Increase In Functional Capillary Density Research Articles

BIO9: The Addition of High Molecular Weight Linear Polymers Improves Microvascular Perfusion in an Animal Model of Veno-arterial Extracorporeal Circulation.

High molecular weight linear polymers have been used in turbulent flow applications such as crude oil transfer to reduce drag. These polymers have branched into bioengineering applications to improve pressure changes within the macrocirculation and improve RBC distribution within the microcirculation. The current study aims to determine whether the addition of these polymers to priming fluids used for veno-arterial extracorporeal circulation (VA-ECC) procedures improve microvascular flow and tissue oxygenation. To assess the microcirculation, male Golden Syrian hamsters were instrumented with a dorsal skinfold window chamber, and an exteriorized carotid artery catheter was implanted for arterial blood and blood pressure access. After baseline (BL) measurements were taken, the hamster underwent surgery under isoflurane to insert a drainage catheter into the jugular vein. A heparin bolus (0.05 IU/g) was then provided, and the animal was connected to the VA-ECC circuit. The circuit, consisting of a peristaltic pump and bubble trap, was primed with lactated ringers (LR, control), LR with 5 ppm of 500 kDa polyethylene glycol (PEG500k) or LR with 5 ppm of 3500kDa polyethylene glycol (PEG3500k). Blood flow was ramped up over 15 minutes, maintained at 15% of the animal’s cardiac output for 60 minutes, then ramped down over 15 minutes. The animal was then surgically closed and placed on a heating pad and allowed at least 30 minutes to wake up from the anesthetic plane before taking measurements at 1, 2, and 24 hours after VA-ECC. Capillary perfusion (Figure 1) within the skinfold preparation showed a significant decrease immediately post-ECC for all three groups. However, the PEG3500k group consistently showed significant increase in functional capillary density (FCD) as compared to both other groups after ECC. 24 hrs after ECC, FCD was recovered close to BL levels for both PEG groups, while the LR control did not. Arteriole and venule velocity (Figure 2) was significantly elevated at both 1 and 2 hrs post-ECC for the PEG3500k group when compared to the other two groups. Arteriole flow for the PEG3500k was significantly improved over the LR control at 24 hrs post-ECC, and was significantly higher than BL levels. Hemoglobin saturation within arterioles and venules (Figure 3) revealed that PEG3500k had higher venule saturation at 1 and 2 hrs post-ECC compared to both other groups. The results indicate that the use of PEG3500k improved microvascular perfusion acutely post-ECC, and continued to up to 24 hrs afterwards. The most important changes were in arteriole perfusion and FCD, since that directly impacts oxygen delivery and metabolic washout respectively. Ultimately, this aids in maintaining organ function and preventing the development of ischemic injury and inflammatory cascades. Future studies could optimize the molecular weight, concentration, and type of polymer, along with testing in a clinical ECC circuit to determine hemodynamic changes.Figure 1. Functional capillary density (FCD), normalized to baseline (BL, represented by the dotted line). † P < 0.05 as compared to BL, within each group. * P < 0.05; ** P < 0.01; *** P < 0.001 between groups, at each timepoint.Figure 2. Perfusion within the microcirculation. From top to bottom: diameter, velocity, blood flow. Arterioles are on the left, while venules are on the right. Note that all values were normalized to baseline (BL, represented by the dashed line) and that blood flow was calculated from the diameter and velocity measurements of each vessel. Bar plots represent mean and standard deviation. † P < 0.05 as compared to BL, within each group. * P < 0.05; ** P < 0.01; *** P < 0.001; **** P < 0.0001 between groups, at each timepoint.Figure 3. Hemoglobin oxygen saturation within the microcirculation. Top = arterioles, bottom = venules. Bar plots show mean and standard deviation. † P < 0.05 as compared to BL, within each group. * P < 0.05; ** P < 0.01; *** P < 0.001; **** P < 0.0001 between groups, at each timepoint.

Acute Effects of Metformin and Vildagliptin after a Lipid-Rich Meal on Postprandial Microvascular Reactivity in Patients with Type 2 Diabetes and Obesity: A Randomized Trial.

Background: Type 2 diabetes mellitus and obesity are both related to endothelial dysfunction. Postprandial lipemia is a cardiovascular risk. Notably, it is known that a high-fat diet may elicit microvascular dysfunction, even in healthy subjects. Since anti-diabetic drugs have different mechanisms of action and also distinct vascular benefits, we aimed to compare the results of two anti-diabetic drugs after the intake of a lipid-rich meal on microcirculation in patients with type 2 diabetes and obesity. In parallel, we also investigated the metabolic profile, oxidative stress, inflammation, plasma viscosity, and some gastrointestinal peptides. Subjects/Methods: We included 38 drug-naïve patients, all women aged between 19 and 50 years, with BMI ≥ 30 kg/m2. We performed endothelial measurements and collected samples before (fasting) and after the intake of a lipid-rich meal at 30, 60, 120, and 180 min. Patients were randomized to metformin or vildagliptin, given orally just before the meal. Endothelial function was assessed by videocapillaroscopy and laser-Doppler flowmetry to investigate microvascular reactivity. Besides, we also investigated plasma viscosity, inflammatory and oxidative stress biomarkers, gastrointestinal peptides, and metabolic profile in all time points. Results: No differences at baseline were noted between groups. Vildagliptin increased glucagon-like peptide-1 compared to metformin. Paired comparisons showed that, during the postprandial period, vildagliptin significantly changed levels of insulin and glucagon-like peptide-1, and also the dipeptidyl peptidase-4 activity, while metformin had effects on plasma glucose solely. Metformin use during the test meal promoted an increase in functional capillary density, while vildagliptin kept non-nutritive microvascular blood flow and vasomotion unchanged. Conclusions: After the intake of a lipid-rich meal, the use of vildagliptin preserved postprandial non-nutritive microflow and vasomotion, while metformin increased capillary recruitment, suggesting protective and different mechanisms of action on microcirculation.

Local Biological Reactions and Pseudotumor-Like Tissue Formation in relation to Metal Wear in a Murine In Vivo Model.

Metal wear debris and released ions (CoCrMo), which are widely generated in metal-on-metal bearings of hip implants, are also found in patients with metal-on-polyethylene bearings due to the mechanically assisted crevice corrosion of modular taper junctions, including head-neck and neck-stem taper interfaces. The resulting adverse reactions to metal debris and metal ions frequently lead to early arthroplasty revision surgery. National guidelines have since been published where the blood metal ion concentration of patients must consistently be monitored after joint replacement to prevent serious complications from developing after surgery. However, to date, the effect of metal particles and metal ions on local biological reactions is complex and still not understood in detail; the present study sought to elucidate the complex mechanism of metal wear-associated inflammation reactions. The knee joints in 4 groups each consisting of 10 female BALB/c mice received injections with cobalt chrome ions, cobalt chrome particles, and ultra-high-molecular-weight polyethylene (UHMWPE) particles or PBS (control). Seven days after injection, the synovial microcirculation and knee joint diameter were assessed via intravital fluorescence microscopy followed by histological evaluation of the synovial layer. Enlarged knee diameter, enhanced leukocyte to endothelial cell interactions, and an increase in functional capillary density within cobalt chrome particle-treated animals were significantly greater than those in the other treatment groups. Subsequently, pseudotumor-like tissue formations were observed only in the synovial tissue layer of the cobalt chrome particle-treated animals. Therefore, these findings strongly suggest that the cobalt chrome particles and not metal ions are the cause for in vivo postsurgery implantation inflammation.

Local shockwave-induced capillary recruitment improves survival of musculocutaneous flaps

BackgroundShockwave (SW) application has been shown to limit flap necrosis. However, the underlying microhemodynamic mechanisms remain unclear. Therefore, the objective of this study was to analyze the effect of SW application on a microcirculatory level. MethodsWe treated 12 C57BL/6 mice with local SW application (500 shockwave impulses at 0.15 mJ/mm2) either 24 h before (preconditioning [PRE]) or 30 min after (postconditioning [POST]) flap elevation. Animals with an untreated flap (CON) or without a flap served as controls. We applied dorsal skinfold chambers to the animals and performed epifluorescence microscopy over a 10-d period to assess microcirculatory parameters (arteriolar diameter, red blood cell velocity, blood flow, functional capillary density, and intercapillary distance) as well as inflammation, apoptotic cell death, and necrosis. ResultsSW application significantly decreased tissue necrosis independently of the application time point (PRE: 29% ± 7%; POST: 25% ± 7% versus CON: 47% ± 2%; day 10, P < 0.05). Arteriolar diameter, red blood cell velocity, and blood flow were not statistically significantly different among the 3 flap groups. However, SW (PRE and POST) resulted in an early and persistent increase in functional capillary density and consequently decreased intercapillary distance compared with CON and the group without a flap (P < 0.05). Also, SW resulted in a significantly decreased inflammatory response (P < 0.05) and induced an angiogenic response, as indicated by new functional microvessel formation observed 5 d after therapy. ConclusionsLocal SW application improved tissue survival by recruitment of sleeping capillaries within the non ischemic tissue and maintenance of capillary perfusion within the critically perfused tissue after induction of ischemia, which was independent of the application time point. Neoangiogenesis occurred beyond the ischemic tolerance of the tissue, and therefore does not seem to contribute to improved tissue survival.

Increase in periosteal angiogenesis through heat shock conditioning

ObjectiveIt is widely known that stress conditioning can protect microcirculation and induce the release of vasoactive factors for a period of several hours. Little, however, is known about the long-term effects of stress conditioning on microcirculation, especially on the microcirculation of the periosteum of the calvaria. For this reason, we used intravital fluorescence microscopy to investigate the effects of heat shock priming on the microcirculation of the periosteum over a period of several days.MethodsFifty-two Lewis rats were randomized into eight groups. Six groups underwent heat shock priming of the periosteum of the calvaria at 42.5°C, two of them (n = 8) for 15 minutes, two (n = 8) for 25 minutes and two (n = 8) for 35 minutes. After 24 hours, a periosteal chamber was implanted into the heads of the animals of one of each of the two groups mentioned above. Microcirculation and inflammatory responses were studied repeatedly over a period of 14 days using intravital fluorescence microscopy. The expression of heat shock protein (HSP) 70 was examined by immunohistochemistry in three further groups 24 hours after a 15-minute (n = 5), a 25-minute (n = 5) or a 35-minute (n = 5) heat shock treatment. Two groups that did not undergo priming were used as controls. One control group (n = 8) was investigated by intravital microscopy and the other (n = 5) by immunohistochemistry.ResultsDuring the entire observation period of 14 days, the periosteal chambers revealed physiological microcirculation of the periosteum of the calvaria without perfusion failures. A significant (p < 0.05) and continuous increase in functional capillary density was noted from day 5 to day 14 after 25-minute heat shock priming. Whereas a 15-minute exposure did not lead to an increase in functional capillary density, 35-minute priming caused a significant but reversible perfusion failure in capillaries. Non-perfused capillaries in the 35-minute treatment group were reperfused by day 10. Immunohistochemistry demonstrated an increase in cytoprotective HSP70 expression in the periosteum after a 15-minute and a 35-minute heat shock pretreatment when compared with the control group. The level of HSP70 expression that was measured in the periosteum after 25 minutes of treatment was significantly higher than the levels observed after 15 or 35 minutes of heat shock exposure.ConclusionA few days after heat shock priming over an appropriate period of time, a continuous increase in functional capillary density is seen in the periosteum of the calvaria. This increase in perfusion appears to be the result of the induction of angiogenesis.

Distinct microhemodynamic efficacy of arteriogenesis and angiogenesis in critically ischemic skin flaps

Angiogenesis and arteriogenesis are regenerative vascular mechanisms dedicated to cope with critical ischemia after the interruption of the anatomical axial blood supply. The aim of the present study was to visualize, quantify and monitor the orchestration of these mechanisms and their microhemodynamic efficacy.A murine skin flap model was used that allowed for repetitive investigation of identical vascular structures by intravital microscopy. In the conduit arterioles, diameter and relative length increased to 133±20% and 260±80% over 7days, respectively (both P<0.01), which reduced vascular resistance in this segment to 82±35%. After 1week, a peak in accumulation of activated leukocytes could be observed in the postcapillary venules (P<0.01) without relevant hemodynamic changes. Thereafter, the arteriolar remodeling was replaced by angiogenesis. Functional capillary density was increased to 141±10% (P<0.01) and capillary diameter to 123±6% (P<0.01) after 14days. Both mechanisms of vascular regeneration were associated with increases in the capillary perfusion index, to 194±42% (P<0.05) after 7days and 366±21% after 14days (P>0.01). Immunohistochemical analysis revealed a correlation of arteriogenesis with eNOS upregulation and of angiogenesis with VEGF upregulation in the corresponding vessels.In conclusion, arteriogenesis was the initial regenerative mechanism leading to arteriolar remodeling, reduction in vascular resistance, and increase in capillary perfusion over the first 7days. Thereafter, capillary perfusion was improved by angiogenesis in terms of an increase in functional capillary density.

Sublingual and muscular microcirculatory alterations after cardiac arrest: A pilot study

Aims of the study Post-cardiac arrest resuscitated patients often develop a “sepsis-like” syndrome, which may be associated with organ dysfunction. Impaired microcirculatory blood flow is thought to play a key role in sepsis-induced organ failure; however, few data are available on the microcirculation after cardiac arrest. We investigated microvascular density and reactivity in the early phase following cardiac arrest. Methods We prospectively evaluated the sublingual microcirculation in 10 patients admitted to the intensive care unit (ICU) after cardiac arrest using a Sidestream Dark Field device. Thenar oxygen saturation (StO 2) was also measured using a tissue spectrometer and a vaso-occlusive test was performed by rapid inflation of a pneumatic cuff around the arm to evaluate the StO 2 reperfusion rate, reflecting microvascular reactivity. In all patients, measurements were performed within the first 12 h after admission (T1) and 24–48 h thereafter (T2). Results There was a significant increase in functional capillary density (FCD, 7.2 ± 1.9–10.0 ± 1.4 N/mm, p = 0.001), in the proportion of small perfused vessels (PSPV, 76 ± 13–92 ± 3%, p = 0.004) and in the mean microvascular flow index (MFI, 2.1 ± 0.5–2.8 ± 0.2, p = 0.003) at T2 compared to T1. FCD and PSPV were significantly correlated to body temperature, but not to cardiac output or mean arterial pressure. The StO 2 reperfusion rate did not change over the study period and showed considerable inter-individual variability. Conclusions The early post-resuscitation phase is characterised by significant abnormalities in microvascular density and flow, which return to normal within 48 h after cardiac arrest. These changes may be influenced by body temperature. Microvascular reactivity is impaired after cardiac arrest.

Inflammatory response against different carbon fiber-reinforced PEEK wear particles compared with UHMWPE in vivo

Poly(ether ether ketone) (PEEK) and its composites are recognized as alternative bearing materials for use in arthroplasty because of their mechanical properties. The objective of this project was to evaluate the biological response of two different kinds of carbon fiber-reinforced (CFR) PEEK compared with ultra-high molecular weight polyethylene (UHMWPE) in vivo as a standard bearing material. Wear particles of the particulate biomaterials were injected into the left knee joint of female BALB/c mice. Assessment of the synovial microcirculation using intravital fluorescence microscopy as well as histological evaluation of the synovial layer were performed 7 days after particle injection. Enhanced leukocyte-endothelial cell interactions and an increase in functional capillary density as well as histological investigations revealed that all tested biomaterials caused significantly (P < 0.05) increased inflammatory reactions compared with control animals (injected with sterile phosphate-buffered saline), without any difference between the tested biomaterials (P > 0.05). These data suggest that wear debris of CFR-PEEK is comparable with UHMWPE in its biological activity. Therefore, CFR-PEEK represents an alternative bearing material because of its superior mechanical and chemical behavior without any increased biological activity of the wear particles, compared with a standard bearing material.

Inflammation‐Induced Intussusceptive Angiogenesis in Murine Colitis

Intussusceptive angiogenesis is a morphogenetic process that forms new blood vessels by the division of a single blood vessel into two lumens. Here, we show that this process of intraluminal division participates in the inflammation-induced neovascularization associated with chemically induced murine colitis. In studies of both acute (4-7 days) and chronic (28-31 days) colitis, intravital microscopy of intravascular tracers demonstrated a twofold reduction in blood flow velocity. In the acute colitis model, the decreased velocity was associated with marked dilatation of the mucosal plexus. In contrast, chronic inflammation was associated with normal caliber vessels and duplication (and triplication) of the quasi-polygonal mucosal plexus. Scanning electron microscopy (SEM) of intravascular corrosion casts suggested that pillar formation and septation, previously linked to the morphogenetic process of intussusceptive angiogenesis, were present within days of the onset of inflammation. Four weeks after the onset of inflammation, SEM of vascular corrosion casts demonstrated replication of the mucosal plexus without significant evidence of sprouting angiogenesis. These data suggest that mucosal capillaries have comparable aggregate cross-sectional area in acute and chronic colitis; however, there is a significant increase in functional capillary density in chronic colitis. We conclude that intussusceptive angiogenesis is a fundamental mechanism of microvascular adaptation to prolonged inflammation.

Is hemoglobin in hemoglobin vesicles infused for isovolemic hemodilution necessary to improve oxygenation in critically ischemic hamster skin?

The aim of this study was to test the influence of hemoglobin, encapsulated in phospholipid vesicles as an oxygen carrier, given in the course of isovolemic hemodilution to improve oxygenation in critically ischemic hamster flap tissue. Capillary hemodynamics and macromolecular leakage were investigated with intravital microscopy and analyzed off-line with the CapImage software. Partial tissue oxygen tension was measured with fluorescence quenching electrodes. The occurrence of apoptosis was assessed with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Vesicles with (HbV) or without (V) encapsulated Hb were suspended in 6% hydroxyethyl starch (HES) used for the 33% blood exchange. In the ischemic tissue, hemodilution led to an increase in functional capillary density by 31% for HES (P < 0.01 vs. other groups), 66% for V-HES, and 62% for HbV-HES (all P < 0.01 vs. control). Capillary diameters behaved inversely proportional to capillary microhemodynamics. The 20% increase in macromolecular leakage found over time in control animals was completely abolished in the vesicles groups (P < 0.01) but not with HES. Oxygen tension was improved from 10.7 to 16.0 mmHg after HbV-HES (P < 0.01 vs. baseline and other groups). Compared with the other groups, apoptosis was significantly reduced after HbV-HES (P < 0.01). We conclude that the encapsulation of Hb was essential to attenuate hypoxia and subsequent cell death in the critically ischemic tissue. However, the effect was partly attributed to the rheological changes exerted by the vesicles.

Blood transfusion increases functional capillary density in the skin of anemic preterm infants.

Direct visualization of the microcirculation at the level of the skin capillaries may provide information on the quality of tissue perfusion. Orthogonal polarization spectral imaging (OPS) enables noninvasively direct observation of those blood vessels. OPS was applied to the upper arm of 13 preterm anemic infants [median (95% confidence interval) gestational age: 26 wk (25-26 wk); birth weight: 730 g (652-789 g)] before and 2 and 24 h after transfusion (Tx). OPS images of skin perfusion were continuously recorded on video. Off-line quantitative data of microvascular perfusion were obtained by measuring functional capillary density, vessel diameter, red blood cell velocity, and flow. We found a significant increase in functional capillary density 2 h after transfusion with an additional significant rise after 24 h [before: 142 (134-155); 2 h after Tx: 185 (166-196); 24 h after Tx: 206 (185-219) cm/cm2; p < 0.001), thus indicating improved microvascular perfusion. Vessel diameter, red blood cell velocity, and flow did not change significantly. There were no significant changes in clinical variables, such as blood pressure, heart rate, or body temperature. Whereas conventional monitoring methods did not show any changes after transfusion, quantitative analyses of OPS images indicated improved perfusion; hence, it seems a useful monitor for assessing the response to therapies aimed to improve tissue perfusion.

Functional capillary density in skeletal muscle during vasodilation induced by isoprenaline and muscular exercise

Functional capillary density in skeletal muscle was studied in an isolated, autoperfused preparation of the abdominal muscles of the rat during different forms of vasodilation. The macromolecule hydroxyethyl starch (MW 450,000), labeled with the fluorochrome lissamine-rhodamine B 200, was intravenously injected. When a certain volume of blood had passed the muscle the tissue was fixed by snap freezing. In histological sections those capillaries which had been perfused by the dye could be visualized in the fluorescence microscope. Increase in total muscular blood flow, measured by arterial drop counting, was induced by intraarterial infusion of isoprenaline and by muscular work (control 30.0 ± 2.6, isoprenaline 48.2 ± 4.4, postcontraction hyperemia 44.2 ± 7.4 ml/min × 100 g). During hyperemia the functional capillary density (stained capillaries per muscle fiber) was affected in a different way: 0.81 ± 0.02 control, 0.71 ± 0.03 isoprenaline, and 0.93 ± 0.04 postcontraction hyperemia. The data support the view that a rise in total blood flow is not necessarily associated with an increase in functional capillary density.