title: Clinical and physiological effects of an acute alpha-1 adrenergic agonist and a beta-1 adrenergic antagonist in chronic orthostatic intolerance.
abstract: BACKGROUND
  Adrenergic agents are commonly used in the treatment of chronic orthostatic intolerance with postural tachycardia syndrome (POTS). POTS may be associated with increased limb blood flow ("high flow") and defective orthostatic vasoconstriction or decreased limb blood flow ("low flow") and potentially with small blood volume.
  
  
  RESULTS
  We investigated the consequences of short-term intravenous administration of an alpha-1 adrenergic agonist, phenylephrine, and a beta-1 adrenergic antagonist, esmolol, in 14 patients with POTS aged 13 to 19 years. Indices of heart rate and blood pressure variability, peripheral blood flow, and arterial resistance were assessed, and the capacitance relation was computed for every subject using venous occlusion plethysmography. Patients were tilted to 35 degrees upright while medicated and while unmedicated, and measurements were repeated. Phenylephrine improved orthostatic tolerance and normalized hemodynamics and indices of heart rate/blood pressure variability while supine and while upright, producing significant peripheral vasoconstriction and venoconstriction (20% capacitance change). Esmolol did not improve orthostatic tolerance or hemodynamics. A subgroup of low-flow POTS patients had exaggerated venoconstriction to phenylephrine (50% capacitance change) but others had no response.
  
  
  CONCLUSIONS
  Phenylephrine, but not esmolol, improves orthostatic tolerance and hemodynamics in POTS. This lends support to the use of oral alpha-1 agonists in the treatment of patients with chronic orthostatic intolerance.
authors.affiliation: Department of Pediatrics, New York Medical College, Valhalla, NY 10595, USA. stewart@nymc.edu
authors.forename: Julian M
authors.initials: JM
authors.lastname: Stewart
authors.forename: Jose
authors.initials: J
authors.lastname: Munoz
authors.forename: Amy
authors.initials: A
authors.lastname: Weldon
mesh_terms: D000293:Adolescent; D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D002908:Chronic Disease; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D007024:Hypotension, Orthostatic / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D007262:Infusions, Intravenous; D007866:Leg / Q000098:blood supply; D008297:Male; D010656:Phenylephrine / Q000008:administration & dosage; D011187:Posture; D011412:Propanolamines / Q000008:administration & dosage; D012039:Regional Blood Flow / Q000187:drug effects; D013577:Syndrome; D013610:Tachycardia / Q000150:complications / Q000503:physiopathology; D018667:Tilt-Table Test; D016896:Treatment Outcome
chemical_list: D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D010656:Phenylephrine; C036604:esmolol