Harutoyo HIRANO

In recent years, the demand for highly nutritious and functional vegetables has been increasing in the agricultural sector. In order to cultivate highly functional vegetables, it is necessary to adjust the nutrients in the soil, such as potassium ions, to an optimal state. Therefore, there is a need for a sensor that can measure soil ion concentration in real time in the field. In this report, we aim to develop an ion concentration sensor using NMR (Nuclear Magnetic Resonance). Since the sensor observes atomic specific behavior, it has the potential to measure the concentration of each ion species in soil where multiple ions exist. In this laboratory, we aim to realize compact NMR and to establish a method for NMR measurement of water ahead of ion measurement. Using an NMR measurement system of our own design, we measured water and air. As a result, NMR signal spectra were obtained only when measuring water under resonance conditions, and resonance frequency of hydrogen atoms were successfully measured. We have established an NMR signal measurement method for measuring ion concentrations using a small NMR sensor that can be installed in the agriculture.

Real time measurement of soil pH is demanded in precision agriculture. Therefore, pH measurement capability in low water content soil was needed to confirm. In this paper, we fabricated an ISFET type pH sensor which can be inserted into soil. The sensor performed to measure two type of experiments. First, we experimented with changes in sensor output due to soil water content. The sensor output voltages were changed by changes in the soil pH value. In contrast, the voltages didn't be changed by changes in the soil water content. Secondly, we experimented whether the output of the sensor shows the same change when the soil pH changes during the measurement. The sensor could detect the pH value of soil which was changed dramatically by passing water. We confirmed that the ISFET type pH sensor can directly measure soil pH in real time.

This paper proposed a novel objective pain intensity assessment technique using the change of peripheral arterial stiffness β, which reacts to a peripheral sympathetic nervous activity. The stiffness β is calculated from continuous arterial pressures and photo-plethysmograms beat-by-beat based on the log-linearized peripheral arterial model. In the experiment, the validity of the proposed method was examined by comparing estimated normalized arterial stiffness β_n with simultaneously-measured numeric rating scale (NRS) as a general index of pain intensity when electrocutaneous stimuli were applied to the healthy subjects. The results showed the maximum amplitude of electrocutaneous current I_max has linear correlation with the normalized stiffness β_n (R² =0.77, p < 0.05). In addition, both the maximum amplitude of electrocutaneous current I_max and the normalized stiffness β_n strongly correlated with NRS values by sigmoidal curves (I_max v.s. NRS: R² =0.91, p < 0.01; β_n v.s. NRS: R² =0.92, p < 0.01). It was therefore concluded that the proposed method can assess pain intensity objectively.

This paper proposes a novel diagnosis support method based on peripheral autonomic nervous activity for patients with Parkinson's disease (PD). The method measures rates of change in fingertip plethysmograms and arterial stiffness in transition between a supine position and a standing position of a subject, and calculates fingertip plethysmogram and arterial stiffness changes associated with angular variation from the pre-standing supine position to the standing position during a head-up tilt test. Based on the measured indices, the classification probability of PD presence is finally obtained as a biomarker using a log-linearized Gaussian mixture network. 25 patients with PD symptoms (15 with autonomic defects and 10 without) took part in the experiment. The results showed non-significant differences between the patient groups with autonomic defects and without autonomic defects in comparison of each single index on fingertip plethysmogram and arterial stiffness, but a significant difference (p<0.001) between the two groups was observed in the output index of the proposed system. Moreover, receiver operation characteristics (ROC) analysis showed that the area under the curve (AUC) of the proposed biomarker was 0.83 and the classification rate of PD presence was 100% for the learning data and 80% for the unlearned test data.

The flow-mediated dilation (FMD) test is a method of evaluating the vascular endothelial function and has been popular as it is noninvasive and readily performed by a skillful ultrasound technician. The FMD test, however, evaluates only the maximal increase in vascular diameter mediated by the increases in blood flow after the release of the occlusive cuff and does not evaluate the arterial viscoelastic properties. Therefore, this paper proposes a new index, called log-linearlized viscoelasticity, to evaluate the arterial viscoelastic properties using the arterial diameter and blood pressure measured in a beat-to-beat manner during the FMD test. To six healthy people, we performed the FMD test to measure the arterial diameter and blood pressure with ultrasound diagnostic imaging equipment and noninvasive continuous arterial blood pressure monitor. As a result, the maximal vasodilatation ratio of FMD (%FMD) was obtained after cuff occlusion. In comparison with the arterial viscoelastic characteristics before FMD test, the stiffness of the arterial wall β and the viscosity of the artery η temporarily decreased and increased, respectively. The change of log-linearlized viscoelasticity after cuff occlusion may be caused by vascular endothelial function. Vascular endothelial function might thus be estimated using the arterial viscoelasticity β and η.

This paper proposes a method for evaluating endothelial function based on the dilation rate of an integrated air-cuff plethysmogram measured using an oscillometric approach. The method is not affected by blood pressure variations, and can be used to assess endothelial function quickly. In the study, the dilation rate of an integrated air-cuff plethysmogram was simulated to verify that the proposed method is suitable for evaluating arterial compliance changes related to endothelial function. The simulation results showed that changes in arterial viscoelastic characteristics can be assessed using the technique. Then, the proposed dilation rate for the integrated air-cuff plethysmogram and the value of percent flow-mediated vasodilation (%FMD) (a standard index used to evaluate endothelial function) were measured in the same subjects, with the results showing a significant correlation (r= 0.589) between the two. In addition, receiver operation characteristics (ROC) analysis was conducted to verify the method's effectiveness in determining the risk of arteriosclerosis. The results showed that the area under the curve (AUC) of the proposed index was 0.914, which was greater than or equal to the %FMD value. It was therefore concluded that the proposed method has potential for clinical use.

This paper proposes a method for qualitatively estimating the mechanical properties of arterial walls on a beat-to-beat basis through noninvasive measurement of continuous arterial pressure and arterial diameter. First, in order to describe the nonlinear relationships between arterial pressure waveforms and arterial diameter waveforms as well as the viscoelastic characteristics of arteries, we developed a second-order nonlinear model (called the log-linearized arterial viscoelastic model) to estimate the viscoelasticity of arterial walls. Next, to verify the validity of the proposed method, carotid viscoelastic indices were estimated based on arterial pressure waveforms measured using an ultrasonic device, and on arterial diameter waveforms measured using a noninvasive sphygmomanometer. The results showed that the proposed model could be used to accurately approximate the mechanical properties of arterial walls, and it was confirmed that the viscoelastic indices of arterial walls were proportional to age (stiffness: r=0.870; viscosity: r=0.668; and modified viscosity: r=-0.720). It was therefore concluded that the proposed model can be used to qualitatively evaluate arterial viscoelastic properties based on noninvasive measurement of arterial pressure and arterial diameter.

This paper proposes a novel technique to monitor peripheral vascular conditions by using biological signals, such as electrocardiogram, arterial pressure, and pulse oximetric plethysmogram. A second-order log-linearized model (called the log-linearized peripheral arterial viscoelastic model) is used to describe the nonlinear viscoelastic relationship between the blood pressure waveform and the transillumination plethysmographic waveform. The proposed index is able to estimate the changes of stiffness of peripheral arterial wall induced by sympathetic nervous activity, and the validity of the proposed method is then discussed by monitoring peripheral vascular conditions during arm position tests and during endoscopic thoracic sympathectomies (ETSs). As results of the arm position tests, the stiffness was arm position-independent (Up: 4.0 [%], Down: 5.5 [%]). Then, as results of the ETSs, the variation of the stiffness was significantly changed between before and during the ETS procedure (p < 0.01), and between during and after the ETS procedure (p < 0.01). The above experimental results clearly show that the proposed method can assess changes in the sympathetic nervous activity during ETSs.

This paper proposes a novel non-invasive and palpable measurement sensor for carotid pulse pressure. The unit consists of a pair of coil printed circuit boards, a pair of springs and a sensing plastic chip, with each spring attached between the circuit board and the chip. The distance between the boards is monitored from the displacement of the springs, and the information is converted into a voltage signal based on electromagnetic induction. First, the optimal forces externally applied to the proposed sensor were examined to allow accurate measurement of carotid pulse wave amplitude variations. It was found that the force applied when the measured maximum amplitudes of the sensor were obtained yielded the best performance. Next, carotid pulse waves were measured using the sensor with these optimal forces, and the results were compared with carotid pulse pressure values measured using a commercialized pulse wave transducer. The resulting coefficient of correlation between the two carotid waves was 0.9 or more. It was therefore concluded that the proposed sensor enables non-invasive measurement of carotid pulse waves.

This paper proposes a noninvasive method for estimating the dynamic characteristics of arterial walls using pulse waves measured in various parts of the body by a foil-type pressure sensor. The sensor not only has high sensitivity and flexibility but also features the ability to continuously measure the alternating-current component of pulse waves. These capabilities make it suitable for estimating the dynamic characteristics of arterial walls. In this paper, a foil-type pressure sensor was employed to measure pulse waves based on the tonometry approach, and a method of estimating changes in arterial viscoelastic indices was proposed based on the measured pulse waves and photoplethysmograms. In order to accurately measure blood pressure, first, we examined suitable mechanical forces to the sensor, and found that values of 5-25[N] yielded the best performance. We then estimated the arterial viscoelastic indices of a radial artery and a dorsal pedis artery when mechanical pain stimuli were applied to the subjects. The results suggested that the estimated indices can be used to quantitatively assess vascular response caused by sympathicotonia. We thus concluded that the proposed method enabled noninvasive measurement of pulse waves in the dorsal pedis artery and estimation of arterial viscoelastic indices.