Presyncopal Cardiac Contractility and Autonomic Activity in Young Healthy Males

摘要

We investigated non-invasively cardiac contractility and autonomic nervous activity during presyncopal orthostatic stress induced in healthy humans. A graded orthostatic stress (GOS) paradigm, consisting of head-up tilt (HUT) combined with lower body negative pressure (LBNP) of increasing magnitude, was used to reach a presyncopal end-point in 15 healthy adults. Continuous beat-to-beat hemodynamic and autonomic parameters were recorded. From supine control (C1) to presyncope ( PS), total peripheral resistance index (TPRI) decreased from 2300 +/- 500 to 1910 +/- 320 dyne*s*m/cm(boolean AND)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 +/- 1.3 vs. 3.6 +/- 0.6 mmHg*L/(min*m(2)) (p=0.0001) and acceleration index (ACI) from 65 +/- 18 vs. 54 +/- 15 100/s(2) (p=0.04). Low frequency variation of diastolic blood pressure (LF(nu)dBP) increased from 51 +/- 14 to 67 +/- 11 % (p=0.0006) and of systolic blood pressure (LF(nu)sBP) from 50 +/- 6 vs. 67 +/- 8 % (p<0.0001). High frequency variation of RR-interval (HFms2RRI) decreased from 385 +/- 320 to 38 +/- 43 ms(2) (p=0.001). From late GOS (G3) to PS, TPRI decreased from 2540 +/- 640 to 1910 +/- 320 dyne*s*m(2)/cm(boolean AND)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/m(2)) (p=0.003), LFnusBP from 71 +/- 8 to 67 +/- 8 % (p=0.03), LF(mmHg2)dBP from 6.6 +/- 4.0 to 4.8 +/- 2.9 mmHg(2) (p=0.0001), LF(mmHg2)sBP from 9.7 +/- 7.8 to 7.4 +/- 4.8 mmHg(2) (p=0.01). HFnuRRI increased from 19 +/- 8 to 28 +/- 13 % (p=0.008). Myocardial contractility indices and parameters of sympathetic activity were reduced in the presyncopal state, while parasympathic activity was increased. This suggests a decrease in cardiac contractility during orthostatically induced presyncope in healthy subjects.