Evaluation of biomaterial properties using THP-1 cells require the establishment of standardized protocols. Two potential methods are available, which differ in the timing of cell contact with the material; i.e. cell differentiation occurring simultaneous with or prior to polarization. No reports have examined the activation state of macrophages during differentiation. The aim of this study was to clarify the effects of biomaterials on THP-1 cells during differentiation. THP-1 cells were seeded on polymeric materials in the absence and presence of phorbol-12-myristate-13-acetate, and M1/M2 polarization was induced. The differentiation from THP-1 cells into macrophages was evaluated by loss of proliferation and acquisition of adhesion. The activation levels and M1/M2 polarization of M0 were assessed by IL-1β and MRC1 mRNA expression. Undifferentiated THP-1 cells were not markedly stimulated by interaction with biomaterials. However, THP-1 cells seeded on all the test materials differentiated into macrophages, and the macrophages polarized into different activated states depending on the material. These findings revealed the effects of material stimulation on macrophage activation state during differentiation. These results suggest that the step of cell differentiation and the step of contact with the material should be separated during systematic evaluation of biomaterials.

In this study, we used Raman spectroscopy to observe the process of osteoblast calcification under microvibration stimulation. Osteoblast cultures were prepared under three conditions: the control group was cultured statically without vibration stimulation, and the 45-Hz vibration group and 90-Hz vibration group were stimulated by microvibration at 45 Hz and 90 Hz, respectively, for 30 minutes per day with an acceleration amplitude of 0.2 G. The incubation periods were 7, 9, 11 and 14 days, and observations were conducted using Raman spectroscopy after fixation. In the 45-Hz vibration group, calcification was accelerated. This group produced a large amount of highly crystalline phosphate with large crystal size and a low proportion of hyaluronan precursor and carbonate. In the 90-Hz vibration group, differentiation into mature osteoblasts was not rapid. This group produced more non-crystalline phosphate containing more hyaluronan precursors and carbonate than the other groups. The results suggest that microvibration stimulation promotes calcification, and that the composition of the calcified area may differ depending on the vibration conditions.

Atrial fibrillation (AF) is a type of arrhythmia that can cause cardiac complications such as stroke, and early detection is therefore important. This study proposes a method for detecting AF from the Holter electrocardiogram (ECG). The AF detection procedure has two stages: arrhythmia extraction based on the R-R interval variation and AF identification from the extracted arrhythmia using a one-dimensional convolutional neural network (1D CNN). Artifacts in the ECG are eliminated through preprocessing using a finite-impulse-response bandpass filter. In the first stage, R waves are detected through a multi-resolution analysis of the ECG, and arrhythmias are extracted by observing the standard deviation of the R-R intervals. In the second stage, AF is identified from the extracted arrhythmic events using a 1D CNN trained using segmented ECG waveforms. An ECG dataset of 100,000 segments obtained from the Holter ECG is prepared for training the CNN. Evaluation using 24-h ECG data from 10 untrained subjects verifies that the performance of the proposed detection method is better than that of the methods without arrhythmia extraction, with an accuracy of 93.1%. This result indicates the feasibility of the proposed method for detecting AF.

Decellularized tissues are used as transplant materials and scaffolding in regenerative medicine. Histological evaluation is used to assess decellularization and reveal residual cell nuclei and changes in the structure of the extracellular matrix. However, qualitative evaluation depends on the subjectivity of the evaluator. Therefore, in this study, an AI-based image classification method for objective evaluation of histological decellularization was developed and used to evaluate decellularization in stained images. Two image classifications were performed: untreated aorta and high hydrostatic pressure (HHP)-decellularized aorta, and untreated aorta and sodium dodecyl sulfate (SDS)-decellularized aorta. Both sets of images were classified with high accuracy. Accuracy, precision, recall [true positive rate (TPR)], false positive rate (FPR), F1-score, and area under the receiver operating characteristics curve (AUC-ROC) of the two classifications indicated that the AI-based classification method developed in this study accurately assessed decellularization. However, the TPR revealed that untreated aortas had a higher probability of being misidentified as HHP-decellularized aortas than as SDS-decellularized aortas. One factor that may have contributed to the misidentification of images of untreated aortas as those of decellularized aortas was that feature weighting was performed on other features other than the presence or absence of cell nuclei. Heatmaps were generated based on the results of image classification of stained images of decellularized aortas prepared by the two decellularization techniques. Therefore, the uniformity of decellularization could be visualized. The method developed in this study allows quantification of decellularization heterogeneity within decellularized tissues, which was previously unquantifiable. This method can be adapted to a wide variety of decellularized tissues and may contribute to rapid and efficient identification of decellularized tissues.

Background: Alterations in central blood volume (CBV) play a pivotal role in the functionality of the respiratory and circulatory systems. This study elucidates the adaptive changes in respiration, cerebral circulation, and cardiovascular function in response to orthostatic stress in male volleyball players compared to healthy non-athletes. The athletes’ unique physiological adaptability may help them cope with the frequent CBV changes related to their sports activities.

Methods: Fourteen male university students participated in this study; seven were volleyball players and seven were non-athletes. Participants underwent a maximal ramp exercise test and a lower body negative pressure (LBNP) test conducted to examine the cardiorespiratory response under LBNP and no-LBNP conditions. Respiratory, metabolic, hemodynamic, and cardiac measurements were collected and analyzed.

Results: Volleyball players (Ath group) were significantly taller and exhibited higher maximal oxygen uptake (V_O2max) and maximum work rate compared to non-athletes (Non-Ath group). Under the LBNP condition, end-tidal CO₂ partial pressure (P_ETCO2) decreased by 4.1% in the Non-Ath group, but was maintained stable in the Ath group. The CBV reduction rate due to LBNP was notably less in the Ath group (−12.5%) compared to the Non-Ath group (−24.5%). In all participants, a significant correlation was observed between the CBV and P_ETCO2 reduction rates. However, cerebral blood flow and cardiovascular responses to LBNP load did not differ between the two groups.

Conclusion: Male volleyball players demonstrate distinctive adaptability in response to orthostatic stress, specifically in maintaining stable P_ETCO2 and attenuating CBV reduction rate under LBNP load. These findings suggest that the sport-specific training in volleyball may induce some protective mechanisms against abrupt changes in CBV, although cerebral blood flow and cardiovascular responses appear unaffected. Further research is warranted to understand the underlying mechanisms of these adaptations.

Investigation of biological response to materials is important in understanding their biocompatibility and cell-material interactions for biomaterial applications. Macrophages are important for early biological response. Responses of macrophages to materials have previously been investigated by quantitating inflammatory and anti-inflammatory cytokines using ELISA and RT-PCR assays, and by assessing phenotype changes using flow cytometry and immunohistochemistry. In this study, we developed a method to evaluate the proinflammatory response to polymeric materials using a macrophage cell line (THP-1) genetically tagged with a luminescent peptide (HiBiT). The gene for the luminescent peptide was inserted into IL-1β in THP-1 cells using the CRISPR/Cas9 system. Upon stimulation of HiBiT-tagged THP-1 cells with lipopolysaccharide, IL-1β secretion could be detected using highly sensitive measurement of luminescence as well as using ELISA and RT-PCR assays. We found that IL-1β production by HiBiT-tagged THP-1 cells differed in response to nylon, cellulose, and polytetrafluoroethylene. Moreover, the time course of IL-1β secretion also differed for these materials. These results indicate that IL-1β production over time in HiBiT-tagged THP-1 cells exposed to a material can be measured. We believe that this method for evaluation of proinflammatory response using genetically engineered macrophages would complement ELISA and RT-PCR in investigating cellular response to different materials.

In recent years, ophthalmic problems such as asthenopia and strabismus due to watching videos on smartphones have increased, particularly among the younger generation. A smartphone can be operated with one hand regardless of posture. Consequently it is possible to use a smartphone at a closer distance than the usual near-sighted working distance (40-30 cm) for long periods. This may be the cause of the problems described above. In this study we aim to investigate the control of eye movements during viewing of a video on a smartphone. The video features intense two-dimensional images with depth information. The gaze of both eyes was measured, and the convergence distance was examined. Six university students participated in the study. They were asked to watch a 15-minute video on a smartphone, during which their eye movements were measured. During the experiment, the participants watched a self-made “video moving through a 3-D maze.” For each viewing distance, the convergence distance was calculated based on the intersection of the eyes' gaze. In some instances, the viewing distance and the convergence distance did not match when watching the video, suggesting that the mismatch could lead to eye strain and strabismus.

Quantitative indices for declined red blood cell functions are required to avoid an inappropriate extracorporeal circulation. Optical methods without chemical treatment attract attention. Although several authors reported the relationship between scattering properties and changes in red blood cell morphology such as acanthocytosis observed in the early stage of functional decline, there are various issues in practical application such as expensive instruments and spectral contamination of the scattering property by hemoglobin absorption. In the present study, we used Monte Carlo simulation to examine the feasibility of evaluating scattering anisotropy of red blood cells in an original thin cuvette that we designed using combinations of cover glasses. First, we modeled the geometry of a goniometer using HeNe laser at 633 nm, detectors, and the original thin cuvette containing intralipid as scatterers with known optical properties. Next, angular conditions appropriate to the evaluation method were examined. The scattered intensity of the simulation in the range of 6 to 60 deg was in good agreement with Henyey-Greenstein function representing single scattering. Based on the simulation, we fabricated a prototype goniometer. The prototype was validated by measuring light scattering of intralipid as sample and comparing the results with those obtained from the simulation. The scattering anisotropy g obtained by fitting the Henyey-Greenstein function was 0.705, and was close to 0.74 set in the simulation. The scattering anisotropy of 1% intralipid measured by the prototype was 0.731. Finally, we measured angular dependence of light scattering in red blood cells. The measured scattering anisotropy of isotonic red blood cells with 5% hematocrit was 0.961, and was almost consistent with the values reported in the literature. The goniometer proposed in this study may be a quantitative tool that can be used as an alternative to blood smear examination.

Manipulative therapy (MT) is a therapy in which a judo therapist manually rubs, presses, or taps the musculoskeletal system. MT is considered a cost-effective physical therapy that noninvasively promotes blood flow, relieves pain, and improves muscle flexibility. However, very few studies have evaluated the effectiveness of MT using objective measures in comparison with other medical fields; moreover, consistent results have not been obtained. In this study, we evaluated the upper trapezius muscles of 36 young adults using diffuse correlation spectroscopy (DCS) and a digital palpation system (Myoton Pro) to examine the effects of MT on local blood flow and stiffness. DCS is a new tissue blood flow measurement technique that can measure dynamic local blood flow in deeper tissue noninvasively using near-infrared light. Myoton Pro is a commercially available digital palpation system that can quantitatively evaluate muscle stiffness. A 5-min MT session significantly increased the blood flow by approximately 2-fold on the treated side, and the effects lasted 20 min. Additionally, muscle stiffness decreased on the treated side, while no change was observed on the untreated side, indicating the clinical benefits of MT in enhancing blood flow and promoting mobility. The results also demonstrated that the greater the initial stiffness of the patient’s muscle, the more effective MT was in reducing muscle stiffness. Although not statistically significant, a correlation trend was observed between the relative increase in blood flow and the decrease in stiffness of the treated muscle, suggesting a relationship between the effects of MT on blood flow and the relaxation of muscle tone.

The global spread of COVID-19 in 2020 had a significant impact on the population. Healthcare workers who have unpreventable contact with infected individuals are at high risk of infection. We therefore proposed “infection control methods in high-risk environments” and demonstrated that appropriate placement of suction devices in otorhinolaryngology examination rooms is effective for aerosol control [Takada M, Fukushima T, Ozawa S, Matsubara S, Suzuki T, Fukumoto I, Hanazawa T, Nagashima T, Uruma R, Otsuka M, Tanaka G: Sci Rep. 12(1), 18230, 2022]. As a further study of the previous research, this study analyzed the specific environmental factors that contribute to reducing the risk of infection by optimizing the manner in which suction devices are set up. The models of a patient and doctor were placed in an examination room. A steady flow of 2.5 m/s was applied to the patient's mouth as exhalation. Aerosol diffusion was analyzed using computational fluid dynamics. The optimization parameters were the position and angle of suction inlet, and suction speed. The objective evaluation was the “maximum number of particles aspirated from the suction inlet”. A total of 150 designs were tested, and the search for the optimal positions was performed in the examination room. The optimization results showed that the maximum particle removal rate was 98.6%. There were six cases in which the particle removal rate was at least 98%. These positions were within the range of x = 0.120 to 0.159 m in the horizontal direction from the patient's mouth to the suction inlet. The suction inlet was placed laterally in front of the patient, along the trajectory of the particles emitted from the patient's mouth. Particle removal rates of over 98% at various suction speeds indicates that the position and direction of the suction inlet are more important than the suction speed. The adjustment of suction devices based on the results of this study would help reduce the risk of infection in healthcare settings.

Hypertension affects many people and increases the risk of serious illnesses. Blood pressure (BP) can be reduced by decreasing heart rate (HR), stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR). We aimed to investigate non-pharmaceutical therapy for reducing hypertension by evaluating the effects of self-administered high-voltage, low-frequency (HV-LF) electrical stimulation of peripheral nerves in the limbs. The hypothesis was that such stimulation would induce a decrease in HR and increase skin blood flow (SBF), leading to a decrease in BP. A crossover trial was used to verify the effects of stimulation of the median nerve (SMN) and superficial peroneal nerve (SSPN) in 16 healthy adult male participants. Patients with hypertension were excluded from the study. Stimulation was performed at 1 Hz for 20 s using an electrical stimulator capable of generating high voltage using a piezoelectric element. HR, SV, and CO were evaluated as parameters of circulatory dynamics, while SBF was an indicator of peripheral blood flow. TPR was calculated from BP and CO values. BP was significantly lower following both SMN and SPPN. In SMN, an immediate decrease in HR and an increase in SBF were observed. In SPPN, transient decreases in HR and CO and an increase in SBF were observed. Thus, both stimuli affected circulatory dynamics and local blood flow, supporting the hypothesis. However, TPR remained unchanged, indicating that the effect of blood pressure reduction was mainly due to central circulation suppression rather than SBF. The decreases in HR and BP were similar in the SMN and SSPN groups; however, CO and SBF showed different response trends in the two groups. This difference suggests that the primary factors that decrease BP may differ between SMN and SSPN, and that this should be investigated further. Thus, self-administered HV-LF electrical stimulation of superficial skin nerves, as used in this study, may be useful as a novel non-pharmacological intervention for the treatment of hypertension, although further studies are needed to optimize stimulation parameters in patients with hypertension.

The lipid bilayer membrane of microorganisms exhibits capacitance that can be used to assess the proliferation, reduction, or transformation of these microorganisms by evaluating the permittivity of their lipid bilayer membrane. Traditionally, the effects of pharmacological substances on viruses have been measured indirectly by observing cytopathic effects on cultured cells. Nevertheless, the novel approach that depends on permittivity is anticipated to provide an innovative assay for preliminary screening of potential drugs against microorganisms. In an effort to quantify directly the pharmacological effects of compounds on microorganisms, we devised a method that avoids the indirect pharmacological effects on cultured cells. Instead, this method measures the direct effect by assessing the permittivity induced by the lipid bilayer membrane itself. To validate the effectiveness of our approach, and to demonstrate the feasibility of permittivity measurements in microorganisms, we designed an electrode-replaceable measuring cell using 3D printing technology. Using this measuring cell, we measured permittivity of egg phosphatidylcholine liposomes and yeast cells, both of which exhibit lipid bilayers and are suitable for experimental purposes. We measured the permittivity of a KCl solution, as well as suspension of liposomes or yeast cells in KCl solution. We observed an increase in permittivity within a frequency range of 10⁴-10⁸ Hz, which can be ascribed to the lipid bilayers of the liposomes and yeast cells. Following lysis of liposomes by adding Triton-X 100, we observed a reduction in the enhanced permittivity. Furthermore, when the yeast cell count was reduced by dilution, there was a corresponding decrease in the enhanced permittivity. A decrease in permittivity was also noted in a suspension of yeast cells in KCl solution following heat and enzyme treatments. These results suggest that the permittivity of lipid bilayer membrane can be measured and harnessed to estimate the concentration of microorganisms in a solution. Consequently, we anticipate that this method will be developed as a pioneering assay for early drug screening, given its capacity to evaluate the pharmacological effects of compounds on viruses, without the necessity for cultured cells.

Interictal high-frequency oscillations (HFOs) hold promise as potential biomarkers for identifying seizure onset zone (SOZ) and monitoring disease activity in patients with drug-resistant epilepsy. However, manual detection of HFOs as well as SOZ in the brain is time-consuming, and the lack of quantitative diagnostic criteria hinders their clinical utilization. To address these challenges, we have developed an automated threshold-based HFO detection and SOZ localization system from electrocorticogram (ECoG) data and investigated the relevance of channel-wise HFO population information in the excised region of four patients who exhibited good postoperative seizure control. Our HFO detection model can accurately predict HFOs from ECoG data and extract channel-wise HFO population information for a new patient without any manually annotated sample. In addition, a general threshold-based solution is provided to automatically localize SOZs from the channel-wise population of detected HFOs. Results show that our SOZ detector performs well in localizing SOZ with accuracy of 87.09%. Our proposed method has the potential to enhance clinical research by supporting accurate HFO detection and precise localization of the epileptogenic zone, contributing to successful epilepsy surgeries.

Implantable devices utilize flexible substrates due to their ability to conform to the complex shapes and movements of living organisms. However, these devices have a limit to the available power and necessitate low-resistance wiring to handle the extra power consumed on the substrate side. Moreover, complex wiring technology with multilayer wiring is essential to enhance the functionality of implantable devices. Previous studies primarily employed sputtering and printing methods for the fabrication of flexible substrate wiring. However, the wiring resistance is tens to hundreds Ω, causing large power loss. In this study, we aimed to create flexible, low-resistance multilayer circuit boards with resistance less than 1 Ω for implantable devices. Polydimethylsiloxane was used as the substrate material, while platinum was used as the wiring material. The wiring pattern was formed by laser micromachining using an ultrashort pulse laser, and interlayer connections were achieved using Pt Vias fabricated by microwelding. The multilayer circuit board fabricated low impedance wires of 0.25 Ω or less. Furthermore, the wiring demonstrated excellent insulation between wires, even after a 3-hour exposure test in a simulated biological environment, with no short-circuiting issues. Regarding mechanical properties, no significant changes were observed after subjecting the circuit boards to 500 cycles of repeated bending in a bending test with a 6-mm radius. In conclusion, these results indicate that the flexible multilayer circuit boards are well suited for various implantable devices that require low resistance.

Virtual reality (VR) is characterized by a high sense of immersion. Objective and quantitative evaluation methods are essential for enhancing the immersiveness of VR technology. The sense of immersion can be represented by attention allocation from the real world to the virtual space. Our previous study (Ogawa et al.: Adv Biomed Eng. 11, 1-9, 2022) proposed a unique approach that utilized auditory P300 responses to measure attention allocation during 2D or 3D video watching. Using sound stimuli, attention allocation from the real world to the virtual space was quantitatively evaluated using P300 amplitudes. However, this method was limited to assessing immersion in VR contents without audio because sound was used as a probe stimulus. In the present study, we adopted the somatic probe stimulus method to quantitatively and objectively evaluate attention allocation while watching audio‒VR videos. We developed a novel somatic P300 system that involves the application of vibration stimuli to the user's fingers during VR video viewing. Ten young adult participants performed a somatic oddball task while experiencing the VR content. The small amplitude of the event-related P300 wave during the oddball task quantified the attention directed towards the VR content. Vibrations of the piezoelectric device, which were delivered randomly as probe stimuli, were applied to the thumb (standard stimulus, 70%), middle finger (target stimulus, 15%), and little finger (deviant stimulus, 15%). EEG signals were recorded at Cz and Pz, filtered from 0.5 to 30 Hz, with a sampling frequency of 1000 Hz. To minimize electromyogram signal contamination, mental counting replaced the switch-pressing method used in the previous study. Event-related potential waveforms obtained by averaging signals from ten subjects revealed distinctive P300 responses for target stimulus and deviant stimulus. The peak amplitudes of the P300 wave for target and deviant stimuli during VR video viewing were significantly smaller than those during no VR video viewing. These results suggest that the proposed method can be used for objective and quantitative measurements of immersion intensity, even in VR environments with audio.

In many memory impairment cases, memory failure is due to impaired retrieval and not loss of memory information. Studies on memory retrieval using electroencephalography have mainly focused on changes in power and connectivity in the gamma band, which is a high-frequency region (> 30 Hz). However, previous research has not focused in detail on network activity during memory retrieval. To clarify this, we quantitatively compared retrieval and non-retrieval conditions using network analysis for time-varying functional connectivity. This study analyzed memory retrieval using a paired associative learning task. Consequently, this research found gamma band responses similar to those observed in previous time-frequency analysis in high gamma band. Furthermore, the high-gamma characteristic path length in the target condition was significantly higher than that in the distractor condition. The network becomes more efficient in the non-retrieval condition in the high-gamma band (50-80 Hz). We considered that this was due to the high workload, resulting in distracted memory retrieval. In non-retrieval conditions, participants must focus only on the next stimuli, which may increase network efficiency. We believe that this study shows the potential of a time-varying network analysis for revealing complex brain network activity.

This study aimed to investigate the effect of UNet++ compression with pruning and principal component analysis (PCA) for kidney and cyst image segmentation of Autosomal Dominant Polycystic Kidney Disease (ADPKD). We used 756 T2-weighted MRI images of kidneys with ADPKD among the Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) cohort. The UNet++, UNet++ with prune compression (prUNet++), and UNet++ with PCA compression (PCAUNet++) were trained, validated, and tested with 604, 76, and 76 kidney images, respectively. The model performance was analyzed using the Dice similarity coefficient (DSC). The training time per epoch for UNet++ was 217±5s and 220±7s respectively for kidneys and cysts. This was used as a pre-trained model for PCAUNet++ and prUNet++ whose training times after compression for kidneys and cysts respectively were 90±3s, 109±6s and, 110±2s, 124±4s. (p<0.0001). The test dataset’s average DSC values for UNet++, prUNet++, and PCAUNet++ were 0.93±0.05, 0.93±0.08, and 0.93±0.07, respectively, for kidney segmentation, while those for cyst segmentation were 0.87±0.04, 0.84±0.08, and 0.84±0.09, respectively, without statistical difference over the three models suggesting the pending rejection of the null hypothesis (p≥0.05). We demonstrated that compression techniques can be employed in segmentation tasks without the need to train a model from scratch and use an already trained model with additional little training, avoiding computational complexity and large training time. PCA-based compression technique significantly decreased the post-training time of UNet++ compared to prUNet++ without a significant reduction in the accuracy of kidney and cyst segmentation for ADPKD.

Muscle tone, an after-effect of stroke, inhibits free limb movement causing muscle shortening, contractures, and joint alterations. A method to reduce muscle tone is manual therapy, called the “piston finger technique”. We previously developed a piston device for fingers, named “PDFin”, that imitates the manual technique, and has applied the device to patients with stroke-related hemiplegia with certain success. In this study, we conducted intervention using the PDFin in eight stroke survivors for 30 s and 10 min and verified the immediate and sustained effects of muscle tone reduction using the modified Ashworth scale (MAS). After each intervention, participants performed a 6-meter walk (WA) and MAS test five times at one-minute intervals. The results showed that immediate effect of the 10-minute intervention on MAS score improvement was significantly greater than that of the 30-second intervention. Moreover, there was a significant difference between the 30-second and 10-minute interventions in the sustained effect on MAS score improvement after the intervention. In particular, the MAS score after the 10-minute intervention and five WA tests did not decrease to the MAS score before the 10-minute intervention in all participants. However, the MAS score after the 30-second intervention and five WAs decreased to the MAS score before the 30-second intervention in 5 participants. The findings showed that a 10-minute intervention using the PDFin further reduced muscle tone, and the effect lasted longer.

Fatigue of the muscles involved in swallowing is regarded as one of the factors that increase the risk of aspiration and choking. However, an objective method for assessing muscle fatigue in swallowing-related muscles during the act of swallowing, which consists of voluntary and involuntary reflexive movements and lasts about 1 s, has yet to be established. Therefore, we aimed to develop a method to noninvasively evaluate muscle fatigue from surface electromyography (sEMG) signals recorded during swallowing. In 12 younger and 11 older healthy adults, 44-channel sEMG signals were measured during swallowing before and after a fatiguing task (FT). The FT involved isometric tongue pressure generation to maintain a load of 60% of the maximum pressure. Muscle synergy analysis was used as an event detector, and the 44-channel sEMG signals were divided into two analysis ranges: one containing muscle activity mainly during the oral phase (Pre-indexA) and the other containing muscle activity mainly during the swallow reflex (Post-indexA). The sEMG signals of each range were converted to swallowing pattern images, and the similarity of the images before and after FT was calculated as the Euclidean distance (ED), using a convolutional neural network and kernel principal component analysis. The results revealed that the normalized ED in Pre-indexA differed significantly between the younger and older adults. This finding suggests the possibility of quantitatively evaluating differences in age-related muscle fatigue from sEMG signals recorded during swallowing.

Because hypothermia in trauma patients is associated with mortality, body temperature control of trauma patients is emphasized in pre-hospital care. Warmed infusion solutions are therefore recommended for hypothermia prevention. In cases of intravenous infusion at outdoor emergency scenes, we used a pre-warmed infusion bag, but the infusion solution inside the tubing turned cloudy and stopped flowing. Although there was no record of the temperature at that time, it occurred on a very cold day with a minimum temperature of −12.8℃. The infusion might have frozen. As the first step to find measures to prevent temperature decrease of the infusion solution, we conducted a preliminary study to investigate the temperature decrease in infusion solution when used in a cold environment. The findings indicated that the pre-warmed infusion solution cooled rapidly while flowing through the infusion circuit. It cooled almost to air temperature by the time it completed the infusion circuit. Given these preliminary findings, after specifically examining the rapid cooling of the infusion solution in the circuit, we proposed a heating method for use in cold environments. First, we heated the infusion circuit to 50℃, 55℃, and 60℃ to find the temperatures to which the infusion circuit needed to be warmed to prevent a decrease in infusion temperature. Then we examined the heating effects obtained in environmental temperatures of 0℃, −5℃, and −10℃. Heating at 55℃ was sufficient to prevent cooling of the infusion solution at environmental temperatures of 0℃ and −5℃. However, the limited heating area did not prevent a temperature decrease of the infusion solution in extremely cold environments such as −10℃. These heating conditions and their effects can be important knowledge for preventing hypothermia in trauma patients at emergency sites during prehospital care. Additionally, after developing a prototype heating device with power supplied by a mobile battery, we examined the possibility of clinical application in actual emergency sites. Decrease of heater temperature remained an issue with our heating device, but results demonstrated the possibility of warming of the infusion solution. A heating device that prevents cooling of infusion solution in cold environments may be useful for prehospital care at emergency sites and for application to disaster medicine.

The incidence of low back pain (LBP) among children is increasing. Although LBP can be classified into LBP during anteflexion (LBPAF) and LBP during postflexion (LBPPF), their causes remain unknown. In previous research, we focused on analysis of the causes of pediatric LBPAF by stepwise regression using multiple logistic regression (MLR) model, but the model tended to overfit. Therefore, this study aimed to explore pediatric LBPPF and examined the causes using MLR model with elastic net (ENET) and conditional inference forest (CIF) model. We enrolled 319 children aged 4-15 years, approximately 12% of whom had LBPPF and all were older than 7 years of age. Pediatric LBPPF exhibited an earlier age of onset and a higher prevalence when compared with previous data of LBPAF. The MLR, ENET-MLR, and CIF models were developed using 15 variables obtained from questionnaires and physical examinations conducted. The areas under the receiver operating characteristic curve (AUC) for the three models ranged from 0.68 to 0.72, with accuracy of 68-72%, sensitivity of 50-60%, and specificity of 71-77%. The ENET-MLR and CIF models showed higher accuracy and specificity than the MLR model. Furthermore, the test data accuracy rate did not decrease compared with the training data accuracy rate when using ENET-MLR, whereas the test data accuracy rate decreased more when using CIF. Notably, the ENET-MLR and MLR models identified the same three explanatory variables with low intercorrelation for discriminating between LBPPF and non-LBPPF, and their influence on LBPPF could be explained by the regression coefficients. These three variables were: a history of LBP, increased anterior thigh muscle flexibility, and increased spinal mobility and posterior thigh muscle flexibility. The results of the CIF model revealed that the same variables identified in the two MLR models were the most important variables when calculating the permutation variable importance measures based on the AUC. In conclusion, ENET-MLR is considered to be the best of the three models for discriminating pediatric LBPPF, because it has higher accuracy and specificity than MLR and less overfitting than CIF. Additionally, three factors can be used to discriminate pediatric LBPPF; namely, a history of LBP, increased anterior thigh muscle flexibility, and increased spinal mobility and posterior thigh muscle flexibility.

With recent advancements in human digital twin study, acquiring human neuromuscular characteristics has become a dire necessity. However, many of these studies use large equipment for imaging, such as computed tomography, and are not suitable for conducting clinical screening examinations. Evoked electromyography (eEMG) and manual muscle testing (MMT) are some of the simple clinical examination methods for acquiring human neuromuscular characteristics. The eEMG method is used to examine neural transmission functions. This method involves electrically stimulating nerves and analyzing the compound action potentials obtained from the muscles. However, it can only identify the time delay in the neuromuscular system. Alternatively, MMT is a simple testing method that can only obtain static muscle-force characteristics. Other methods to obtain muscle dynamic characteristics do not consider multiple muscle coordination. In this study, we developed a method to acquire the dynamics of human wrist-joint neuromuscular systems as a second-order and time delay system for clinical screening examinations. This method applies functional electrical stimulation (FES) to agonist-antagonist muscle pairs and achieve isometric force-sensing. The parameters of this dynamic system are indicators of the neuromuscular characteristics of this dynamic system. We confirmed the possibility of using these indicators for clinical examinations. The results suggest that the damping ratio is reproducible and can be applied to the clinical test, particularly for sarcopenia. However, further studies are needed to expand the frequency range of the input FES wave and examine the change of optimization method to fit the transfer function for system identification. In addition, a further study with a larger sample size is needed after strictly defining and recruiting the subject group.