POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY DURING UPRIGHT TILTTEST - A COMPARISON OF PATIENTS WITH SYNCOPE AND NORMAL SUBJECTS

We analyzed heart variability (HRV) response to tilt in 35 patients wi th a history of neurocardiogenic syncope and in 8 normal volunteers. F requency domain examination was performed using power spectral analysi s of RR variability during resting supine position and during the 256 beats preceding the onset of syncope or completion of 60 min of uprigh t tilt to 70 degrees. Both low (0.05-0.15 Hz) and high frequency (0.15 -0.4 Hz) spectral components of HRV increased markedly in all groups a s a result of tilting. Statistically significant differences were note d between the patient groups at completion of upright tilting. However , these differences in spectral components between groups were of smal l magnitude when compared to the overall increase in spectral power oc curring in all groups as a result of the tilt and are difficult to cor relate clinically with the appearance, or lack of appearance of tilt-i nduced syncope. Power spectral analysis of HRV, as presently performed , appears to lack discriminative power to detect the rapid and marked changes in sympathovagal modulation known to occur during tilt test in patients with neurocardiogenic syncope.