An interesting new study available as a preprint on the medRxiv* server suggests that vagally-mediated heart rate variability (vmHRV) is a physiological marker of resilience to stress by indicating how well an individual handles the emotions when faced with changes in the surroundings.
The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection that was first reported towards the end of 2019, in Wuhan, China, rapidly grew into the ongoing coronavirus disease 2019 (COVID-19) pandemic. With tens of millions of hospitalizations and almost four million deaths, governments worldwide were hard-pressed to contain the virus in the absence of effective pharmaceutical interventions.
Social distancing, face masks, hand hygiene and restrictions on movement outside one’s residence, as well as large-scale business closures, were among the public health strategies used to limit the size of the outbreak. However, such lockdowns have negative economic and social consequences by restricting normal human interactions.
People with pre-existing susceptibility to the virus are liable to develop mental issues during such lockdowns, leading to the prioritization of research into the risk factors, level of vulnerability and protective factors for such problems.
Tonic vmHRV is a measure of the parasympathetic nervous regulation of heart activity and has been suggested to indicate the level of stress resilience. Most earlier studies on this marker have been cross-sectional, providing a snapshot of the individual’s state at a single moment of time.
Most such research indicates that adults in whom HRV is reduced before or after a troubling experience are likely to develop post-traumatic stress disorder (PTSD). A history of trauma is related to deteriorating mental health during the current pandemic as well.
In contrast to the earlier cross-sectional studies, the current study followed up vmHRV over time in relation to the stress induced by COVID-19 lockdowns. This relationship has been examined in only a single study that indicated a link between HRV changes during and after the lockdown period and the individual’s feeling of well-being.
The scientists theorized that an elevated resting vmHRV would be an accurate predictor of better emotional regulation and stable affect, or mood, in healthy adults during a COVID-19 lockdown approximately 22 months later.
In order to measure emotional regulation, the participants were asked to complete online questionnaires, namely, the subjective Perceived Coronavirus Risk scale (PCRS); the Center for Epidemiological Studies Depression Scale (CES-D), for self-reported symptoms of depression over the previous week; and the 10-item Emotion Regulation Questionnaire (ERQ) to assess the habitual use of functional and dysfunctional strategies for emotion regulation – cognitive reappraisal and emotional suppression, respectively.
The participants also recorded the vmHRV using fingertip photoplethysmography under resting conditions, using a free smartphone application. This involved avoiding coffee, alcohol, energy drinks, eating, smoking and exercise for two hours beforehand. They also described emotions like anxiety, sadness, worry, optimism and safety at two-hourly intervals when awake for two successive days.
What did the study find?
In 66 healthy adults, the vmHRV was not found to be linked to baseline demographic or lifestyle factors. However, when measured at baseline, between May 2018 and October 2019, it was found to be positively correlated to the use of cognitive reappraisal, from May 1 to May 31, 2020, a functional, emotional regulation strategy.
Conversely, a lower vmHRV at the first time point was linked to the use of emotional suppression, a dysfunctional strategy indicative of poor mental health, at the second time point. This marker was therefore accurate in predicting emotional coping skills when faced with the COVID-19 lockdown.
Again, participants who reported feeling safe or worried had corresponding high or low vmHRV at the earlier time points. Anxiety, sadness and optimism did not yield such associations.
The vmHRV at the earlier time point also predicted the later value in part. The latter was inversely associated with the CESD score, indicating a higher risk of depression with lower vmHRV. Depressive symptoms were also correlated with a higher probability of perceived COVID-19 risk. However, the vmHRV at the later time point was not correlated with the subjective feeling of risk or with cognitive reappraisal.
What are the implications?
The investigators found that a higher tonic vmHRV predicted that the individual would use functional strategies to cope with upheavals during the COVID-19 lockdown almost two years later. These individuals also experienced more feelings of being safe and were less worried during this period.
This longitudinal study thus supports the hypothesis that as the resting tonic vmHRV decreases, the individual is more likely to use dysfunctional emotional regulation strategies. This includes being unable to admit negative emotions instead of suppressing them.
A higher resting vmHRV, in contrast, indicates the greater use of cognitive reappraisal, as well as accepting one’s upset feelings, having compassion towards oneself, and being freer in the use of emotional regulation strategies.
Interestingly, the scientists also found that people with a lower vmHRV were correctly predicted to use emotional suppression strategies more heavily. Since failing to accept and regulate one’s emotions positively is linked to poor health outcomes, both bodily and mental, especially during high-stress situations like COVID-19, it is necessary to consider these findings carefully.
The findings also demonstrate that feeling depressed about the lockdown is linked to feeling unsafe about the COVID-19 risk and to a lower vmHRV. This interesting and robust association between neurological-cardiac-emotional axes suggests that “HRV might be not only be a marker of but also a precursor of vulnerability/resilience to stress.”
However, the resting vmHRV is linked only to a feeling of being safe and inversely to worry, but not to anxiety, optimism or sadness. It is, therefore, very specific for the inner perception of safeness.
The researchers write:
This is in line with the idea that HRV measures index the activity of a core set of neural structures that continuously assess the environment for signs of threat and safety and prepare the organism to adaptively regulate cognition, behavior, and physiology.”
Further research will be necessary to increase the accuracy of the measured vmHRV and to include a larger sample size. Nonetheless, these findings indicate that HRV measures will be useful in picking up those at risk for symptoms arising from stress to use early therapies like HRV biofeedback or transcutaneous vagus nerve stimulation. These could help raise vmHRV and improve resilience during such periods.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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