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 autĂŽnomo (SNA) desempenha um papel importante na regulação dos processos fisiolĂłgicos do organismo humano tanto em condiçÔes normais quanto patolĂłgicas. Dentre as tĂ©cnicas utilizadas para sua avaliação, a variabilidade da frequĂȘncia cardĂaca (VFC) tem emergido como uma medida simples e nĂŁo-invasiva dos impulsos autonĂŽmicos, representando um dos mais promissores marcadores quantitativos do balanço autonĂŽmico. A VFC descreve as oscilaçÔes no intervalo entre batimentos cardĂacos consecutivos (intervalos R-R), assim como oscilaçÔes entre frequĂȘncias cardĂacas instantĂąneas consecutivas. Trata-se de uma medida que pode ser utilizada para avaliar a modulação do SNA sob condiçÔes fisiolĂłgicas, tais como em situaçÔes de vigĂlia e sono, diferentes posiçÔes do corpo, treinamento fĂsico, e tambĂ©m em condiçÔes patolĂłgicas. Mudanças nos padrĂ”es da VFC fornecem um indicador sensĂvel e antecipado de comprometimentos na