IPC has been shown to restore blood flow by reducing venous volume and venous pressure, increasing the arteriovenous pressure gradient, abolishing Var and thus restoring arterial blood flow (Level 1. 86 In summary, the sitting position leads to distension of leg veins and activation of the Var resulting in a decrease in blood flow in the leg. Finally, one study that investigated the hemodynamic effects of IPC in patients with criti- cal limb ischemia showed that those with significant venous reflux may not benefit from IPC, an observation that supports the theory that one of the mechanisms by which IPC enhances flow is by increasing the arteriove- nous pressure gradient. 85 Intra-arterial injec- tion of the alpha-blocker phentolamine abolished the in- crease of vascular constriction in the leg during head-up tilt indicating that alpha-adrenergic tone was involved in this observation.

aNgIology In an investigation of the sympathetic reflex con- trol of resistance in collateral arteries in the lower ex- tremities in patients with diabetes mellitus, resistance of collateral arteries increased by 40% during head-up tilt compared with the horizontal position, and total leg resistance was increased by 24%.

Sisyphus painting