Deoxygenation Reduces Sickle Cell Blood Flow at Arterial Oxygen Tension

Abstract

The majority of morbidity and mortality in sickle cell disease is caused by vaso-occlusion: circulatory obstruction leading to tissue ischemia and infarction. The consequences of vaso-occlusion are seen clinically throughout the vascular tree, from the relatively high-oxygen and high-velocity cerebral arteries to the relatively low-oxygen and low-velocity postcapillary venules. Prevailing models of vaso-occlusion propose mechanisms that are relevant only to regions of low oxygen and low velocity, leaving a wide gap in our understanding of the most important pathologic process in sickle cell disease. Progress toward understanding vaso-occlusion is further challenged by the complexity of the multiple processes thought to be involved, including, but not limited to 1) deoxygenation-dependent hemoglobin polymerization leading to impaired rheology, 2) endothelial and leukocyte activation, and 3) altered cellular adhesion. Here, we chose to focus exclusively on deoxygenation-dependent rheologic processes in an effort to quantify their contribution independent of the other processes that are likely involved in vivo. We take advantage of an experimental system that, to our knowledge, uniquely enables the study of pressure-driven blood flow in physiologic-sized tubes at physiologic hematocrit under controlled oxygenation conditions, while excluding the effects of endothelium, leukocyte activation, adhesion, inflammation, and coagulation. We find that deoxygenation-dependent rheologic processes are sufficient to increase apparent viscosity significantly, slowing blood flow velocity at arterial oxygen tension even without additional contributions from inflammation, adhesion, and endothelial and leukocyte activation. We quantify the changes in apparent viscosity and define a set of functional regimes of sickle cell blood flow personalized for each patient that may be important in further dissecting mechanisms of in vivo vaso-occlusion as well as in assessing risk of patient complications, response to transfusion, and the optimization of experimental therapies in development.

A microfluidic platform to study the effects of vascular architecture and oxygen gradients on sickle blood flow

“…First, we note that most of the samples measured here were stored for more than 24 hours, and we recognize that many properties of the blood do change with storage such as the functional status of platelets and WBCs and that blood biophysical properties may change with improper storage . Despite these concerns, we have observed little effect of storage on rheological properties in previous studies . Moreover, in this study, we measured a fresh blood sample (measured within 5 hours of collection), which showed qualitatively similar results to the stored samples.…”

“…The device consists of three layers: (i) a 15‐μm‐tall blood microchannel layer, (ii) a 100‐μm‐tall hydration layer, and (iii) a 150‐μm‐tall oxygen gas tension control layer (Figure ). This multilayered approach allows us to diffusively couple the oxygen control layer with the blood microchannel layer to control the oxygen tension directly in the blood microchannels . Each of the layers is separated by a 100 μm‐thick PDMS membrane.…”

“…To assemble the device, we first cast 10:1 elastomer/curing agent ratio PDMS onto the oxygen gas layer mold at a 5 mm height. Compression molding was then utilized to create individual PDMS layers of specified thickness for the blood microchannel and hydration layer molds as described previously . Each of the PDMS layers is bonded together and sealed to a glass microscope slide at a power of 100 W, an oxygen flow rate of 100 cc/min, and an exposure time of 30 seconds.…”

Biomechanics and biorheology of red blood cells in sickle cell anemia

“…Recent experimental studies have captured information among all of the aforementioned processes in physiologic regimes, providing insight into the overall dynamics of a vaso-occlusive event (Du et al, 2015; Higgins et al, 2007; Wood et al, 2012; Lu et al, 2016b). In these experiments, whole blood or RBC suspensions from SCA patients flowed through microfluidic channels under constant pressure and low the oxygen concentration, thereby simulating most basic features of a vaso-occlusive event.…”

“…In these experiments, whole blood or RBC suspensions from SCA patients flowed through microfluidic channels under constant pressure and low the oxygen concentration, thereby simulating most basic features of a vaso-occlusive event. For example, Higgins and his colleagues found that oxygen tension regulate blood flow for individual SCA patients (Higgins et al, 2007; Wood et al, 2012; Lu et al, 2016b). Recently, Du et al (2015) developed a high-throughput microfluidics-based model to investigate the sickle cell behavior under transient hypoxia (Fig.…”