Development of a Core Body Thermometer Applicable for High-Temperature Environment Based on the Zero-Heat-Flux Method.

Monitoring core body temperature (CBT) allows observation of heat stress and thermal comfort in various environments. By introducing a Peltier element, we improved the zero-heat-flux core body thermometer for hot environments. In this study, we performed a theoretical analysis, designed a prototype probe, and evaluated its performance through simulator experiments with human subjects. The finite element analysis shows that our design can reduce the influence of external temperature variations by as much as 1%. In the simulator experiment, the prototype probe could measure deep temperatures within an error of less than 0.1 °C, regardless of outside temperature change. In the ergometer experiment with four subjects, the average difference between the prototype probe and a commercial zero-heat-flux probe was +0.1 °C, with a 95% LOA of -0.23 °C to +0.21 °C. In the dome sauna test, the results measured in six of the seven subjects exhibited the same trend as the reference temperature. These results show that the newly developed probe with the Peltier module can measure CBT accurately, even when the ambient temperature is higher than CBT up to 42 °C.

Development of a Rigidity Tunable Flexible Joint Using Magneto-Rheological Compounds-Toward a Multijoint Manipulator for Laparoscopic Surgery.

Laparoscopic surgery is a representative operative method of minimally invasive surgery. However, most laparoscopic hand instruments consist of rigid and straight structures, which have serious limitations such as interference by the instruments and limited field of view of the endoscope. To improve the flexibility and dexterity of these instruments, we propose a new concept of a multijoint manipulator using a variable stiffness mechanism. The manipulator uses a magneto-rheological compound (MRC) whose rheological properties can be tuned by an external magnetic field. In this study, we changed the shape of the electromagnet and MRC to improve the performance of the variable stiffness joint we previously fabricated; further, we fabricated a prototype and performed basic evaluation of the joint using this prototype. The MRC was fabricated by mixing carbonyl iron particles and glycerol. The prototype single joint was assembled by combining MRC and electromagnets. The configuration of the joint indicates that it has a closed magnetic circuit. To examine the basic properties of the joint, we conducted preliminary experiments such as elastic modulus measurement and rigidity evaluation. We confirmed that the elastic modulus increased when a magnetic field was applied. The rigidity of the joint was also verified under bending conditions. Our results confirmed that the stiffness of the new joint changed significantly compared with the old joint depending on the presence or absence of a magnetic field, and the performance of the new joint also improved.

NIR spectroscopic determination of urine components in spot urine: preliminary investigation towards optical point-of-care test.

Presently, there is no convenient method to measure 24-h urinary Na excretion, which is an important index of daily Na intake, and 24-h urine collection involves a complex process. However, the Na-to-creatinine ratio (NCR) in spot urine has the potential to evaluate 24-h Na excretion and is useful for point-of-care testing. Thus, this study aimed to realize a near-infrared spectroscopic system to assess NCR in spot urine: (1) We attempted to estimate Na concentration using fewer than 10 wavelengths; (2) we calculated NCR using creatinine concentrations from our previous report and verified the NCR predictability. A calibration model was created using multi-linear regression analysis using 10 selected wavelengths in the range of Fourier-transform infrared spectrometer. Spot urine samples were obtained from healthy adults, and glucose powder was added to them to simulate diabetic samples. NCR was calculated using only six wavelengths, and the results confirmed the high accuracy of the estimated Na concentration even though inorganic components do not absorb near-infrared light. Our method enables to optically estimate NCR in spot urine, and it will be useful for point-of-care testing. Graphical abstract.

Adaptive control with self-tuning for non-invasive beat-by-beat blood pressure measurement.

Up to now, we have successfully carried out the non-invasive beat-by-beat measurement of blood pressure (BP) in the root of finger, superficial temporal and radial artery based on the volume-compensation technique with reasonable accuracy. The present study concerns with improvement of control method for this beat-by-beat BP measurement. The measurement system mainly consists of a partial pressurization cuff with a pair of LED and photo-diode for the detection of arterial blood volume, and a digital self-tuning control method. Using healthy subjects, the performance and accuracy of this system were evaluated through comparison experiments with the system using a conventional empirically tuned PID controller. The significant differences of BP measured in finger artery were not showed in systolic (SBP), p=0.52, and diastolic BP (DBP), p=0.35. With the advantage of the adaptive control with self-tuning method, which can tune the control parameters without disturbing the control system, the application area of the non-invasive beat-by-beat measurement method will be broadened.

Attempt of a novel calibration method of pulse oximetry using support vector machines regression.

A novel calibration method using support vector machines regression (SVMsR) of pulse oximetry was proposed and attempted. Conventional calibration method of pulse oximetry that based on an optical density ratio of transmitted visible red light and infrared radiation whereas a proposed method here was not based on the optical density ratio directly. In theory, conventional calibrations using the ratio can be considered as a technique for nonlinear problem: nonlinear relation between two optical densities (red and IR) and oxygen saturation could be linearized by the ratio calculation. We thought, that nonlinear problem could be solved by using nonlinear analyses. Among them, the support vector machines regression method that has been studied well in this decade was attempted to be applied for pulse oximetry calibration. As an experiment, two photo plethysmograms (PPGs) by red and IR were measured on five subjects. Simultaneously, oxygen saturation (SpO(2)) level was measured by a commercial pulse oxymeter. SpO(2)) level was controlled by breathing 10% oxygen gas obtaining 98-75% SpO(2) level. Sequentially, feature points of two PPGs were extracted in beat by beat. Convex peaks and concave valleys on waveform and DC levels of PPGs were selected as feature points. Then, nonlinear regression using SVMs were attempted to obtain relationship between SpO2 by meter (regressand) and feature points of PPG (regressor). In result, a regression model was constructed from training data that is three fourths of measured cardiac data by using SVMsR. Finally, the constructed calibration model was evaluated by other one third data (validation data). The root mean squared error for the validation data is 1.90 [SpO(2)) level %] and 89% of validation data fell within +/- 2 % of SpO(2) level by the meter. In conclusion, SVMsR might be applicable on calibration for pulse oximetry.

A new method for determining the servo reference value (Vo) of the volume-compensation method.

A new technique for swiftly determine a servo reference value (Vo) of the volume-compensation method was developed. To determine the Vo values, high frequency vibration (frequency: 20 Hz, pulse pressure: 10 mmHg) was superimposed on cuff pressure (Pc), and artificially produced arterial wall oscillation was detected as photoplethys-mographic (PG) pulsation signal. In this signal, maximum oscillation points were observed when the mean value of Pc is equal to blood pressure, and Vo value was then determined from the mean level of PG signal at this maximum point. The values obtained by this method coincide well with those obtained by the previous method (the volume-oscillometric method), indicating the validity of the present method.

Support vector machines as multivariate calibration model for prediction of blood glucose concentration using a new non-invasive optical method named Pulse Glucometry.

A novel optical non-invasive in vivo blood glucose concentration (BGL) measurement technique, named "Pulse Glucometry", was combined with a kernel method; support vector machines. The total transmitted radiation intensity (I lambda) and the cardiac-related pulsatile changes superimposed on I lambda in human adult fingertips were measured over the wavelength range from 900 to 1700 nm using a very fast spectrophotometer, obtaining a differential optical density (delta OD lambda) related to the blood component in the finger tissues. Subsequently, a calibration model using paired data of a family of delta OD lambda s and the corresponding known BGLs was constructed with support vector machines regression instead of using calibration by a conventional partial least squares regression (PLS). Our results show that the calibration model based on the support vector machines can provide a good regression for the 183 paired data, in which the BGLs ranged from 89.0-219 mg/dl (4.94-12.2 mmol/l). The resultant regression was evaluated by the Clarke error grid analysis and all data points fell within the clinically acceptable regions (region A: 93%, region B: 7%).

Experimental and numerical study on optimal spot-electrodes arrays in transthoracic electrical impedance cardiography.

Transthoracic electrical impedance (or admittance) cardiography is a simple technique for the non-invasive and continuous monitoring of stroke volume or cardiac output by detecting the electrical impedance of a thorax which is roughly assumed to be a two-compartment coaxial cylindrical model composed of the aorta and its surrounding thoracic tissues. A tetra-polar band-electrodes method by Kubicek et al. has been widely used for the detection of the electrical impedance. However, this band-electrodes attachment makes a subject troublesome. Replacement of the band- to a spot-electrodes array is therefore highly required for practical use. In our previous reports, we have confirmed that a thorax is nearly assumed as an electrical cylinder model when a pair of current injection spot-electrodes are placed far from the thorax like a placement of the forehead - left medial knee or the mastoid process - lower right abdomen, and that the changes in current distributions associated with cardiac blood ejection are roughly homogeneous around the medial line of the thorax. The present study concerns with determination of an optimal spot-electrodes array for voltage pick-up through the detailed measurements of pulsatile components of the thoracic impedance along the medial line of the thorax using an 11x2 channels impedance mapping system. Additionally, we have investigated the influence of blood volume change in the heart itself by a finite element method.

Assessment of slow-breathing relaxation technique in acute stressful tasks using a multipurpose non-invasive beat-by-beat cardiovascular monitoring system.

Recently, several studies revealed that daily slow-breathing exercise lowered blood pressure and increased baroreflex sensitivity. With this interesting finding, we have been contemplating to design a compact breath-controllable device for relaxation to stress reaction during daily living for home as well as ambulatory use, as a final goal, towards reduction of cognitive hemodynamic disorders, hypertension, and acute stress-induced hemodynamic disorders. The present study thereby describes, as a first step, to design a prototype system combining a compact multipurpose non-invasive beat-by-beat cardiovascular monitor developed previously with a wrist-type vibrator to make a respiration rhythm, and to assess an effect of slow-breathing relaxation on the cardiovascular hemodynamics in response to acute stressful conditions. The cardiovascular hemodynamic monitor can measure beat-by-beat systolic (SBP), mean (MBP) and diastolic (DBP) pressure in a finger based on the volume-compensation method, cardiac output (CO) by the electrical admittance method and the other hemodynamic-related parameters (e.g., total peripheral resistance (TPR=MBP/CO), heart rate (HR), respiratory rate, pulse wave velocity, etc.). The wrist-type vibrator can give various breathing rhythms quietly to a subject using a small vibration motor. The stressful tasks loaded to healthy volunteers (3 males, 23-34 yrs.) in the experiments were cold pressor and arithmetic ones as a representative of daily passive and active coping tasks, respectively, under conditions with (respiratory rate of 6 1/min) and without breath control.. The results showed that the slow-breathing technique could have a significant effect on improvement of the hemodynamic changes following the acute stressful tasks, especially in the passive coping task.

Accuracy assessment of a noninvasive device for monitoring beat-by-beat blood pressure in the radial artery using the volume-compensation method.

For the noninvasive and accurate measurement of instantaneous blood pressure (BP) in the radial artery, the performance of a device based on the principle of volume-compensation was assessed by comparison with simultaneous measurement of direct (invasive) radial artery pressure in nine healthy subjects. Bias and precision of systolic BP (SBP) and diastolic BP (DBP) derived from Bland-Altman plots of data from the present system and the direct method averaged -0.5 +/- 2.1 mmHg and 0.6 +/- 1.8 mmHg respectively, over a wide range of SBP and DBP. These results clearly indicate that, using this system, instantaneous radial artery pressure can be measured noninvasively with high accuracy.

Feasibility study of a urine glucose level monitor for home healthcare using near infrared spectroscopy.

Urine glucose level monitoring technique using near infrared spectroscopy in conjunction with the chemometric method was newly developed aiming for the use of home health care. The calibration models were obtained by the partial least square method and their validity were assessed using albumin added glucose solution and urine samples. From the results obtained, it was clearly demonstrated that the present method had a capability of predicting urine glucose level with reasonable accuracy (standard error of prediction; 22.3 mg/dl, correlation coefficient; 0.99) and appeared to be a useful means for long-term home health care.

An optimal spot-electrodes array for electrical impedance cardiography through determination of impedance mapping of a regional area along the medial line on the thorax.

Electrical impedance or admittance cardiography is a simple method for non-invasive, continuous measurement the stroke volume and cardiac output. For the electrical impedance cardiography, the band-electrodes array proposed by Kubicek et al has been widely used, and various spot-electrodes array have been experimented in search of a less uncomfortable and equally reliable electrodes array that is easier to attach. From the uniformity of current distribution on the thorax, we have reinvestigated focusing on the measurement of contour maps of static and pulsatile components of a regional area along the medial line on the frontal part of the thorax. Consequently, the appropriate electrodes locations for current injection were determined as the back of an ear and on the lower abdomen, while those for voltage pick-up was on the medial portion at the level of clavicle and on the portion above the xiphisternum. Preliminary comparison experiments between the cardiac output values obtained by the electrical impedance cardiography and by a pulse dye-densitometry showed a fairy good agreement.

Assessment of stress-induced hemodynamic responses using multipurpose non-invasive continuous cardiovascular monitoring system.

In order to develop a simple and reliable assessment method of the stress induced psychosomatic and hemodynamic responses against various stress situations, especially for evaluating of the effectiveness of stress reduction methods, a multipurpose non-invasive continuous cardiovascular monitoring system was developed. The monitoring system could measure beat-by-beat finger blood pressure (SBP, MBP, DBP based on the volume-compensation method), cardiac output (CO, electrical admittance method), total peripheral resistance (TPR=MBP/CO), and the other hemodynamic related parameters (e.g. RR-interval, respiratory rate, pulse wave velocity, etc.). As controlled stress conditions, the human subjects would be exposed to the various stresses such as flash video display, electrical stimulation and so on. In this study, after 5 minutes resting, the stress induced hemodynamic responses were measured during 10-min presentation of floating vertical stripes image using 5 healthy subjects. The image presentation was discontinued when the subject gave his/her self-assessment due to considerable discomfort. The results showed that although BP increased during the presentation in all the subjects, there observed two types of cardiovascular responses; one is a type of increase in CO (or of almost unchanging or decrease in TRP), and the other of increase in TPR. These results strongly suggested that the detection of the change in TPR might be an important factor for the evaluation of stress conditions. Further investigations would be required for the reasons why these two types were observed in the same stressful condition.

Fully automatic system for monitoring blood pressure from a toilet-seat using the volume-oscillometric method.

Daily monitoring of health condition at home is very important subject not only as an effective scheme for early diagnosis and treatment of cardiovascular and other diseases, but also for prevention and control of such diseases. From this point of view, we have been developing a fully automated "non-conscious" monitoring system for home health care. In this paper are described, structural detail of a newly developed toilet-seat-installed blood pressure measurement system and some results obtained by the system. Also described is outline of a newly designed system for measuring hydrostatic pressure difference between the heart and the measuring site, i.e., thigh, during blood pressure measurement.

Development of an optical arterial hematocrit measurement method: pulse hematometry.

The blood hematocrit is well recognized as the versatile index of various physiological conditions especially for anemia, polycythemia and dehydration. However, the conventional method of the hematocrit measurement was conducted with the direct blood sampling. In this study, based on the similar principle of the pulse oximetry, a simple principle of optical noninvasive hematocrit measurement method, pulse hematometry, was introduced. And the performance of the optical sensor evaluated with healthy subjects was also reported. Because of its simplicity, the pulse hematometry would be promising technique as patients monitoring and daily healthcare.

Development of a tissue oxygen consumption measurement method based on near-infrared photoplethysmography.

A dual-wavelength reflectance optical oximeter sensor in combination with a simple photoplethysmographic technique was developed to measure the local tissue oxygen consumption from the simultaneous measurement of the arterio-venous oxygen saturation (SaO2, SvO2) differences, the physiological Fick principle. The performance of the reflectance oximeter was demonstrated in the theoretical simulation of the three-dimensional photon diffusion theory and the experimental study in the human subjects. As the results, the good agreements between theoretical and experimental studies of the oximeter were observed in the range of 70-100% SaO2 and 70-90% SvO2. The reflectance optical local tissue oxygen consumption measurement sensor would be applicable for various fields especially for the sports medicine, the patients monitoring and the transplanting organs monitoring.