Quantification and Visualization of Reliable Hemodynamics Evaluation Based on Non-Contact Arteriovenous Fistula Measurement.

The condition of arteriovenous fistula (AVF) blood flow is typically checked by using auscultation; however, auscultation should require a qualitative judgment dependent on the skills of doctors, and further attention to contact infection is required. For these reasons, this study developed a non-contact and non-invasive medical device to measure the pulse wave of AVFs by applying optical imaging technology. As a first step toward realization of the quantification judgment based on non-contact AVF measurement, we experimentally validated the developed system, whereby the hemodynamics of 168 subjects were visually and quantitatively evaluated based on clinical tests. Based on the evaluation results, the fundamental statistical characteristics of the non-contact measurement, including the average and median values, and distribution of measured signal-to-noise power ratio, were demonstrated. The clinical test results contributed to the future construction of quantified criteria for the AVF condition with the non-contact measurement.

Heat Stroke Prevention in Hot Specific Occupational Environment Enhanced by Supervised Machine Learning with Personalized Vital Signs.

Recently, wet-bulb globe temperature (WBGT) has attracted a lot of attention as a useful index for measuring heat strokes even when core body temperature cannot be available for the prevention. However, because the WBGT is only valid in the vicinity of the WBGT meter, the actual ambient heat could be different even in the same room owing to ventilation, clothes, and body size, especially in hot specific occupational environments. To realize reliable heat stroke prevention in hot working places, we proposed a new personalized vital sign index, which is combined with several types of vital data, including the personalized heat strain temperature (pHST) index based on the temperature/humidity measurement to adjust the WBGT at the individual level. In this study, a wearable device was equipped with the proposed pHST meter, a heart rate monitor, and an accelerometer. Additionally, supervised machine learning based on the proposed personalized vital index was introduced to improve the prevention accuracy. Our developed system with the proposed vital sign index achieved a prevention accuracy of 85.2% in a hot occupational experiment in the summer season, where the true positive rate and true negative rate were 96.3% and 83.7%, respectively.

Effect of Position and Fastening Belt Pressure on the Accuracy of PPG-Based Heart Rate Sensor.

Photoplethysmography (PPG) is simple, non-invasive and unobtrusive, so it has been commonly used for heart rate (HR) sensing during exercise. PPG-based HR sensor can be applied for almost any part of human body where there is an artery close to the sensor, just by stabilizing it on the skin surface with belt. However, in order to make the HR sensor stable even during vigorous exercise, it requires a high fastening belt pressure, which results in discomfort for the sensor wearer. In this paper, we investigate the relationship between fastening belt pressure and accuracy for PPG-based HR sensors put on two positions such as forearm and wrist. First of all, we conducted a preliminary experiment using 10 subjects to associate fastening belt pressure (from 10hPa to 90hPa) to human comfort or discomfort (loose, moderate, tight, and very tight). Then, we conducted an experiment to measure HR for 10 subjects during exercise, changing the belt pressure and exercise intensity. Experimental results reveal that the forearm position gives higher accuracy for HR sensing than the wrist position, however, exercise severely introduces motion artifact (MA) even for the for earm position. Therefore, if we want to achieve higher accuracy during exercise with moderate fastening belt pressure, a technique to cancel MA is required even for forearm-type PPG-based HR sensors.

Motion artifact cancellation and outlier rejection for clip-type ppg-based heart rate sensor.

Heart rate sensing can be used to not only understand exercise intensity but also detect life-critical condition during sports activities. To reduce stress during exercise and attach heart rate sensor easily, we developed a clip-type photoplethysmography (PPG)-based heart rate sensor. The sensor can be attached just by hanging it to the waist part of undershorts, and furthermore, it employs the motion artifact (MA) cancellation technique. However, due to its low contact pressure, sudden jumps and drops, which are called "outliers," are often observed in the sensed heart rate, so we also developed a simple outlier rejection technique. By an experiment using five male subjects (4 sets per subject), we confirmed the MA cancellation and outlier rejection capabilities.

Cancellation of motion artifact induced by exercise for PPG-based heart rate sensing.

Heart rate (HR) sensing during exercise is essential for medical, healthcare and sport physiological purposes. Photo-Plethysmo-Graphy (PPG) is a simple and non-invasive technique for HR sensing, but it is highly sensitive to motion artifact. This paper proposes a cancellation technique of motion artifact in PPG-based HR sensing for a man during exercise. The canceller is equipped with two sensors; one is a normal PPG sensor where an LED/Photo-Detector (PD) contacts the skin to detect Blood Volume Pulse (BVP) (+motion artifact) and the other is a motion artifact sensor where an LED/PD does not contact the skin to detect only motion artifact. Experimental results show that the proposed technique, which is implemented in adaptive algorithms, can sense HR correctly by cancelling motion artifact induced by exercises such as running and jumping.