title: Fractal correlation property of heart rate variability in chronic obstructive pulmonary disease.
abstract: BACKGROUND
  It was reported that autonomic nervous system function is altered in subjects with chronic obstructive pulmonary disease (COPD). We evaluated short- and long-term fractal exponents of heart rate variability (HRV) in COPD subjects.
  
  
  METHODS
  We analyzed data from 30 volunteers, who were divided into two groups according to spirometric values: COPD (n = 15) and control (n = 15). For analysis of HRV indices, HRV was recorded beat by beat with the volunteers in the supine position for 30 minutes. We analyzed the linear indices in the time (SDNN [standard deviation of normal to normal] and RMSSD [root-mean square of differences]) and frequency domains (low frequency [LF], high frequency [HF], and LF/HF), and the short- and long-term fractal exponents were obtained by detrended fluctuation analysis. We considered P < 0.05 to be a significant difference.
  
  
  RESULTS
  COPD patients presented reduced levels of all linear exponents and decreased short-term fractal exponent (alpha-1: 0.899 ± 0.18 versus 1.025 ± 0.09, P = 0.026). There was no significant difference between COPD and control groups in alpha-2 and alpha-1/alpha-2 ratio.
  
  
  CONCLUSIONS
  COPD subjects present reduced short-term fractal correlation properties of HRV, which indicates that this index can be used for risk stratification, assessment of systemic disease manifestations, and therapeutic procedures to monitor those patients.
authors.affiliation: Departamento de Fisioterapia da Faculdade de Ciências e Tecnologia, Universidade Estadual Paulista, Presidente Prudente, São Paulo, Brasil. carvalho.td1@gmail.com
authors.forename: Tatiana D
authors.initials: TD
authors.lastname: Carvalho
authors.forename: Carlos Marcelo
authors.initials: CM
authors.lastname: Pastre
authors.forename: Moacir Fernandes
authors.initials: MF
authors.lastname: de Godoy
authors.forename: Celso
authors.initials: C
authors.lastname: Fereira
authors.forename: Fábio O
authors.initials: FO
authors.lastname: Pitta
authors.forename: Luiz Carlos
authors.initials: LC
authors.lastname: de Abreu
authors.forename: Ercy Mara Cipulo
authors.initials: EM
authors.lastname: Ramos
authors.forename: Vitor E
authors.initials: VE
authors.lastname: Valenti
authors.forename: Luiz Carlos Marques
authors.initials: LC
authors.lastname: Vanderlei
mesh_terms: D000368:Aged; D001938:Brazil; D016022:Case-Control Studies; D005260:Female; D017709:Fractals; D006334:Heart Function Tests; D006339:Heart Rate; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000503:physiopathology*; D012815:Signal Processing, Computer-Assisted; D013147:Spirometry; D016683:Supine Position; D013997:Time Factors