Clinical Autonomic Research

, Volume 11, Issue 1, pp 19–27 | Cite as

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance

  • Giosuè Gulli
  • Victoria L. Wight
  • Roger Hainsworth
  • Antonio Cevese
Research Article


The mechanisms leading to vasovagal syncope are still unclear. A simple discriminating test for the identification of syncopeprone subjects is not presently available. Fifty-two subjects had a stepwise orthostatic test with 60o tilt and −20 and −40 mm Hg lower-body negative pressure before the appearance of impending syncope symptoms. Spectral and cross-spectral analyses of heart period and systolic pressure time series were performed to estimate the power of the high-frequency (≈0.25 Hz) and low-frequency (≈0.1 Hz) oscillations, the coherence between heart period and systolic pressure, and the mean low-frequency and high-frequency central frequency, phase shift, and transfer function at maximal coherence. According to time to presyncope, the 52 subjects were divided into two groups: 25 with normal orthostatic tolerance, and 27 with poor orthostatic tolerance. In the supine positions, the mean central low-frequency was significantly lower in poortolerance group than in normal-tolerance group, discriminating poor from normal orthostatic tolerance with 80% specificity and 83% sensitivity, and was significantly correlated to time to presyncope. In the 2 to 3 minutes preceding syncopem subjects with poor orthostatic tolerance had less tachycardia, lower low-frequency power of systolic pressure, higher respiratory frequency, and a less negative phase shift in high-frequency range. In presyncope, sympathetic activation is reduced in subjects with poor orthostatic tolerance. In addition, the higher breathing frequency and the smaller negativity of phase shift in high-frequency range, which may indicate an inadequate engagement of the baroreflex, suggest a causal role of respiration in the development of syncope. Supine central values of low frequency may be proposed as a valuable clinical index of orthostatic intolerance.

Key words

blood pressure heart rate nervous system autonomic syncope tests 


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Copyright information

© Lippincott Williams & Wilkins 2001

Authors and Affiliations

  • Giosuè Gulli
    • 1
  • Victoria L. Wight
    • 2
  • Roger Hainsworth
    • 2
  • Antonio Cevese
    • 1
  1. 1.Department of Neurological Sciences and Vision, Section of PhysiologyUniversity of VeronaVeronaItaly
  2. 2.Institute for Cardiovascular ResearchUniversity of LeedsLeedsUK

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