Addressing the complexity of cardiovascular regulation

Abstract

The cardiovascular system plays a key role in complex living organisms since it provides supplies for maintaining vital functions and, contemporaneously, gets rid of waste materials. It is formed by highly specialized subsystems that interact with each other to accomplish tasks (e.g. the optimization of arterial and pulmonary circulation) and even compete for resources as in, for example, the maintenance of the cerebral circulation during a massive haemorrhage. Subsystems have their own local regulatory mechanisms (e.g. mechanisms regulating blood flow in proximal microvascular districts) that interact with central neural commands reflecting the activity of the vasomotor and respiratory autonomous oscillators, with reflex neural commands occurring in response to changes in some controlled variables (e.g. arterial pressure) and with humoral factors. All these regulatory mechanisms act rhythmically, producing incessant adjustments in cardiovascular variables visible from beat-to-beat recordings. These variations are referred to as 'cardiovascular variability' and occur over a wide frequency range including very slow rhythms (e.g. ultradian periodicities) and oscillations even faster than heart rate. The magnitude of these variations depends on the gross amount of the activities of the autonomous central oscillators, on the resonance of the closed-loop mechanisms, on the gain of the relationship between variables and on the possibility that a network of distributed oscillators with negligible activities becomes entrained or remains sparse.The presence of multiple regulatory mechanisms contemporaneously active over different time scales and capable of varying over time the relationships among variables generates the dynamic complexity of cardiovascular variables. This complexity also depends on the presence of mechanisms favouring synchronization among the activities of subsystems according to n : m coupling ratios (i.e. n cycles of activity of one subsystem correspond to m cycles of the other), thus reducing dimensionality of the cardiovascular system, and on the amount of information exchanged among subsystems (i.e. on their degree of isolation).Current evidence suggests that the assessment of the complexity of cardiovascular regulation could provide important information about the underlying regulatory mechanisms. In particular, it has been shown that a modification of complexity indices, resulting from depressed organ function, a loss of interaction among subsystems, an overwhelming action of a subsystem over others and an impairment of regulatory mechanisms, is a clear hallmark of a pathological situation. Interestingly, since the complexity of cardiovascular regulation can be evaluated from variables that are routinely and non-invasively estimated during the most common medical examinations, this assessment does not require additional procedures and devices. On the contrary, it necessitates

Conditional symbolic analysis detects nonlinear influences of respiration on cardiovascular control in humans

“…We applied the proposed framework to face the issue of the description of the cardiovascular control from spontaneous beat-to-beat fluctuations of cardiovascular variables. This problem poses the abovementioned challenges owing to the presence of multiple, contemporaneously active, regulatory mechanisms and the lack of a strict formalization of the causal relations among them [28,29]. The proposed indexes distinguished experimental conditions, identified early signs of syncope, detected nonlinear interactions and allowed sound interpretations and the formulation of hypotheses.…”

Relação entre a variabilidade da frequência cardíaca e VO 2pico em mulheres ativas

“…Em contrapartida, em relação ao grupo controle, os grupos AER e AER+FOR apresentaram predomínio da modulação vagal (AFun e 2UV%) e menor modulação simpática (BFnu e 0V%). De acordo com Porta et al 19 , a complexidade da regulação cardiovascular promove informações importantes sobre os mecanismos regulatórios subjacentes. Portanto, a modificação dos índices de complexidade, neste caso, pode ser resultante da grande função do órgão, um aumento de interação entre os subsistemas e aperfeiçoamento de mecanismos de regulação, o que pode sugerir uma adaptação autonômica cardíaca.…”

Complex and Nonlinear Analysis of Heart Rate Variability in the Assessment of Fetal and Neonatal Wellbeing

“…It is well proven that schizophrenia is related to panic attacks [111,112], further supporting the altered CRC in SZ might be at least partly related to panic attacks in the acute psychotic state. It was shown that changed complexity indices, resulting from depressed organ function, a loss of interaction among subsystems, an overwhelming action of a subsystem over others and an impairment of regulatory processes, is a clear hallmark of a pathological situation [113]. We believe that the found alterations in CRC might reflect arousal and permeant stress situation in acutely ill SZ patients.…”