The maximum cross-correlation coefficient (ρ_max) between blood pressure (BP) and heart rate (HR) variability for frequency components limited to the Mayer wave-related band is useful for the evaluation of baroreflex function. However, continuous BP measurement with an expensive and bulky measuring device is required to calculate ρ_max. This study proposes a simpler method to obtain ρ_max using a green light photoplethysmogram (PPG). A green PPG sensor is less affected by motion artifacts than a near-infrared PPG sensor. In this study, an electrocardiogram, continuous BP, green PPG, and near-infrared PPG were obtained from the subjects. HR, mean BP, and pulse transit time were estimated from the signals, and ρ_max was subsequently calculated. Compared to the ρ_max obtained from the near-infrared PPG signal, the ρ_max obtained from the green PPG signal is closer in value to the ρ_max obtained from mean BP. These results show that the green PPG sensor can be used to estimate baroreflex function instead of using continuous BP measurement.

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Atonia during rapid eye movement (REM) sleep is absent in patients with REM sleep behavior disorder (RBD), a phenomenon called REM sleep without atonia (RWA). RBD patients have symptoms in common with neurodegenerative diseases, and data from follow-up studies on idiopathic RBD patient indicate that RBD predicts development of neurodegenerative diseases, particularly Parkinson's disease (PD). Therefore, early diagnosis of RWA can help identify and possibly prevent neurodegenerative diseases. Currently, RWA assessment by visual analysis of polysomnogram (PSG) is only moderately reliable and extremely time-consuming, making it difficult to obtain objective, quantifiable results. We developed an algorithm to automatically quantify tonic and phasic electromyographic (EMG) activities of the musculus mentalis during REM sleep using the scoring manual proposed by the American Academy of Sleep Medicine. Hilbert transform and average rectification were used to calculate the amplitudes of phasic and tonic muscular activities, respectively. Parameter values in the algorithm were optimized by cross-referencing the classification result obtained from the algorithm with the result from epoch-by-epoch visual inspection by a neurologist. A total of 2315 REM epochs from 24 PD patients were analyzed. We calculated the optimal parameter set, at which the sum of sensitivity and specificity was the highest, as well as the area under the receiver operating characteristic (ROC) curve (AUC). Verification tests showed good detection accuracy (phasic: sensitivity = 88%, specificity = 82%, AUC = 0.92; tonic: sensitivity = 88%, specificity = 85%, AUC = 0.93). Thus, this automated RWA detection algorithm is potentially useful for rapid and accurate diagnosis of RBD.

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We determined the anatomical geometry and thicknesses distribution of the triceps surae aponeuroses from anatomical observation of a human cadaver. Geometry of the aponeuroses was examined by two dimensional photoanalysis. The thicknesses of slices dissected from various regions of the aponeuroses were measured with digital microscope. The results of quantified geometry and thickness of the aponeuroses suggest that the portions frequently experiencing large forces, such as the aponeuroses at the insertion of the posterior soleus and origin of anterior soleus, possess thicker tissues. This quantitative information may contribute to biomechanical simulation and modeling to reveal the function of the muscle-aponeurosis-tendon complex, and development of realistic simulation models would facilitate surgical and treatment design.

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The purpose of this study is to develop a simple back assistive device that generates sufficient assistive moment and is not subject to resistant forces while walking. It is widely known that many labor workers suffer from low back pain. To diminish their low back pain, development of a simple and practical back assistive device for use in the workplace is highly recommended. Some simple back assistive devices using elastic elements have been proposed. However, under walking conditions, elastic tension generated by flexion of the hip joint exerts a resistant force against walking. Since the majority of physical workers in industries or other fields have to walk while performing tasks, they require a back assistive device that has sufficient assistive moment in a bending forward posture and does not generate a resistant force while walking. The problem is how to decrease the undesirable resistant force from elastic elements caused by walking, while maintaining a back-supporting property in bending forward tasks. Focusing on the reciprocal motion of legs in walking, we devised a simple mechanism by which elastic tension is diminished under walking conditions. On the other hand, the tension of elastic elements is available in bending forward posture. Making use of the reciprocal motion of legs, two swing arms mounted on the device rotate synchronously with legs. Using this mechanism, elastic tension is almost completely eliminated under walking conditions. The swing arms rotate in the same direction under walking condition, but they cannot rotate in the opposite direction, so that elastic elements are stretched to produce an assistive moment for the back in a bending forward posture. The device proved to be effective in reducing undesirable tension in the lower belt under walking condition. The tension of elastic elements caused by walking decreased to less than one-quarter compared with that of conventional back assistive devices.

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Gaze information has been used in numerous fields such as cognitive psychology research, input interfaces, and intelligent transport systems. In this study, we focused on electro-oculographic methods because of the low level of inconvenience to users, and developed a simple method for gaze estimation based on planar approximations of the voltage ratios (Vr) calculated from multiple electro-oculogram signals. The results suggest that Vr can be used for estimating gaze without being affected by the drift phenomenon that reduces the estimation accuracy. Numerical experiments using an eyeball battery model reveal that the proposed method can be used in yaw and pitch ranging from −40° to 40° and −30° to 30°, respectively, with an estimated error of approximately 3.5°, using at least nine electrodes arranged in an L shape.

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We previously proposed the use of acoustic microbubble delivery in blood vessels as a therapeutic application of microbubbles to improve the efficiency of high-intensity focused ultrasound and the efficacy of acoustic targeted drug therapy. Among the technical requirements for this technique is detailed visualization of the blood vessel network for navigation around a target such as a tumor. For this purpose, three-dimensional (3D) Doppler volumes, which can be acquired by matrix array imaging probes, are quite convenient because they allow the blood vessel structure to be extracted without segmentation. However, the acquirable volume is limited and incomplete because the Doppler signal depends on flow direction. To compensate for these issues, an ultrasound volume fusion technique is required. In this study, we propose a blood vessel volume fusion method by automatic registration among shared bifurcations. In addition, we propose a novel 3D ultrasound calibration method, which is needed to determine the initial transformation. Several optical markers are used as fiducial markers in this calibration. To examine the feasibility of the proposed methods, calibration accuracy and volume fusion accuracy assessments were conducted using an artificial blood vessel and in human subjects. Regarding calibration accuracy, the target registration error of the proposed method was 2.2 mm. Regarding volume fusion accuracy in the artificial blood vessel, the mean distance between the shared bifurcations was reduced from 2.4 mm (initial transformation by tracking data) to 0.5 mm (registration of shared bifurcations). Regarding the volume fusion of blood vessels in human subjects, the distance was also reduced from 10.4 mm to 0.3 mm. The results demonstrate that the proposed methods are accurate for constructing large and complete blood vessel networks for navigation of microbubble delivery. Moreover, the methods may also be useful for extracting intraoperative blood vessel network to support minimally invasive surgery or therapy.

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The aim of this study was to identify factors affecting the relationship between heart rate variability (HRV) and physical acceleration (PA) in daily lives of free-moving adults. In 65 subjects comprising 18 young (20 to 39 years), 26 middle-aged (40 to 59 years), and 21 elderly (≥ 60 years) subjects, ECG R-R intervals and PA data were simultaneously obtained every minute for 24 hours as the subjects went about their normal daily lives. The R-R intervals were subjected to linear frequency domain analysis, and the low frequency (LF)/high frequency (HF) and HF/(LF+HF) ratios were used as HRV indices. Lag was defined as the time difference that gave maximum cross-correlation between the HRV parameters and PA. The proportion of subjects who exhibited no lag was significantly higher in young subjects, and was significantly lower in elderly subjects. After waking, the proportion of subjects who exhibited no lag tended to decrease in all groups. The lag between HRV and PA correlated significantly with psychological conditions and/or mental stress.

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Recently, ultra-low field MRI (ULF-MRI) has attracted attention as a medical imaging technique. In ULF-MRI, because nuclear magnetization is very weak, hyperpolarized nuclear magnetization is expected to increase the intensity of MR signals. The use of hyperpolarized xenon gas, which has substantially larger polarization ratio than protons, has been proposed. However, MR signals decay rapidly when a large gradient field is used in MR signal detection. Meanwhile, the sweep imaging with Fourier transformation (SWIFT) approach, which utilizes an adiabatic radio frequency pulse with amplitude and frequency modulations and small gradient field, has been proposed. In this study, we evaluated the influence of the parameters used in the SWIFT approach on hyperpolarized xenon imaging in ULF-MRI. To simulate signal reconstruction of hyperpolarized xenon with the SWIFT approach, we calculated motions of magnetization according to the Bloch equation using a fourth-order Runge–Kutta method. Two pyramidal profiles with widths of 25 and 75 mm were simulated as nuclear magnetization density profiles. The motions of magnetization and the acquired MR signals caused by magnetization were subsequently computed using various parameters comprising sampling points, bandwidth, and duration of excitation. The signals were finally reconstructed using a cross-correlation method. The results indicated that reconstructed signals could be calculated from the MR signals acquired by the SWIFT approach at a bandwidth of 1, 10 or 100 kHz and a matrix size of 100, 200 or 400. However, signals reconstructed using a bandwidth of 1 kHz or a matrix size of 100 were distorted near the position where the signal changed. These results suggest that a wide bandwidth (≥10 kHz) and a large matrix size (≥200) should be used for better signal reconstruction from the MR signals acquired by the SWIFT approach, and that the Larmor frequency of ULF-MRI should be greater than 10 kHz to achieve wide bandwidth. In addition, DC component distortions in the reconstructed signals increased when distribution of nuclear magnetization density in the field-of-view (FOV) was large. Therefore, a wide FOV should be selected to reduce DC component distortions.

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Many different quadrupedal walking patterns (gaits), such as “walking”, “trotting”, “bounding” and “galloping” can be generated by systems of coupled central pattern generators (CPG). However, the physiological mechanisms for the walking patterns are unclear. As a result, from an engineering viewpoint, many different mathematical models have been proposed to describe these walking patterns. In this report, we propose a hard-wired CPG network based on Rybak's model that can reproduce quadrupedal locomotion walking patterns. In this network, we use the beating model proposed by Hoshimiya et al. and the bursting model proposed by Maeda and Makino. The main purpose of this study was to reproduce the typical walking patterns; “walking” and “bounding”, with a hardware model, and to switch between these patterns using only one parameter, which can be interpreted as voltage stimulation from the midbrain locomotor region. We found the transition from the “walking” to the “bounding” behavior to be due to a relative weakening of the coupling between the CPGs in the network by stimulation from the midbrain locomotor region.

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In this study, we proposed and examined the evaluation method for image processing of capillary vessels in the fingertips. Objectification of an image has many problems; especially, it is difficult to evaluate meandering of a blood vessel. Therefore we extracted the vessel shape from a clinical image, and simplified it to numeric data representing the characteristics of the shape. Using clinical illustration of the nailfold capillary, we investigated the characteristics of the nailfold capillary by feature point extraction techniques. We created a simplified program that automatically calculates the parameters of fingertip blood vessels from clinical images. This technique may be potentially useful to evaluate the status of capillaries after intake of supplements, by measuring the parameters of the microcapillary shape.

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Mitochondria are subcellular organelles that synthesize ATP, generate reactive oxygen species (ROS), and control cellular fates such as apoptosis and aging. Mitochondria generate different amounts of ROS in association with their morphologies. Cyclic stretch is a mechanical stimulation exerted on cells due to arterial pulsation, and induces cells to generate mitochondrial ROS. Therefore, one can speculate that morphological changes of mitochondria may play a role in mitochondrial ROS generation in cells under cyclic stretch. However, whether the morphologies of mitochondria are actually altered under cyclic stretch remains unclear. This study attempted to answer this question by time-lapse imaging the morphological dynamics of mitochondria in bovine aortic endothelial cells (BAECs) subjected to two levels of uniaxial cyclic stretch: (1) a physiologic level (5% at 1 Hz) for 1 hour, and (2) a supra-physiologic level (20% at 1 Hz) for 1 hour. Mitochondria were stained with Mito-tracker Orange, and MicroP software and FibrilTool were used for mitochondrial alignment and length analyses. No clear changes in the average length of mitochondria were observed at the physiological level of stretch (5%) compared to no stretch (0%), while the average length was decreased by the supra-physiological level of stretch (20%). In addition, cellular alignment was not different between 0% and 5% stretches, but the cells became perpendicularly aligned in the direction of stretch when 20% stretch was applied. Cellular circularity was not significantly different among the three levels of cyclic stretch. Thus, BAECs exhibited changes in both mitochondrial dynamics and cellular remodeling dynamics under 20% stretch, but showed no changes in both under 5% stretch. The results indicate that changes in morphological dynamics of mitochondria correlate with changes in cellular dynamics, particularly change in cellular alignment.

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Artifacts that contaminate electroencephalography (EEG) signals make it difficult to analyze EEG. The aim of this study was to removal artifacts on EEG, especially those caused by motion, to measure EEG in unconstrained situations. In a previous study, head movements were detected by an accelerometer, and motion artifact components were separated from the recorded EEG by independent component analysis (ICA). This method is effective for reducing the effect of artifacts, but has a risk that EEG components are also removed. In this paper, we introduce an improved artifact removal method based on ICA and filtering. EEG were decomposed by ICA, and a Pearson's correlation coefficient was calculated between each independent component and each hybrid accelerometer value to distinguish artifact components. Artifact components were then high-pass filtered. In this study, subjects were instructed to move their heads randomly, while keeping their eyes closed. The previous method was adapted using 1, 2, 3, 5 and 10 s to find the most suitable epoch to minimize the mean absolute amplitude of the cleaned EEG. Then, using this epoch, the proposed method was compared with the previous method by frequency analysis. Low frequency power (0.1–3 Hz) was normalized to unity because most power caused by motion artifacts exists in the low power band. If the normalized theta (4–8 Hz), alpha (8–13 Hz) and beta (13–40 Hz) powers of cleaned EEG are higher than that of raw EEG, this indicates that the effect of motion artifacts is small and EEG components are retained. The results obtained from theta and alpha power comparison showed that the proposed method performed better than the previous method. This result suggests that the proposed artifact removal method is more effective to reduce the effect of artifacts while retaining the EEG components.

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Control of vasospasm is one of the most important problems in postoperative management after the occurrence of subarachnoid hemorrhage. Transcranial Doppler ultrasonography (TCD) is a non-invasive test that measures cerebral blood flow. However, high-intensity interference returned from the cranium causes estimation errors. A moving target indicator (MTI) filter is widely used to suppress the interference. The MTI filter suppresses only static target echoes, and hence the time-varying interference component caused by movement of the probe remains. To suppress the time-varying component, we apply spatial domain interferometry (SDI) with the Capon method to the MTI filtered signal. The method suppresses interference by minimizing the output power under the constraint condition of a constant response from a desired direction. The method requires estimation of the covariance matrix between signals received at the elements by averaging independent data. Conventional imagers based on SDI with the Capon method average the matrix in the temporal direction only in order to achieve high axial resolution. In TCD, both high temporal resolution and sufficient accuracy in measuring blood flow velocity are desired. Therefore, we propose a technique that averages the covariance matrix in both temporal and axial directions. We evaluated the performance of an SDI imager using the proposed technique in a simulation study, in which the array size was 12 elements, the transmit center frequency was 2.0 MHz, and the temporal and axial averaging lengths were 0.70 ms and 5.6 mm, respectively. The ratio of desired signal intensity to cranium interference intensity was −40 dB. The delay and sum (DAS) beamformer failed to estimate blood flow velocity of 1.0 m/s, and estimation error and standard deviation of 1.9 and 0.92 m/s, respectively. When the size for spatial averaging ranged from 25% to 50% of the number of elements, the proposed SDI beamformer succeeded to estimate the velocity of 1.0 m/s with estimation error and standard deviation of 0.044 m/s and 0.035 m/s, respectively. In contrast, the conventional SDI beamformer had estimation error and standard deviation of 0.17 and 0.25 m/s, respectively. These results indicate the effectiveness of the proposed technique in applying the SDI imaging method to TCD.

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Pituitary tumors frequently compress the optic chiasm, causing visual field deficits. Surgical removal of these tumors could improve visual functions. Thus, predicting the prognosis of visual field function is required, but currently there is no method for predicting postoperative visual field status from preoperative data of tumor and optic chiasm characteristics. In this study, we performed preoperative evaluation of visual field prognosis using numerical parameters in 40 patients with pituitary tumors. Data from 30 patients were used to calculate the regression equation and those from the remaining 10 patients were used to confirm the validity of these equations. We defined quantitative values (area of tumor, A_tumor; curvature of chiasm, C_chiasm; and area of chiasm, A_chiasm) based on tumor size, tumor shape, and optic chiasm shape as determined using magnetic resonance imaging. We determined pre- and postoperative visual field sizes by ophthalmologic methods, and quantified them as numerical values (TNR). Postoperative recovery of the visual fields (obtained by comparing the post- and preoperative visual fields) was confirmed by increased postoperative TNRs (P < 0.01 for 4 isopters and P = 0.01 for 1 isopter, t-test). We attempted to predict postoperative visual field size using preoperative A_tumor, C_chiasm, and A_chiasm. Multiple regression analysis was performed, and three significant regression equations for predicting visual field size were obtained (N = 30, P < 0.01, F-test). The measured and predicted visual field sizes showed strong correlation (N = 10, r > 0.70). Thus, the quantitative parameters defined in this study clearly predicted postoperative visual functions in patients with pituitary tumor, and could find clinical applications in preoperative evaluation of visual field prognosis in neurosurgery.

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This paper reviews endeavors over the past decades to achieve seamless monitoring of various types of physiological information by a variety of high user-affinity approaches applicable to the daily life environment. Developments in academic research and commercialization from the early period are reviewed. The latest outcomes are briefly investigated and roughly categorized into three main models: miniature portable monitors for ambulatory application, functional fabric-based wearable monitors for better comfort, and unobtrusively deployed invisible monitors for optimum usability. Monitors for seamless monitoring of physiological information in the daily life environment differ from conventional devices that are hospital-centered and aimed at short-term use in clinics. Through scrutinizing the current systems and examining their various pros and cons, we identify existing common concerns, provide insight into problem determinants, and suggest research topics for further study. In the near future, we envision that the home will be transformed into an intelligent hub for lifelong healthcare through seamless monitoring of the human body in the daily life environment, which will foster the development of a new discipline “Metrology of Health” or “Healthology” based on a holistic view of health.

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Minimally invasive therapies by applying cavitation bubbles, such as histotripsy and gene transfer, have recently attracted attention. As a method to generate bubbles, the use of expansion waves is expected to be more effective than using shock waves or ultrasound. However, few studies have confirmed the effectiveness of expansion waves in generating bubbles. Previous studies have investigated this issue using biological targets. When contrast agents were injected prior to exposure to expansion waves, a larger hemorrhage was observed after the exposure. However, without contrast agents, little difference in hemorrhage was observed. Thus, at least with biological targets, it is still uncertain whether cavitation bubbles are generated more effectively by expansion waves or by shock waves. In this study, we developed a novel cavitation bubble observation system, and used it to observe bubble dynamics created by either expansion waves or shock waves. A spherical wave generated by electric discharge was focused using two reflectors: one was made of stainless steel for focusing shock waves, and the other was made of polydimethylsiloxane for focusing expansion waves. Using the new system, we clearly observed the generation and growth of bubbles. Comparing the dynamics of bubbles produced by expansion waves with those produced by shock waves, both generation and growth of bubbles were more remarkable with expansion waves. To understand the impact of albumin, which is present in vivo, on the generation of bubbles, bovine serum albumin (BSA) concentration at the focus region was altered. However, BSA concentration had little effect on the effectiveness of the expansion waves. Moreover, several parameters of the expansion wave, such as peak negative pressure and full width of half maximum (FWHM), were investigated to clarify which was the main contributor to the observed promotion of bubble dynamics. The results showed that peak negative pressure contributed substantially to the generation of bubbles when produced by expansion waves. In contrast, FWHM contributed mainly to the growth of bubbles. These results provide insight to understand the mechanisms of cavitation and may lead to clinical applications of expansion waves.

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We simulated the three-dimensional contraction of the lateral rectus muscle using the finite element method. We proposed a hyperelastic, transversely isotropic constitutive model for extraocular muscle, which incorporates the force–length–activation relationship and the effect of changes in fraction of interweaving tendon. The model successfully reproduced the experimental force–length–activation relationship when applied to a unit cube for validation. We also propose a method to incorporate the effect of tendon weaving using the tendon fraction. The electrical potential method was applied to define the fiber direction and tendon fraction in muscle geometry derived from magnetic resonance imaging. Finally, the model was applied to a forced duction test of the lateral rectus muscle. Although our model requires further validation, the proposed constitutive model and definition of geometrical information are a step toward future medical application by facilitating three-dimensional modeling with improved accuracy.

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Volatile organic compounds (VOCs) are organic chemical substances that volatilize easily in ambient air at normal temperature and pressure. VOCs in human expired gas have been reported to be useful in the diagnosis of various diseases, but measurement of VOCs in human expired gas is technically difficult because the concentrations in expired gas are extremely low and almost the same as the concentrations in ambient air. Accurate VOC measurement usually requires a large system, and no VOC measuring systems suitable for clinical practice are available. We developed a compact, simple, double cold trap system that can measure the concentrations of VOCs originating in humans. Our system detects a limited number of VOCs with very high sensitivity at concentrations as low as 0.05 ppb. We evaluated the reproducibility of our system and measured VOCs in ambient air, purified air, and human expired gas from smokers, non-smokers, and patients. Errors of ±10% seem unavoidable in our system. Our verification experiment using human expired gas strongly suggests that the reproducibility and detection sensitivity of our system allow the detection of most VOCs in human expired gas.

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This paper presents a novel gait analysis system that is easy to use by patients and doctors. The system uses a new gait analysis device called “CAterpillar Type trAnsParent treadmill (CaTTaP)” and an image processing method. The CaTTaP has a “caterpillar” type of walking surface made of acrylic resin plates. A camera embedded in the CaTTaP walking surface continuously captures images of the sole during walking. Image processing of the plantar images extracts the plantar regions and determines the position of the subject's sole on the CaTTaP. To evaluate the usefulness of the proposed method, we calculated the step length and width. For this study, we recruited 6 robust elderly persons. We conducted measurements with each subject walking at 3 different velocities. A total of 302 step lengths and widths were calculated from the image data, and the accuracy of the results were estimated by comparing with measurements obtained simultaneously using a motion capture system. Analysis of the absolute values of differences showed that the accuracy of the proposed system varied among subjects. In the higher accuracy group, step length and width were estimated with absolute differences of approximately 16.1 mm and 31.2 mm, respectively, and the entire sole was stably and steadily in ground contact from the heel to the toe. However, in the lower accuracy group, step length and width were estimated with absolute differences of approximately 61.2 mm and 34.4 mm, respectively, and the toes were sometimes off ground. The results suggest that the accuracy of the proposed system varies depending on the type of gait, and that the image processing method requires further improvement. However, the proposed system provides a new approach to gait analysis that requires a short walk and no preparations or special wear. In addition, the CaTTaP has the potential to measure parameters such as the plantar contact area, plantar skin deformation, and shape of the sole with clearer dynamic plantar images that are difficult to obtain continuously by other devices. The novel CaTTaP is one of the best gait analysis systems available for clinical use.

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We applied the conventional multivariate analysis to detect a mismatch field in individual subjects' evoked magnetoencephalographic (MEG) responses. Multichannel MEG signals at time points spanning a certain duration were formed into measurement vector. The problem was then to determine the significance of the difference between two mean vectors. While the conventional multivariate analysis is well known, it has not been used for the above purpose. Although other new nonparametric methods have been proposed and have proved promising for similar purposes, parametric methods will continue to be used and it is necessary to examine the behaviors of the conventional method when applied to mismatch field detection. Simulation study was conducted using known signal sources in a brain model. Simulated MEG signals were obtained by ‘forward calculation’ and they were converted to measurement vector. The significance of the difference between mean responses was calculated while the parameter values controlling the signal source and the vectorization conditions were changed. The simulation results showed dependence of the detection power on parameter values, and demonstrated that multivariate analysis works well to detect a mismatch field in individual subjects. We also applied the method to human MEG responses to omission of a tone in the musical scale and showed that the brain responses to this stimulus were diverse among subjects.

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Magnetic and inertial sensors are becoming increasingly popular to measure three-dimensional (3D) orientation, because they are well suited to the ambulatory monitoring of posture and movements of subjects. This paper presents a complete implementation of the measurement and estimation of 3D orientation based on a magnetic and inertial measurement unit (MIMU) that we developed. The measurement unit was a combination of a 3D accelerometer, a 3D gyroscope, and a 3D magnetometer. A Kalman filter-based sensor fusion algorithm was proposed to implement the measurements and 3D orientation estimates. The accuracy of the orientation estimation, calculated by a sensor fusion algorithm, was assessed by comparison with a laboratory-bound optical measurement system. Several simulation experiments were executed to evaluate the performance of the measurement unit under various states, including static, periodically rotational, arbitrarily dynamic, and vibration states. Experimental results showed accurate and drift-free orientation estimates. The averaged root-mean-square errors (RMSE) of the roll, pitch, and yaw Euler angles in static state were ≤0.6°. The averaged RMSE of the three angles in dynamic state or in dynamic tests at different angular velocities were ≤2.1°, regardless of periodic rotations and arbitrary motions.

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Right ventricular outflow tract (RVOT) reconstruction surgery is one of the surgical strategies for congenital heart failure, and is commonly used for the treatment of severe heart failure with pulmonary valvular problems. An expanded polytetrafluoroethylene (ePTFE) pulmonary valve was invented for RVOT reconstruction, and the authors have tested its hemodynamic and hydrodynamic characteristics for design improvement. The special features of the ePTFE valve are as follows: (a) anatomically identical trileaflet structure, and (b) bulging sinuses in the vicinity of leaflets. In this study, we used three types of pulmonary valves; an ePTFE valve with bulging sinuses, an ePTFE valve in straight conduit, and a natural pulmonary arterial valve extracted from a goat after the animal experiment. Then we measured the hemodynamic characteristics of the various types of ePTFE valves using a mechanical pulmonary circulatory system. Next, using the pressure and flow data derived from the mechanical circulatory system, we calculated the mechanical design parameters of the ePTFE valves based on a numerical modeling method by inverse analyses. The mathematical parameters we used in the model were inertia, damping, and stiffness coefficients, and we compared these values among three types of pulmonary valves. We succeeded to estimate the mechanical parameters for each valve from the hemodynamic data. The results suggest that the ePTFE valve with bulging sinuses may exhibit similar parametric characteristics to those calculated from the natural pulmonary heart valves.

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Biomaterials that come in contact with blood require excellent antithrombogenicity. The antithrombogenicity of newly developed biomaterials is evaluated by in vitro tests and animal experiments. However, no in vitro evaluation system has been established that can sufficiently evaluate the complicated mechanisms of thrombus formation within the body. Even in animal experiments, it is difficult to observe the chronology of thrombus formation in real time. In this study, we aimed to develop a method for the evaluation of antithrombogenicity of biomaterials. To this end, we examined the optical detection of platelet aggregation occurring on the surface of biomaterials. An apparatus that optically detects platelet aggregation in a test tube or in an in vitro blood circulation circuit was constructed. We used the luciferin-luciferase (L-L) reaction that emits light with an intensity proportional to the concentration of adenosine triphosphate (ATP) s released from platelets after aggregation on the surface of biomaterials. Blood with L-L luminescent reagent added was allowed to aggregate, and chronological changes in intensity of the resulting emission were detected using a photomultiplier tube. This experimental apparatus was able to detect the emission intensity corresponding to the amount of platelet aggregation. The results of in vitro blood circulation tests using a polyvinyl chloride tube or a porcine carotid artery showed a significant and strong correlation between maximum emission intensity based on platelet aggregation and dry weight of thrombus formed within the circulation circuit (r = 0.727, p = 0.007). Thus, this experimental system was proven to be useful as an alternative to animal experiments for the evaluation of antithrombogenicity of biomaterials.

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Near-infrared multispectral imaging (NIR-MSI) is a potentially effective technique for quantitative evaluation of atherosclerotic plaque. NIR light shows high penetration for biological tissues and the NIR region includes the characteristic absorptions of lipid-rich vulnerable plaques, especially at wavelengths near 1200 nm. In this study, a quantitative method for assessing lipid volume fraction in plaques—one of the factors of plaque vulnerability—was developed using NIR-MSI at three wavelengths around 1200 nm. Atherosclerotic phantoms with lipid volume fractions of 100, 80, 60, 40, and 20 vol% were prepared and measured by NIR-MSI at three wavelengths: 1150, 1200, and 1300 nm. The acquired datasets were processed by the spectral angle mapper method. Consequently, lipid-enhanced multispectral images of the phantoms were created. In addition, the differences in lipid volume fraction were evaluated and the fractions were classified into six grades quantitatively. These results show the potential of NIR-MSI for the quantitative evaluation of vulnerable plaques.

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Body motions required for postural control while standing on a marine craft have not yet been characterized despite the popularity of such vehicles. It also remains unclear whether exercise loads for such postural control are greater than those of activities of daily living. The purpose of this study was, therefore, to investigate the kinematic characteristics and exercise load of passengers' postural control against ship motion. We hypothesized that the exercise load of postural control while standing on a marine craft is greater than that while standing on land, which requires more rotations of the joints to maintain upright stability. In this paper, we report passengers' standing postural motion, passengers' exercise load and compared with other exercise loads on land. The measurement system consisted of three orientation sensors, a calorimeter, and a patient monitor. Orientation sensors capable of measuring linear and angular accelerations were placed on the head and waist of each participant, and on the floor of a small marine craft. Human energy expenditure was measured using the calorimeter. In the small marine craft, participants were either sitting or standing. In the laboratory, participants were sitting, standing, or performing step tests at 30, 40 and 50 steps/min. Standing postural motion against ship motion was analyzed by calculating the root mean square (RMS). On the marine craft, standing postural motions of participants were compared with the motions of a vertical standing rod to show the kinematic characteristics of the standing postural motion. Exercise load was calculated by dividing the 5-min mean energy expenditure in each condition by that in the sitting condition. Passengers' standing postural motion on the craft was mainly rotational motion. Passengers' exercise load increased with an increase in floor heave motion. The exercise load during postural control against ship motion was greater than that during quiet standing but was similar to that during stepping on land, with fairly low exercise intensity. We thus found that passengers had an exercise load attributable to postural motion.

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Hypertrophic scars are frequently observed at wound sites that had been subjected to cyclical stretch stimuli, such as skin of the anterior chest wall and lower abdomen. Previous studies found that cyclic stretch modulated fibroblast infiltration and collagen fiber remodeling compared with static culture conditions. However, these studies used homogeneous cultures that poorly replicated the physiological organization at the wound site. Similar to early studies, we hypothesized that cyclic stretch modulated fibroblast infiltration and collagen fiber remodeling compared with static culture conditions. However, we replaced the homogeneous culture condition used in previous studies with a novel two-gel wound model consisting of an inner decellularized collagen gel mimicking the wound site and an outer fibroblast gel simulating the epidermis. These models were then subjected to either 1-Hz uniaxial cyclical stretch for 3 h each day or were placed under static culture conditions. After day 4 in culture, we found two significant differences between specimens under the cyclic stretch conditions and those under static conditions. First, there were fewer fibroblast infiltrates in the inner wound-mimicking gel in cyclically stretched specimens than in statically stretched specimens. Second, the microstructure and orientation of collagen fibers in cyclically stretched specimens differed histologically from those in static culture. These results add to the growing evidence that cyclical stretch modulates the wound-healing process.

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Recently, decellularized liver (DC-liver) has been developed as a scaffold for the generation of liver tissue because DC-liver has a vascular structure that is used for oxygen delivery. The structure has been evaluated by the appearance of the resin cast. In the present study, three-dimensional computed tomography was used to obtain images of the vascular structure. Imaging at the hepatic lobule level was achieved by coating the resin cast with a contrast dye or gold. We defined indices to evaluate blood vessel conformation and structure. The indices were measured and calculated from the images. The results suggest that DC-liver has a fine vascular structure quantitatively similar to that of native liver. This method is valuable for the development of whole liver engineering.

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