Hyperviscosity syndromes; hemorheology for physicians and the use of microfluidic devices

Abstract

Purpose of review: Hyperviscosity syndromes can lead to significant morbidity and mortality. Existing methods to measure microcirculatory rheology are not readily available and limited in relevance and accuracy at this level. In this review, we review selected hyperviscosity syndromes and the advancement of their knowledge using microfluidic platforms.

Recent findings: Viscosity changes drastically at the microvascular level as the physical properties of the cells themselves become the major determinants of resistance to blood flow. Current, outdated viscosity measurements only quantify whole blood or serum. Changes in blood composition, cell number, or the physical properties themselves lead to increased blood viscosity. Given the significant morbidity and mortality from hyperviscosity syndromes, new biophysical tools are needed and being developed to study microvascular biophysical and hemodynamic conditions at this microvascular level to help predict those at risk and guide therapeutic treatment.

Summary: The use of 'lab-on-a-chip' technology continues to rise to relevance with point of care, personalized testing and medicine as customizable microfluidic platforms enable independent control of many in vivo factors and are a powerful tool to study microcirculatory hemorheology.

Figure 1.. What is viscosity?.

Simply put, a fluid’s resistance to flow. Homogenous fluids with increasing viscosity from left to right as depicted with water, olive oil and honey.

Figure 2.. Hemorheology, macro to microcirculation.

As vessel cross-sectional area increases markedly from arterioles to capillaries, applied pressure and blood velocity drop significantly. Travelling from capillaries to venules to veins, cross-sectional area decreases resulting in continued decrease in applied pressure with small increases in blood velocity. Myers DR, Lam WA. Vascularized microfluidics and their untapped potential for discovery in diseases of the microvasculature. Annu Rev Biomed Eng. 2021 Jul 13;23(1):407–32.

Figure 3.. “Hyperviscosity Syndrome.”

Characterized by mucous membrane bleeding, retinopathy and loss of vision and neurological disorders associated with elevated serum viscosity.

Figure 4.. Microfluidic technology.

Illustration depicting microfluidic technology. Sample fluid is pumped at physiologic flowrate into PDMS device designed with specific microvascular geometry and size. Data is collected via videomicroscopy.