Leg crossing with muscle tensing, a physical counter-manoeuvre to prevent syncope, enhances leg blood flow
Résumé
In patients with orthostatic intolerance the mechanisms to maintain blood pressure fail. A physical counter-manoeuvre to postpone or even prevent orthostatic intolerance in these patients is leg crossing combined with muscle tensing. Although the central haemodynamic effects of physical counter-manoeuvres are well documented, not much is known about the peripheral haemodynamic events. Therefore, the purpose of the present study was to examine the peripheral haemodynamic effects of leg crossing combined with muscle tensing during 70 o} head-up tilt (HUT). Thirteen healthy subjects were monitored for 10 minutes in the supine position followed by 10 minutes in 70 0}HUT and, finally, 2 minutes of leg crossing with muscle tensing in 70 o} HUT. Mean arterial blood pressure (MAP), heart rate, stroke volume, cardiac output and total peripheral resistance were measured continuously by Portapres. Leg blood flow was measured using Doppler ultrasound. Leg vascular conductance was calculated as leg blood flow divided by MAP. Results show a significant increase in MAP (13 mmHg), stroke volume (27%) and cardiac output (18%), a significant decrease in heart rate (-5 bpm) and no change in total peripheral resistance during the physical counter-manoeuvre when compared to baseline 70 o} HUT. A significant increase in leg blood flow (325 ml/min) and leg vascular conductance (2.9 AU) were seen during the physical counter-manoeuvre when compared to baseline 70 o} HUT. The present study indicates that the physical counter-manoeuvre of leg crossing combined with muscle tensing clearly enhances leg blood flow and at the same time elevates mean arterial blood pressure.
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