title: Effects of guided breath exercise on complex behaviour of heart rate dynamics.
abstract: BACKGROUND
  Cardiac autonomic regulation is influenced by changes in respiratory rate, which has been demonstrated by linear analysis of heart rate variability (HRV). Conversely, the complex behaviour is not well defined for HRV during this physiological state. In this sense, Higuchi Fractal Dimension is applied directly to the time series. It analyses the fractal dimension of discrete time sequences and is simpler and faster than correlation dimension and many other classical measures derived from chaos theory. We investigated chaotic behaviour of heart rate dynamics during guided breath exercises.
  
  
  METHODS
  We investigated 21 healthy male volunteers aged between 18 and 30 years. HRV was analysed 10 min before and 10 min during guided breath exercises. HRV was analysed in the time and frequency domain for linear analysis and through HFD for non-linear analysis.
  
  
  RESULTS
  Linear analysis indicated that SDNN, pNN50, RMSSD, LF, HF and LF/HF increased during guided breath exercises. HFD analysis illustrated that between Kmax20 to Kmax120 intervals, was enhanced during guided breath exercises.
  
  
  CONCLUSIONS
  Guided breath exercises acutely increased chaotic behaviour of HRV measured by HFD.
authors.affiliation: Autonomic Nervous System Study Center (CESNA), Department of Physiotherapy and Occupational Therapy, Faculty of Philosophy and Sciences, UNESP Marilia, Marilia, SP, Brazil.
authors.forename: Bruna S
authors.initials: BS
authors.lastname: Tavares
authors.affiliation: Autonomic Nervous System Study Center (CESNA), Department of Physiotherapy and Occupational Therapy, Faculty of Philosophy and Sciences, UNESP Marilia, Marilia, SP, Brazil.
authors.forename: Giovanna
authors.initials: G
authors.lastname: de Paula Vidigal
authors.affiliation: Cardiorespiratory Research Group, Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, UK.
authors.forename: David M
authors.identifier: http://orcid.org/0000-0002-8114-9055
authors.initials: DM
authors.lastname: Garner
authors.affiliation: Laboratory of Design in Research and Scientific Writing, School of Medicine of ABC, Santo Andre, SP, Brazil.|Department of Environmental Health, Harvard Medical School of Public Health, Boston, MA, USA.|Faculty of Public Health, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Rodrigo D
authors.initials: RD
authors.lastname: Raimundo
authors.affiliation: Laboratory of Design in Research and Scientific Writing, School of Medicine of ABC, Santo Andre, SP, Brazil.
authors.forename: Luiz Carlos
authors.initials: LC
authors.lastname: de Abreu
authors.affiliation: Autonomic Nervous System Study Center (CESNA), Post-Graduate Program in Physiotherapy, Faculty of Sciences and Technology, UNESP Presidente Prudente, Marilia, SP, Brazil.
authors.forename: Vitor E
authors.initials: VE
authors.lastname: Valenti
mesh_terms: D000293:Adolescent; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D001945:Breathing Exercises; D017709:Fractals; D064368:Healthy Volunteers; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006801:Humans; D016014:Linear Models; D008297:Male; D008955:Models, Cardiovascular; D017711:Nonlinear Dynamics; D015656:Respiratory Mechanics; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D055815:Young Adult
keywords: autonomic nervous system; cardiovascular system; respiratory rate