Yasuaki Ohtaki

Development of Advanced Portable Device for Daily Physical Assessment

Main objective of this study was to propose an advanced method to evaluate ones physical activity by means of a portable device which is capable of long-term non-restrictive measurement. The device includes accelerometers and a barometer specially designed to catch features of vertical movements such as stair climbing. The embedded algorithm classified activity type and quantifies its exercise intensity in realtime. Usefulness of the proposed method was demonstrated in simple experiments. Healthy young and elderly subjects participated in the experiments. Two kinds of daily outdoor situations were considered in the experiment; mountain climbing and city walking. Experimental results showed that the method correctly classified all type of activities, and accomplished feasible energy consumption estimation in both situations. It was also suggested that the consideration of vertical movements made an improvement in energy consumption estimation, and then provided more precise and reliable estimation of physical activity

The Effects of Physical Activity and Autonomic Nerve Tone on the Daily Fluctuation of Blood Pressure

The effects of daily activity and autonomic nerve tone on the fluctuation of ambulatory blood pressure were studied in hypertensive patients. The autonomic nerve tone was measured by frequency domain analysis of the RR interval. Physical activity was evaluated by a walk count, converted to a walk rate (WR), recorded using a digital Holter ECG fitted with an accelerometer, with simultaneous monitoring of blood pressure (Bp). Average values of the WR, H and L/H components were calculated for the 15 min. period just prior to Bp monitoring. The relationship between the average WR, H and L/H values and the Bp was determined by a linear regression analysis. Hypertension was classified into three types, autonomic nerve dominant (AN), exercise dominant (EX), and irregular (IR), based on a high correlation coefficient between Bp and either H or L/H (AN type), between Bp and WR (EX type), or no significant correlation between Bp and any of the parameters (IR type). Of the thirty hypertensive patients studied 11 were classified as AN, 12 as EX, and 7 as IR. Patients of the EX type had significantly lower Bp than patients in the other two classes. Furthermore, all of the IR type patients showed non‐dipper type hypertension, suggesting that the Bp regulation mechanisms were impaired. The results suggest the significance of simultaneous monitoring of physical activity and autonomic nerve function at the time of Bp monitoring.

Analysis of the effect of fatigue on walking gait stability

Effect of fatigue on the stability of normal walking is studied in this paper. A 3D accelerometer sensor was used to measure the accelerations of center of gravity of a walking person. Variability of acceleration in lateral, vertical and anterior/posterior directions was used as an index to assess the walking stability. We observed decreases in walking stability in lateral, vertical and anterior/posterior directions after fatigue.

A method of personal positioning for indoor customer tracking utilizing wearable inertial sensors

This paper presents a method for indoor personal positioning especially addressing on a simple gait measurement using a body-mounted inertial sensor, a walk path estimation algorithm, and a trajectory identification technique. Considering utility of on-site customer traffic tracking, the method was designed to be autonomous needless of neither external measures nor cumbersome installations to the environment. The inertial sensor combining three-dimensional accelerometer, angular rate sensors, and geomagnetic sensors was used to assess walking dynamics and to obtain changes of heading directions. To avoid an inherent problem of the walk trajectory estimation by conventional dead-reckoning algorithm, an advanced probabilistic map matching method which employs a Particle filter was developed. The experiment with healthy male adults was evaluated to confirm the utility of the method in a condition of small retail store. The result showed that the proposed method demonstrated sufficientlyfeasibletacking whichdelineated personal trajectoriesand positioning whileshopping. Themethodshowed possible availability with the portable instrument and improved estimation accuracy by the advanced probabilistic map matching which identifies proper routings on the basis of the maximum likelihood. The method will be useful to enhance ambulatory personal tracking technique in daily indoor environment.

Circadian Variation of the Myocardial Ischemic Threshold in Patients with Ischemic Heart Disease

Purpose. Circadian variation of the heart rate (HR) at the myocardial ischemic threshold was compared with that of the HR at the sympathetic tone threshold in 16 cases of effort angina pectoris. Methods. The high (0.15–0.40 Hz, Hf) and low (0.03–0.15 Hz, Lf) frequency spectral components were extracted every twenty seconds, using frequency domain analysis of the RR interval recorded by a 24-hour Holter ECG with an accelerometer. HR-Hf data collected every five minutes were plotted as the X-Y coordinates, and a two-compartment analysis was performed. The HR at the autonomic tone threshold was then determined at the intersection point of the lines. A loop of the HR-ST segment was drawn during walking to determine the ischemic threshold at which heart rate ischemic ST segment depression began and circadian variation was observed. Results. The circadian rhythm at the sympathetic tone threshold and the HR at the ischemic threshold were high during the day and low at night. The HR at the ischemic threshold was 15–20% higher than that at the sympathetic tone threshold at night but only 9–13% higher during the day. Also, there was a period during which there was no significant difference between the HR at the two thresholds. Conclusion. In comparing circadian variation between HR at the sympathetic tone threshold and HR at the ischemic threshold, there was a period during which there was no significant difference between the HRs. This might suggest a period in which a high incidence of cardiac ischemic attack is likely. This information could provide a feasible indicator for appropriate exercise training for patients with ischemic heart disease.

Walking gait stability in young and elderly people and improvement of walking stability using optimal cadence

Walking stability of human beings varies with age and reduces in the elderly people. Lesser walking stability causes many falls in the elderly people. In this paper, we have investigated the walking stability of young and elderly subjects using approximate entropy, a nonlinear time series analysis method. Walking stability of young and elderly persons are tested on different walking speed (steps/min.) or cadences in controlled walking mode. Results showed that young and most of the elderly subjects tries to optimize their cadence to get better walking stability. This method can be used as a mean to suggest a better walking speed to elderly people to increase their walking stability.

Assessment of walking stability by Lyapunov exponent estimation

This paper presents a unique technique to estimate walking stability utilizing a small and light-weight portable instrument. Lyapunov exponent estimation, a method of nonlinear time series analysis, was applied to quantify the dynamic stability of body sway during walking as measured by accelerometry. Fourteen young and twenty-one elderly subjects participated this study. Lyapunov exponent of the elderly subjects tended to be higher suggesting lower stability as compared to the younger subjects. Moreover, the elderly subjects suffering knee pain or frequent history of fall presented higher value as compared to those having exercise habit. The results suggest that Lyapunov exponent estimation of walking stability is useful to assess locomotive ability.

QUANTIFICATION OF DYNAMIC WALKING STABILITY OF ELDERLY BY USING NONLINEAR TIME-SERIES ANALYSIS AND SIMPLE ACCELEROMETRY

ABSTRACT This study presented a technique to assess dynamic walking stability utilizing a nonlinear time-series analysis and a portable instrument. Main objective was to investigate its usefulness in the assessment of elderly walking. The method was consisted of measurement of three-dimensional acceleration of the upper body, and estimation of the Lyapunov exponents, thereby directly quantifying local dynamic stability while walking. Straight level walking of young and elderly subjects was investigated in the experimental study. Effects and efficacies of the interventions for the elderly were demonstrated by the proposed method. The experimental results suggested that the method was useful in revealing degree of improvements on the walking stability.

Evaluation of the Severity of Dementia Using Expectation Control Function

The results of an animal experiment without anesthesia suggested the presence of expectation control in which sympathetic nerve tone increases at rest immediately before behaviors to prepare for the subsequent behavior. We investigated whether such function is present in humans in their daily living and whether patients with dementia could be differentiated from healthy adults based on this finding. Using a Holter electrocardiograph with an acceleration sensor, electrocardiograms (ECG) and behavioral states were recorded. The total recorded ECG was divided by 20 sec, and high (HF, 0.15–0.4 Hz) and low (LF, 0.03–0.15 Hz) frequency components were extracted by frequency analysis of the RR interval. We used the HF component, L/H ratio, and RR interval as the index grade of parasympathetic/sympathetic nerve tone. The mean value of each parameter was calculated and compared between the time zone during which resting persisted for 1 min or more (3 intervals) and that during which behaviors occurred immediately after a 1-min rest. In 32 patients with dementia, Holter ECG and behaviors were serially recorded, and the time zone during which intentional behaviors occurred was detected. RR interval and HF component decreased and L/H increased. Increasing in sympathetic nerve tone was observed at rest condition immediately before intentional behaviors, suggesting a presence of expectation control function. The expectation control mechanism will present inhumans and involved in this function by severity of dementia. This parameter may be useful for objectively evaluating the severity of dementia.