Heart rate variability as a marker of stress and health - measurements with the 'magic ring'

This post is a follow-up to the previous post on brain-heart interplay in emotional arousal, and points to Thayer et al.'s meta-analysis of heart rate variability (HRV) and neuroimaging studies to evaluate HRV as a marker of stress and health. I'm curious about the practical usefulness of the heart rate (HR) and heart rate variability (HRV) measurements that have been reported by the Oura Ring bio-monitor I purchased over six months ago, and has been measuring my sleep, heart rate, activity, and body temperature (I call it the 'magic ring'). I'm finding an allmost complete correlation between the ring's HRV overnight measurements and my subjective sense of robustness and health on waking in the mornings. HRV is lower after a previous day of physical, social, (or gastronomic!) stress, and higher after a day of rest and relaxation. Here I pass on just one clip from the text:

Resting HRV, in our view, is a marker for flexible dynamic regulation of autonomic activity; thus, higher HRV signals the availability of context- and goal-based control of emotions. We have investigated the role of HRV in emotional regulation at two different levels of analysis. One level is at the trait or tonic level where individual differences in resting HRV have been associated with differences in emotional regulation. We have shown that individuals with higher levels of resting HRV, compared to those with lower resting levels, produce context appropriate emotional responses as indexed by emotion-modulated startle responses, fear-potentiated startle responses, and phasic heart rate responses in addition to behav- ioral and self-reported emotional responses (Melzig et al., 2009; Ruiz-Padial et al., 2003; Thayer and Brosschot, 2005). In addition, we have recently shown that individuals with low resting HRV show delayed recovery from psychological stressors of cardiovascular, endocrine, and immune responses compared to those with higher levels of resting HRV (Weber et al., 2010). Thus, individuals with higher resting levels of HRV appear more able to produce context appropriate responses including appropriate recovery after the stressor has ended.

And here is the article's abstract:

The intimate connection between the brain and the heart was enunciated by Claude Bernard over 150 years ago. In our neurovisceral integration model we have tried to build on this pioneering work. In the present paper we further elaborate our model and update it with recent results. Specifically, we per- formed a meta-analysis of recent neuroimaging studies on the relationship between heart rate variability and regional cerebral blood flow. We identified a number of regions, including the amygdala and ventro- medial prefrontal cortex, in which significant associations across studies were found. We further propose that the default response to uncertainty is the threat response and may be related to the well known neg- ativity bias. Heart rate variability may provide an index of how strongly ‘top–down’ appraisals, mediated by cortical-subcortical pathways, shape brainstem activity and autonomic responses in the body. If the default response to uncertainty is the threat response, as we propose here, contextual information repre- sented in ‘appraisal’ systems may be necessary to overcome this bias during daily life. Thus, HRV may serve as a proxy for ‘vertical integration’ of the brain mechanisms that guide flexible control over behavior with peripheral physiology, and as such provides an important window into understanding stress and health.