Tejash Patel

Comparison of methods for estimating Wet-Bulb Globe Temperature index from standard meteorological measurements.

Environmental heat illness and injuries are a serious concern for the Army and Marines. Currently, the Wet-Bulb Globe Temperature (WBGT) index is used to evaluate heat injury risk. The index is a weighted average of dry-bulb temperature (Tdb), black globe temperature (Tbg), and natural wet-bulb temperature (Tnwb). The WBGT index would be more widely used if it could be determined using standard weather instruments. This study compares models developed by Liljegren at Argonne National Laboratory and by Matthew at the U.S. Army Institute of Environmental Medicine that calculate WBGT using standard meteorological measurements. Both models use air temperature (Ta), relative humidity, wind speed, and global solar radiation (RG) to calculate Tnwb and Tbg. The WBGT and meteorological data used for model validation were collected at Griffin, Georgia and Yuma Proving Ground (YPG), Arizona. Liljegren (YPG: R(2) = 0.709, p < 0.01; Griffin: R(2) = 0.854, p < 0.01) showed closer agreement between calculated and actual WBGT than Matthew (YPG: R(2) = 0.630, p < 0.01; Griffin: R(2) = 0.677, p < 0.01). Compared to actual WBGT heat categorization, the Matthew model tended to underpredict compared to Liljegrens classification. Results indicate Liljegren is an acceptable alternative to direct WBGT measurement, but verification under other environmental conditions is needed.

Wearable oximetry for harsh environments

A wearable oximeter is needed to help people safely perform missions in environmental extremes. Key initial needs are to monitor for hypoxemia at high altitudes, and to monitor for shock in the event of trauma and hemorrhage. An initial investigation has been performed to assess design parameters for a wearable oximeter. Initial data was collected to assess the forehead, manubrium, and xiphoid process as wear locations; to assess required power; and to characterize the types and significance of motion artifacts that will need to be mitigated. The forehead was confirmed to be an excellent site with respect to signal quality, but signal corruption from changes in contact pressure will need to be mitigated. The sternal locations are initially assessed to be more challenging, likely requiring more power and site-specific motion artifact mitigation.

Detecting and tracking gait asymmetries with wearable accelerometers

Gait asymmetry can be a useful indicator of a variety of medical and pathological conditions, including musculoskeletal injury (MSI), neurological damage associated with stroke or head trauma, and a variety of age-related disorders. Body-worn accelerometers can enable real-time monitoring and detection of changes in gait asymmetry, thereby informing medical conditions and triggering timely interventions. We propose a practical and robust algorithm for detecting gait asymmetry based on summary statistics extracted from accelerometers attached to each foot. By registering simultaneous acceleration differences between the two feet, these asymmetry features provide robustness to a variety of confounding factors, such as changes in walking speed and load carriage. Evaluating the algorithm on natural walking data with induced gait asymmetries, we demonstrate that the extracted features are sensitive to the sign and magnitude of gait asymmetries and enable the detection and tracking of asymmetries during continuous monitoring.