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Brain & Heart Automatic cardiac autonomic modulation assessment

1. Introduction models for the time-varying analysis of both linear and NL
HRV parameters have enhanced the ability to assess CAM
Cardiac autonomic modulation (CAM), regulated responses to clinical or real-world stressors, even in real
by the balance between the sympathetic (SNS) and time. 34-39
parasympathetic nervous systems (PNS), is vital in both
health and disease, making its evaluation crucial. The Recently, the software has been developed to
1,2
study of heart rate variability (HRV), which reflects automatically compute time-varying parasympathetic
autonomic nervous system (ANS) function, began in the (PNSi), sympathetic (SNSi), and Baevsky stress (BSTRi)
1960s, initially for monitoring astronauts in space. Since indexes, enabling faster assessments of CAM, particularly
3
the 1980s, HRV analysis has been widely used as a non- in acute stress situations. Although HRV parameters are
40
invasive method to evaluate CAM in clinical settings, with well-established, the normal ranges for these new indexes,
autonomic imbalance recognized as a strong predictor of especially BSTRi, remain unclear, particularly in stressful
all-cause cardiac mortality. 4 conditions. 41-46
Early HRV assessments followed a “reductionist” This pilot study aims to determine the average values
approach, relying on linear methods such as time-domain of PNSi, SNSi, and BSTRi in a healthy population during
5
(TD) and frequency-domain (FD) analysis. 4,6,7 Many studies various activities (rest, daily activities, non-rapid eye
were based on the premise that increased sympathetic movement (NREM) sleep, graded physical effort, and
activity corresponds with decreased parasympathetic acute psychophysiological stress) to create a preliminary
activity, with the spectral low frequency/high frequency reference for CAM assessment in real-world high-stress or
(LF/HF) ratio suggested as a marker for stress responses, pathological conditions, such as dysautonomic syndromes.
though this remains debated. 7,8
2. Methods
HRV tends to decline with age due to structural and
functional changes, 9-12 and significant reductions in HRV 2.1. Study population, ethics, and inclusion criteria
are associated with lower life expectancy and various We retrospectively analyzed 24-h Holter electrocardiogram
diseases. 5,9-18 It is important to note that the LF component (ECG) recordings from 104 healthy individuals,
is not exclusively a marker of sympathetic activity, as both categorized into three age groups: Age1 (16–34 years),
SNS and PNS influence LF. In addition, the very-low- Age2 (35–52 years), and Age3 (53–84 years), all
5
frequency (VLF) band may reflect broader systemic stress, consecutively evaluated in our clinic for fitness or clinical
not just cardiac stress. 19-21 evaluations. Among these participants, 16 were police
A more systematic perspective suggests that HRV is officers monitored during fitness assessments and highly
not only a marker of ANS dysfunction but also a means stressful, realistic tactical training. In addition, ECG
for understanding interactions between bodily systems, data from a 75-year-old healthy male who volunteered
especially between the brain and cardiovascular system. to be monitored 3 times/week from April to November
5
In health, “organized variability” is present, whereas 2022 during training on a professional bicycle ergometer
disease leads to a “decomplexification” of this variability, (Technogym, Italy) were included (Table 1).
resulting in more periodic and cyclic behaviors, as seen in All participants were free of cardiovascular and
conditions such as Cheyne–Stokes breathing, Parkinson’s neurological conditions based on clinical history, physical
disease tremors, or cyclic neutrophil oscillations in chronic examinations, and laboratory results. They were required
myelogenous leukemia. 22 to refrain from smoking, consuming coffee, or using any
The vagal system plays a key role in brain–heart substances or medications that could affect their natural
interaction, particularly in stress regulation, as explained by sympathovagal balance for at least 24 h before ECG
Porges’ “polyvagal theory” 23,24 and Thayer’s “neurovisceral recording.
integration model,” which links HRV to emotional and All participants provided informed consent for ECG
stress responses. 25-30 recording and monitoring, primarily related to preventive
To better study these complex interactions, non-linear checkups for non-competitive sports or fitness-for-duty
(NL) mathematical methods have been introduced. For evaluations. They also agreed to the anonymous use of
instance, NL entropy is associated with vagal activity, their ECG data for scientific and publication purposes.
whereas recurrence plot analysis reflects sympathetic All recording procedures were conducted in accordance
activation. 31,32 In stress-related studies, such as those with good clinical practice (GPC) guidelines and ethical
examination-induced stress, combining linear and NL standards outlined in the Helsinki Declaration of 1975,
methods has improved stress detection. Mathematical revised in 2013. 47
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Volume 2 Issue 4 (2024) 2 doi: 10.36922/bh.3503