title: Effects of hormone replacement therapy on heart rate variability in postmenopausal women.
abstract: BACKGROUND
  Hormone replacement therapy (HRT) is associated with reduced cardiovascular risk, but the underlying mechanism(s) are not fully understood. This study investigated the effects of a 6-month course of HRT on cardiac autonomic function parameters assessed by heart rate variability (HRV) in postmenopausal women.
  
  
  METHODS
  Forty-six healthy postmenopausal women (age 48 +/- 5, range 40-60) with normal baseline electrocardiogram and negative exercise testing were enrolled. HRT, which was either 0.625 mg/day conjugated equine estrogen (CEE) plus 2.5 mg/day medroxyprogesterone acetate or 0.625 mg/day CEE alone were administered depending on hysterectomy status. Power spectral analysis of HRV was performed to calculate the low frequency component in absolute (LF) and normalized units (LF nu), high frequency component in absolute (HF), and normalized units (HF nu), and the LF/HF ratio. The standard deviation of RR intervals (SDNN) was calculated from the time series of RR intervals.
  
  
  RESULTS
  A 6-month course of HRT did not significantly alter resting heart rate (P > 0.05). The LF/HF ratio and LF nu significantly decreased after HRT (P = 0.022 and P = 0.032), whereas a significant increase was noted in the HF component of HRV (P = 0.043), indicating an improvement in cardiac autonomic function. The SDNN value, which was 28.8 +/- 11.8 ms before HRT significantly increased to 35.4 +/- 16.7 ms after 6 months (P = 0.011).
  
  
  CONCLUSIONS
  Our results indicate that a 6-month course of HRT may significantly improve cardiac autonomic function parameters, a finding that could at least partly explain the potential cardioprotective effect(s) of HRT.
authors.affiliation: Department of Cardiology, Hacettepe University, Ankara, Turkey. ayliny@ato.org.tr
authors.forename: A
authors.initials: A
authors.lastname: Yildirir
authors.forename: G
authors.initials: G
authors.lastname: Kabakci
authors.forename: H
authors.initials: H
authors.lastname: Yarali
authors.forename: F
authors.initials: F
authors.lastname: Aybar
authors.forename: E
authors.initials: E
authors.lastname: Akgul
authors.forename: O
authors.initials: O
authors.lastname: Bukulmez
authors.forename: L
authors.initials: L
authors.lastname: Tokgozoglu
authors.forename: T
authors.initials: T
authors.lastname: Gurgan
authors.forename: A
authors.initials: A
authors.lastname: Oto
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000502:physiology; D002318:Cardiovascular Diseases / Q000517:prevention & control; D015914:Estrogen Replacement Therapy; D004966:Estrogens, Conjugated (USP) / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause / Q000502:physiology*; D018709:Statistics, Nonparametric
chemical_list: D004966:Estrogens, Conjugated (USP)