Macefield, Vaughan G

Heart rate variability (HRV) is a widely utilized approach for investigating cardiovascular health and human performance. Methodological approaches, analyses, and interpretations of HRV can vary extensively, and scientific debates on HRV reliability and utility remain. These debates have been amplified in recent years by the rapid growth and ubiquity of wearable devices, and their incorporation into scientific research studies. The present guidelines paper takes an evidence-based approach to propose more consistent and rigorous measurement and interpretation of HRV within human cardiovascular research and application. First, HRV has some utility as a cardiovascular risk stratification tool, but is not appropriate to employ as a specific marker of cardiac sympathetic outflow or sympathovagal balance. While time-domain and spectral analysis can more accurately reflect respiratory modulation of cardiac vagal (parasympathetic) activity, caution is necessary to avoid overinterpretation, particularly with respect to the concept of “vagal tone”. Numerous experimental, demographic, and environmental factors influence HRV assessment, interpretation, and reliability. Specifically, it is critical to account for non-modifiable (age, sex, race/ethnicity, etc.) and modifiable (i.e., exercise, physical fitness, etc.) factors within participant samples. Furthermore, technical approaches such as the HRV input signal (e.g., electrocardiography vs. photoplethysmography), length of recording, location of recordings (i.e., laboratory vs. field), respiratory rate and depth, and analytical approaches (i.e., time vs. frequency domain) can all impact rigor, reliability, and study interpretations. Finally, with respect to the rapid advancements of HRV assessment using wearable technology, investigators should interpret and contextualize findings within the limitations outlined in this guideline review.

Key pointsResearch indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress.In this study, we examined the early blood pressure responses (including the peak, time of peak and rate of rise in blood pressure) to mental stress in positive and negative responders.Negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex‐mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA‐driven.This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task.AbstractResearch indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress. The aim was to examine the early blood pressure response to stress in positive and negative responders and thus its influence on the direction of change in MSNA. Blood pressure and MSNA were recorded continuously in 21 healthy young males during 2 min mental stressors (mental arithmetic, Stroop test) and physical stressors (cold pressor, handgrip exercise, post‐exercise ischaemia). Participants were classified as negative or positive responders according to the direction of the mean change in MSNA during the stressor tasks. The peak changes, time of peak and rate of changes in blood pressure were compared between groups. During mental arithmetic negative responders experienced a significantly greater rate of rise in diastolic blood pressure in the first minute of the task (1.3 ± 0.5 mmHg s−1) compared with positive responders (0.4 ± 0.1 mmHg s−1;P = 0.03). Similar results were found for the Stroop test. Physical tasks elicited robust parallel increases in blood pressure and MSNA across participants. It is concluded that negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex‐mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA‐driven. This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task.