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Brain & Heart Automatic cardiac autonomic modulation assessment

with Porges’ “polyvagal theory,” which suggests that the 5. Conclusion
unmyelinated vagus (the most primitive parasympathetic
pathway), is activated when other defensive strategies (the The automatic calculation of PNSi, SNSi, and BSTRi indexes
myelinated social vagus and the sympathetic “fight or flight” provides a quicker and more comprehensive assessment
response) fail to manage behavioral and physiological of adaptive CAM in both physiological and pathological
adaptation in life-threatening situations. 23,54 conditions. Monitoring these indexes over time and in real
time could greatly improve our understanding of heart–
According to the “neurovisceral integration model,” the brain interaction dynamics, especially during acute stress
interaction with the complex “brain–heart–body system,” from real-life critical events. 51
which allows for flexibility and adaptability to stressors,
can be assessed through HRV analysis. Specifically, the HF In this study, PNSi and SNSi remained within the
40
spectral component serves as a reliable parasympathetic suggested normality range at rest, with their variations
biomarker for measuring self-regulation and health. 27,28,55 during physical and psychophysiological stress showing
the expected inverse correlation. If further research
A significant challenge in psychophysiology is quantifying confirms that the inverse correlation between PNSi and
the extent of stress-induced psychophysiological overload SNSi (and BSTRi) under stress is NL and better fitted by
with HRV analysis and its correlation with adaptive or NL functions (Figure 3), it could introduce a new approach
56
maladaptive behaviors. The previously unreported finding for assessing sympathovagal interaction in complex real-
that, under stress, the inverse correlation between the PNSi world situations.
and the SNSi (and BSTRi) is NL (Figure 3), rather than
the usual linear relationship at rest, could introduce a new Given the relatively small sample size in this pilot
framework for evaluating sympathovagal interaction in study, although the results are promising, further research
complex real-life critical situations. This may help define a involving a larger population under dynamic physiological
conditions is necessary to establish a reliable and potentially
critical level of dysfunctional parasympathetic modulation unbiased normality database. The BSTRi values calculated
that impairs the “brain–heart–body system’s” flexibility, using Kubios software did not match those derived from
resulting in insufficient rational control of stressful the original Baevsky formula. Squaring the values obtained
situations. This is supported by two additional findings from this study of healthy individuals under effort or
indicating a significant mechanistic difference in CAM psychophysiological stress resulted in units that exceeded
based on the type of stress encountered: (1) Although the the range suggested by Baevsky, even for critical cardiac
relationship between the two indexes is NL in both cases, conditions. 43,44 Therefore, the evaluation of the normality
the nature of the non-linearity differs, with cubic functions range for BSTRi calculated with Kubios software requires
providing a better fit for physical stress than quadratic further investigation.
functions. (2) For SNSi values between 10 and 20 units,
the level of parasympathetic withdrawal was greater under Acknowledgments
psychophysiological stress, averaging nearly one SD of
PNSi. If confirmed through targeted experimental studies, None.
examining the dynamic relationship between PNSi and Funding
SNSi could serve as a valuable tool for identifying individual
psychophysiological stress levels, which may influence the None.
success or failure of operational outcomes, particularly in
complex real-world situations that also involve physical Conflict of interest
effort, as seen in sports competitions or tactical operations. The authors declare they have no competing interests.
Finally, the time-varying calculation of the PNS,
SNS, and BSTR indexes effectively provided a quick Author contributions
overview of how CAM adapts to increasing physical effort Conceptualization: Donatella Brisinda, Riccardo Fenici
(Figure 4) and the temporary rise in sympathetic drive Investigation: Donatella Brisinda, Riccardo Fenici
alongside parasympathetic withdrawal during realistic Methodology: Donatella Brisinda, Riccardo Fenici, Marco
tactical training (Figure 5). Further research is needed to Picerni
determine if these additional parameters can enhance the Formal analysis: Donatella Brisinda, Riccardo Fenici,
ability to differentiate between psychophysiological stress Marco Picerni
and concurrent physical strain during real-world critical Writing–original draft: Donatella Brisinda, Riccardo Fenici
events. 36,37 Writing–review & editing: All authors

Volume 2 Issue 4 (2024) 13 doi: 10.36922/bh.3503