Monitoring the oxygenation levels of the prefrontal cortex during exercise is crucial in assessing decision-making abilities and cognitive responsibilities. Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that measures and monitors tissue oxygenation levels in real-time. This study aimed to investigate the feasibility of using NIRS to monitor and compare patterns of cerebral and muscle oxygenation during progressive exercise, both before and after the anaerobic threshold (AT) is reached. A cohort of healthy adults with moderate to high fitness levels participated in an incremental exercise protocol using an indoor exercise bike. Two wearable NIRS sensors were used to monitor tissue oxygenation from the forehead and the thigh vastus lateralis (VL) muscle during the exercise. To estimate the anaerobic threshold (AT) time point, we used the Respiratory Exchange Ratio (RER) value greater than 1.0 as measured by a metabolic cart. The concentration difference between oxygenated and deoxygenated hemoglobin (Hb-diff), which indicates the level of tissue oxygenation, exhibited a significant decrease (p<0.05) in the VL muscle of all participants after the AT was reached. Conversely, there was a significant increase in Hb-diff in the cerebral cortex after the AT (p< 0.05). The results of this study demonstrate the efficient hemodynamics autoregulation of the brain even when the body is affected by metabolic fatigue during high-intensity exercise. This study confirms the feasibility of NIRS to monitor prefrontal cortex and muscle oxygenation during exercise as a unique application in exercise science.
A pressure injury is a complex chronic wound that forms when the delivery of oxygen and nutrients to soft tissue regions is compromised due to prolonged pressure, commonly over bony prominences, which results in local ischemia, cell death and potentially fatal infections. Its early diagnosis and prediction are challenging, despite technological advancements. It remains one of the most burdensome, costly and fatal secondary medical conditions, which affects millions of people annually. Here, we present a soft, flexible and stretchable pressure sensor array made out of silicone elastomer material, carbon black particles and stretchable, conductive, silver-plated fabric. Its working principle is based on capacitive sensing, where electrodes form an array of parallel plate-like capacitors that enable the detection of pressure due to the deformation of the dielectric layer. We explored a variety of different dielectric architectures consisting of pillar structures of various shapes that make it compressible and potentially increase sensitivity. The sensor array is designed to be shape-conformable, scalable in size and resolution, and able to detect and measure pressure within the desired pressure range for pressure injuries (0-200 mmHg) over short (≤15 minutes) and long periods (≥8 hours) with consistent accuracy and low repeatability error.
The anaerobic threshold (AT) is a point during intense exercise that can be used to predict muscular fatigue. Determining the AT non-invasively helps to adjust exercise intensity and prevent overuse injuries. Near-infrared spectroscopy (NIRS) is an optical technology that can provide real-time information about muscle oxidative metabolism. The objective of this pilot study was to investigate the relationship between NIRS parameters of muscle oxygenation and traditional measures of exercise monitoring, such as heart rate and relative body oxygen consumption (VO2). Healthy adults with moderate to high fitness levels participated in an incremental exercise protocol on a stationary bicycle. NIRS parameters were compared to ventilatory VO2 using a metabolic cart. Respiratory Exchange Ratio (RER) < 1.0 was used as a proxy for determining the AT. NIRS data were collected from the primary locomotor muscle (vastus lateralis - VL) and a control muscle (deltoid) using two wearable NIRS sensors. Heart rate data were collected by a wearable ECG sensor. The NIRS data showed a significant decline in VL muscle oxygenated hemoglobin (O2Hb) concentration (p<0.05) at one exercise stage after the AT was identified. Muscle O2Hb did not show a significant decrease in the deltoid at the AT. Furthermore, there were no noticeable changes in heart rate at the AT. Our results indicate that a wearable NIRS sensor can predict the AT in exercising muscles and may provide a localized measure of muscular fatigue during exercise.
Understanding the effects of risk factors contributing to pressure injuries is critical for preventing the formation of these complex chronic wounds. Near-infrared spectroscopy (NIRS) provides a means to measure tissue oxygenation when external pressure is applied to soft tissue regions. In this study, we investigated the effects of external pressure on soft tissue oxygenation, while considering various intrinsic factors in healthy participants. Our preliminary results suggest an inverse correlation between tissue oxygenation levels and externally applied pressure, with variation in TSI and recovery time between participants indicating the potential effects of intrinsic factors on tissue oxygenation. Further research is required to fully characterize the observed relationship for pressure injury prevention.
There is increasing interest in creating bendable and stretchable electronic interfaces that can be worn or applied to virtually any surface. The electroactive polymer community is well placed to add value by incorporating sensors and actuators. Recent work has demonstrated transparent dielectric elastomer actuation as well as pressure, stretch or touch sensing. Here we present two alternative forms of sensing. The first uses ionically conductive and stretchable gels as electrodes in capacitive sensors that detect finger proximity. In this case the finger acts as a third electrode, reducing capacitance between the two gel electrodes as it approaches, which can be detected even during bending and stretching. Very light finger touch is readily detected even during deformation of the substrate. Lateral resolution is achieved by creating a sensor array. In the second approach, electrodes placed beneath a salt containing gel are able to detect ion currents generated by the deformation of the gel. In this approach, applied pressure results in ion currents that create a potential difference around the point of contact, leading to a voltage and current in the electrodes without any need for input electrical energy. The mechanism may be related to effects seen in ionomeric polymer metal composites (IPMCs), but with the response in plane rather than through the thickness of the film. Ultimately, these ionically conductive materials that can also be transparent and actuate, have the potential to be used in wearable devices.
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