title: Hyperthyroidism is characterized by both increased sympathetic and decreased vagal modulation of heart rate: evidence from spectral analysis of heart rate variability.
abstract: OBJECTIVE
  The clinical manifestations of hyperthyroidism resemble those of the hyperadrenergic state. This study was designed to evaluate the impact of hyperthyroidism on the autonomic nervous system (ANS) and to investigate the relationship between serum thyroid hormone concentrations and parameters of spectral heart rate variability (HRV) analysis in hyperthyroidism.
  
  
  METHODS
  Thirty-two hyperthyroid Graves' disease patients (mean age 31 years) and 32 sex-, age-, and body mass index (BMI)-matched normal control subjects were recruited to receive one-channel electrocardiogram (ECG) recording.
  
  
  METHODS
  The cardiac autonomic nervous function was evaluated by the spectral analysis of HRV, which indicates the autonomic modulation of the sinus node. The correlation coefficients between serum thyroid hormone concentrations and parameters of the spectral HRV analysis were also computed.
  
  
  RESULTS
  The hyperthyroid patients revealed significant differences (P < 0.001) compared with the controls in the following HRV parameters: a decrease in total power (TP), very low frequency power (VLF), low frequency power (LF), high frequency power (HF), and HF in normalized units (HF%); and an increase in LF in normalized units (LF%) and in the ratio of LF to HF (LF/HF). After correction of hyperthyroidism in 28 patients, all of the above parameters were restored to levels comparable to those of the controls. In addition, serum thyroid hormone concentrations showed significant correlations with spectral HRV parameters.
  
  
  CONCLUSIONS
  Hyperthyroidism is in a sympathovagal imbalanced state, characterized by both increased sympathetic and decreased vagal modulation of the heart rate. These autonomic dysfunctions can be detected simultaneously by spectral analysis of HRV, and the spectral HRV parameters could reflect the disease severity in hyperthyroid patients.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, China Medical University Hospital, Taichung, Taiwan.
authors.forename: Jin-Long
authors.initials: JL
authors.lastname: Chen
authors.forename: Hung-Wen
authors.initials: HW
authors.lastname: Chiu
authors.forename: Yin-Jiun
authors.initials: YJ
authors.lastname: Tseng
authors.forename: Woei-Chyn
authors.initials: WC
authors.lastname: Chu
mesh_terms: D000328:Adult; D013956:Antithyroid Agents / Q000627:therapeutic use; D001341:Autonomic Nervous System / Q000502:physiology*; D016022:Case-Control Studies; D015716:Electrocardiography, Ambulatory; D005260:Female; D006111:Graves Disease / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology*; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D018709:Statistics, Nonparametric; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D013956:Antithyroid Agents; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine