Lower body negative pressure exposure (LBNPE) produces hemodynamic modifications similar to those produced by head-up tilt test (HUT). Patients with
vasovagal syncope are more susceptible to HUT than healthy persons. The supine position during LBNPE would facilitate the simultaneous performance of complementary methods. The aim of this study was to compare tolerance to LBNPE between a group of patients with
vasovagal syncope and a group of healthy volunteers. Eleven patients with
vasovagal syncope and positive HUT and 13 healthy volunteers without prior history of
syncope and negative HUT were included. The following protocol was used: -10 mmHg, 1 minute; -20 mmHg, 1 minute; -30 mmHg, 3 minutes, and -40, -50, -60, and -70 mmHg, 5 minutes for each stage. Tolerance was expressed as: maximum tolerated negative pressure (Max NP), maximum tolerated time (Max T), and sigma P x T, where P = pressure and T = time.
Syncope or
presyncope during the test was considered positive LBNPE. LBNPE was positive at -50 or -60 mmHg in 8 of 11 patients (73%). One healthy volunteer had
presyncope after 5 minutes at -70 mmHg. Tolerance, as expressed by any of the three parameters, was significantly higher for the healthy volunteers (Max NP: -59.1 +/- 7.9 vs -70, P < 0.01; Max T: 19.1 +/- 4.2 vs 24.4 +/- 0.3, P < 0.01; sigma P x T: 836.3 +/- 269.5 vs 1214.6 +/- 18, P < 0.01). We conclude that patients with
neurocardiogenic syncope have a significantly lower tolerance to LBNPE than subjects with no previous history of
syncope.