the ANS on heart activity.
Theoretical Background and Mathematical Bases of
the Normalization Procedure and the LF/HF Ratio
The concept of autonomic balance and its mathematical expression
is based on the traditional doctrine of autonomic reciprocity.
According to this doctrine, the sympathetic and parasympathetic
branches of the ANS are subjected to reciprocal central nervous
control in the sense that increased activation of one system is
accompanied by inhibition of the other. This implies that auto-
nomic control can be regarded as a continuum extending from
parasympathetic to sympathetic dominance. This view, however,
seems rather simplistic. The two branches of the ANS are not
algebraically additive. Instead they interact in a dynamic fashion
and either reciprocity or coactivation of both branches may occur
(Berntson, Cacioppo, & Quigley, 1993). In this manner, variability
of cardiovascular signals reflects the complex interplay between
perturbations of cardiovascular function and the dynamic responses
of multiple regulatory systems. Complex interactions between the
sympathetic and vagal determinants of HR were shown in the
framework of the concept of accentuated antagonism (Levy &
Zieske, 1969; Uijtdehaage & Thayer, 2000), which emphasizes
Fourier Transformations with Interbeat Interval (IBI), Pulse
Transit Time (PTT), and Baroreflex Sensitivity (BRS) Recorded
during Baseline (BL) and Cognitive Load (Task) in the Duschek,
Muckenthaler, et al. (2009; Panel A, n = 60) and Duschek et al.
(2013; Panel B, n = 54) Studies
IBI
VLF
LF
HF
Panel A
IBI-BL
.543*
.268+
.291+
IBI-Task
.005
.212
.541*
PTT-BL
.149
.154
.009
.051
PTT-Task
.224
.161
.370*
.173
BRS-BL
.723*
.583*
.234
.587*
BRS-Task
.749*
.141
.202
.696*
Panel B
IBI-BL
.360*
.179
.531*
IBI-Task
-.054
.368*
.540*
PTT-BL
.440*
.129
.170
.020
PTT-Task
.562*
-.104
.310+
.149
BRS-BL
.738*
.438*
.223
.814*
BRS-Task
.808*
-.025
.425*
.707*
Note.
VLF = very
low
frequency,
LF = low
frequency,
HF = high
frequency.
+p < .05.
*p < .01.
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