Exaggerated Vasoconstriction in Complex Regional Pain Syndrome-1 Is Associated with Impaired Resistance Artery Endothelial Function and Local Vascular Reflexes

### Objective Local regulatory mechanisms and microvascular function play a major role in the pathogenesis of hemodynamic and trophic changes in patients with complex regional pain syndrome-1 (CRPS). Venoarteriolar and venoarteriolar-myogenic reflexes (VAR, VMR, respectively) as well as endothelial-dependent vasodilatation are important contributors to local vasoregulation. We examined whether VAR and VMR as well as resistance artery endothelial function are damaged in affected limbs of patients with CRPS. ### Methods We measured reactive hyperemic response as an index of resistance artery endothelial function, VAR and VMR in extremity soft-tissue vasculature in patients with CRPS. ### Results Baseline blood flow values were not different between CRPS affected and unaffected upper and lower limbs. Resistance artery endothelial function indices, i.e., values of maximal flow after ischemia and the area under the flow-time curve (AUC), were significantly higher in the unaffected versus CRPS-affected upper limbs (19 ± 3 vs 16 ± 3 ml*min−1*dl−1 and 373 ± 71 vs 319 ± 70 units, for maximal flow AUC, respectively) and lower limbs (9 ± 2 vs 6 ± 1.5 ml*min−1*dl−1 and 160 ± 51 vs 130 ± 42 units, for maximal flow and AUC, respectively). Flow indices reflecting VAR were lower in the lower, but not upper CRPS-affected limbs compared with unaffected contralaterals (2 ± 0.24 vs 1.55 ± 0.3 ml*min−1*dl−1; p = 0.027). Microvascular myogenic reflex-VMR indices, however, were not different in the upper or in the lower CRPS-affected limbs compared with their unaffected contralaterals. ### Conclusion Impaired balance exists in CRPS-affected limbs between vascular regulation systems responsible for vasoconstriction and vasodilation.