title: Diminished chaos of heart rate time series in patients with major depression.
abstract: BACKGROUND
  Depression and anxiety have been linked to serious cardiovascular events in patients with preexisting cardiac illness. A decrease in cardiac vagal function as suggested by a decrease in heart rate (HR) variability has been linked to sudden death.
  
  
  METHODS
  We compared LLE and nonlinearity scores of the unfiltered (UF) and filtered time series (very low, low, and high frequency; VLF, LF and HF) of HR between patients with depression (n = 14) and healthy control subjects (n = 18).
  
  
  RESULTS
  We found significantly lower LLE of the unfiltered series in either posture, and HF series in patients with major depression in supine posture (p <.002). LLE (LF/UF), which may indicate relative sympathetic activity was also significantly higher in supine and standing postures in patients (p <.05); LF/HF (LLE) was also higher in patients (p <.05) in either posture.
  
  
  CONCLUSIONS
  These findings suggest that major depression is associated with decreased cardiac vagal function and a relative increase in sympathetic function, which may be related to the higher risk of cardiovascular mortality in this group and illustrates the usefulness of nonlinear measures of chaos such as LLE in addition to the commonly used spectral measures.
authors: Department of Psychiatry, Wayne State University School of Medicine, Detroit, Michigan, USA.
authors: Vikram Kumar
authors: VK
authors: Yeragani
authors: K A Radha Krishna
authors: KA
authors: Rao
authors: M Ramesh
authors: MR
authors: Smitha
authors: Robert B
authors: RB
authors: Pohl
authors: Richard
authors: R
authors: Balon
authors: K
authors: K
authors: Srinivasan
mesh_terms: D000328:Adult; D003866:Depressive Disorder / Q000503:physiopathology* / Q000523:psychology*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D017711:Nonlinear Dynamics; D011569:Psychiatric Status Rating Scales