title: Neurocirculatory abnormalities in chronic orthostatic intolerance.
abstract: BACKGROUND
  Chronic orthostatic intolerance (COI) occurs in postural tachycardia syndrome (POTS) and in some individuals with repeated neurocardiogenic syncope/presyncope (NCS), without POTS. This study addressed whether patients with COI and POTS or NCS have neurocirculatory abnormalities during supine rest.
  
  
  RESULTS
  Adult patients referred for COI who had POTS (n=90, mean+/-SEM age 40+/-1 years, 86% women) or NCS (n=36, 41+/-2 years old, 78% women) underwent measurements of plasma levels of catecholamines and forearm hemodynamics. Comparison data were obtained from 32 age- and gender-matched normal volunteers (39+/-2 years old, 81% women). The POTS group had a relatively fast mean heart rate (79+/-2 bpm) during supine rest compared with the NCS group (69+/-1.6 bpm, P=0.03) and normal volunteers (66+/-3 bpm, P=0.0004). The POTS group also had higher mean arterial norepinephrine (1.61+/-0.11 nmol/L, n=37) and epinephrine (0.39+/-0.03 nmol/L, n=37) concentrations than the NCS group (1.03+/-0.12 nmol/L, n=20, P=0.0012; 0.21+/-0.03 nmol/L, n=20, P=0.0005) and normal volunteers (1.13+/-0.11 nmol/L, n=20, P=0.006; 0.17+/-0.03 nmol/L, n=15, P=0.0001). The NCS group had higher mean forearm vascular resistance (52+/-6 U) than the POTS group (36+/-2 U, P=0.003).
  
  
  CONCLUSIONS
  Overall, POTS features increased heart rate and sympathetic nervous and adrenomedullary hormonal system outflows during supine rest. Increased sympathetic outflow may contribute to the relative tachycardia in POTS. NCS features forearm vasoconstriction during supine rest but not sympathoneural or adrenomedullary activation.
authors.affiliation: Clinical Neurocardiology Section, NINDS, National Institutes of Health, Bethesda, Md, USA. goldsteind@ninds.nih.gov
authors.forename: David S
authors.initials: DS
authors.lastname: Goldstein
authors.forename: Basil
authors.initials: B
authors.lastname: Eldadah
authors.forename: Courtney
authors.initials: C
authors.lastname: Holmes
authors.forename: Sandra
authors.initials: S
authors.lastname: Pechnik
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Moak
authors.forename: Yehonatan
authors.initials: Y
authors.lastname: Sharabi
mesh_terms: D000293:Adolescent; D000313:Adrenal Medulla / Q000502:physiology; D000328:Adult; D000368:Aged; D001794:Blood Pressure; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D005260:Female; D005542:Forearm; D006339:Heart Rate; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D011187:Posture / Q000502:physiology*; D012189:Retrospective Studies; D016683:Supine Position; D013564:Sympathetic Nervous System; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D013610:Tachycardia / Q000503:physiopathology*; D014661:Vasoconstriction
chemical_list: D009638:Norepinephrine; D004837:Epinephrine