Combined head-up tilt and lower body negative pressure as an experimental model of orthostatic syncope

The combination of head-up tilt and incremental lower body negative pressure has shown promise in the diagnosis of orthostatic hypotension and neurocardiogenic syncope, although prior methodologies limited conclusions as to the reproducibility of the test. The aim of this study was to assess the efficacy and reproducibility of a protocol combining tilt and stages of incremental lower body negative pressure.

Ten volunteers (6 men and 4 women; mean age 21 +/- 1 years) participated in the study, which was composed of three sessions, 1 month apart, each consisting of 60 degrees tilt followed by lower body suction in incremental levels of -10 mmHg for 5 minutes at each level. The primary outcome variable was the time to presyncope. Secondary variables were the levels of heart rate, blood pressure, cerebral blood flow, and end-tidal CO2 at each level of the test. Presyncope could be achieved in all subjects. The mean times to presyncope were 24.6 +/- 1.4 minutes, 26.2 +/- 1.8 minutes, and 31.8 +/- 1.6 minutes and were not different across tests (P = 0.3). Intrasubject variability was assessed by determining the mean average deviation from the mean, which was 3.2 +/- 2.0 minutes. Changes in heart rate, blood pressure, end-tidal CO2, and cerebral blood flow were consistent with repeat testing.

Lower body negative pressure combined with head-up tilt in a staged protocol can safely and reliably induce presyncope in all normal subjects tested. The test is a potent and reproducible investigational tool for inducing hypotension and transient cerebral hypoperfusion.