title: Evidence of parasympathetic impairment in some patients with cardiac syndrome X.
abstract: OBJECTIVE
  Cardiac syndrome X (SX) is a clinical condition characterised by angina, positive exercise stress test and negative coronary angiography; it has often been attributed to sympathetic hyperactivity. Here we tested the hypothesis that a parasympathetic, rather than a sympathetic, dysfunction could be the cause of the autonomic imbalance observed in SX.
  
  
  METHODS
  In 20 subjects with diagnosed SX and in 12 age-matched controls, we studied autonomic function by performing spectral analysis of RR interval and finger arterial pressure (SAP), in supine position and during head-up tilting. We also carried out a set of tests of parasympathetic function.
  
  
  RESULTS
  The group of SX patients did not differ significantly from control subjects in any of the variables tested. In a subgroup of 13 SX, however, tilting increased the low-frequency power of SAP, but did not induce the expected increase in low-frequency and decrease in high-frequency power of RR. These patients, in supine position, had significantly lower sinus arrhythmia and a higher ratio of low to high frequency of RR, in comparison with control subjects. We interpreted these differences as signs of reduced parasympathetic, but essentially normal sympathetic, activity. The parasympathetic tests confirmed vagal impairment in the same SX subjects. On the other hand, all the tests indicated normal parasympathetic functions in the control subjects and in those SX patients who displayed the expected spectral changes in tilting.
  
  
  CONCLUSIONS
  In about two thirds of the patients with SX, the pathophysiological mechanism causing the symptoms could be related to the reduced parasympathetic tone, rather than to an augmented sympathetic activity.
authors.affiliation: Department of Neurological Science and Vision, Section of Human Physiology, University of Verona, Strada Le Grazie 8, 37134, Verona, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Gulli
authors.forename: R
authors.initials: R
authors.lastname: Cemin
authors.forename: P
authors.initials: P
authors.lastname: Pancera
authors.forename: G
authors.initials: G
authors.lastname: Menegatti
authors.forename: C
authors.initials: C
authors.lastname: Vassanelli
authors.forename: A
authors.initials: A
authors.lastname: Cevese
mesh_terms: D000704:Analysis of Variance; D001794:Blood Pressure; D016022:Case-Control Studies; D003080:Cold Temperature; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D017566:Microvascular Angina / Q000503:physiopathology*; D008875:Middle Aged; D010275:Parasympathetic Nervous System / Q000503:physiopathology*; D017156:Photoplethysmography; D012815:Signal Processing, Computer-Assisted; D018667:Tilt-Table Test