HRV Studies

An Overview of Heart Rate Variability Metrics and Norms

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624990/. Date: 2017.09

This study explores how autonomic neurons and hormones influence the heart's rhythm, with heart rate variability (HRV) reflecting the complex interplay of these regulatory systems over different time scales. 

Dietary Sodium Effects on Heart Rate Variability in Salt-Sensitivity of Blood Pressure

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2399901/ Date: 2008.05

'This study investigated the effects of low and high salt diets on physiological measures in salt-sensitive (SS) and salt-insensitive (SI) women. It found that high salt intake increased parasympathetic activity, as indicated by heart rate variability (HRV), particularly in SS individuals, who also exhibited greater cardiac vagal tone at rest compared to SI subjects. The results suggest that sodium balance influences autonomic control of the heart, and that SS individuals might have distinct cardiovascular responses to dietary sodium changes, which could be relevant to the development of sodium-sensitive hypertension.

Heart rate variability as a function of menopausal status, menstrual cycle phase, and estradiol level

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9127980/. Date: 2022.05

This study examines the relationship between heart rate variability (HRV), a cardiovascular risk marker, and estradiol levels in women of varying menopausal status. The research found that postmenopausal women exhibited reduced baseline HRV compared to premenopausal women, indicating higher cardiovascular risk, though these differences diminished when adjusted for age and BMI. Additionally, premenopausal women in the high estradiol phase showed reduced HRV in response to stress, similar to postmenopausal women, suggesting that estradiol levels and menopausal status play a significant role in modulating cardiovascular risk through HRV. Understanding these dynamics may aid in developing strategies to mitigate cardiovascular risk in women.

Low levels of dehydroepiandrosterone sulfate are associated with the risk of developing cardiac autonomic dysfunction in elderly subjects

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10118840/. Date: 2019.02

This study investigates the relationship between serum dehydroepiandrosterone sulfate (DHEA-S) levels and heart rate variability (HRV) across different age groups. The researchers found that older men had lower DHEA-S levels and reduced HRV compared to younger men. Specifically, the decline in DHEA-S was associated with decreased parasympathetic modulation of the heart, suggesting diminished cardiac autonomic control with age. The findings imply that the age-related reduction in DHEA-S may contribute to a decline in cardiovascular function, increasing the risk of cardiovascular disease as people age.

Evaluating the Clinical Utility of Daily Heart Rate Variability Assessment for Classifying Meaningful Change in Testosterone-to-Cortisol Ratio: A Preliminary Study

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8136555/ Date: 2021.04

This study examined the relationship between daily heart rate variability (HRV) and the testosterone-to-cortisol (T) ratio during a 9-week high-intensity functional training (HIFT) program. The results showed that while HRVdaily could detect changes in T ratio with high sensitivity (95% accuracy in identifying "no risk" cases), it lacked specificity (only 5% accuracy in detecting "at risk" cases). The findings suggest that HRVdaily might be a useful tool for monitoring recovery in recreational athletes but may require additional, more specific assessments for high-performance athletes. The study also highlighted the significant individual variability in hormonal responses to physiological stress.

The very low-frequency band of heart rate variability represents the slow recovery component after a mental stress task

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5555691/ Date: 2017.08

HRV is a measure of autonomic nervous system activity. The HF band has been used to measure vagal activity, and the LF/HF ratio was used as a measure of sympathetic activity. The VLF band has several unique characteristics; however, its underlying mechanism of action remains unclear. In this study, we investigated the different HRV component changes following a mental task. Our results revealed that only the VLF band exhibited delayed recovery, which lasted for 2 h following the mental task. Therefore, we propose that the VLF band is the “slow recovery” component of HRV and that the HF band and LF/HF ratio are the “quick recovery” components of HRV.

The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181830/ Date: 2006.12

Maintenance of homeostasis in the presence of real or perceived challenges requires activation of a complex range of responses involving the endocrine, nervous, and immune systems, collectively known as the stress response. Inappropriate regulation of the stress response has been linked to a wide array of pathologies including autoimmune disease, hypertension, affective disorders, and major depression. In this review we briefly discussed the major neuronal and endocrine systems that contribute to maintenance of homeostasis in the presence of stress. Clearly deciphering the role of each of these systems and their regulatory mechanisms may provide new therapeutic targets for treatment and prophylaxis of stress-related disorders including anxiety, feeding, addiction, and energy metabolism.