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1 Dipartimento di Fisica, Università di Trento, and Istituto Trentino di Cultura-ist, 38050 Povo, Trento; 2 Dipartimento Scienze Precliniche di Vialba, Università di Milano, 20157 Milano; and 3 Unità Operativa di Cardiologia, Ospedale S. Chiara, 38100 Trento, Italy
The interactions between
systolic arterial pressure (SAP) and R-R interval (RR) fluctuations
after acute myocardial infarction (AMI) were investigated by measures
of synchronization separating the feedback from the feedforward control
and capturing both linear and nonlinear contributions. The causal
synchronization, evaluating the ability of RR to predict SAP
(
s/t) or vice versa (t/s), and the global
synchronization () were estimated at rest and after head-up tilt in
35 post-AMI patients, 20 young and 12 old. Significance and
nonlinearity of the coupling were assessed by surrogate data analysis.
Tilting increased the number of young subjects in which RR-SAP link was
significant (from 17 to 19) and linear (from 11 to 18). In AMI, both
significance and linearity of the coupling were low at rest (26 significant and 24 nonlinear) and further reduced after tilt (17 significant and 16 nonlinear). Old subjects showed a partial recovery
of linearity after tilt (rest: 1 linear of 7 significant; tilt: 5 linear of 8 significant). In young subjects, the causal synchronization
indexes were balanced and increased from rest (t/s = 0.072 ± 0.037 and s/t = 0.054 ± 0.028) to tilt (t/s = 0.125 ± 0.071 and
s/t = 0.108 ± 0.053). On the contrary, in old
subjects and AMI patients, the feedforward was prevalent to the
feedback coupling at rest (old: t/s = 0.041 ± 0.023 and s/t = 0.069 ± 0.042; AMI:
t/s = 0.050 ± 0.030 and s/t = 0.089 ± 0.053). Tilting blunted the
unbalance in old subjects (t/s = 0.065 ± 0.052 and s/t = 0.069 ± 0.044) but not in AMI patients (t/s = 0.040 ± 0.019 and
s/t = 0.060 ± 0.040). Thus, after AMI,
nonlinear mechanisms are elicited in RR-SAP interactions. Furthermore,
the neural regulation of the cardiovascular system resulted in
imbalance as a consequence of impaired feedback and enhanced
feedforward control mechanisms.
causal analysis; nonlinear coupling; synchronization; baroreflex regulation
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