Central and cerebrovascular effects of leg crossing in humans with sympathetic failure.

Leg crossing increases arterial pressure and combats symptomatic orthostatic hypotension in patients with sympathetic failure. This study compared the central and cerebrovascular effects of leg crossing in patients with sympathetic failure and healthy controls. We addressed the relationship between MCA Vmean (middle cerebral artery blood velocity; using transcranial Doppler ultrasound), frontal lobe oxygenation [O2Hb (oxyhaemoglobin)] and MAP (mean arterial pressure), CO (cardiac output) and TPR (total peripheral resistance) in six patients (aged 37-67 years; three women) and age- and gender-matched controls during leg crossing. In the patients, leg crossing increased MAP from 58 (42-79) to 72 (52-89) compared with 84 (70-95) to 90 (74-94) mmHg in the controls. MCA Vmean increased from 55 (38-77) to 63 (45-80) and from 56 (46-77) to 64 (46-80) cm/s respectively (P<0.05), with a larger rise in O2Hb [1.12 (0.52-3.27)] in the patients compared with the controls [0.83 (-0.11 to 2.04) micromol/l]. In the control subjects, CO increased 11% (P<0.05) with no change in TPR. By contrast, in the patients, CO increased 9% (P<0.05), but also TPR increased by 13% (P<0.05). In conclusion, leg crossing improves cerebral perfusion and oxygenation both in patients with sympathetic failure and in healthy subjects. However, in healthy subjects, cerebral perfusion and oxygenation were improved by a rise in CO without significant changes in TPR or MAP, whereas in patients with sympathetic failure, cerebral perfusion and oxygenation were improved through a rise in MAP due to increments in both CO and TPR.