POWER SPECTRAL ANALYSIS OF HEART RATE VARIABILITY DURING GRADED HEAD‐UP TILTING IN PATIENTS WITH VASODEPRESSOR SYNCOPE

Publisher Website
Google Scholar
Abstract
1. Two groups of age- and sex-matched subjects, eight healthy controls and 10 patients, suffering from recurrent vasodepressor syncope, participated in a study to examine autonomic function and sequential changes in power distribution of heart rate (HR) variability during graded head-up tilt. 2. The following autonomic function tests were performed valsalva ratio, HR responses to deep breathing and posture, BP responses to sustained handgrip and postural change. Each subject was tilted at 15°, 30°, 45°, 60° and 80° head-up, each for 15 min, or until symptoms occurred. The eight control subjects completed the tilt study without any symptoms, while all 10 patients developed presyncope and/or syncope at various tilt angles. 3. Resting blood pressure (BP) was lower in the patient group, while resting HR, autonomic function tests and resting HR variability components were similar in the two groups. 4. The control group showed a progressive increase in low frequency power component (LF) from supine to end tilt (ΔLF 20.06 ± 14.50%) and a progressive fall in high frequency (HF) component (ΔHF—24.62 ± 10.64%). In contrast, in the patient group, LF fell during tilt in the presyncope period (ΔLF -10.57 ± 12.93%, P < 0.01 vs control group). HF and HF: LF ratio responses did not differ significantly in the two groups. 5. At end tilt, the increase in plasma noradrenaline was significantly greater in the control group than in the patient group (ΔNA 0.83 ± 0.27 vs 0.28 ± 0.14 pmol/mL, P < 0.01). Plasma adrenaline: noradrenaline ratio at end tilt did not change in the control group, but increased significantly in the patient group (supine 0.07 ± 0.03, end tilt 0.16 ± 0.09, P < 0.05). 6. It was concluded that sympathetic withdrawal plays a major role in the mechanism of vasodepressor syncope.