Presyncopal cardiac contractility and autonomic activity in young healthy males

We investigated non-invasively cardiac contractility andautonomic nervous activity during presyncopal orthostatic stressinduced in healthy humans. A graded orthostatic stress (GOS)paradigm, consisting of head-up tilt (HUT) combined with lowerbody negative pressure (LBNP) of increasing magnitude, wasused to reach a presyncopal end-point in 15 healthy adults.Continuous beat-to-beat hemodynamic and autonomicparameters were recorded. From supine control (C1) topresyncope (PS), total peripheral resistance index (TPRI)decreased from 2300±500 to 1910±320 dyne*s*m²/cm^5(p=0.004), index of contractility (IC) from 59±14 to 27±6 1000/s(p<0.0001), left ventricular working index (LVWI) from 5.2±1.3vs. 3.6±0.6 mmHg*L/(min*m²) (p=0.0001) and accelerationindex (ACI) from 65±18 vs. 54±15 100/s² (p=0.04). Lowfrequency variation of diastolic blood pressure (LFnudBP)increased from 51±14 to 67±11 % (p=0.0006) and of systolicblood pressure (LFnusBP) from 50±6 vs. 67±8 % (p<0.0001).High frequency variation of RR-interval (HFms²RRI) decreasedfrom 385±320 to 38±43 ms² (p=0.001). From late GOS (G3) toPS, TPRI decreased from 2540±640 to 1910±320dyne*s*m²/cm^5 (p=0.003), IC from 35±6 to 27±6 1000/s(p=0.003), LVWI from 4.6±0.9 to 3.6±0.6 mmHg*L/(min/m²)(p=0.003), LFnusBP from 71±8 to 67±8 % (p=0.03), LFmmHg²dBPfrom 6.6±4.0 to 4.8±2.9 mmHg² (p=0.0001), LFmmHg²sBP from9.7±7.8 to 7.4±4.8 mmHg² (p=0.01). HFnuRRI increased from19±8 to 28±13 % (p=0.008). Myocardial contractility indices andparameters of sympathetic activity were reduced in thepresyncopal state, while parasympathic activity was increased.This suggests a decrease in cardiac contractility duringorthostatically induced presyncope in healthy subjects.