Blood distribution adaptations in paraplegics during posture changes: peripheral and central reflex response

The veno-arteriolar reflex (VAR) in spinal-cord-injured subjects (SCI) has been attributed little interest, although it might contribute substantially to their blood redistribution. This peripheral reflex response. which is b ased on an axon reflex, consists of a reduction in limb blood flow followin g an increase in venal transmural pressure. The purpose of the present inve stigation was to assess the peripheral and central cardiovascular adaptatio ns of paraplegics with high (HP) and low (LP) spinal lesions to subsequent, passive posture changes involving leg dependency and upright sitting, and to compare them to able-bodied (AB) subjects. Lower-limb cutaneous vascular conductance (CVC) was evaluated from skin blood flow measurements (laser D oppler flowmetry) taken from the dorsal foot, and from ankle blood pressure . Cardiac stroke volume, heart rate and myocardial performance were assesse d using impedance cardiography and brachial blood pressure. During leg depe ndency, a significant vasoconstriction was noted in all three groups. The i nitial decrease in CVC was higher in HP (-76.82%) than in AB (-45.82%), the values for LP (-67.08%) lying in between these two (significant group x ti me interaction: F = 2.832, P = 0.042). There were no differences for parame ters of central hemodynamics, No between-group differences were noted in an y parameter tested during upright sitting, CVC remained at a similar low le vel as compared to leg dependency, stroke volume decreased, heart rate and blood pressure increased, and myocardial performance remained constant. The present results suggest that paraplegics have a peripheral VAR in their pa ralyzed lower limbs, and that this contributes to their cardiovascular stab ility.