title: Effect of low-dose scopolamine on autonomic control of the heart.
abstract: BACKGROUND
  In low doses, scopolamine paradoxically enhances parasympathetic outflow to the heart. The mechanisms which mediate this action are not fully understood. Moreover, there are conflicting data regarding the potential role of sympathetic activity. This study in 17 healthy individuals was designed to characterize the influence of low dose transdermal scopolamine on the gain of the baroreflex and respiratory heart rate reflex and to determine the role of sympathetic activity.
  
  
  METHODS
  The effect of scopolamine was analyzed in the time and frequency domain by computing heart rate variability indices. The gains of the respiratory heart rate reflex and the baroreflex were estimated simultaneously by means of a cardiovascular system identification approach using an optimized autoregressive moving average algorithm. Measurements were repeated in the upright posture to assess the influence of enhanced sympathetic activity. In six subjects ambulatory ECGs were recorded to determine whether there are diurnal variations of the effect of scopolamine.
  
  
  RESULTS
  Scopolamine enhances vagal modulation of heart rate through both the respiratory-heart rate reflex and the baroreflex, as the gains of both were augmented by the drug in the supine and in the upright postures.
  
  
  CONCLUSIONS
  Scopolamine increases parasympathetic cardiac control by augmenting the gain of the respiratory-heart rate and baroreflex. This action is not attenuated in the upright posture when sympathetic tone is increased.
authors.affiliation: Cardiology Division, State University of New York at Stony Brook, USA. raederea@msn.com
authors.forename: E A
authors.initials: EA
authors.lastname: Raeder
authors.forename: A
authors.initials: A
authors.lastname: Stys
authors.forename: R J
authors.initials: RJ
authors.lastname: Cohen
mesh_terms: D000279:Administration, Cutaneous; D000328:Adult; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D018727:Muscarinic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D010275:Parasympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D010276:Parasympatholytics / Q000008:administration & dosage / Q000494:pharmacology*; D011187:Posture / Q000502:physiology; D012143:Respiratory Physiological Phenomena; D012601:Scopolamine / Q000008:administration & dosage / Q000494:pharmacology*; D016683:Supine Position / Q000502:physiology
chemical_list: D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D012601:Scopolamine