New Insights into the Microvascular Mechanisms of Drag Reducing Polymers: Effect on the Cell-Free Layer

Drag-reducing polymers (DRPs) significantly increase blood flow, tissue perfusion, and tissue oxygenation in various animal models. In rectangular channel microfluidic systems, DRPs were found to significantly reduce the near-wall cell-free layer (CFL) as well as modify traffic of red blood cells (RBC) into microchannel branches. In the current study we further investigated the mechanism by which DRP enhances microvascular perfusion. We studied the effect of various concentrations of DRP on RBC distribution in more relevant round microchannels and the effect of DRP on CFL in the rat cremaster muscle in vivo. In round microchannels hematocrit was measured in parent and daughter branch at baseline and after addition of DRP. At DRP concentrations of 5 and 10 ppm, the plasma skimming effect in the daughter branch was eliminated, as parent and daughter branch hematocrit were equivalent, compared to a significantly lowered hematocrit in the daughter branch without DRPs. In anesthetized rats (N=11) CFL was measured in the cremaster muscle tissue in arterioles with a diameter of 32.6 ± 1.7 µm. In the control group (saline, N=6) there was a significant increase in CFL in time compared to corresponding baseline. Addition of DRP at 1 ppm (N=5) reduced CFL significantly compared to corresponding baseline and the control group. After DRP administration the CFL reduced to about 85% of baseline at 5, 15, 25 and 35 minutes after DRP infusion was complete. These in vivo and in vitro findings demonstrate that DRPs induce a reduction in CFL width and plasma skimming in the microvasculature. This may lead to an increase of RBC flux into the capillary bed, and thus explain previous observations of a DRP mediated enhancement of capillary perfusion.     

Investigation of platelet margination phenomena at elevated shear stress

Thrombosis is a common complication following the surgical implantation of blood contacting artificial organs. Platelet transport, which is an important process of thrombosis and strongly modulated by flow dynamics, has not been investigated under the shear stress level associated with these devices, which may range from tens to several hundred Pascal.The current research investigated platelet transport within blood under supra-physiological shear stress conditions through a micro flow visualization approach. Images of platelet-sized fluorescent particles in the blood flow were recorded within microchannels (2 cm x 100 microm x 100 microm). The results successfully demonstrated the occurrence of platelet-sized particle margination under shear stresses up to 193 Pa, revealing a platelet near-wall excess up to 8.7 near the wall (within 15 microm) at the highest shear stress. The concentration of red blood cells was found to influence the stream-wise development of platelet margination which was clearly observed in the 20% Ht sample but not the 40% Ht sample. Shear stress had a less dramatic effect on the margination phenomenon than did hematocrit. The results imply that cell-cell collision is an important factor for platelet transport under supra-physiologic shear stress conditions. It is anticipated that these results will contribute to the future design and optimization of artificial organs.     

Analysis of early embryonic great-vessel microcirculation in zebrafish using high-speed confocal μPIV

In the developing cardiovascular system, hemodynamic vascular loading is critical for angiogenesis and cardiovascular adaptation. Normal zebrafish embryos with transgenically-labeled endothelial and red blood cells provide an excellent in vivo model for studying the fluid-flow induced vascular loading. To characterize the developmental hemodynamics of early embryonic great-vessel microcirculation in the zebrafish embryo, two complementary studies (experimental and numerical) are presented. Quantitative comparison of the wall shear stress (WSS) at the first aortic arch (AA1) of wild-type zebrafish embryos during two consecutive developmental stages is presented, using time-resolved confocal micro-particle image velocimetry (μPIV). Analysis showed that there was significant WSS difference between 32 and 48 h post-fertilization (hpf) wild-type embryos, which correlates with normal arch morphogenesis. The vascular distensibility of the arch wall at systole and the acceleration/deceleration rates of time-lapse phase-averaged streamwise blood flow curves were also analyzed. To estimate the influence of a novel intermittent red-blood cell (RBC) loading on the endothelium, a numerical two-phase, volume of fluid (VOF) flow model was further developed with realistic in vivo conditions. These studies showed that near-wall effects and cell clustering increased WSS augmentation at a minimum of 15% when the distance of RBC from arch vessel wall was less than 3 μm or when RBC cell-to-cell distance was less than 3 μm. When compared to a smooth wall, the WSS augmentation increased by a factor of ~1.4 due to the roughness of the wall created by the endothelial cell profile. These results quantitatively highlight the contribution of individual RBC flow patterns on endothelial WSS in great-vessel microcirculation and will benefit the quantitative understanding of mechanotransduction in embryonic great vessel biology, including arteriovenous malformations (AVM).     

Platelet Dynamics in Three-Dimensional Simulation of Whole Blood

A high-fidelity computational model using a 3D immersed boundary method is used to study platelet dynamics in whole blood. We focus on the 3D effects of the platelet-red blood cell (RBC) interaction on platelet margination and near-wall dynamics in a shear flow. We find that the RBC distribution in whole blood becomes naturally anisotropic and creates local clusters and cavities. A platelet can enter a cavity and use it as an express lane for a fast margination toward the wall. Once near the wall, the 3D nature of the platelet-RBC interaction results in a significant platelet movement in the transverse (vorticity) direction and leads to anisotropic platelet diffusion within the RBC-depleted zone or cell-free layer (CFL). We find that the anisotropy in platelet motion further leads to the formation of platelet clusters, even in the absence of any platelet-platelet adhesion. The transverse motion, and the size and number of the platelet clusters are observed to increase with decreasing CFL thickness. The 3D nature of the platelet-RBC collision also induces fluctuations in off-shear plane orientation and, hence, a rotational diffusion of the platelets. Although most marginated platelets are observed to tumble just outside the RBC-rich zone, platelets further inside the CFL are observed to flow with an intermittent dynamics that alters between sliding and tumbling, as a result of the off-shear plane rotational diffusion, bringing them even closer to the wall. To our knowledge, these new findings are based on the fundamentally 3D nature of the platelet-RBC interaction, and they underscore the importance of using cellular-scale 3D models of whole blood to understand platelet margination and near-wall platelet dynamics.     

Platelet Dynamics in Three-Dimensional Simulation of Whole Blood

A high-fidelity computational model using a 3D immersed boundary method is used to study platelet dynamics in whole blood. We focus on the 3D effects of the platelet-red blood cell (RBC) interaction on platelet margination and near-wall dynamics in a shear flow. We find that the RBC distribution in whole blood becomes naturally anisotropic and creates local clusters and cavities. A platelet can enter a cavity and use it as an express lane for a fast margination toward the wall. Once near the wall, the 3D nature of the platelet-RBC interaction results in a significant platelet movement in the transverse (vorticity) direction and leads to anisotropic platelet diffusion within the RBC-depleted zone or cell-free layer (CFL). We find that the anisotropy in platelet motion further leads to the formation of platelet clusters, even in the absence of any platelet-platelet adhesion. The transverse motion, and the size and number of the platelet clusters are observed to increase with decreasing CFL thickness. The 3D nature of the platelet-RBC collision also induces fluctuations in off-shear plane orientation and, hence, a rotational diffusion of the platelets. Although most marginated platelets are observed to tumble just outside the RBC-rich zone, platelets further inside the CFL are observed to flow with an intermittent dynamics that alters between sliding and tumbling, as a result of the off-shear plane rotational diffusion, bringing them even closer to the wall. To our knowledge, these new findings are based on the fundamentally 3D nature of the platelet-RBC interaction, and they underscore the importance of using cellular-scale 3D models of whole blood to understand platelet margination and near-wall platelet dynamics.     

Fringe mode transmittance laser Doppler microscope anemometer: its adaptation for measurement in the microcirculation

Blood flow analysis in the microcirculation requires accurate measurement of velocity, volume flow and shear-rate versus shear-stress relationships. The resolution of most anemometers is too limited to obtain useful measurements, especially near the blood vessel wall and at branches and bifurcations. To make such measurements possible with a noninvasive, high resolution, accurate technique, we have developed a fringe mode, transmittance laser Doppler microscope anemometer (LDMA). This system has an intrinsically high spatial resolution (10 × 12 μm), and does not require a high concentration (10⁶/cm³) of scatterers or red blood cells (RBC) as in our application. Preliminary measurements of water flow in a rectangular channel were conducted to ascertain the reliability and accuracy of velocity measurements using the LDMA. Velocity profiles were then measured by the LDMA system in arterioles 38–135 μm in diameter, in the transparent, everted cheek pouch of the anaesthelized hamster. The extremely high resolution of the optical system, and the ultra-fine traversing mechanism of the microscope slage, made velocity readings larger than 0.02 mm/s with accuracy and reproducibility better than 1%, possible near the wall to within 7–10 μm.     

Increased glucose metabolism by enzyme-loaded erythrocytes in vitro and in vivo normalization of hyperglycemia in diabetic mice.

The main metabolic properties of human red blood cells (RBC) overloaded with glucose catabolizing enzymes such as hexokinase and glucose oxidase were evaluated. Human erythrocytes loaded with human hexokinase metabolized 3.1 +/- 0.2 mumol/h/ml RBC of glucose, an amount double that consumed by normal and unloaded cells (1.46 +/- 0.16 mumol/h/ml RBC), while glucose oxidase-loaded erythrocytes consumed up to 5.5 +/- 0.5 mumol/h/ml RBC of glucose but with a time-dependent increase in methemoglobin formation due to the H2O2 produced in the glucose oxidase reaction. This methemoglobin production was greatly reduced while glucose consumption was increased (8.1 +/- 0.4 mumol/h/ml RBC) by coentrapment of hexokinase and glucose oxidase. Similar results were obtained in mouse red blood cells, although the role of hexokinase was less pronounced due to a higher basal level of this enzyme. When administered to diabetic mice the hexokinase/glucose oxidase-overloaded erythrocytes had a circulating half-life of 5 days and were able to regulate blood glucose at near physiological levels. A single intraperitoneal administration of 500 microliters of enzyme-loaded cells maintained a near-normal blood glucose concentration for 7 +/- 1 days, while repeated administrations at 10-day intervals were effective in the regulation of blood glucose levels for several weeks. These results suggest that enzyme-loaded erythrocytes can behave as circulating bioreactors and can provide a new way to reduce abnormally elevated blood glucose.     

Exercise and arterial adaptation in humans: uncoupling localized and systemic effects

Previous studies have established effects of exercise training on arterial wall thickness, remodeling, and function in humans, but the extent to which these changes are locally or systemically mediated is unclear. We examined the brachial arteries of the dominant (D) and nondominant (ND) upper limbs of elite racquet sportsmen and compared them to those of matched healthy inactive controls. Carotid and superficial femoral artery responses were also assessed in both groups. High-resolution duplex ultrasound was used to examine resting diameter, wall thickness, peak diameter, and blood flow. We found larger resting arterial diameter in the preferred arm of the athletes (4.9 ± 0.5 mm) relative to their nonpreferred arm (4.3 ± 0.4 mm, P < 0.05) and both arms of control subjects (D: 4.1 ± 0.4 mm; ND: 4.0 ± 0.4, P < 0.05). Similar limb-specific differences were also evident in brachial artery dilator capacity (5.5 ± 0.5 vs. 4.8 ± 0.4, 4.8 ± 0.6, and 4.8 ± 0.6 mm, respectively; P < 0.05) following glyceryl trinitrate administration and peak blood flow (1,118 ± 326 vs. 732 ± 320, 737 ± 219, and 698 ± 174 ml/min, respectively; P < 0.05) following ischemic handgrip exercise. In contrast, athletes demonstrated consistently lower wall thickness in carotid (509 ± 55 μm), brachial (D: 239 ± 100 μm; ND: 234 ± 133 μm), and femoral (D: 479 ± 38 μm; ND: 479 ± 42 μm) arteries compared with control subjects (carotid: 618 ± 74 μm; brachial D: 516 ± 100 μm; ND: 539 ± 129 μm; femoral D: 634 ± 155 μm; ND: 589 ± 112 μm; all P < 0.05 vs. athletes), with no differences between the limbs of either group. These data suggest that localized effects of exercise are evident in the remodeling of arterial size, whereas arterial wall thickness appears to be affected by systemic factors.     

A Criterion for the Complete Deposition of Magnetic Beads on the Walls of Microchannels

This paper analyzes numerical simulations of the trajectories of magnetic beads in a microchannel, with a nearby permanent cubical magnet, under different flow and magnetic conditions. Analytically derived local fluid velocities and local magnetic forces have been used to track the particles. A centered position and a lateral position of the magnet above the microchannel are considered. The computed fractions of deposited particles on the walls are compared successfully with a new theoretically derived criterion that imposes a relation between the sizes of the magnet and the microchannel and the particle Stokes and Alfvén numbers to obtain the complete deposition of the flowing particles on the wall. In the cases in which all the particles, initially distributed uniformly across the section of the microchannel, are deposited on the walls, the simulations predict the accumulation of the major part of particles on the wall closest to the magnet and near the first half of the streamwise length of the magnet.     

Myxidium volitans sp. nov., a parasite of the gallbladder of the fish, Dactylopterus volitans (Teleostei: Triglidae) from the Brazilian Atlantic coast--morphology and pathology

Myxidium volitans sp. nov. (Myxozoa: Myxidiidae) parasitizing the hypertrophied green-brownish gallbladder of the teleost Dactylopterus volitans, collected in the Atlantic coast near Niterói, Brazil was described based on ultrastructural studies. The spores were fusiform, sometimes slightly crescent-shaped on average 21.7 ± 0.3 μm (mean ± standard deviation) (n = 50) long and 5.6 ± 0.4 μm (n = 30) wide. The spore wall was thin and smooth, comprising two equally-sized valves joined by a hardly visible sutural ridge. Spores containing two pyriform polar capsules (PC) (5.0 ± 0.4 × 2.3 ± 0.3 μm) (n = 30) are situated in each extremity of the spore. The PC wall was composed of hyaline layer (0.20-0.29 μm thick) and by a thin external granular layer. Each PC contains a polar filament (PF) with irregular arrangements that was projected from its apical region to the bases of PC and coiled laterally from bases to the tip of PC. Some regular striations and S-like structures in the periphery of the PFs with four-five irregular sections were observed. Based on the spore morphology, ultrastructural differences and the specificity of the host we describe this parasite as a new myxosporidian, named M. volitans sp. nov.     

In?Vitro Measurement of Particle Margination in the Microchannel Flow: Effect of Varying Hematocrit

It has long been known that platelets undergo margination when flowing in blood vessels, such that there is an excess concentration near the vessel wall. We conduct experiments and three-dimensional boundary integral simulations of platelet-sized spherical particles in a microchannel 30 μm in height to measure the particle-concentration distribution profile and observe its margination at 10%, 20%, and 30% red blood cell hematocrit. The experiments involved adding 2.15-μm-diameter spheres into a solution of red blood cells, plasma, and water and flowing this mixture down a microfluidic channel at a wall shear rate of 1000 s⁻¹. Fluorescence imaging was used to determine the height and velocity of particles in the channel. Experimental results indicate that margination has largely occurred before particles travel 1 cm downstream and that hematocrit plays a role in the degree of margination. With simulations, we can track the trajectories of the particles with higher resolution. These simulations also confirm that margination from an initially uniform distribution of spheres and red blood cells occurs over the length scale of O(1 cm), with higher hematocrit showing faster margination. The results presented here, from both experiments and 3D simulations, may help explain the relationship between bleeding time in vessel trauma and red blood cell hematocrit as platelets move to a vessel wall.     

Coated-wall microreactor for continuous biocatalytic transformations using immobilized enzymes

Microstructured flow reactors are emerging tools for biocatalytic process development. A compelling design is that of the coated-wall reactor where enzyme is present as a surface layer attached to microchannel walls. However, preparation of a highly active wall biocatalyst remains a problem. Here, a stainless steel microreactor was developed where covalent immobilization of the enzyme in multiple linear flow channels of the reaction plate was supported by a macroporous wash-coat layer of gamma-aluminum oxide. Using surface functionalization with aminopropyl triethoxysilane followed by activation with glutardialdehyde, the thermophilic beta-glycosidase CelB from Pyrococcus furiosus was bound with retention of half of the specific activity of the free enzyme (800 U/mg), yielding a high catalyst loading of about 500 U/mL. This microreactor was employed for the continuous hydrolysis of lactose (100 mM) at 80 degrees C, providing a space-time yield of 500 mg glucose/(mL h) at a stable conversion of > or =70%. The immobilized enzyme displayed a half-life of 15 days under the operational conditions. Due to the absence of hydrophobic solute-material interactions, which limit the scope of microstructures fabricated from poly(dimethylsiloxane) for biocatalytic applications, the new microreactor was fully compatible with the alternate enzyme substrate 2-nitro-phenyl-beta-D-galactoside and the 2-nitro-phenol product resulting from its hydrolysis catalyzed by CelB.     

内毒素在大剂量顺铂所致大鼠急性肾损伤过程中的变化及意义

目的利用大剂量顺铂（cisplatin,DDP）所致大鼠急性肾功能衰竭的动物模型,观察外周血内毒素（endotoxin）在大鼠急性肾损伤中的变化及其意义。方法SD大鼠36只,雌雄各半,依体重随机分为DDP用药6h、48h、对照组和生理盐水（NS）用药6h、48h、对照组,每组6只。10mg／kgDDP单次腹腔内注射,等量Ns对照。观察并记录用药后对照组大鼠的毒副反应;用药6、48h各组大鼠无菌条件下心脏穿刺取血、肝素抗凝,检测外周血内毒素含量,同时内眦静脉取血,测定血清尿素氮、肌酐浓度,并进行统计学分析。结果DDP用药后6h,大鼠体重开始明显降低,用药48h后,大鼠腹泻逐渐加重,用药3d后大鼠死亡。DDP用药后6h大鼠血尿素氮、肌酐的含量与对照组比较差异无显著性（P〉0．05）;DDP用药后48h血尿素氮升至（18．71±9．9）mmol／L,明显高于对照组（7．48±0．6）mmol／L（P〈0．05）,同时血肌酐含量亦升至（49．6±14．1）μmol／L,与对照组（27．17±1．7）μmol／L比较差异具有显著性（P〈0．05）。DDP用药后6h所有大鼠外周血内毒素含量都低于0．0218Eu／rrd最低检出限,明显低于NS对照组大鼠（0．3141±0．1477）Eu／ml（P〈0．01）;DDP用药后48h大鼠外周血内毒素的含量增高均超过0．70Eu／ml最高检出限,明显高于NS对照组大鼠（0．1661±0．1198）Eu／ml（P〈0．01）。结论外周血内毒素含量的变化与大剂量顺铂所致大鼠急性肾损伤早期的发病机制无关,但与大鼠肾功能衰竭有关的发生相关。     

Dependence of red blood cell dynamics in microvessel bifurcations on the endothelial surface layer’s resistance to flow and compression

Red blood cells (RBCs) make up 40–45% of blood and play an important role in oxygen transport. That transport depends on the RBC distribution throughout the body, which is highly heterogeneous. That distribution, in turn, depends on how RBCs are distributed or partitioned at diverging vessel bifurcations where blood flows from one vessel into two. Several studies have used mathematical modeling to consider RBC partitioning at such bifurcations in order to produce useful insights. These studies, however, assume that the vessel wall is a flat impenetrable homogeneous surface. While this is a good first approximation, especially for larger vessels, the vessel wall is typically coated by a flexible, porous endothelial glycocalyx or endothelial surface layer (ESL) that is on the order of 0.5–1 µm thick. To better understand the possible effects of this layer on RBC partitioning, a diverging capillary bifurcation is analyzed using a flexible, two-dimensional model. In addition, the model is also used to investigate RBC deformation and RBC penetration of the ESL region when ESL properties are varied. The RBC is represented using interconnected viscoelastic elements. Stokes flow equations (viscous flow) model the surrounding fluid. The flow in the ESL is modeled using the Brinkman approximation for porous media with a corresponding hydraulic resistivity. The ESL’s resistance to compression is modeled using an osmotic pressure difference. One cell passes through the bifurcation at a time, so there are no cell–cell interactions. A range of physiologically relevant hydraulic resistivities and osmotic pressure differences are explored. Decreasing hydraulic resistivity and/or decreasing osmotic pressure differences (ESL resistance to compression) produced four behaviors: (1) RBC partitioning nonuniformity increased slightly; (2) RBC deformation decreased; (3) RBC velocity decreased relative to blood flow velocity; and (4) RBCs penetrated more deeply into the ESL. Decreasing the ESL’s resistance to flow and/or compression to pathological levels could lead to more frequent cell adhesion and clotting as well as impaired vascular regulation due to weaker ATP and nitric oxide release. Potential mechanisms that can contribute to these behaviors are also discussed.

     

Effects of cardiac preload reduction and dobutamine on hepatosplanchnic blood flow regulation in porcine endotoxemia

Insufficient cardiac preload and impaired contractility are frequent in early sepsis. We explored the effects of acute cardiac preload reduction and dobutamine on hepatic arterial (Qha) and portal venous (Qpv) blood flows during endotoxin infusion. We hypothesized that the hepatic arterial buffer response (HABR) is absent during preload reduction and reduced by dobutamine. In anesthetized pigs, endotoxin or vehicle (n = 12, each) was randomly infused for 18 h. HABR was tested sequentially by constricting superior mesenteric artery (SMA) or inferior vena cava (IVC). Afterward, dobutamine at 2.5, 5.0, and 10.0 μg/kg per minute or another vehicle (n = 6, each) was randomly administered in endotoxemic and control animals, and SMA was constricted during each dose. Systemic (cardiac output, thermodilution) and carotid, splanchnic, and renal blood flows (ultrasound Doppler) and blood pressures were measured before and during administration of each dobutamine dose. HABR was expressed as hepatic arterial pressure/flow ratio. Compared with controls, 18 h of endotoxin infusion was associated with decreased mean arterial blood pressure [49 ± 11 mmHg vs. 58 ± 8 mmHg (mean ± SD); P = 0.034], decreased renal blood flow, metabolic acidosis, and impaired HABR during SMA constriction [0.32 (0.18-1.32) mmHg/ml vs. 0.22 (0.08-0.60) mmHg/ml; P = 0.043]. IVC constriction resulted in decreased Qpv in both groups; whereas Qha remained unchanged in controls, it decreased after 18 h of endotoxemia (P = 0.031; constriction-time-group interaction). One control and four endotoxemic animals died during the subsequent 6 h. The maximal increase of cardiac output during dobutamine infusion was 47% (22-134%) in controls vs. 53% (37-85%) in endotoxemic animals. The maximal Qpv increase was significant only in controls [24% (12-47%) of baseline (P = 0.043) vs. 17% (-7-32%) in endotoxemia (P = 0.109)]. Dobutamine influenced neither Qha nor HABR. Our data suggest that acute cardiac preload reduction is associated with preferential hepatic arterial perfusion initially but not after established endotoxemia. Dobutamine had no effect on the HABR.     

Prevention of systemic and regional haemodynamic alterations, hypercreatininemia, hyperuremia and hyperphosphatemia by losartan in hypertension with acute renal failure

Patients with pre-existing hypertension are at a particular risk of fatal outcome due to acute renal failure (ARF). We investigate the effects of angiotensin II type-1 receptor blocker (ARB) losartan, on haemodynamics and biochemical parameters in adult male spontaneously hypertensive rats (SHR) with ischemia/reperfusion ARF. SHR were randomly selected in three experimental groups: sham-operated group (SHAM), ARF group, and ARF+LOS group (losartan, 10 mg/kg/b.w. given by infusion during the period of three hours after reperfusion). Beside the improvement of systemic haemodynamics 24 h after reperfusion, losartan significantly increased renal blood flow (RBF: 19.33±3.29 ml/min/kg vs. 8.03±1.04 ml/min/kg, p<0.05) and decreased renal vascular resistance (RVR) compared to ARF (8.85±1.21 mmHg × min × kg/ml vs. 19.90±2.35 mmHg × min × kg/ml, p<0.001). Plasma creatinine (Pcr), urea (Pu) and phosphates (Pphos) were significantly reduced in ARF+LOS group compared to ARF group (Pcr: 99.11±14.56 μmol/l vs. 242.71±20.25 μmol/l, p<0.001; Pu: 33.72±4.69 mmol/l vs. 61.90±3.93 mmol/l, p<0.001; 2.7±0.42 mmol/l vs. 5.57±0.61 mmol/l, p<0.01). Our results demonstrate that losartan improves systemic and regional haemodynamic and biochemical parameters in hypertension with ARF.     

Exercise training blunts oxidative stress in sickle cell trait carriers

The aim of this study was to analyze the effects of exercise training on oxidative stress in sickle cell trait carriers. Plasma levels of oxidative stress [advanced oxidation protein products (AOPP), protein carbonyl, malondialdehyde (MDA), and nitrotyrosine], antioxidant markers [catalase, glutathione peroxidase (GPX), and superoxide dismutase (SOD)], and nitrite and nitrate (NOx) were assessed at baseline, immediately following a maximal exercise test (T(ex)), and during recovery (T(1h), T(2h), T(24h)) in trained (T: 8 h/wk minimum) and untrained (U: no regular physical activity) sickle cell trait (SCT) carriers or control (CON) subjects (T-SCT, n = 10; U-SCT, n = 8; T-CON, n = 11; and U-CON, n = 11; age: 23.5 ± 2.2 yr). The trained subjects had higher SOD activities (7.6 ± 5.4 vs. 5.2 ± 2.1 U/ml, P = 0.016) and lower levels of AOPP (142 ± 102 vs. 177 ± 102 μM, P = 0.028) and protein carbonyl (82.1 ± 26.0 vs. 107.3 ± 30.6 nm/ml, P = 0.010) than the untrained subjects in response to exercise. In response to exercise, U-SCT had a higher level of AOPP (224 ± 130 vs. 174 ± 121 μM, P = 0.012), nitrotyrosine (127 ± 29.1 vs.70.6 ± 46.6 nM, P = 0.003), and protein carbonyl (114 ± 34.0 vs. 86.9 ± 26.8 nm/ml, P = 0.006) compared with T-SCT. T-SCT had a higher SOD activity (8.50 ± 7.2 vs. 4.30 ± 2.5 U/ml, P = 0.002) and NOx (28.8 ± 11.4 vs. 14.6 ± 7.0 μmol·l(-1)·min(-1), P = 0.003) in response to exercise than U-SCT. Our data indicate that the overall oxidative stress and nitric oxide response is improved in exercise-trained SCT carriers compared with their untrained counterparts. These results suggest that physical activity could be a viable method of controlling the oxidative stress. This could have a beneficial impact because of its involvement in endothelial dysfunction and subsequent vascular impairment in hemoglobin S carriers.     

Electrochemical analysis of blood cell/substrate interactions under flow conditions

Interactions of blood cells (RBCs) with a microelectrode of 50 (im diameter have been examined under flow conditions using impedance measurements at high frequencies. At such frequencies, the electrolyte resistance (R_e,) is assimilated to the real part of impedance, and interactions are associated with transient fluctuations of R_e. Sedimentation experiments suggest that one erythrocyte contributes to a 1.1% R_e, increase. Effects of wall shear rate (from 25 to 140 s¹) and RBC concentration (from 8.4 × 10⁵ to 2.7 × 10⁶ cells/ml) have been investigated; the number of interactions rapidly decreases with wall shear rate. Event frequency is proportional to RBC concentration ranging from 3.1 × 10⁶ cells/ml to 1.3 × 10⁷ cells/ml. At high concentrations of RBCs, some transient events overlap. Videotaped images help to determine how many RBCs interact with the microelectrode at the same time on separate surface areas. Under flow conditions, the contribution of one RBC on the R_e increase is similar to the mathematical value obtained by sedimentation and decreases slightly with wall shear rate.     

Near-wall micro-PIV reveals a hydrodynamically relevant endothelial surface layer in venules in vivo

High-resolution near-wall fluorescent microparticle image velocimetry (micro-PIV) was used in mouse cremaster muscle venules in vivo to measure velocity profiles in the red cell-depleted plasma layer near the endothelial lining. micro-PIV data of the instantaneous translational speeds and radial positions of fluorescently labeled microspheres (0.47 microm) in an optical section through the midsagittal plane of each vessel were used to determine fluid particle translational speeds. Regression of a linear velocity distribution based on near-wall fluid-particle speeds consistently revealed a negative intercept when extrapolated to the vessel wall. Based on a detailed three-dimensional analysis of the local fluid dynamics, we estimate a mean effective thickness of approximately 0.33 micro m for an impermeable endothelial surface layer or approximately 0.44 micro m assuming the lowest hydraulic resistivity of the layer that is consistent with the observed particle motions. The extent of plasma flow retardation through the layer required to be consistent with our micro-PIV data results in near complete attenuation of fluid shear stress on the endothelial-cell surface. These findings confirm the presence of a hydrodynamically effective endothelial surface layer, and emphasize the need to revise previous concepts of leukocyte adhesion, stress transmission to vascular endothelium, permeability, and mechanotransduction mechanisms.