A novel hydrodynamic approach to the treatment of coronary artery disease

Hemorheological Approach to Improve Perfusion of Red Blood Cells with Reduced Deformability Using Drag-Reducing Polymer (In Vitro Study)

Drag-reducing polymers (DRPs) are nontoxic water-soluble blood additives that have been shown to beneficially alter hemodynamics when delivered intravenously in nanomolar concentrations. This study examines the ability of DRPs to alter the traffic of mixtures of normal and less-deformable red blood cells (RBCs) through branched microchannels and is intended to support and expand upon previous experiments within straight capillary tubes to promote DRPs for future clinical use. Branched polydimethylsiloxane microchannels were perfused with a mixture of normal bovine RBCs also containing heat-treated less-deformable RBCs at a hematocrit of 30% with 10 ppm of the DRP poly(ethylene oxide) (MW 4M Da). Suspensions were driven by syringe pump, collected at outlets, and RBC dimensions measured while subject to shear stress to determine the proportion of healthy RBCs in each sample. DRPs eliminated evidence of the plasma skimming phenomena and significantly increased the pressure drop across microchannels. Further, DRPs were found to cause an increase in the proportion of healthy RBCs exiting the branch outlet from -8.5 ± 2.5% (control groups) to +12.1 ± 5.4% (n = 6, p = 0.02). These results suggest DRP additives may be used to improve the perfusion of less-deformable RBCs in vivo and indicates their potential for future clinical use.

Dapagliflozin effect on endothelial dysfunction in diabetic patients with atherosclerotic disease: a randomized active-controlled trial

Background

The glucose-lowering independent effect of sodium glucose cotransporter-2 inhibitors (SGLT2i) on arterial wall function has not yet been clarified. This study aims to assess whether SGLT2i treatment can attenuate endothelial dysfunction related to type 2 diabetes mellitus (T2D) compared with glucose-lowering equivalent therapy.

Methods

In a prospective, open-label, single-center, randomized clinical trial, 98 patients with T2DM and carotid intima-media thickness above the 75th percentile were randomized 1:1 to 12 weeks of therapy with dapagliflozin or glibenclamide in addition to metformin in glucose-lowering equivalent regimens. The coprimary endpoints were 1-min flow-mediated dilation (FMD) at rest and 1-min FMD after 15 min of ischemia followed by 15 min of reperfusion time (I/R).

Results

Ninety-seven patients (61% males, 57 ± 7 years) completed the study. The median HbA1c decreased by − 0.8 (0.7)% and -0.7 (0.95)% following dapagliflozin and glibenclamide, respectively. The first coprimary endpoint, i.e., rest FMD changed by + 3.3(8.2)% and − 1.2(7.5)% for the dapagliflozin and glibenclamide arms, respectively (p = 0.0001). Differences between study arms in the second coprimary endpoint were not significant. Plasma nitrite 1 min after rest FMD was higher for dapagliflozin [308(220) nmol/L] than for glibenclamide (258[110] nmol/L; p = 0.028). The resistive indices at 1 min [0.90 (0.11) vs. 0.93 (0.07); p = 0.03] and 5 min [0.93 (0.07) vs. 0.95 (0.05); p = 0.02] were higher for the glibenclamide group than for the dapagliflozin group. Plasma biomarkers for inflammation and oxidative stress did not differ between the treatments.

Conclusions

Dapagliflozin improved micro- and macrovascular endothelial function compared to glibenclamide, regardless of glycemic control in patients with T2DM and subclinical carotid atherosclerotic disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01264-z.

Drag reducing polymers decrease hepatic injury and metastases after liver ischemia-reperfusion

Introduction

Surgery, a crucial therapeutic modality in the treatment of solid tumors, can induce sterile inflammatory processes which can result in metastatic progression. Liver ischemia and reperfusion (I/R) injury, an inevitable consequence of hepatic resection of metastases, has been shown to foster hepatic capture of circulating cancer cells and accelerate metastatic growth. Efforts to reduce these negative consequences have not been thoroughly investigated. Drag reducing polymers (DRPs) are blood-soluble macromolecules that can, in nanomolar concentrations, increase tissue perfusion, decrease vascular resistance and decrease near-wall microvascular concentration of neutrophils and platelets thereby possibly reducing the inflammatory microenvironment. We hypothesize that DRP can potentially be used to ameliorate metastatic capture of tumor cells and tumor growth within the I/R liver.

Methods

Experiments were performed utilizing a segmental ischemia model of mice livers. Five days prior or immediately prior to ischemia, murine colon adenocarcinoma cells (MC38) were injected into the spleen. DRP (polyethylene oxide) or a control of low-molecular-weight polyethylene glycol without drag reducing properties were administered intraperitoneally at the onset of reperfusion.

Results

After three weeks from I/R, we observed that liver I/R resulted in an increased ability to capture and foster growth of circulating tumor cells; in addition, the growth of pre-existing micrometastases was accelerated three weeks later. These effects were significantly curtailed when mice were treated with DRPs at the time of I/R. Mechanistic investigations in vivo indicated that DRPs protected the livers from I/R injury as evidenced by significant decreases in hepatocellular damage, neutrophil recruitment into the liver, formation of neutrophil extracellular traps, deposition of platelets, formation of microthrombi within the liver sinusoids and release of inflammatory cytokines.

Conclusions

DRPs significantly attenuated metastatic tumor development and growth. DRPs warrant further investigation as a potential treatment for liver I/R injury in the clinical setting to improve cancer-specific outcomes.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

A mechanistic investigation of thrombotic microangiopathy associated with IV abuse of Opana ER

Since 2012, a number of case reports have described the occurrence of thrombotic microangiopathy (TMA) following IV abuse of extended-release oxymorphone hydrochloride (Opana ER), an oral opioid for long-term treatment of chronic pain. Here, we present unique clinical features of 3 patients and investigate IV exposure to the tablet's inert ingredients as a possible causal mechanism. Guinea pigs were used as an animal model to understand the hematopathologic and nephrotoxic potential of the inert ingredient mixture (termed here as PEO+) which primarily contains high-molecular-weight polyethylene oxide (HMW PEO). Microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury were found in a group of 3 patients following recent injection of adulterated extended-release oxymorphone tablets. Varying degrees of cardiac involvement and retinal ischemia occurred, with TMA evident on kidney biopsy. A TMA-like state also developed in guinea pigs IV administered PEO+. Acute tubular and glomerular renal injury was accompanied by nonheme iron deposition and hypoxia-inducible factor-1α upregulation in the renal cortex. Similar outcomes were observed following dosing with HMW PEO alone. IV exposure to the inert ingredients in reformulated extended-release oxymorphone can elicit TMA. Although prescription opioid abuse shows geographic variation, all physicians should be highly inquisitive of IV drug abuse when presented with cases of TMA.

A novel hydrodynamic approach of drag-reducing polymers to improve left ventricular hypertrophy and aortic remodeling in spontaneously hypertensive rats

Drag-reducing polymers (DRPs), when added in minute concentrations, have been shown to decrease peripheral vascular resistance. In this study, the effect of DRPs on the hypertension-induced left ventricular hypertrophy and aortic remodeling was evaluated in spontaneously hypertensive rats (SHR). Male SHR and age-matched Wistar rats were divided into four groups and received intravenous injection of normal saline (NS) or DRPs. Body weight (BW), heart rate (HR) and systolic blood pressure (SBP) were measured. Echocardiography was used to evaluate the changes in left ventricle (LV) function and global wall motion. The LV and aorta were stained by hematoxylin and eosin. Cell size of cardiomyocytes and aortic medial thickness were evaluated for each section. The expression of endothelin-1 (ET-1) of LV and aorta was examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry. There was no significant difference in the increase of SBP among SHR + NS, SHR + 10DRP and SHR + 20DRP groups. SHR + NS group had markedly smaller left ventricular end-systolic diameter and left ventricular end-diastolic diameter but bigger anterior and posterior systolic wall thicknesses, while there was no significant difference in fractional shortening and ejection fraction. The cross-sectional areas (CSAs) of cardiomyocytes and the medial thickness of the aorta in SHR + 10 (ppm) DRP and SHR + 20 (ppm) DRP groups were significantly reduced compared with SHR + NS group. The expression of ET-1 in SHR + 10DRP and SHR + 20DRP groups was significantly attenuated. These results suggest that chronic treatment with DRPs can protect against left ventricular hypertrophy and aortic remodeling. DRPs may offer a new approach to the treatment of left ventricular hypertrophy and aortic remodeling caused by hypertension.

Protective effects of drag-reducing polymers on ischemic reperfusion injury of isolated rat heart

Drag-reducing polymers (DRPs) are blood-soluble macromolecules that can increase blood flow and reduce vascular resistance. The purpose of the present study was to observe the effect of DRPs on ischemic reperfusion (I/R) injury of isolated rat hearts. Experiments were performed on isolated rat hearts subjected to 30 min of ischemia followed by 90 min of reperfusion in Langendorff preparations. Adult Wistar rats were divided into the following five groups: control group, I/R group, group III (I/R and 2×10(-7)  g/ml PEO reperfusion), group IV (I/R and 1×10(-6)  g/ml PEO reperfusion), and group V (I/R and 5×10(-6)  g/ml PEO reperfusion). Left ventricular end-diastolic pressure (LVEDP), left ventricular systolic pressure (LVSP), maximum rate of ventricular pressure increase and decrease ( ± dp/dtmax), heart rate (HR) and coronary flow were measured. Lactate dehydrogenase (LDH) and creatine kinase (CK) activity and coronary flow, myocardial infarction size and cardiomyocytes apoptosis were also assayed. Our results showed that PEO decreased LVEDP and increased LVSP, ± dP/dtmax in group IV and group V compared with the I/R group (all P <  0.05). The coronary flow significantly increased and the activities of LDH and CK in the coronary flow significantly decreased in group IV and group V compared with those in the I/R group (all P <  0.05). Cell apoptosis and myocardial infarction size were reduced in group IV and group V compared with the I/R group (all P <  0.05). Collectively, these results suggested that DRPs had a protective effect on cardiac I/R injury of isolated rat hearts and it may offer a new potential approach for the treatment of acute ischemic heart diseases.

Protective effects of drag-reducing polymers in a rat model of monocrotaline-induced pulmonary hypertension

OBJECTIVES

Drag-reducing polymers (DRPs) are blood-soluble macromolecules which may increase blood flow and reduce vascular resistance. The purpose of the present study was to observe the effect of DRPs on monocrotaline-induced pulmonary hypertension (PH) in the rat model.

METHODS

A total of 64 male Wistar rats were randomly divided into four groups: Group I (pulmonary hypertension model + DRP treatment); Group II (pulmonary hypertension model + saline treatment); Group III (control + DRP treatment); Group IV (control + saline treatment). After five weeks, comparisons were made of the following indices: survival rate, body weight, blood pressure, right ventricular systolic pressure, right ventricular hypertrophy, wall thickness of pulmonary arteries, the internal diameter of small pulmonary arteries, plasma IL-1β and IL-6.

RESULTS

The survival rate after 5 weeks varied significantly across all groups (P=0.013), but the survival rates of Groups I and II were not statistically significantly different. Administration of DRP (intravenous injection twice weekly) attenuated the PH-induced increase in right ventricular systolic pressure and suppressed the increases in right ventricular (RV) weight and the ratio of right ventricular weight to left ventricle plus septum weight (RV/LV + S). DRP treatment also significantly decreased the wall thickness of pulmonary arteries, augmented the internal diameter of small pulmonary arteries, and suppressed increases in the plasma levels of IL-1β and IL-6.

CONCLUSIONS

DRP treatment with intravenous injection effectively inhibited the development of monocrotaline-induced pulmonary hypertension in the rat model. DRPs may have potential application for the treatment of pulmonary hypertension.

Drag-Reducing Polymer Enhances Microvascular Perfusion in the Traumatized Brain with Intracranial Hypertension

Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood-soluble, nontoxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and ischemic limb, but have not yet been studied in the brain. We recently demonstrated that DRP improved microvascular perfusion and tissue oxygenation in a normal rat brain. We hypothesized that DRP could restore microvascular perfusion in hypertensive brain after TBI. Using in vivo two-photon laser scanning microscopy we examined the effect of DRP on microvascular blood flow and tissue oxygenation in hypertensive rat brains with and without TBI. DRP enhanced and restored capillary flow, decreased microvascular shunt flow, and, as a result, reduced tissue hypoxia in both nontraumatized and traumatized rat brains at high intracranial pressure. Our study suggests that DRP could constitute an effective treatment for improving microvascular flow in brain ischemia caused by high intracranial pressure after TBI.

Protective effects of polyethylene oxide on the vascular and organ function of rats with severe hemorrhagic shock

This study examined the effects of polyethylene oxide (PEO) on the survival rate, hemodynamics, blood gas indexes, lactic acid levels, microcirculation, and inflammatory cytokine levels in rats subjected to severe hemorrhagic shock. The shocked rats were resuscitated with either Ringer's lactate solution or 20 ppm of PEO in Ringer's lactate solution for 1 h. It was found that infusion of PEO effectively improved the survival, metabolic acidosis, oxygen delivery, hyperlactacidemia, tissue perfusion, and inflammatory responses of rats subjected to hemorrhagic shock. In addition, we found, for the first time, that PEO showed protective effects on hepatic and renal injury, as evidenced by the significant decreases in the elevated levels of alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, and creatinine caused by shock induction after infusion of PEO (p < 0.05, 60 min post-resuscitation by comparison with pre-resuscitation). All of these findings indicate that PEO exhibits strong therapeutic effects under conditions of severe hemorrhagic shock,which also provides theoretical and experimental bases for the clinical use of PEO.

Drag-reducing polymers increase exercise tolerance in an ischemic hind-limb rat model

OBJECTIVE

Drag-reducing polymers are long-chain, blood soluble macromolecules that can improve microcirculation in vivo. This study aimed to examine the effects of drag-reducing polymers on exercise tolerance in a rat model of hind-limb ischemia.

METHODS

After adaptive running training, bilateral femoral artery ligation models were established in 64 Wistar rats. During an exhaustive exercise, polyethylene oxide or normal saline was intravenously injected to each group (n = 32) at 4 mL/h for 10 min. The exhaustive exercise time was recorded, and lactic acid levels in gastrocnemius muscle and serum were measured. Serum levels of nitric oxide, creatine kinase and lactate dehydrogenase were measured as biomarkers of physical fatigue.

RESULTS

Compared with saline-treated control group, rats in polyethylene oxide-treated group had longer exhaustive exercise time (774.7 ± 171.5 s vs. 687.6 ± 166.1 s, p = 0.043), and lower lactic acid level in gastrocnemius muscle (p < 0.01) but no significant difference in serum lactic acid level between two groups was observed (p > 0.05). Nitric oxide level was higher in polyethylene oxide group than in controls (p < 0.05), but no significant differences in serum creatine kinase and lactate dehydrogenase levels between two groups were observed (p > 0.05).

CONCLUSION

Drag-reducing polymers contribute to the enhancement of exercise endurance and exert anti-fatigue effect.

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.

Modulation of pre-capillary arteriolar pressure with drag-reducing polymers: a novel method for enhancing microvascular perfusion

OBJECTIVE

We have shown that drag-reducing polymers (DRP) enhance capillary perfusion during severe coronary stenosis and increase red blood cell velocity in capillaries, through uncertain mechanisms. We hypothesize that DRP decreases pressure loss from the aorta to the arteriolar compartment.

METHODS

Intravital microscopy of the rat cremaster muscle and measurement of pressure in arterioles (diameters 20-132 μm) was performed in 24 rats. DRP (polyethylene oxide, 1 ppm) was infused i.v. and measurements were made at baseline and 20 minutes after completion of DRP infusion. In a 10-rat subset, additional measurements were made three minutes after the start, and one to five and 10 minutes after completion of DRP.

RESULTS

Twenty minutes after the completion of DRP, mean arteriolar pressure was 22% higher than baseline (from 42 ± 3 to 49 ± 3 mmHg, p < 0.005, n = 24). DRP decreased the pressure loss from the aorta to the arterioles by 24% (from 35 ± 6 to 27 ± 5 mmHg, p = 0.001, n = 10). In addition, there was a strong trend toward an increase in pressure at 10 minutes after the completion of DRP (n = 10).

CONCLUSIONS

Drag-reducing polymers diminish pressure loss between the aorta and the arterioles. This results in a higher pre-capillary pressure and probably explains the observed DRP enhancement in capillary perfusion.

Drag reduction by polyethylene glycol in the tail arterial bed of normotensive and hypertensive rats

This study was designed to evaluate the effect of drag reducer polymers (DRP) on arteries from normotensive (Wistar) and spontaneously hypertensive rats (SHR). Polyethylene glycol (PEG 4000 at 5000 ppm) was perfused in the tail arterial bed with (E+) and without endothelium (E-) from male, adult Wistar (N = 14) and SHR (N = 13) animals under basal conditions (constant flow at 2.5 mL/min). In these preparations, flow-pressure curves (1.5 to 10 mL/min) were constructed before and 1 h after PEG 4000 perfusion. Afterwards, the tail arterial bed was fixed and the internal diameters of the arteries were then measured by microscopy and drag reduction was assessed based on the values of wall shear stress (WSS) by computational simulation. In Wistar and SHR groups, perfusion of PEG 4000 significantly reduced pulsatile pressure (Wistar/E+: 17.5 ± 2.8; SHR/E+: 16.3 ± 2.7%), WSS (Wistar/E+: 36; SHR/E+: 40%) and the flow-pressure response. The E- reduced the effects of PEG 4000 on arteries from both groups, suggesting that endothelial damage decreased the effect of PEG 4000 as a DRP. Moreover, the effects of PEG 4000 were more pronounced in the tail arterial bed from SHR compared to Wistar rats. In conclusion, these data demonstrated for the first time that PEG 4000 was more effective in reducing the pressure-flow response as well as WSS in the tail arterial bed of hypertensive than of normotensive rats and these effects were amplified by, but not dependent on, endothelial integrity. Thus, these results show an additional mechanism of action of this polymer besides its mechanical effect through the release and/or bioavailability of endothelial factors.

[Microcirculatory alterations in critically ill patients: pathophysiology, monitoring and treatments]

Microcirculation represents a complex system devoted to provide optimal tissue substrates and oxygen. Therefore, pathophysiological and technological knowledge developments tailored for capillary circulation analysis should generate major advances for critically ill patients' management. In the future, microcirculatory monitoring in several critical care situations will allow recognition of macro-microcirculatory decoupling, and, hopefully, it will promote the use of treatments aimed at preserving tissue oxygenation and substrate delivery.

Intravenous injections of soluble drag-reducing polymers reduce foreign body reaction to implants

We tested whether soluble viscoelastic drag-reducing polymers (DRPs), which modify blood flow in the macro- and microcirculation, affect host response to implanted biomaterials and control biodegradation and tissue ingrowth processes. Porous poly(L-lactate) (PLLA) implants, which are naturally hydrolyzed by foreign body giant cells, were used to evaluate differences in host response. Intravenous DRPs, high-molecular weight poly(ethylene oxide) (PEO) or poly(mannose) (PMNN), were given biweekly at 0.3-0.4 nM in saline (equivalent volumes of saline in controls) to rats with subcutaneous PLLA implants. After 7 weeks, there was no difference in weight gain or behavior between control and DRP-injected groups. Implanted PLLA scaffolds in controls were almost totally degraded and replaced by giant cell granulomas. On the contrary, PEO- or PMNN-treated animals retained a significant part of the implanted scaffold (p < 0.0001 vs. controls). The foreign body reaction was markedly decreased, and there was an increase in well-oriented collagen deposition within the implanted scaffold area in the animals treated with DRPs. The DRP-mediated effects observed in this study potentially reflect alteration in inflammatory events in response to implanted bioengineered materials, and, thus, warrant further investigation.

Drag-reducing hyaluronic acid increases survival in profoundly hemorrhaged rats

We tested the hypothesis that the infusion of a small volume of a drag-reducing polymer (DRP) solution can prolong survival in rats subjected to lethal hemorrhagic shock (HS; shed 51% of estimated blood volume) in the absence of complete resuscitation with fluids or blood. In this set of experiments, we used a newly designed mixture of hyaluronic acid (molecular weight, approximately 2.0 x 10 d; 0.4 mg/mL) and polyethylene oxide (molecular weight, approximately 4 x 10 d; 0.05 mg/mL) dissolved in sterile phosphate-buffered saline. Anesthetized rats were subjected to a volume-controlled HS. During the first 20 min, blood (21.7 mL/kg) was withdrawn. During the next 40 min, additional blood (14 mL/kg) was withdrawn, and during the final 20 min, saline vehicle or saline + DRP (2.8 mL/kg) was simultaneously infused. The survival rate of the rats treated with the hyaluronic acid/polyethylene oxide was significantly higher (P < 0.01). The mean survival times for control and DRP-treated animals were 100.4 +/- 9.5 vs. 154.8 +/- 7.0 min (P < 0.001). MAP was higher (P < 0.005) and skin perfusion was significantly improved in the DRP-treated group after the end of the DRP infusion. These results support the use of nanomolar concentrations of DRP to prolong survival in rats after lethal HS in the absence of fluid resuscitation. The DRP formulation studied here warrants further evaluation for the amelioration of critical illness associated with profound shock when access to resuscitation fluids may not be possible or delayed.

Drag reducing polymers improve tissue perfusion via modification of the RBC traffic in microvessels

This paper reports a novel, physiologically significant, microfluidic phenomenon generated by nanomolar concentrations of drag-reducing polymers (DRP) dissolved in flowing blood, which may explain previously demonstrated beneficial effects of DRP on tissue perfusion. In microfluidic systems used in this study, DRP additives were found to significantly modify traffic of red blood cells (RBC) into microchannel branches as well as reduce the near-wall cell-free layer, which normally is found in microvessels with a diameter smaller than 0.3 mm. The reduction in plasma layer size led to attenuation of the so-called "plasma skimming" effect at microchannel bifurcations, increasing the number of RBC entering branches. In vivo, these changes in RBC traffic may facilitate gas transport by increasing the near vessel wall concentration of RBC and capillary hematocrit. In addition, an increase in near-wall viscosity due to the redirection of RBC in this region may potentially decrease vascular resistance as a result of increased wall shear stress, which promotes endothelium mediated vasodilation. These microcirculatory phenomena can explain the previously reported beneficial effects of DRP on hemodynamics in vivo observed in many animal studies. We also report here our finding that DRP additives reduce flow separations at microchannel expansions, deflecting RBC closer to the wall and eliminating the plasma recirculation zone. Although the exact mechanism of the DRP effects on RBC traffic in microchannels is yet to be elucidated, these findings may further DRP progress toward clinical use.

Early signaling of inflammation in acute ischemic stroke: clinical and rheological implications

INTRODUCTION

Several studies have highlighted the role of interleukin-6 (IL-6) as an early signal of the inflammatory response following acute ischemic stroke. This study examines the potential advantage of employing high-sensitivity (hs)-IL-6 as a possible biomarker at the early stages of acute stroke for identifying an acute phase response and its potential rheological and clinical implications.

METHODS

Venous blood was obtained from 186 stroke patients within 24 h of hospital admission and 3-5 days thereafter in order to characterize an inflammatory and hemorheological profile (including erythrocyte aggregation). Neurological state was assessed by the National Institutes of Health Stroke Scale (NIHSS) and the modified Rankin scale (mRs).

RESULTS

While most biomarkers displayed elevated concentrations with time, serum concentrations of hs-IL-6 declined 3-5 days following acute stroke. Initially elevated levels of hs-IL-6 at presentation further correlated with unfavorable clinical outcomes (by NIHSS and mRs) at both time points. Analysis of variance in the different quartiles identified an hs-IL-6 gradient-dependent correlation at both time points, such that the higher the initial hs-IL-6 concentration, the higher the elevation in inflammatory biomarkers and the poorer the neurological state at both time points (p<0.001 for NIHSS and p=0.001 for mRs, for trend across quartiles).

CONCLUSIONS

This study demonstrates the potential of employing hs-IL-6 as an early stage biomarker for the prognosis of acute ischemic stroke. Such an advance would provide the means to identify at an early stage the patients who would require closer clinical surveillance and/or administration of therapeutic interventions.