Toshikazu Shiga

Study of an algorithm based on model experiments and diffusion theory for a portable tissue oximeter.

A portable tissue oximeter that uses light-emitting diodes and two-wavelength near infrared spectroscopy has been developed. The tissue oximeter is compact enough to be portable and it is therefore expected to make better use of the advantages of NIRS-based oximetry and to expand the scope of applications of monitoring tissue oxygen. The algorithm for this instrument was deduced through systematic experiments by varying blood volume and scattering intensity in a tissuelike phantom. The experimental results were compared with theoretical results obtained from diffusion theory. Experimentally determined coefficients of the algorithm were in close agreement with the theoretically derived coefficients. From evaluation tests of the algorithm applied to in vitro and in vivo measurements, it was confirmed that a good linear response to the concentration of oxygenated and deoxygenated blood can be obtained by this algorithm within a range of about a 50% change in concentration from an initial state.

Development of a portable tissue oximeter using near infra-red spectroscopy

NON-INVASIVE AND continuous monitoring of physiological conditions during cxcrcise is very important for clinical diagnosis, sports medicine, healthcare monitoring etc. For the continuous monitoring of cardiovascular conditions, several types of instruments have been developed, such as the Holter ECG (HOLTER, 1961; ISHn3A et al., 1990) and ambulatory blood pressure monitors (YAMAKOSHI, 1991); these instruments are now widely accepted for clinical and research use. On the other hand, for monitoring metabolic conditions which also provide important physiological information, only a few methods have been developed, such as MRS (WANG et al., 1990; ZATINA et al., 1986); they are expensive and complicated systems, and are not appropriate for use during exercise. The optical method is more convenient to use and is capable of detecting tissue metabolism, as has been shown in previous work (CHANCE et al., 1992). Therefore, this method may be useful as a portable monitor of metabolic conditions during exercise. Many attempts have been made to use this method for research. Study by the optical method began with the work of Kramer and Millikan, followed by the work of Chance and Weber on isolated tissue metabolism monitoring (KR~IER, 1935; MmLm~aq, 1937; CHANGE and WEBER, 1963). Jobsis first showed that near infra-red (NIR) region light has the characteristic of excellent penetration through biological tissues (JOBStS; 1977) after this the NIR method then attracted attention. Cope and Delpy and Rolfe et aL applied the multiwavelength NIR method to neonates, and Chance et al. applied simple ~jal wavelength spectroscopy for muscle studies (COPE and DELPY, 1988; ROLFE et aL, 1991; CHANCE et al., 1992). In recent years, Chance et. al. have developed quantitative noninvasive methods by using timeand frequency-resolved spectroscopy to determine the optical path length (CHANCE et aL, 1988; 1990). By using time-resolved spectroscopy, Delpy et al. esftmated the optical path length through tissue, and 9 Ferrari et a/. examined the spectral properties of muscle tissue (DELPY et al., 1988; FEBRARI et aL, 1992). However, many of these instruments, which have complex

Accurate NIRS measurement of muscle oxygenation by correcting the influence of a subcutaneous fat layer

Although the inhomogeneity of tissue structure affects the sensitivity of tissue oxygenation measurement by reflectance near-infrared spectroscopy, few analyses of this effect have been reported. In this study, the influence of a subcutaneous fat layer on muscle oxygenation measurement was investigated by Monte Carlo simulation and experimental studies. In the experiments, measurement sensitivity was examined by measuring the falling rate of oxygenation in occlusion tests on the forearm using a tissue oxygen monitor. The fat layer thickness was measured by ultrasonography. Results of the simulation and occlusion tests clearly showed that the presence of a fat layer greatly decreases the measurement sensitivity and increases the light intensity at the detector. The correction factors of sensitivity were obtained from this relationship and were successfully validated by experiments on 12 subjects whose fat layer thickness ranged from 3.5 to 8 mm.

A Simple Measurement Method of Visceral Fat Accumulation by Bioelectrical Impedance Analysis

Simple measurement of visceral fat accumulation is essential for diagnosis and treatment of metabolic syndrome. Bioelectrical impedance method is most suitable for theses measurements. However, measuring visceral fat volume without the influence of subcutaneous fat has been difficult because of the low spatial resolution of bioelectrical impedance method. In the present study, we have developed a simple method for the measurement of visceral fat accumulation using visceral fat bioelectrical impedance analysis (VF-BIA). For VF-BIA, an electric current (250 μA, 50 kHz) was applied to electrodes bilaterally fixed on the hands and feet, and the voltage was measured between six pairs of electrodes placed around the trunk at the umbilical level. The impedance reflects the total amount of abdomen fat, in addition to obtain the impedance of the body surface which reflects the amount of subcutaneous fat, the voltage induced by applying electric current to the electrodes placed on the body surface around the trunk at the umbilical level was measured with electrodes between the stimulating electrodes. Regarding to measure these two impedance values we adopted the four electrodes method.

A new simple measurement system of visceral fat accumulation by bioelectrical impedance analysis

Measurement of visceral fat accumulation is essential for the diagnosis of obesity. Currently, the visceral fat area (VFA) obtained from the abdominal cross-sectional image measured by X-ray CT is used as the gold standard. However it has problems of complexity, cost, and X-ray exposure. On the other hand, the waist circumference is used as a simple index, but it is indirect method and is affected by subcutaneous fat. Bioelectrical impedance analysis (BIA) is a proven method practically used to measure total body fat, and is the most suitable for the measurement of visceral fat accumulation. For the latter purpose, we developed a new simple measurement system using dual current pathways bioelectrical impedance analysis (dual-BIA). This proposed system measures imped ance reflecting the subcutaneous fat volume (SFV) and the fat free volume (FFV) in the abdomen by passing current via respective pathways. Regarding to measure these two imped ance values we adopted the four electrodes method. The VFA was calculated by using these two impedance values and abdominal body shape data to minimize the influence of FFV and SFV. We compared the VFA measured by dual-BIA system with that measured by X-ray CT in 98 subjects, and found a high correlation coefficient (r=0.888, p<0.001). Our proposed system is suggested to be useful for a simple visceral fat accumulation measurement.

Influence of a fat on muscle oxygenation measurement using near-IR spectroscopy: quantitative analysis based on two-layered phantom experiments and Monte Carlo simulation.

The influence of a subcutaneous fat layer on measurement of muscle oxygenation using near-IR spectroscopy was quantitatively investigated by two-layered phantom experiments and Monte Carlo simulations, with the aim of developing an algorithm that can correct this influence. The phantom consisted of a fat-like layer, which was a mixture of agar and titanium dioxide powder, and a muscle-like layer, which was suspension of washed bovine blood in Intralipid solution. An LED with 760 and 840 nm elements was used as an optical source, and the backscattered light was detected by photodiodes at source-detector distances of 20, 30 and 40 mm. The relationships between changes in optical density and blood concentrations were obtained at fat-like layer thicknesses of 0, 5, 10 and 15 mm under fully oxygenated and fully deoxygenated states. It was experimentally found that the change in optical density is significantly decreased and the linearity of measurement characteristics is clearly distorted by the presence of a fat layer. In the simulations, normalized light reflectance and mean optical pathlength in a muscle layer were calculated. The simulation results of the light reflectance agreed well with the experimental results. When the absorption in a muscle layer was relatively high, the mean optical pathlength in the muscle layer, or the measurement sensitivity, was not so dependent on the absorption. Therefore, the modified Beer-Lambert law can still be applied to estimate changes in muscle absorption from changes in optical density, even when a fat layer is involved. The results of simulation also suggested that the influence of a fat layer can be eliminated by correcting the measurement sensitivity using the fat layer thickness.

A Wearable Healthcare System With a 13.7

To prevent lifestyle diseases, wearable bio-signal monitoring systems for daily life monitoring have attracted attention. Wearable systems have strict size and weight constraints, which impose significant limitations of the battery capacity and the signal-to-noise ratio of bio-signals. This report describes an electrocardiograph (ECG) processor for use with a wearable healthcare system. It comprises an analog front end, a 12-bit ADC, a robust Instantaneous Heart Rate (IHR) monitor, a 32-bit Cortex-M0 core, and 64 Kbyte Ferroelectric Random Access Memory (FeRAM). The IHR monitor uses a short-term autocorrelation (STAC) algorithm to improve the heart-rate detection accuracy despite its use in noisy conditions. The ECG processor chip consumes 13.7 μA for heart rate logging application.

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The objective of this study was to determine the optimal number and type of casual (spot) urine specimens required to estimate an individual’s urinary sodium/potassium (Na/K) ratio. A total of 48 participants, 25 men and 23 women, aged between 25 and 59 years, was recruited from healthy volunteers. The Na/K ratio in each casual urine and 7-day 24-h urine sample was measured. Correlation analysis and the quality of agreement by the Bland and Altman method between casual urine and 24-h urine were analyzed. The mean Na/K ratio of 7-day 24-h urine was 4.3. The mean Na/K ratio of six random specimens of daytime (collected between 09 and 17 hours) casual urine correlated most strongly with the Na/K ratio of 7-day 24-h urine (r=0.87). The bias for the mean Na/K ratio between 7-day 24-h urine and daytime casual urine was almost negligible (0.03), and the quality of agreement for the mean of the six random, daytime casual urine specimens on different days was similar to that of the 2-day 24-h urine samples for estimating 7-day 24-h values. Our findings show that the mean Na/K ratio of six random daytime casual urine specimens on different days was a good substitute for the 2-day 24-h urine Na/K ratio.

A Noise Tolerant ECG Processor

Because almost all nations have come into aging society, it has been much more important to provide systems approach on health care than ever. There are many studies on human body from the view points of diseases however health has not been clearly defined. It would be difficult to clarify the notion of health because of various concepts of values and some cultural issues. With regarding this situation, Systems Healthcare would be new study area considering human health and wellness based on sensing and information technology. There have been developed various smart devices and services to prevent diseases and to improve health based on sensory data to realize the condition of our health. Causality between lifestyle and vital signals plays a important role for realizing them. In this article, the notion of Systems Healthcare is proposed and discussed.

Six random specimens of daytime casual urine on different days are sufficient to estimate daily sodium/potassium ratio in comparison to 7-day 24-h urine collections.

Summary Objective To develop a clinical method for evaluating skeletal muscle (SM) mass using whole-body bioelectrical impedance (BI) analysis in the standing position. Subjects Two hundred and forty-four volunteers (men=106 and women=138) participated in this study. The subjects were randomly separated into validation and cross-validation groups. Methods The whole-body impedance ( Z ) between the hands and feet was measured in the standing position. A stepwise multiple regression analysis was used to develop the prediction equation for SM mass. Whole-body SM mass, measured by magnetic resonance imaging (MRI), was used as a reference. Results BI index (height 2 / Z ), body surface area (BSA), gender, and age were selected as significant contributors to predict SM in the validation group. There was no significant difference between the measured and estimated SM mass and no systematic error in BI analysis in the cross-validation group. All data were pooled to generate the final regression equation: SM mass \( kg \) = \( 0.126 × BI index \) + \( 1.937 × BSA \) + \( − 0.062 × age \) + \( − 2.186 × gender \) − 2.881 , where age is in years. Gender for men=1 and women=2. Analysis revealed that the slope and intercept were not significantly different from one and zero, respectively. The r 2 and SEE values of the regression equation were 0.893 and 1.65kg, respectively. Conclusions Using our developed prediction equation, the BIA system can be used to accurately evaluate whole-body skeletal muscle mass with the subject in the standing position.