Objectives. This study aimed to characterize subcutaneous blood flow changes during neurally mediated syncope and to determine whether microvasculature oscillation (vasomotion) is characteristically altered in conjunction with syncopal events. Background. Marked pallor is commonly associated with neurally mediated syncope. However, little attention has been paid to the evaluation of subcutaneous blood flow and vasomotion in this setting. Methods. This study utilized laser Doppler flowmetry to assess changes in subcutaneous microvascular blood flow during head-up tilt table testing in 13 patients with syncope and 6 control subjects. Blood flow and vasomotion frequency were measured continuously before, during and after completion of 80° head-up tilt testing (≤25-min duration). Results. Among the 13 patients with syncope, tilt testing reproduced syncopal symptoms in 9 (tilt-positive group) but not in 4 (tilt-negative group). None of the six control subjects developed symptoms during testing. Baseline mean subcutaneous blood flow did not differ significantly among the three groups. However, during upright tilt, blood flow gradually diminished in the tilt-positive group, reaching a nadir of 0.8 ± 0.33 ml/min per 100 g of tissue (mean ± SD), but remained relatively constant in the tilt-negative group and control subjects. The difference in mean blood flow response to tilt was statistically significant when the tilt-positive group was compared with either the tilt-negative group or control subjects (p < 0.001). Similarly, baseline blood flow oscillation frequency did not differ significantly in the three subgroups (tilt-positive group 0.2 ± 0.11 Hz; tilt-negative group 0.2 ± 0.02 Hz; control subjects 0.2 ± 0.11 Hz). Subsequently, during tilt testing only the tilt-positive group exhibited increased oscillation frequency; oscillation frequency remained essentially constant throughout the tilt test in the tilt-negative group and control subjects (p < 0.001, tilt-positive group vs. either the tilt-negative group or control subjects). Conclusions. These findings document an expected diminution of subcutaneous blood flow in association with neurally mediated syncope and indicate that characteristic changes in microvasculature oscillation frequency occur in conjunction with syncopal symptoms. To the extent that microvasculature vasomotion is influenced by neural control, the changes in vasomotion frequency are consistent with relative diminution of peripheral sympathetic neural influence during neurally mediated syncopal episodes.
Bibliographical noteFunding Information:
From the Cardiac Arrhythmia Service, Cardiovascular Division, Department of Medicine, University of Minnesota, Minneapolis, Minnesota. Dr. Chen was supported in part by a grant from the Education Ministry, Beijing, People's Republic of China and by the Cardiac Electrophysiology Research Fund, Minneapolis, Minnesota. Dr. Hansen was supported by a fellowship grant from the Howard Hughes Medical Institute, Chevy Chase, Maryland. This work was completed in part during Dr. Buetikofer's tenure as a fellow of the North American Society of Pacing and Electrophysiology, Newton Upper Falls, Massachusetts.