title: After-exercise heart rate variability is attenuated in postmenopausal women and unaffected by estrogen therapy.
abstract: OBJECTIVE
  Delayed heart rate (HR) recovery in the immediate postexercise period has been linked to adverse cardiovascular prognosis. The after effects of an acute bout of exercise on HR modulation in postmenopausal women (PMW) and the influence of estrogen therapy are unknown.
  
  
  METHODS
  In 13 sedentary PMW (54 ± 2 y, mean ± SEM), we assessed HR variability (HRV)--an index of HR modulation--and the influence of estrogen therapy on HRV. HRV in the frequency domain was quantified during supine rest and again 60 minutes after treadmill exercise for 45 minutes, at 60% VO2peak. PMW were studied before and after 4 weeks of oral estradiol. To obtain reference values for the after effects of exercise on HRV in healthy young women, 14 premenopausal women (PreM) completed the identical exercise protocol.
  
  
  RESULTS
  Compared with PreM, PMW demonstrated lower high frequency (vagal modulation) and total HRV (P < 0.05) at rest. In PreM, all HRV values were similar before and after exercise. In contrast, in PMW after exercise, despite having identical HR to PreM, high frequency and total HRV were all lower (all P ≤ 0.01) compared with pre-exercise HRV values. Estrogen therapy had no effect on pre or postexercise values for HRV.
  
  
  CONCLUSIONS
  When compared with PreM, PMW have identical HR, but lower vagal HR modulation at rest and delayed HRV recovery after exercise. Estrogen does not restore baseline HRV or accelerate HRV recovery postexercise, suggesting aging rather than estrogen deficiency per se may lower HRV in PMW.
authors.affiliation: 1Division of Cardiology, Women's College Hospital 2Division of Cardiology, University Health Network 3Mount Sinai Hospital, Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Harvey
authors.forename: Emma
authors.initials: E
authors.lastname: O'Donnell
authors.forename: Peter
authors.initials: P
authors.lastname: Picton
authors.forename: Beverley L
authors.initials: BL
authors.lastname: Morris
authors.forename: Catherine F
authors.initials: CF
authors.lastname: Notarius
authors.forename: John S
authors.initials: JS
authors.lastname: Floras
mesh_terms: D001794:Blood Pressure; D004562:Electrocardiography; D015914:Estrogen Replacement Therapy; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D010101:Oxygen Consumption; D017698:Postmenopause / Q000502:physiology*; D017697:Premenopause / Q000502:physiology; D012146:Rest; D014630:Vagus Nerve / Q000502:physiology