AUTONOMIC NERVOUS-SYSTEM ACTIVITY DURING TILT TESTING IN SYNCOPAL PATIENTS, ESTIMATED BY POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY

Spectral analysis of heart rate variability (HRV) was used to assess c hanges in autonomic function before and during postural tilt in 28 syn copal patients: 14 (group A) with positive and 14 (group B) with negat ive tilting test, and 14 normal controls (group C). Frequency-domain m easurements of the high (HF) and low (LF) frequency bands and the rati o LF/HF were derived from Holter recordings, computed by Fast Fourier analysis for 4-minute intervals immediately before tilt testing, immed iately after tilting, and just before the end of the test. in group A, the mean values of LF and HF decreased slightly in response to tiltin g while the LF/HF ratio increased, though these changes were not stati stically significant. All parameters showed a statistically significan t increase just before the onset of syncope. in group B, there were no significant changes in the parameters measured throughout the test. I n group C, there was an increase in the LF and LF/HF ratio and a decre ase in the HF immediately after tilting. There were no further signifi cant changes in any of the parameters during the test. Syncopal patien ts have a different pattern of response to the orthostatic stimulus, i n that they do not show the increase in sympathetic tone observed in n ormal individuals immediately after tilting. In the patients with a po sitive tilt test, there is a shift in the balance of ANS activity towa rds the sympathetic system shortly before the onset of syncope.