Microvascular angina: assessment of coronary blood flow, flow reserve, and metabolism

Flow of Red Blood Cells in Stenosed Microvessels

A computational study is presented on the flow of deformable red blood cells in stenosed microvessels. It is observed that the Fahraeus-Lindqvist effect is significantly enhanced due to the presence of a stenosis. The apparent viscosity of blood is observed to increase by several folds when compared to non-stenosed vessels. An asymmetric distribution of the red blood cells, caused by geometric focusing in stenosed vessels, is observed to play a major role in the enhancement. The asymmetry in cell distribution also results in an asymmetry in average velocity and wall shear stress along the length of the stenosis. The discrete motion of the cells causes large time-dependent fluctuations in flow properties. The root-mean-square of flow rate fluctuations could be an order of magnitude higher than that in non-stenosed vessels. Several folds increase in Eulerian velocity fluctuation is also observed in the vicinity of the stenosis. Surprisingly, a transient flow reversal is observed upstream a stenosis but not downstream. The asymmetry and fluctuations in flow quantities and the flow reversal would not occur in absence of the cells. It is concluded that the flow physics and its physiological consequences are significantly different in micro- versus macrovascular stenosis.

Validated methods for assessment of subclinical atherosclerosis in rheumatology

Rheumatoid arthritis, as well as other types of arthritides and connective tissue diseases, is associated with accelerated atherosclerosis, and increased cardiovascular morbidity and mortality. The early signs of cardiovascular disease therefore need to be recognized in patients with these conditions so that effective cardiovascular protection can be introduced. This Review provides an overview of validated techniques that are currently available to determine subclinical atherosclerosis in patients with rheumatic conditions. Techniques for early assessment of endothelial dysfunction include brachial artery flow-mediated vasodilation and laser Doppler flowmetry. Coronary circulation can be assessed by measuring coronary flow reserve using CT, MRI or PET based techniques. The standard indicators of arterial stiffness are pulse-wave velocity and the augmentation index. Carotid atherosclerosis is determined by the common carotid intima-media thickness (ccIMT) measurement or by the assessment of plaques and plaque areas. The combination of ccIMT with plaque assessment is likely to increase the predictive value of this approach. The potential use of a multimarker approach to increase the diagnostic and prognostic value of these clinical assessments is also discussed.