Noções básicas de variabilidade da frequência cardíaca e sua aplicabilidade clínica

Abstract

Autonomic nervous system (ANS) plays an important role in the regulation of the physiological processes of the human organism during normal and pathological conditions. Among the techniques used in its evaluation, the heart rate variability (HRV) has arising as a simple and non-invasive measure of the autonomic impulses, representing one of the most promising quantitative markers of the autonomic balance. The HRV describes the oscillations in the interval between consecutive heart beats (RR interval), as well as the oscillations between consecutive instantaneous heart rates. It is a measure that can be used to assess the ANS modulation under physiological conditions, such as wakefulness and sleep conditions, different body positions, physical training and also pathological conditions. Changes in the HRV patterns provide a sensible and advanced indicator of health involvements. Higher HRV is a signal of good adaptation and characterizes a health person with efficient autonomic mechanisms, while lower HRV is frequently an indicator of abnormal and insufficient adaptation of the ANS, provoking poor patient's physiological function. Because of its importance as a marker that reflects the autonomic nervous system activity on the sinus node and as a clinical instrument to assess and identify health involvements, this study reviews conceptual aspects of the HRV, measurement devices, filtering methods, indexes used in the HRV analyses, limitations in the use and clinical applications of the HRV.Descriptors: Autonomic nervous system. Heart rate. Parasympathetic nervous system. Sympathetic nervous system. ResumoO sistema nervoso autônomo (SNA) desempenha um papel importante na regulação dos processos fisiológicos do organismo humano tanto em condições normais quanto patológicas. Dentre as técnicas utilizadas para sua avaliação, a variabilidade da frequência cardíaca (VFC) tem emergido como uma medida simples e não-invasiva dos impulsos autonômicos, representando um dos mais promissores marcadores quantitativos do balanço autonômico. A VFC descreve as oscilações no intervalo entre batimentos cardíacos consecutivos (intervalos R-R), assim como oscilações entre frequências cardíacas instantâneas consecutivas. Trata-se de uma medida que pode ser utilizada para avaliar a modulação do SNA sob condições fisiológicas, tais como em situações de vigília e sono, diferentes posições do corpo, treinamento físico, e também em condições patológicas. Mudanças nos padrões da VFC fornecem um indicador sensível e antecipado de comprometimentos na

Effects of a multidisciplinary program on autonomic modulation in overweight or obese children and adolescents

“…The temporal and spectral indices of HRV which represent overall variability (SDNN, SD2, TINN and RRtri), and the LF (ms²) index which shows the sympathetic component of the autonomic nervous system 19 , also increased after implementing the intervention program. The literature highlights evidence of reduced sympathetic activity in obese children 7,22 which could represent another negative aspect in these children as the sympathetic nervous system participates in the modulation of glucose and lipid metabolism 24 and, thus, a reduction in sympathetic activity is associated with less energy expenditure and consequent weight gain 25 .…”

“…Regarding the temporal and spectral indices of HRV which represent the parasympathetic autonomic nervous system (rMSSD, HF (ms²), and SD1) 19 , there was an increase in values when comparing the moments before and after the intervention. There is evidence that obese children demonstrate reduced parasympathetic activity 7,22 , which is an important negative factor as this reduction is associated with the development of risk factors and an increase in morbidity and mortality 23 .…”

“…In the time domain, the following indices were used: rMSSD (the root mean square of successive differences between normal intervals of consecutive cardiac beats in an interval of time expressed in milliseconds [ms]) and SDNN (the standard deviation of normal-to-normal intervals in an interval of time expressed in ms) 19 .…”

“…In the frequency domain, the spectral components of low frequency (LF:0.004 to 0.15 Hertz [Hz]) and high frequency (HF: 0.15 to 0.40Hz) were used, expressed in DOI: http://dx.doi.org/10.7322/jhgd.119257 ms² (ms squared) and normalized units (nu), which represent the relative value of each spectral component at the total potency minus the very low frequency, and the ratio between them (LF/HF) 19 . These analyses were calculated using the Fast Fourier Transform algorithm.…”

“…The duration of an interval (RRn) was represented on the "x" axis, and the length of the next interval (RRn+1) on the "y" axis, so each point on the graph (RRn, RRn+1) corresponded to two successive heart beats. For quantitative analysis of the plot, the indices calculated were: SD1 (standard deviation of instantaneous beat to beat variability), SD2 (standard deviation of long term continuous iRR) and the SD1/SD2 ratio 19 .…”