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Rationale: The purpose of our research was to test for cardiovascular stability within 16 Austromars candidates, and to determine hemodynamic variables and hormones in a presyncopal state as evoked by a specific test protocol.
Procedures and methods: We used a graded orthostatic stress (GOS) paradigm consisting of head-up tilt (HUT) combined with lower body negative pressure (LBNP) up to a presyncopal end-point on 15 males and one healthy female. Hemodynamic parameters were monitored and venous blood samples taken.
Results: From supine control to presyncope, mean standing time was 12.3 ± 1.2 min, heart rate (HR) increased by 68 ± 12% (p < 0.0001) and thoracic impedance (TI) rose by 12 ± 1% (p < 0.0001), whereas following parameters decreased: stroke volume index (SI) 44 ± 4% (p < 0.0001), systolic pressure (SBP) 26 ± 3% (p < 0.0001), diastolic pressure (DBP) 16 ± 5% (p = 0.004), mean arterial blood pressure (MAP) 19 ± 3% (p < 0.0001), pulse pressure 41 ± 8% (p = 0.0003) and total peripheral resistance index (TPRI) 11 ± 5% (p = 0.03). Heart rate and blood pressure variabilities decreased together with pulse pressure. Plasma volume decreased by 11 ± 2% (p = 0.0004). Plasma norepinephrine (NE) increased by 86 ± 16% (p = 0.0001), epinephrine (E) by 460 ± 266% (p = 0.06), cortisol by 10 ± 6% (p = 0.02), plasma renin activity by 147 ± 26% (p = 0.002) and aldosterone by 24 ± 21% (p = 0.2).
Conclusion: Our combined HUT- graded LBNP paradigm is useful to study CV regulation and hormonal responses under severe stress conditions.