Real-Time Quality Index to Control Data Loss in Real-Life Cardiac Monitoring Applications.

Wearable cardiac sensors pave the way for advanced cardiac monitoring applications based on heart rate variability (HRV). In real-life settings, heart rate (HR) measurements are subject to motion artifacts that may lead to frequent data loss (missing samples in the HR signal), especially for commercial devices based on photoplethysmography (PPG). The current study had two main goals: (i) to provide a white-box quality index that estimates the amount of missing samples in any piece of HR signal; and (ii) to quantify the impact of data loss on feature extraction in a PPG-based HR signal. This was done by comparing real-life recordings from commercial sensors featuring both PPG (Empatica E4) and ECG (Zephyr BioHarness 3). After an outlier rejection process, our quality index was used to isolate portions of ECG-based HR signals that could be used as benchmark, to validate the output of Empatica E4 at the signal level and at the feature level. Our results showed high accuracy in estimating the mean HR (median error: 3.2%), poor accuracy for short-term HRV features (e.g., median error: 64% for high-frequency power), and mild accuracy for longer-term HRV features (e.g., median error: 25% for low-frequency power). These levels of errors could be reduced by using our quality index to identify time windows with few or no data loss (median errors: 0.0%, 27%, and 6.4% respectively, when no sample was missing). This quality index should be useful in future work to extract reliable cardiac features in real-life measurements, or to conduct a field validation study on wearable cardiac sensors.

The Effect of Stress Management Programs on Physiological and Psychological Components of Stress: The Influence of Baseline Physiological State.

Military personnel are particularly exposed to stressful events, and overexposure to stress is both physically and mentally unhealthy. While stress management programs, such as the Tactics of Optimized Potential (TOP) and Heart Coherence (HC) have been implemented, their efficiency remains to be evaluated. The objective of this randomized control trial was to evaluate the effectiveness of the two programs among a young male population of 180 military fire fighter recruits. Based on two psychological, and one physiological measurement, namely heart rate variability (HRV), we found that both TOP and HC programs significantly increased HRV. This is promising as we know that higher HRV is consistent with better health, in most cases. Moreover, the TOP program significantly reduced perceived stress and negative mood, unlike the HC program. Combining these results, we conclude that while both TOP and HC programs influence physiological measurements, only the TOP modifies psychological evaluations. Finally, we distinguished the effects of the programs on two samples characterized by their HRV level. For the low HRV group, both programs tended to increase their HRV level, while for the high HRV group neither program had a significant effect.