[Blood rheology in Raynaud's disease]

The part played by blood rheological factors in any vasomotor phenomenon is still difficult to define, in relation to its onset, maintenance and possible worsening. A high viscosity may contribute towards a difficulty in flow and viscosity is known to vary in an inverse manner with temperature. Many studies have been published reporting results of rheological investigations in Raynaud's syndromes, but whereas the majority describe both blood and plasma hyperviscosity, others report negative results or those that are interpretable with difficulty. A recent study in 49 patients with Raynaud's syndromes confirmed the presence of elevated blood and plasma viscosity values, particularly in Raynaud's syndromes secondary to other disorders and in digital arteritis. Elevated viscosity levels in "essential" Raynaud's syndromes were significant at low speeds only, suggesting the association of a disorder of erythrocyte aggregation with the properly termed vasomotor disturbance.