JMIR Publications

ABSTRACT

Background:

The emergence of smartphones and wearable sensor technologies enables opportunities to easily and unobtrusively monitor physiological and psychological data related to an individual’s resilience. Heart Rate Variability (HRV) has promise as a biomarker for resilience based on between-subject population studies, but observational studies that apply a within-subject design and use wearable sensors in order to observe HRV in a naturalistic context of real-life are needed.

Objective:

This study explores whether resting HRV and Total Sleep Time (TST) are indicative of and predictive for the within-day accumulation of the negative consequences of stress and mental exhaustion. The tested hypotheses are that (1) demands are positively associated with stress and resting HRV buffers against this association, (2) stress is positively associated with mental exhaustion and resting HRV buffers against this association, (3) stress negatively impacts subsequent-night Total Sleep Time (TST) and (4) prior-evening mental exhaustion negatively impacts resting HRV, while prior-night TST buffers against this association.

Methods:

Twenty-six interns used consumer-available wearables (Fitbit Charge 2 and Polar H7), a consumer-available smartphone app (Elite HRV), and an Ecological Momentary Assessment (EMA) smartphone app to collect resilience-related data on resting HRV, TST, as well as perceived demands, stress and mental exhaustion on a daily basis during 15 weeks.

Results:

Multiple linear regression analysis of within-subject standardized data collected on 2379 unique person-days showed that having a high resting HRV buffered against the positive association between demands and stress (hypothesis 1), as well as between stress and mental exhaustion (hypothesis 2). Stress did not affect TST (hypothesis 3). Finally, mental exhaustion negatively predicted resting HRV on the subsequent morning, but TST did not buffer against this (hypothesis 4).

Conclusions:

To our knowledge, this study provides first evidence that having a low within-subject resting HRV may be both indicative of and predictive for the short-term accumulation of the negative effects of stress and mental exhaustion, potentially forming a negative feedback loop. If these findings can be replicated and expanded upon in future studies, they may contribute to the development of automated resilience interventions that monitor daily resting HRV and aim to give users an early warning signal when a negative feedback loop forms in order to prevent the negative impact of stress on long-term health outcomes.