The utility of heart rate variability (HRV) for characterizing psychological stress is primarily impacted by methodological considerations such as study populations, experienced versus induced stress, and method of stress assessment. Here, we review studies on the associations between HRV and psychological stress, examining the nature of stress, ways stress was assessed, and HRV metrics used. The review was performed according to the PRISMA guidelines on select databases. Studies that examined the HRV-stress relationship via repeated measurements and validated psychometric instruments were included (n = 15). Participant numbers and ages ranged between 10 and 403 subjects and 18 and 60 years, respectively. Both experimental (n = 9) and real-life stress (n = 6) have been explored. While RMSSD was the most reported HRV metric (n = 10) significantly associated with stress, other metrics, including LF/HF (n = 7) and HF power (n = 6) were also reported. Various linear and nonlinear HRV metrics have been utilized, with nonlinear metrics used less often. The most frequently used psychometric instrument was the State-Trait Anxiety Inventory (n = 10), though various other instruments have been reported. In conclusion, HRV is a valid measure of the psychological stress response. Standard stress induction and assessment protocols combined with validated HRV measures in different domains will improve the validity of findings.

Background: The standard 12-lead Holter ambulatory ECG monitor is complex in construction and uncomfortable for the wearer. A 12-lead equivalent ECG monitor was developed based on the EASI configuration with electronic-textile electrodes to meet these needs. Objective: In this study, we evaluated the accuracy and reliability of the EASI 12-lead equivalent ECG prototype. Results: The ECG hardware reproduced cardiac abnormalities from a ProSim 3.0 Vital signal simulator without significant deviation from a reference C.P. 200™ 12-Lead resting ECG. The vest and textile electrodes were subjected to 10 washing cycles. The joint connecting the snap fastener and the integrated wires were the weakest points, starting to fail after eight washing cycles; however, ten cycles of washing did not produce a noticeable loss of signal quality. The compression pressure for a stable-skin electrode interface of the vest was experimentally determined to be 15.92mmHg (minimum compression pressure at the ’I’ electrode position) and 29.45mmHg (maximum compression pressure at ’E’ electrode position). Conclusion: The textile-based ECG smart vest was non-inferior to standard 12-lead resting ECG and could be an alternative solution to monitor patients outside of a hospital setting, pending a larger scale trial with a clinical population.

Point-of-care (POC) medical devices have become very popular to help diagnose and monitor health conditions without the need for specialized staff or attendance at medical centers. A large portion of these devices use light intensity-based measurements; however, the accuracy and repeatability of these measurements are affected by variations both within and between devices. Therefore, a universal method for device calibration and ratiometric measurement is presented which can provide a robust ratiometric light intensity measurement. The method can be applied to different light intensity measurement devices which utilize different sensor types, such as CMOS cameras or photodiodes (PDs). Results show that the method is able to produce a more accurate and repeatable ratiometric measurement when exposed to variations in both the intensity of the light source and the sensitivity of the sensors used to capture the light intensity.