title: [Variability of heart rate].
abstract: OBJECTIVE
  The basic principles of the physiological mechanisms of heart rate variability are discussed. The different methods used in its assessment are evaluated. An overview of its clinical utility is presented.
  
  
  METHODS
  We reviewed the papers on this area until May 1994 we thought relevant. The more or less succinct description of their conclusions is made and commented.
  
  
  RESULTS
  Heart rate frequency and its oscillations are regulated by the autonomic nervous system. Heart rate variability analysis is an easy non invasive means of investigating the autonomic control of the heart. There is a wealth of experimental and clinical evidence linking abnormalities of the autonomic nervous system with the development of serious ventricular arrhythmia and sudden death, and it has been clearly shown that decreased heart rate variability is associated with increased mortality in diabetes and after myocardial infarction. Abnormal heart rate variability has been detected in several other disorders such as hypertension, neurologic diseases, heart failure, renal failure, etc., although here its clinical usefulness is yet to be set. Heart rate variability is influenced by various drugs whose potential protective cardiovascular effect is under investigation.
  
  
  CONCLUSIONS
  Heart rate variability analysis is a promising method that can be used as an index of cardiac autonomic balance and has been shown to be of significant clinical value. RR interval variation is controlled by the activity of cardiac sympathetic and parasympathetic nervous system, the function of which is influenced by many factors such as age, sex, position, breathing, hour of the day, therapeutics, etc. Different methods and results have been used by various authors. Standard values are not yet available to be used or compared in different settings. From the interest it has raised all over the world it is expected that very soon this method will have a widespread use in clinical practice, providing useful tools both for diagnostic and prognostic purposes and to monitor and guide therapeutic interventions.
authors.affiliation: Serviço Titulado em Cardiologia, UTIC-AC do Hospital de Santa Maria de Lisboa.
authors.forename: A
authors.initials: A
authors.lastname: Longo
authors.forename: D
authors.initials: D
authors.lastname: Ferreira
authors.forename: M J
authors.initials: MJ
authors.lastname: Correia
mesh_terms: D002318:Cardiovascular Diseases / Q000503:physiopathology; D003920:Diabetes Mellitus / Q000503:physiopathology; D006334:Heart Function Tests; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D009422:Nervous System Diseases / Q000503:physiopathology
vernacular_title: Variabilidade da frequência cardíaca.