1) Develop and validate laser speckle flowmetry (LSF) as a quantitative tool for individual microvessel hemodynamics in large networks. 2) Use LSF to determine if structural differences in the dorsal skinfold microcirculation (DSFWC) of C57BL/6 and BALB/c mice impart differential network hemodynamic responses to occlusion.
We compared LSF velocity measurements to known/measured velocities in vitro using capillary tube tissue phantoms and in vivo using mouse DSFWCs and cremaster muscles. Hemodynamic changes induced by feed arteriole occlusion were measured using LSF in DSFWCs implanted on C57BL/6 and BALB/c.
In vitro, we found that the normalized speckle intensity (NSI) versus velocity linear relationship (R2≥0.97) did not vary with diameter or hematocrit and can be shifted to meet an expected operating range. In vivo, DSFWC and cremaster muscle preparations (R2=0.92 and 0.95, respectively) demonstrated similar linear relationships between NSI and centerline velocity. Stratification of arterioles into predicted collateral pathways revealed significant differences between C57BL/6 and BALB/c strains in response to feed arteriole occlusion.
These data demonstrate the applicability of LSF to intravital microscopy microcirculation preparations for determining both relative and absolute hemodynamics on a network-wide scale while maintaining the resolution of individual microvessels.
laser speckle flowmetry; hemodynamics; network blood flow; intravital microscopy; microvascular imaging
Chronic kidney disease (CKD) is histologically characterized by interstitial fibrosis, which may be driven by peritubular capillary dropout and hypoxia. Surprisingly, peritubular capillaries have little repair capacity. We sought to establish long-term cultures of rat kidney endothelial cells to investigate their growth regulatory properties.
Kidney endothelial cells from adult rats (AKEC) or young rats (YKEC) were isolated using CD31 based isolation techniques and sustained in long-term cultures.
Although YKEC grew slightly better than AKEC, both performed poorly compared to endothelial cells of the rat adult pulmonary microvasculature (PMVEC), pulmonary artery (PAEC), or HUVEC cells. PMVEC and PAEC contained a large percentage of cells with high colony forming potential. By contrast, KECs were incapable of forming large colonies and most remained as single non-dividing cells. KEC expressed high levels of mRNA for VEGF receptors but were surprisingly insensitive to VEGF stimulation. KECs did not form branching structures on Matrigel when cultured alone, but in mixed cultures KECs incorporated into branching structures with PMVECs.
These data suggest that the intrinsic growth of rat kidney endothelial cells is limited by unknown mechanisms. The low growth rate may relate to the minimal intrinsic regenerative capacity of renal capillaries.
angiogenesis; progenitor; hypoxia; CKD
One important contributor to tissue graft viability is angiogenic maturation of the graft tissue bed. This study uses scale-invariant microvascular morphological quantification to track vessel maturation and remodeling in a split-thickness skin grafting model over 21 days, comparing the results to classical techniques.
Images from a previous study of split-thickness skin grafting in rats were analyzed. Microvascular morphology (fractal and multifractal dimensions, lacunarity, and vessel density) within fibrin interfaces of samples over time was quantified using classical semi-automated methods and automated multifractal and lacunarity analyses.
Microvessel morphology increased in density and complexity, from 3 to 7 days after engraftment and then regressed by 21 days. Vessel density increased from 0.07 on day 3 to 0.20 on day 7 and then decreased to 0.06 on day 21. A similar trend was seen for the fractal dimension which increased from 1.56 at 3 days to 1.77 at 7 days then decreased to 1.57 by 21 days. Vessel diameters did not change while complexity and density did, signaling remodeling.
This new automated analysis identified design parameters for tissue engraftment and could be used in other models of graft vessel biology to track proliferation and pruning of complex vessel beds.
Microcirculation; Split Thickness Skin Graft; Microvascular Morphology; Multifractal Analysis
Vascular networks respond to chronic alterations in blood supply by structural remodeling. Previously, we showed that blood flow changes in the mouse gracilis artery lead to transient diameter increases, which can generate large increases in circumferential wall stress. Here, we examine the associated changes in the medial area of the arterial wall and the effects on circumferential wall stress.
To induce blood flow changes, one of the two feeding vessels to the gracilis artery was surgically removed. At 7 to 56 days after blood flow interruption, the vasculature was perfused with India ink for morphological measurements, and processed for immuno-cytochemistry to mark the medial cross-section area. Theoretical simulations of hemodynamics were used to analyze the data.
During adaptive increases in vessel diameter, increases in medial area were observed, most strongly in the middle region of the artery. Simulations showed that this increase in medial area limits the increase in estimated circumferential stress during vascular adaptation to less than 50%, in contrast to an increase of up to 250% if the medial area had remained unchanged.
During vascular adaptation, increases in circumferential stress are limited by growth of the media coordinated with diameter changes.
vascular adaptation; blood flow; ischemia; smooth muscle cells; endothelial cells
Erythrocytes appear to be ideal sensors for regulating microvascular O2 supply since they release the potent vasodilator adenosine 5′-triphosphate (ATP) in an O2 saturation dependent manner. Whether erythrocytes play a significant role in regulating O2 supply in the complex environment of diffusional O2 exchange among capillaries, arterioles and venules, depends on the efficiency with which erythrocytes signal the vascular endothelium. If one assumes that the distribution of purinergic receptors is uniform throughout the microvasculature, then the most efficient site for signaling should occur in capillaries, where the erythrocyte membrane is in close proximity to the endothelium. ATP released from erythrocytes would diffuse a short distance to P2y receptors inducing an increase in blood flow possibly the result of endothelial hyperpolarization. We hypothesize that this hyperpolarization varies across the capillary bed dependent upon erythrocyte supply rate and the flux of O2 from these erythrocytes to support O2 metabolism. This would suggest that the capillary bed would be the most effective site for erythrocytes to communicate tissue oxygen needs. Electrically coupled endothelial cells conduct the integrated signal upstream where arterioles adjust vascular resistance, thus enabling ATP released from erythrocytes to regulate the magnitude and distribution of O2 supply to individual capillary networks.
Microvascular regulation; O2 supply; O2 dependent ATP release; erythrocyte; capillary
To evaluate the expression and regulation of a novel B7-like protein, PD-L1, the ligand for the immunoinhibitory receptor PD-1 expressed on activated T-cells, on microvascular endothelial cells (ECs)
PD-L1 expression on ECs in vitro and in vivo was quantified by using a dual radiolabeled antibody technique after treatment with interferons (IFN) and IL-12, respectively. Changes in the level of PD-L1 mRNA were determined by using RT-PCR.
PD-L1 was observed to be present on ECs under basal conditions. Treatment of ECs with IFN-α, -β and -γ, but not LPS, was observed to induce elevations in the mRNA and surface expression of PD-L1 on ECs. By using a dual radiolabeled monoclonal antibody (mAb) technique, PD-L1 expression in various tissues of control and IL-12 challenged wild-type and IFN-γ-deficient mice was measured. A significant increase in PD-L1 expression was observed in tissues at 24 hours after IL-12-challenge, with peak levels of PD-L1 occurring 72 hours after IL-12 challenge. IL-12 was not effective at inducing PD-L1 expression in tissues of IFN-γ-deficient mice.
These data show the expression of a novel B7-like molecule on murine ECs that is mediated by IFN-α, -β, and -γ, and suggest a potential pathway by which ECs may modulate T-cell function.
endothelial cell; costimulation; T-lymphocyte; cellular activation
We describe a systematic approach to modeling blood flow using reconstructed capillary networks and in vivo hemodynamic measurements. Our objective was to produce flow solutions that represent convective O2 delivery in vivo. Two capillary networks, I & II, (84×168×342 & 70×157×268 μm3) were mapped using custom software. Total network red blood cell supply rate (SR) was calculated from in vivo data and used as a target metric for the flow model. To obtain inlet hematocrits, mass balances were applied recursively from downstream vessels. Pressure differences across the networks were adjusted to achieve target SR. Baseline flow solutions were used as inputs to existing O2 transport models. To test the impact of flow redistribution, asymmetric flow solutions (Asym) were generated by applying a ±20% pressure change to network outlets. Asym solutions produced a mean absolute difference in SR per capillary of 27.6 ± 33.3% in network I & 33.2 ± 40.1% in network II vs. baseline. The O2 transport model calculated mean tissue PO2 of 28.2 ± 4.8 & 28.1 ± 3.5 mmHg for baseline and 27.6 ± 5.2 & 27.7 ± 3.7 mmHg for Asym. This illustrates that moderate changes in flow distribution within a capillary network have little impact on tissue PO2 provided that total SR remains unchanged.
blood flow; capillary networks; oxygen transport modeling; red blood cell supply rate
Recent methods for imaging microvascular structures provide geometrical data on networks containing thousands of segments. Prediction of functional properties, such as solute transport, requires information on blood flow rates also, but experimental measurement of many individual flows is difficult. Here, a method is presented for estimating flow rates in a microvascular network based on incomplete information on the flows in the boundary segments that feed and drain the network.
With incomplete boundary data, the equations governing blood flow form an underdetermined linear system. An algorithm was developed that uses independent information about the distribution of wall shear stresses and pressures in microvessels to resolve this indeterminacy, by minimizing the deviation of pressures and wall shear stresses from target values.
The algorithm was tested using previously obtained experimental flow data from four microvascular networks in the rat mesentery. With two or three prescribed boundary conditions, predicted flows showed relatively small errors in most segments and fewer than 10% incorrect flow directions on average.
The proposed method can be used to estimate flow rates in microvascular networks, based on incomplete boundary data and provides a basis for deducing functional properties of microvessel networks.
Hemodynamics; flow simulation; imaging; microvascular function
Embolotherapy is a potential means to treat a variety of cancers. Our approach – gas embolotherapy – introduces the droplets upstream from the tumor and then acoustically activates them to form bubbles for occlusion – a process known as acoustic droplet vaporization (ADV). We wanted to provide the first optical documentation of ADV, lodged bubbles, or vessel occlusion in vivo.
We used the rat cremaster muscle for in vivo microscopy. Perfluorocarbon droplets were administered into the aortic arch. Ultrasound exposures in the cremaster induced vaporization. The cremaster was examined pre- and post-exposure for ADV-related effects. Two sets of experiments compared the effect of exposure in the capillaries versus the first order arteriole.
Bubbles that lodge following capillary exposure are significantly larger (76μm mean length, 36μm mean diameter) than those following feeder vessel exposure (25μm mean length, 11μm mean diameter). Despite the differing sizes in bubbles, the ratio of bubble length to the hydraulic diameter of all lodged bubbles was 2.11 (±0.65; N=112), which agrees with theoretical predictions and experimental observations.
Our results provide the first optical evidence of targeted vessel occlusion through ADV. These findings could lay the groundwork for the advancement of gas embolotherapy.
gas embolotherapy; cancer therapy; ultrasound; perfluorocarbon droplets; acoustic droplet vaporization
To evaluate the feasibility of conjunctival hemodynamic measurements based on assessment of reproducibility, validity, and response to acute hypotension.
Image sequences of the conjunctival microvasculature of rabbits were captured using a slit lamp biomicroscope under a steady state condition, after topical administration of phenylephrine, and after intravenous administration of esmolol. Venous hemodynamic parameters (diameter, blood velocity, blood flow, wall shear stress) were derived.
Conjunctival venous diameters ranged from 9 to 34 μm and blood velocities ranged from 0.08 to 0.95 mm/s. Coefficients of variation of venous diameter and blood velocity were on average 6% and 14%, respectively. Automated and manual measurements of venous diameter and velocity were highly correlated (R = 0.97; p < 0.001; N = 16). With phenylephrine administration, diameter and velocity were reduced by 21% and 69%, respectively. Following esmolol administration, blood pressure was reduced with a concomitant decrease in velocity, followed by recovery to baseline. Venous blood velocity, flow, and wall shear stress were correlated with blood pressure (R ≥ 0.52; p ≤ 0.01).
The feasibility of quantifying alterations in microvascular hemodynamics in the bulbar conjunctiva was established. The method is of potential value in evaluating microcirculatory hemodynamics related to cardiovascular function.
conjunctiva; microcirculation; hypotension; blood flow; wall shear stress; rabbit
Previous studies have shown that physiological levels of shear stress can protect endothelial cells (ECs) from apoptotic stimuli. Here we differentiate between acute and chronic protection and demonstrate the use of proteomic technologies to uncover mechanisms associated with chronic protection of endothelial cells. We hypothesized that changes in abundance of proteins associated with the TNF-alpha signaling cascade orchestrate shear stress-mediated protection from TNF-alpha when cells are pre-conditioned with shear prior to the exposure of apoptotic stimuli.
Detection of cleaved caspase 3 through Western blot analysis confirmed chronic shear-stress mediated protection from TNF-alpha. In the presence of the nitric oxide synthase (NOS) inhibitor, LMNA, chronic protection remained. Treatment with a de novo protein synthesis inhibitor, cycloheximide, eliminated this protective effect. Isotopic labeling experiments, coupled with liquid chromatography tandem mass spectrometry, (LC MS/MS) of isolated components of the TNF-alpha pathway revealed that CARD9, a known activator of the NF-κB pathway, was increased (60%) in sheared cells versus non-sheared cells. This result was confirmed through Western blot analysis. Our data suggests that de novo formation of proteins is required for protection from TNF-alpha in endothelial cells chronically exposed to shear stress, and that CARD9 is a candidate protein in this response.
endothelium; shear stress; apoptosis; proteomics
In complex organisms, both intracellular and intercellular communication is critical for the appropriate regulation of the distribution of perfusion to assure optimal oxygen (O2) delivery and organ function. The mobile erythrocyte is in a unique position in the circulation since it both senses and responds to a reduction in O2 tension in its environment. When erythrocytes enter a region of the microcirculation in which O2 tension is reduced, they release both O2 and the vasodilator, adenosine triphosphate (ATP) via activation of a specific and dedicated signaling pathway that requires increases in cAMP, that are regulated by phosphodiesterase 3B. The ATP released initiates a conducted vasodilation that results in alterations in the distribution of perfusion to meet the tissue’s metabolic needs. This delivery mechanism is modulated by both positive and negative feedback regulators. Importantly, defects in low O2-induced ATP release from erythrocytes have been observed in several human disease states in which impaired vascular function is present. Understanding of the role of erythrocytes in controlling perfusion distribution and the signaling pathways that are responsible for ATP release from these cells makes the erythrocyte a novel therapeutic target for the development of new approaches for the treatment of vascular dysfunction.
Red blood cells; blood flow regulation; O2 delivery; prostacyclin; phosphodiesterase
Vascular Dementia (VaD) is the second most common form of dementia second only to that caused by Alzheimer's Disease. As the name indicates, VaD is predominantly considered a disease caused by vascular phenomena. In this opinion, we introduce the reader to recent developments in defining VaD as a unique form of dementia. We discuss the clinical and experimental evidence which supports the notion that the microcirculation, specifically cell-to-cell communication, likely contributes to the development of VaD. Through exploration of the concept of the neurovascular unit, we will elucidate the extensive cerebro-vascular communication which exists and highlight models which may help test the contribution(s) of cell-to-cell communication at the microvascular level to the development and progression of VaD. Lastly we explore the possibility that some dementia, generally considered to be purely neurodegenerative, may actually have a vascular component at the neurovascular level. This recognition potentially broadens the critical involvement of microvascular events that contribute to the numerous dementias affecting an increasingly larger sector of the adult population.
Dementia; neurovascular unit; cerebral microcirculation; animal model; cell-to-cell communication; tauopathy; CADASIL
The endothelium is vital to normal vasoregulation. Although acute vasodilation associated with broad endothelial Ca2+ elevation is well-known, the control and targeting of Ca2+ dependent signals in the endothelium is poorly understood. Recent studies have revealed localized IP3-motivated Ca2+ events occurring basally along the intima that may provide the fundamental basis for various endothelial influences. Here, we provide an overview of dynamic endothelial Ca2+ signals and discuss the potential role of these signals in constant endothelial control of arterial tone and the titration of functional responses in vivo. In particular, we focus on the functional architecture contributing to the properties and ultimate impact of these signals and explore new avenues in evaluating their prevalence and specific modalities in intact tissue. Finally, we discuss spatial and temporal effector recruitment through modification of these inherent signals. It is suggested that endothelial Ca2+ signaling is a continuum in which the specific framework of store-release components and cellular targets along the endothelium allows for differential modes of Ca2+ signal expansion and distinctive profiles of effector recruitment. The precise composition and distribution of these inherent components may underlie dynamic endothelial control and specialized functions of different vascular beds.
Calcium; endothelium; artery; dynamic; modality; analysis
In this paper, we describe the histological and contractile properties of the thoracodorsal artery (TDA), which indirectly feeds the spinotrapezius muscle. Our results demonstrate that the TDA is composed of approximately one-two layers of smooth muscle cells, is highly innervated with adrenergic nerves, and develops spontaneous tone at intraluminal pressures above 80 mmHg. The reactivity of the TDA in response to various contractile agonists such as phenylephrine, noradrenaline, angiotensin II, serotonin, endothelin 1 and ATP as well as vasodilators show that the TDA exhibits a remarkably comparable reactivity to what has been observed in mesenteric arteries. We further studied the different components of the TDA response to acetylcholine and found that the TDA was sensitive to TRAM 34, a blocker of the intermediate conductance potassium channel, which is highly suggestive of an endothelium-dependent hyperpolarization. We conclude that the TDA exhibits comparable characteristics to other current vascular models, with the additional advantage of being easily manipulated for molecular and ex vivo vasoreactivity studies.
Vascular model; Vasoreactivity
Regional blood flow to the diaphragm muscle varies with the workload of inspiration. To provide anatomical insight into coupling between muscle fiber recruitment and oxygen supply, we tested whether arterioles are physically associated with motor nerve branches of the diaphragm.
Following vascular casting, intact diaphragm muscles of C57BL/6 and CD-1 mice were stained for motor innervation. Arteriolar networks and nerve networks were mapped (~2 μm resolution) to evaluate their physical proximity.
Neurovascular proximity was similar between muscle regions and mouse strains. Of total mapped nerve lengths (C57BL/6, 70±15 mm; CD-1, 87±13 mm), 80±14% and 67±10% were ≤ 250 μm from the nearest arteriole and associated predominantly with arterioles ≤ 45 μm in diameter. Distances to the nearest arteriole encompassing 50% of total nerve length (D50) were consistently within 200 μm. With nerve networks repositioned randomly within muscle borders, D50 values nearly doubled (P<0.05). Reference lines within anatomical boundaries reduced proximity to arterioles (P<0.05) as they deviated from the original location of motor nerves.
Across 2 strains of mice, motor nerves and arterioles of the diaphragm muscle are more closely associated than can be explained by chance. We hypothesize that neurovascular proximity facilitates local perfusion upon muscle fiber recruitment.
breathing; microcirculation; muscle blood flow; phrenic nerve; proximity analysis
Chronic wounds represent a rising health and economic burden to our society. Emerging studies indicate that miRNAs play a key role in regulating several hubs that orchestrate the wound inflammation and angiogenesis processes. Of interest to wound inflammation are the regulatory loops where inflammatory mediators elicited following injury, are regulated by miRNAs as well as regulate miRNA expression. Adequate angiogenesis is a key determinant of success in ischemic wound repair. Hypoxia and cellular redox state are among the key factors that drive wound angiogenesis. We provided first evidence demonstrating that miRNAs regulate cellular redox environment via a NADPH oxidase dependent mechanism in human microvascular endothelial cells (HMECs). We further demonstrated that hypoxia-sensitive miR-200b is involved in induction of angiogenesis by directly targeting Ets-1 in HMECs. These studies points towards a potential role of miRNA in wound angiogenesis. miRNA-based therapeutics represents one of the major commercial hot spots in today’s biotechnology market space. Understanding the significance of miRs in wound inflammation and angiogenesis may help design therapeutic strategies for management of chronic non-healing wounds.
miRNA; Inflammation; angiogenesis; oxidants; redox
MicroRNAs (miRs) are small non-coding RNAs implicated mainly in post-transcriptional gene silencing by interacting with the unstranslated region of the transcript. miR-210 represents a major hypoxia-inducible miRs, also known as hypoxamirs, which is ubiquitously expressed in a wide range of cells, serving versatile functions. This review article summarizes the current progress on biogenesis of miR-210 and its physiological roles including arrest of cell proliferation, repression of mitochondrial respiration, arrest of DNA repair, vascular biology, and angiogenesis. Given the fact that miR-210 is aberrantly expressed in a number of diseases such as tumor progression, myocardial infarction and cutaneous ischemic wounds, miR-210 could serve as an excellent candidate for prognostic purposes and therapeutic intervention. With the advancement of computational prediction, high-throughput target validation methodology, sequencing, proteomic analysis and microarray, it is anticipated that more down-stream targets of miR-210 and its-associated biological consequences under hypoxia will be unveiled establishing miR-210 as a major hub in the biology of hypoxia-response.
miR-210; hypoxamiRs; microRNAs; tissue repair
Xenobiotic particles can be considered in two genres: air pollution particulate matter and engineered nanoparticles. Particle exposures can occur in the greater environment, the workplace, and our homes. The majority of research in this field has, justifiably, focused on pulmonary reactions and outcomes. More recent investigations indicate that cardiovascular effects are capable of correlating with established mortality and morbidity epidemiological data following particle exposures. While the preliminary and general cardiovascular toxicology has been defined, the mechanisms behind these effects, specifically within the microcirculation, are largely unexplored. Therefore, the purpose of this review is several fold: first, a historical background on toxicological aspects of particle research is presented. Second, essential definitions, terminology, and techniques that may be unfamiliar to the microvascular scientist will be discussed. Third, the most current concepts and hypotheses driving cardiovascular research in this field will be reviewed. Lastly, potential future directions for the microvascular scientist will be suggested. Collectively speaking, microvascular research in the particle exposure field represents far more than a “niche”. The immediate demand for basic, translational, and clinical studies is high and diverse. Microvascular scientists at all career stages are strongly encouraged to expand their research interests to include investigations associated with particle exposures.
particulate matter; microcirculation; nanoparticles; exposure; cardiovascular
We examined the effects of exogenously delivered thrombin on cell recruitment in skeletal muscle and the formation of new collateral arterioles in the microvasculature in response to ligation-induced ischemia.
Thrombin or vehicle was locally applied to both ligated and non-operated Balb/c spinotrapezius muscles which were harvested after three or seven days, imaged using confocal microscopy, and analyzed.
Thrombin treatment resulted in accelerated arterialization of collateral capillaries and accelerated tissue reperfusion in ischemic muscles. Uninjured muscle treated with thrombin displayed increased vascular cell adhesion molecule 1 expression on arteriole and venule endothelium, increased expression of smooth muscle α-actin on capillary-sized vessels, increased infiltration by CD11b+ leukocytes, and mast cell infiltration and degranulation.
Exogenous delivery of thrombin enhances microvascular collateral development in response to ischemic insult and accelerates tissue reperfusion. Elicited responses from multiple cell types likely contribute to these effects.
thrombin; arteriogenesis; collateral vessel; ischemia
To study the effect of myoendothelial communication on vascular reactivity, we integrated detailed mathematical models of Ca2+ dynamics and membrane electrophysiology in arteriolar smooth muscle (SMC) and endothelial (EC) cells. Cells are coupled through the exchange of Ca2+, Cl−, K+, and Na+ ions, inositol 1,4,5-triphosphate (IP3), and the paracrine diffusion of nitric oxide (NO). EC stimulation reduces intracellular Ca2+ ([Ca2+]i) in the SMC by transmitting a hyperpolarizing current carried primarily by K+. The NO-independent endothelium-derived hyperpolarization was abolished in a synergistic-like manner by inhibition of EC SKCa and IKCa channels. During NE stimulation, IP3 diffusing from the SMC induces EC Ca2+ release, which, in turn, moderates SMC depolarization and [Ca2+]i elevation. On the contrary, SMC [Ca2+]i was not affected by EC-derived IP3. Myoendothelial Ca2+ fluxes had no effect in either cell. The EC exerts a stabilizing effect on calcium-induced calcium release–dependent SMC Ca2+ oscillations by increasing the norepinephrine concentration window for oscillations. We conclude that a model based on independent data for subcellular components can capture major features of the integrated vessel behavior. This study provides a tissue-specific approach for analyzing complex signaling mechanisms in the vasculature.
calcium dynamics; gap junctions; nitric oxide; EDHF; computer simulations
Blood is modeled as a suspension of red blood cells using the dissipative particle dynamics method. The red blood cell membrane is coarse-grained for efficient simulations of multiple cells, yet accurately describes its viscoelastic properties. Blood flow in microtubes ranging from 10 to 40 μm in diameter is simulated in three dimensions for values of hematocrit in the range of 0.15–0.45 and carefully compared with available experimental data. Velocity profiles for different hematocrit values show an increase in bluntness with an increase in hematocrit. Red blood cell center-of-mass distributions demonstrate cell migration away from the wall to the tube center. This results in the formation of a cell-free layer next to the tube wall corresponding to the experimentally observed Fahraeus and Fahraeus–Lindqvist effects. The predicted cell-free layer widths are in agreement with those found in in vitro experiments; the results are also in qualitative agreement with in vivo experiments. However, additional features have to be taken into account for simulating microvascular flow, e.g., the endothelial glycocalyx. The developed model is able to capture blood flow properties and provides a computational framework at the mesoscopic level for obtaining realistic predictions of blood flow in microcirculation under normal and pathological conditions.
apparent viscosity; red blood cell; blood flow resistance; dissipative particle dynamics
Provide regional flow measurement in the hearts of small mammals using a new, higher-resolution technique based on the deposition of a molecular marker.
We determined the instantaneous extraction and retention of the “molecular microsphere” radiolabeled desmethylimipramine in retrogradely perfused hamster hearts. In a separate series of experiments, autoradiography was used to measure regional myocardial deposition densities in hamster hearts of about 0.5 g with spatial area resolution of 16 × 16 μm.
Radiolabeled desmethylimipramine is almost 100% extracted during a single transcapillary passage and is retained in the tissue for many minutes. Autoradiographic images demonstrated a spatial flow heterogeneity with standard deviations of 31 ± 4% of the mean flow (N = 5) in 16 × 16 × 20-μm3 voxels. This is equivalent to the projections made using fractal relationships from cruder observations obtained with microspheres in the hearts of baboons, sheep, and rabbits.
Autoradiography using a molecular deposition marker provides quantitative information on myocardial flow heterogeneities with resolution at the size of cardiac myocytes. Because the regions resolved are smaller than the volume of regions supplied by single arterioles, the results must slightly exaggerate the true heterogeneity of regional flows.
2-Iododesmethylimipramine; molecular microsphere; hamster; quantitative autoradiography; coronary blood flow; microcirculation; fractal myocardial blood flows
Keratin proteins have been utilized as biomaterials for decades and are currently under investigation for a variety of tissue regeneration and trauma applications. It has been suggested that certain keratins may have the capacity to act as a colloid in fluid resuscitation applications, providing viscosity and oncotic properties that may be beneficial during acute ischemic events. Oxidized keratin derivatives, also known as keratoses, show good blood and cardiovascular compatibility and thus are the subject of this study.
The effects of Keratose compounds will be assessed using a topload intravenous infusion model and observation of changes in the microvasculature of the cremaster muscle of rats.
Keratose resuscitation fluid (KRF) administration resulted in significant vasodilation in the cremaster muscle. This effect was blocked with pretreatment of L-NA to inhibit nitric oxide. Another keratin fraction, alpha keratose, which is the primary viscosic compound, was not found to induce vasodilation.
The apparent mechanism of vasodilation was found to be nitric oxide- mediated and isolated to a particular purified fraction, the keratin associated proteins (KAP).
keratin; biomaterial; keratin-associated protein; KAP; vasodilation; resuscitation; ischemia