Yunhee Ku

Slit-flow ektacytometry: Laser diffraction in a slit rheometer

Deformability of red blood cells (RBCs) is a determinant of blood flow resistance as RBCs pass through small capillaries of the microcirculation. Available techniques for measuring RBC deformability often require a washing process after each measurement, which is not optimal for day‐to‐day clinical use.

Laser-diffraction slit rheometer to measure red blood cell deformability

The laser-diffraction technique has been applied to design a slit rheometer for measuring red blood cell deformability over a range of shear stress. Flow-rate and pressure-drop measurements are replaced with a measurement of pressure variation with time. Using a precision pressure transducer, one can measure the variation of pressure in the vacuum chamber, p(t), from which the shear stress and shear rate are mathematically calculated. In addition, a laser beam traverses a diluted blood suspension and is diffracted by red blood cells (RBCs) in the volume. The diffraction patterns are captured by a charge coupled device-video camera, linked to a frame grabber integrated with a computer. When deforming under decreasing shear stress, RBCs change gradually from the prolate ellipsoid towards a circular biconcave morphology. The elongation index as a measure of RBC deformability is determined from an isointensity curve in the diffraction pattern using an ellipse-fitting program. The advantages of this design are...

Characteristics of Blood Flow Resistance Under Transverse Vibration: Red Blood Cell Suspension in Dextran-40

AbstractVibration under shear flow causes the reduction of flow resistance for shear-thinning fluids. The present study investigates the effect of vibration on the flow resistance of a nonaggregating red blood cell (RBC) suspension with a newly designed pressure-scanning capillary viscometer (PSCV). The PSCV was originally designed to measure non-Newtonian viscosity continuously over a range of shear rates at a time, which was slightly modified and used for the present study. Low-frequency vibration was applied perpendicular to the direction of the flow. The effect of the transverse vibration was investigated for both Newtonian fluids and nonaggregating RBC suspensions. The experimental results showed that the vibration had no effect on the flow resistance of the Newtonian fluids. However, the vibration caused a reduction of the flow resistance of the RBC suspension. The reduction of the flow resistance was strongly dependent on both frequency and amplitude of vibration.

Deformability of red blood cells: A determinant of blood viscosity

The suspension of hardened red blood cells (RBCs) differs from the suspension of normal RBCs with respect to their rheological behavior. The present study investigated the effect of deformability of RBCs on blood viscosity. RBC deformability and blood viscosity were measured with a recently developed slit-flow laser-diffractometer and the pressure-scanning capillary viscometer, respectively. At the same level of cell concentration, the viscosity of the hardened RBC suspension is higher than that of the normal RBCs suspension. An increase in cell percentage for hardened RBCs shows the significant increase in the level of blood viscosity compared to the normal RBCs. In addition, it was found that RBC deformability played an important role in reducing viscosity at low shear rates as well as high shear rates. These results present the evidence for the effect of RBC deformability on blood viscosity using newly developed methods, which can be used in early diagnosis of the cardiovascular diseases.

Simultaneous measurement of red blood cell aggregation and viscosity: Light transmission slit rheometer

Aggregation of red blood cells (RBCs) is a major determinant of blood viscosity. There have not been available techniques for measuring RBC aggregation and viscosity, simultaneously. A laser transmission technique has been combined with a slit rheometry, which shows significant advances in rheometer design, operation and data analysis. A laser beam traverses a blood suspension flowing through a slit and is scattered by RBCs in the volume. The transmitted light is captured by a photodiode, linked to a computer, while the differential pressure variation is measured by a pressure transducer. Both measurements of the laser-transmitted intensity and pressure with respect to time enable to determine the aggregation index and the viscosity. The advantages of this design are in its simplicity, i.e., ease of operation and no moving parts, low cost and a short operating time. In addition, the slit-flow aggregometer can be easily used in a clinical setting owing to the incorporation of a disposable element that holds the blood sample.Aggregation of red blood cells (RBCs) is a major determinant of blood viscosity. There have not been available techniques for measuring RBC aggregation and viscosity, simultaneously. A laser transmission technique has been combined with a slit rheometry, which shows significant advances in rheometer design, operation and data analysis. A laser beam traverses a blood suspension flowing through a slit and is scattered by RBCs in the volume. The transmitted light is captured by a photodiode, linked to a computer, while the differential pressure variation is measured by a pressure transducer. Both measurements of the laser-transmitted intensity and pressure with respect to time enable to determine the aggregation index and the viscosity. The advantages of this design are in its simplicity, i.e., ease of operation and no moving parts, low cost and a short operating time. In addition, the slit-flow aggregometer can be easily used in a clinical setting owing to the incorporation of a disposable element that holds the blood sample.

Light-transmission aggregometer using a vibration-induced disaggregation mechanism

The vibration-induced disaggregation technique of red blood cell (RBC) aggregates has been applied to design a new light-transmission aggregometer for measurement of aggregation index. For disaggregation of RBCs, the rotational shear flow in the Couette system is replaced with a simple low-frequency vibration in a disposable cavity slide glass. Using a vibration generator, one can disaggregate the RBC aggregates stored in the cavity slide glass. After applying the vibration for a specified duration, RBCs tend to reaggregate and instantaneous light-transmittance intensity is measured over time. A syllectogram (the transmitted light intensity versus time) consists of an initial decrease caused by the vibration-induced disaggregation, immediately followed by an increase in the light intensity due to RBC aggregation. The indices of aggregation are determined from the syllectogram using a curve-fitting program. The noble feature of this design is the vibration-induced disaggregation mechanism, which enables to...

Disposable biosensor for measuring red blood cell deformability using laser-diffraction technique

The laser-diffraction technique has been applied to design a microfluidic channel for measuring red blood cell deformability over a range of shear stress. A laser beam traverses a diluted blood suspension and is diffracted by RBCs in the volume. The diffraction patterns are captured by a CCD-video camera, linked to a frame grabber integrated with a computer. When deforming under decreasing shear stress in the microchannel, RBCs change gradually from the prolate ellipsoid towards a circular biconcave morphology. Both the laser-diffraction image and pressure were measured with respect to time, which enable to determine the elongation index (EI) and the shear stress. The range of shear stress is 0~20Pa and the measuring time is less than 2min. The elongation index (EI) is determined from an isointensity curve in the diffraction pattern using an ellipse-fitting program. The key advantage of this design is the incorporation of a disposable element that holds the blood sample, which enables the present system to be easily used in a clinical setting.

Early diagnosis of diabetic vascular complications: impairment of red blood cell deformability

Reduced deformability of red blood cells (RBCs) may play an important role on the pathogenesis of chronic vascular complications of diabetes mellitus. However, available techniques for measuring RBC deformability often require washing process after each measurement, which is not optimal for day-to-day clinical use at point of care. The objectives of the present study are to develop a device and to delineate the correlation of impaired RBC deformability with diabetic nephropathy. We developed a disposable ektacytometry to measure RBC deformability, which adopted a laser diffraction technique and slit rheometry. The essential features of this design are its simplicity (ease of operation and no moving parts) and a disposable element which is in contact with the blood sample. We studied adult diabetic patients divided into three groups according to diabetic complications. Group I comprised 57 diabetic patients with normal renal function. Group II comprised 26 diabetic patients with chronic renal failure (CRF). Group III consisted of 30 diabetic subjects with end-stage renal disease (ESRD) on hemodialysis. According to the renal function for the diabetic groups, matched non-diabetic groups were served as control. We found substantially impaired red blood cell deformability in those with normal renal function (group I) compared to non-diabetic control (P = 0.0005). As renal function decreases, an increased impairment in RBC deformability was found. Diabetic patients with chronic renal failure (group II) when compared to non-diabetic controls (CRF) had an apparently greater impairment in RBC deformability (P = 0.07). The non-diabetic cohort (CRF), on the other hand, manifested significant impairment in red blood cell deformability compared to healthy control (P = 0.0001). The newly developed slit ektacytometer can measure the RBC deformability with ease and accuracy. In addition, progressive impairment in cell deformability is associated with renal function loss in all patients regardless of the presence or absence of diabetes. In diabetic patients, early impairment in RBC deformability appears in patients with normal renal function.

Hemodynamic investigation on blood flow in a rugged microchannel

The biological flow characteristics inside a rugged surface type microchannel are investigated experimentally using a micro-particle image velocimetry (micro-PIV) method. The main objectives of this study are to understand the blood flow structure inside a micro-domain blood vessel and to identify the feasibility of nano-scale fluorescent particles for velocity field measurement in a micron-sized channel. The flow field is analyzed with a spatial resolution of 1K×1K pixels at low Reynolds number flow. To obtain the spatial distributions of mean velocity, 100 instantaneous velocity fields are captured and ensemble-averaged. As a result, for the case of blood flow, there are substantial cell deformation and variations to pass through the rugged surface of a microchannel and the clear velocity vector field was acquired by using the present micro-PIV technique.

Disposable laser-diffraction ektacytometry to measure red blood cell deformability

The laser-diffraction technique has been applied to design a slit rheometer for measuring red blood cell deformability over a range of shear stress. A laser beam traverses a diluted blood suspension and is diffracted by RBCs in the volume. The diffraction patterns are captured by a CCD-video camera, linked to a frame grabber integrated with a computer. When deforming under decreasing shear stress, RBCs change gradually from the prolate ellipsoid towards a circular biconcave morphology. Both the laser-diffraction image and pressure were measured with respect to time. Which enable to determine the elongation index (EI) and the shear stress. The range of shear stress is 0~35 Pa and the measuring time is less than 2 min. The elongation index (EI) is determined from an isointensity curve in the diffraction pattern using an ellipse-fitting program. The key advantage of this design is the incorporation of a disposable element that holds the blood sample, which enables the present system to be easily used in a clinical setting.