present study is to conduct a basic investigation into an efficient defibrillation method. In order to evaluate the defibrillation method, the propagation of excitation in the myocardial sheet is measured during the normal state and during fibrillation, respectively. The advantages of the low-energy defibrillation technique are then discussed based on the stimulation timing.

Wavelet analysis for quantification of mental stress stage by finger-tip photo-plethysmography

Wavelet analysis of the finger-tip photo-plethysmogram (PTG) was performed in order to quantify the stress stage. From the result of the wavelet transform of the PTG, we proposed stress index, with which quantification of the mental stress level was easy. In order to confirm the validity of this index, we compared the stress indexes between the stress and resting stages. The relationship between the stress index and the heart rate variability (HRV) was also investigated. The obtained results indicated that using the wavelet transform in analysis showed a remarkable change in the stress index from the resting stage to the stress stage. This change appears in the tidal wave area of the PTG.

Modified Weiss's equation for strength-duration curve in magnetic stimulation

There is increasing interest in the use of magnetic stimulation as a modality for clinical examination and therapy. It is desirable that the eddy current density produced by a change in the strength of a magnetic field should be greater than the excitability threshold of the muscles or nerves to be stimulated. The eddy current waveform differs from rectangular current waveform common in electrical applications. Little basic study has been done on the effects of magnetic stimulation on threshold values, chronaxies and other aspects of the eddy current waveforms. In this paper, the authors have attempted to measure the strength-duration curve (S-D curve) of eddy currents on the sural muscle of the bullfrog and have proposed a new S-D curve formula for eddy currents in place of Weiss's equation for rectangular current waveforms.

Study on optimization for current distribution in magnetic stimulation therapy for urinary incontinence

It has been reported that magnetic stimulation effectively eliminates urinary incontinence. However, this type of therapy has not been established as a practical treatment for urinary incontinence because of its poor power conversion efficiency and the leakage of current to regions other than that of the target of stimulation. It is therefore necessary to develop magnetic stimulators that are more efficient in stimulating the sphincter muscles and the peripheral nerves, and are more convenient than those presently available. By using a large-diameter coil, the magnetic stimulation method offers a larger current distribution over a wider area of the target region than electrical stimulation method, and the placement of the coil can be relatively easily changed to obtain better therapeutic results. We attempted, with a computer simulation model of the female abdomen, to simulate the distribution of the induced current density on the basis of biological tissue conductivity. We determined which method of stimulation is the most efficient by varying the stimulator coil location and size. A genetic algorithm (GA) was used for optimization.