Changes In Microvascular Hemodynamics Research Articles

Immunological consequences of ageing microvascular hemodynamic changes in view of cancer development and treatment.

Risk factors of cardiovascular diseases have long been implicated as risk factors for carcinogenesis, but clear explanations for their association have not been presented. In this article, fundamental concepts from carcinogenesis, microvascular hemodynamics, and immunity are collectively reviewed and analyzed in context of the known features of vascular ageing effects, in formulating a theory that suggests reduced microvascular immunity as an important driving factor for carcinogenesis. Furthermore, scientific, preclinical, and clinical evidence that support this new theory are presented in an interdisciplinary manner, offering new explanations to previously unanswered factors that impact cancer risks and its treatment outcome such as chronic drug use, temperature, stress and exercise effects among others. Forward-looking topics discussing the implications of this new idea to cancer immunotherapeutics are also discussed.

Microhemodynamic aberrations created by transfusion of stored blood

Human red blood cells (RBCs) can be stored for up to 42 days under controlled conditions. Physical and chemical changes occur during RBC storage, altering their function. This study links stored cell mechanical changes with hemodynamic functional alterations upon transfusion. Mechanical properties of fresh and stored RBCs were evaluated in vitro. Their transfusion effects were evaluated in vivo using intravital microscopy of the rat's cremaster muscle preparation. Rats were hemodiluted to 30% hematocrit, to mimic an anemic state before transfusion, and then exchange-transfused with fresh or stored cells. In vitro studies on rheology and oxygen affinity of stored cells confirmed previously published results. Storage was found to modify static and dynamic RBC mechanic behavior. After transfusion, systemic hemodynamics were similar for fresh and stored cells; however, microvascular hemodynamics were drastically affected by stored cells. Stored cells reduced blood flow and oxygen delivery. Additionally, the presence of stored cells in circulation affected cell-to-cell and cell-to-wall interactions and affected cell hydrodynamics. Stored cells disrupted the RBC cell-free layer and wall shear stress signals. The reduced cell deformability due to RBC "storage lesions" caused pathologic changes in microvascular hemodynamics, endothelial cell mechanotransduction, and RBC dynamics. Thus, the mechanical changes of blood-banked cells can limit transfusion ability to achieve its intended goal.

In vivo laser speckle imaging reveals microvascular remodeling and hemodynamic changes during wound healing angiogenesis

Laser speckle contrast imaging (LSCI) is a high-resolution and high contrast optical imaging technique often used to characterize hemodynamic changes in short-term physiological experiments. In this study, we demonstrate the utility of LSCI for characterizing microvascular remodeling and hemodynamic changes during wound healing angiogenesis in vivo. A 2mm diameter hole was made in the mouse ear and the periphery of the wound imaged in vivo using LSCI over 12days. We were able to visualize and quantify the vascular and perfusion changes that accompanied wound healing in the microenvironment proximal to the wound, and validated these changes with histology. We found that consistent with the stages of wound healing, microvessel density increased during the initial inflammatory phase (i.e., day 0-3), stayed elevated through the tissue formation phase (i.e., until day 7) and returned to baseline during the tissue remodeling phase (i.e., by day 12). Concomitant "wide area mapping" of blood flow revealed that tissue perfusion in the wound periphery initially decreased, gradually increased from day 3-7, and subsided as healing completed. Interestingly, some regions exhibited a reestablishment of tissue perfusion approximately 6days earlier than the ~18days usually reported for the long term remodeling phase. The results from this study demonstrate that LSCI is an ideal platform for elucidating in vivo changes in microvascular hemodynamics and angiogenesis, and has the potential to offer invaluable insights in a range of disease models involving abnormal hemodynamics, such as diabetes and tumors.

人工血液(PFC乳剤)の投与による微小循環血行動態の変化

人工血液(PFC乳剤)の投与による微小循環血行動態の変化

Nitric oxide prevents cardiovascular collapse during shock

This study investigated the systemic and microvascular hemodynamic changes after severe hemorrhage. Nitric oxide (NO) availability was increased by administration of NO releasing nanoparticles (NO‐nps). Hemodynamic responses to hemorrhagic shock were studied in the hamster window chamber. Acute hemorrhage was induced by arterial controlled bleeding of 50% of blood volume, and the resulting hemodynamic parameters were followed over 90 min. Exogenous NO was administered in the form of NO‐nps (5 mg/kg suspended in 50 μl saline) 10 min following induced hemorrhage. Control groups received equal dose of NO free nanoparticles (Control‐nps) and Vehicle solution (50 μl saline). Animals treated with NO‐nps partially maintained systemic and microvascular function during hypovolemic shock compared to animals treated with Control‐nps or the Vehicle. The continuous NO released by the NO‐nps reverted arteriolar vasoconstriction, partially recovered both functional capillary density and microvascular blood flows. Additionally, NO supplementation prevented cardiac decompensation. Paradoxically, peripheral vasodilation induced by the NO‐nps did not decrease blood pressure or vascular resistance. NO‐nps promoted intravascular pressure redistribution, increased blood flow and prevented ischemia. Therefore, NO released from NO‐nps can ultimately increase survivability and reduce shock sequelae.

Exogenous nitric oxide prevents cardiovascular collapse during hemorrhagic shock

This study investigated the systemic and microvascular hemodynamic changes related to increased nitric oxide (NO) availability following significant hemorrhage, made available by administration of NO releasing nanoparticles (NO-nps). Hemodynamic responses to hemorrhagic shock were studied in the hamster window chamber. Acute hemorrhage was induced by arterial controlled bleeding of 50% of blood volume, and the resulting hemodynamic parameters were followed over 90 min. Exogenous NO was administered in the form of NO-nps (5 mg/kg suspended in 50 μl saline) 10 min following induced hemorrhage. Control groups received equal dose of NO free nanoparticles (Control-nps) and Vehicle solution. Animals treated with NO-nps partially maintained systemic and microvascular function during hypovolemic shock compared to animals treated with Control-nps or the Vehicle (50 μl saline). The continuous NO released by the NO-nps reverted arteriolar vasoconstriction, partially recovered both functional capillary density and microvascular blood flows. Additionally, NO supplementation post hemorrhage prevented cardiac decompensation, and thereby maintained and stabilized the heart rate. Paradoxically, the peripheral vasodilation induced by the NO-nps did not decrease blood pressure, and combined with NO's effects on vascular resistance, NO-nps promoted intravascular pressure redistribution and blood flow, avoiding tissue ischemia. Therefore, by increasing NO availability with NO-nps during hypovolemic shock, it is possible that cardiac stability and microvascular perfusion can be preserved, ultimately increasing survivability and local tissue viability, and reducing hemorrhagic shock sequelae. The relevance, stability, and efficacy of exogenous NO therapy in the form of NO-nps will potentially facilitate the intended use in battlefield and trauma situations.

Exogenous nitric oxide induces protection during hemorrhagic shock

Introduction This study analyzed the systemic and microvascular hemodynamic changes related to increased nitric oxide (NO) availability during the early phase of hemorrhagic shock. Hemodynamic responses to hemorrhagic shock were studied in the hamster window chamber. Materials and Methods Exogenous NO was administered in the form of nitrosothiols (nitrosylated glutathione, GSNO) and was given prior the onset of hemorrhage. Moderate hemorrhage was induced by arterial controlled bleeding of 50% of the blood volume, and the hypovolemic shock was followed over 90 min. Results Animals pre-treated with GSNO maintained systemic and microvascular conditions during hypovolemic hemorrhagic shock, when compared to animal treated with glutathione (GSH) or the Sham group. Low concentrations of NO released during the early phase of hypovolemic shock from GSNO mitigated arteriolar vasoconstriction, increased capillary perfusion and venous return, and improved cardiac function (recovered of blood pressure and stabilized heart rate). GSNO's effect on resistance vessels influenced intravascular pressure redistribution and blood flow, preventing tissue ischemia. Discussion Increases in NO availability during the early phase of hypovolemic shock could preserve cardiac function and microvascular perfusion, sustaining organ function. Direct translation into a clinical scenario may be limited, although the pathophysiological importance of NO in the early phase of hypovolemia is clearly highlighted here.

Intestinal microvascular changes associated with the induction and perpetuation of chronic gut inflammation

Adoptive transfer of naïve CD4+ T‐cells into lymphopenic mice induces chronic small and large bowel inflammation similar to Crohn's disease. Although much is now known regarding the immunopathology in this model of inflammatory bowel disease, virtually nothing is known about the microvascular hemodynamic changes in the induction and perpetuation of chronic gut inflammation. In this study, CD4+CD45RBhigh T‐cells obtained from healthy C57BL6 donors were transferred into lymphopenic recombinase activating gene‐1 deficient (RAG ko) mice, and in the following weeks, intravital microscopy was used to examine the ileum and proximal colon. Measurements included arteriolar diameters and the velocity of labeled platelets (indicator of blood velocity), with the results compared to unreconstituted RAG ko controls. In < 1 wk following reconstitution, velocity and wall shear rate of the arterioles decreased by > 50% compared to controls, with this decrease also observed at 4‐5 and 7‐9 weeks post‐reconstitution. At 7‐9 weeks, arteriolar diameters were found to be ~15% larger than in controls, but despite this dilation, flow rates in the individual vessels were decreased by ~30%. Whether the overall intestinal flow rate is decreased in this model may be dependent on the reported angiogenesis, which could explain the lower individual vessel flows despite the late vasodilation. Supported by Projects 1 & 2 of NIH P01DK043785.

Altered microvascular hemodynamics during the induction and perpetuation of chronic gut inflammation

Adoptive transfer of naïve CD4+ T cells into lymphopenic mice induces chronic small and large bowel inflammation similar to Crohn's disease. Although much is now known regarding the immunopathology in this model of inflammatory bowel disease, virtually nothing is known about the microvascular hemodynamic changes during the induction and perpetuation of chronic gut inflammation. In this study, CD4+CD45RBhigh T cells obtained from healthy C57BL/6 donor mice were transferred into lymphopenic recombinase-activating gene-1-deficient (RAG knockout) mice, which induced small and large bowel inflammation. At various time points following reconstitution (3 days-9 wk), intravital microscopy was used to examine the microvessels in the submucosa of the ileum and proximal colon following infusion of fluorescently labeled platelets and injection of rhodamine 6G (to label leukocytes). Hemodynamic measurements and the extent of blood cell adhesion to the venular wall were compared with measurements in unreconstituted RAG knockout controls. In <1 wk following reconstitution, velocity and wall shear rate of the arterioles decreased by >50% compared with controls, with this decrease also observed at 4-5 and 7-9 wk postreconstitution. At 7-9 wk, arteriolar diameters were found to be approximately 15% larger than in controls, but, despite this dilation, flow rates in the individual vessels were decreased by approximately 30%. Venular platelet and leukocyte adherence were not significantly elevated above controls; however, an association was found between platelet adherence and venular shear rate. In summary, significant decreases in arteriolar velocity and shear rates are observed in this model of chronic gut inflammation.

Microvascular and systemic effects following top load administration of saturated carbon monoxide-saline solution*

To determine how top loads with different doses of carbon monoxide (CO)-saturated saline solutions (CO-saline) affect microvascular and systemic hemodynamics and to delineate the corresponding biochemical mechanisms. Prospective study. University research laboratory. Male Golden Syrian hamsters. Hamsters implemented with a dorsal window chamber were given different volumes (characterized as percent of blood volume, BV) by intravenous injection of CO-saturated saline. Hamsters were observed until 90 mins after infusion of CO-saline solution. In the 20% BV CO-saline infusion group, observation was extended until 180 mins. Systemic variables measured included mean arterial pressure, heart rate, systemic arterial blood gases, and cardiac output and index. Microvascular hemodynamic measurements included vessel diameter, red blood cell velocity, and functional capillary density. Cyclic guanosine monophosphate (cGMP) content in the chamber tissue was measured by enzyme immunoassay. 10% BV of CO-saline increased flow maximally in the microcirculation at 30 mins after infusion (207% in arterioles and 238% in venules, p < .05 vs. baseline). Functional capillary density was significantly increased in both 10% and 15% groups (p < .05 vs. baseline), and cardiac index increased 130% (p < .05 vs. baseline) at 10 mins after 10% CO-saline infusion. There were no changes of microhemodynamic variables and functional capillary density with 2.5%, 5%, and 20% CO-saline infusion during the observation period. Microvascular hemodynamic changes by 10% CO-saline infusion were inhibited completely by L-NAME pretreatment and partially by 1H-[1,2,4]oxadiazole[4,3-a]quinoxqalin-1-one pretreatment. cGMP content in skin fold tissues was related to changes of vessel diameter. Intravenous injection of CO-saturated saline caused vasodilation and improved microvascular hemodynamics in the hamster window chamber model in a dose-dependent manner. These changes were related to increased cardiac output and local cGMP content. These results support the possible use of CO-saturated solutions as a vasodilator in critical conditions.

Vascular endothelial growth factor-C stimulates the lymphatic pump by a VEGF receptor-3-dependent mechanism

Vascular endothelial growth factor (VEGF)-C plays an important role in lymphangiogenesis; however, functional responses of lymphatic vessels to VEGF-C have not been characterized. We tested the hypothesis that VEGF-C-induced activation of VEGF receptor (VEGFR)-3 increases lymphatic pump output. We examined the in vivo pump activity of rat mesenteric collecting lymphatics using intravital microscopy during basal conditions and during treatment with 1 nM recombinant VEGF-C, the selective VEGFR-3 agonist VEGF-Cys(156)Ser mutation (C156S; 1 nM), or 0.1 nM VEGF-A. Their specific responses were also analyzed during selective inhibition of VEGFR-3 with MAZ-51. Contraction frequency, end-diastolic diameter, end-systolic diameter, stroke volume index, pump flow index, and ejection fraction were evaluated. We also assessed arteriolar diameter and microvascular extravasation of FITC-albumin. The results show that both VEGF-C and VEGF-C156S significantly increased contraction frequency, end-diastolic diameter, stroke volume index, and pump flow index in a time-dependent manner. VEGF-A caused a different response characterized by a significantly increased stroke volume after 30 min of treatment. MAZ-51 (5 muM) caused tonic constriction and decreased contraction frequency. In addition, 0.5 and 5 muM MAZ-51 attenuated VEGF-C- and VEGF-C156S-induced lymphatic pump activation. VEGF-A caused vasodilation of arterioles, whereas VEGF-C and VEGF-C156S did not significantly alter arteriolar diameter. Also, VEGF-A and VEGF-C caused increased microvascular permeability, whereas VEGF-C156S did not. Our results demonstrate that VEGF-C increases lymphatic pumping through VEGFR-3. Furthermore, changes in microvascular hemodynamics are not required for VEGFR-3-mediated changes in lymphatic pump activity.

Inflammatory cells in ischemic acute renal failure

Ischemic acute renal failure (ARF) is increasingly recognized as involving a complex cascade of mechanisms with both acute and chronic consequences. Attention to nontraditional mediators of ARF such as inflammatory pathways and microvascular events has yielded new paradigms and avenues of research. The initiation phase of renal ischemia/reperfusion (I/R) injury damage involves microvascular hemodynamic changes characterized by red blood cell sludging with platelets and leukocytes. Blocking leukocyte-endothelial interactions has yielded significant protection from renal I/R injury in experimental models. However, experiments focusing on the role of the neutrophil have led to a modest expectation of its role in ARF. Recent studies have found that T cells directly mediate renal injury in experimental I/R injury. The CD4+ T cell, working both via interferon-gamma (IFN-gamma) and costimulatory molecules appears to be an important modulator of ARF. The B cell has recently been implicated in ARF. Little is known about the role for the macrophage. Finally, resident kidney cells likely contribute to the inflammatory pathogenesis of I/R damage and protection/repair, but how, and to what extent they are involved is not known. New tools to modulate inflammatory cells, particularly mononuclear leukocytes, hold promise for clinical trials in ARF.

Approaches to the detection of coronary artery disease using myocardial contrast echocardiography

In the presence of an epicardial coronary stenosis, changes in microvascular hemodynamics after the administration of pharmacologic stress agents result in a decrease in myocardial blood volume (MBV) from capillary derecruitment. Because capillaries provide the greatest resistance to flow during maximal hyperemias, changes in capillary volume are closely coupled to changes in hyperemic myocardial blood flow (MBF). A wide array of imaging techniques are now available with myocardial contrast echocardiography to assess both the spatial and temporal aspects of myocardial perfusion, providing many options for the detection of coronary stenosis by evaluating changes in MBV, MBF, or both.

Chronic ethanol consumption exacerbates microcirculatory damage in rat mesentery after reperfusion.

Although the negative effect of excessive alcohol consumption on later stressful events has long been recognized, pathophysiological mechanisms are incompletely understood. We examined possible roles of oxygen radicals and glutathione content in mesenteric venules of chronically ethanol-fed rats exposed to ischemia-reperfusion. Changes in microvascular hemodynamics, such as red blood cell (RBC) velocity, leukocyte adherence, and albumin extravasation, were monitored in postcapillary venules by intravital fluorescence microscopy. Chronic ethanol feeding significantly exaggerated the magnitude of the decrease in RBC velocity, the increased number of adherent leukocytes, and increased albumin leakage elicited by 10 min of ischemia followed by 30 min of reperfusion. Oxidative stress in the endothelium of venules monitored by dihydrorhodamine 123 (DHR) fluorescence was more severe in rats fed ethanol chronically. Both superoxide dismutase and N-acetyl-L-cysteine, which is known to increase glutathione content, reduced the ischemia-reperfusion-induced decrease in RBC velocity, the number of adherent leukocytes, and the increase in albumin leakage, as well as oxidative activation of DHR. This suggests that the increased reperfusion-induced microvascular disturbances in the mesenteric venules of rats fed ethanol chronically are significantly correlated with excessive production of oxygen-derived free radicals and decreased glutathione synthesis.

Coagulation in vivo microcirculation and in vitro caused by endothelin-1

This study was designed to elucidate the participation of endothelin-1(ET-1) in vivo and in vitro coagulation. The microvascular hemodynamic changes in terms of intravascular thrombus formation in rat mesentery induced by the superfusion of ET-1 (0.5, 1 and 2 pmol) were visualized by an intravital microscope system assisted by television-video tape recorder system. In addition to vasoconstriction we observed the blockade of circulation by clumps resembling thrombus in a dose dependent fashion by ET-1. Thrombus formation could be attenuated by pretreatment with superfusion of 3.8% Na citrate solution but not by the prior superfusion of 1 to 3 ng of nitroglycerine. Thrombus formation was found after the administration of 10 μl of CaCl 2 (100nM) solution in Na citrate ( 3.8 %, 20 μl) and ET-1 treated field. In vitro study, a dose dependent increase in TAT (thrombin-antithrombin complexes) and decrease in AT III (antithrombin III) (%) activity, the prolongation of PT (prothrombin time) and APTT (activated partial thromboplastin time) was found by administering ET-1 immediately in native (unanticoagulated) blood in silicon coated test tubes (p<0.05; n=6). However in citrated blood, TAT complexes, AT III (%) activity, PT and APTT were not significantly changed after administration of the same doses of ET-1 (p>0.05; n=6). Therefore, this study suggested that endothelin-1 caused intravascular thrombosis and enhanced intra test tube coagulation which could be attenuated by blocking ionic calcium.

Involvement of Platelet-Activating Factor in Endothelin-Induced Vascular Smooth Muscle Cell Contraction

This study was designed to elucidate the participation of platelet-activating factor (PAF) in endothelin-induced vascular constriction in vivo and in vitro. The microvascular hemodynamic changes in rat mesentery induced by the superfusion of endothelin-1 (ET-1) were visualized through an intravital microscopic system. It was revealed in vivo that ET-1 in a range of 100 fM-10 pM caused a sustained arteriolar constriction in a dose-dependent manner. Pretreatment with CV-6209, a selective PAF antagonist, significantly attenuated the constrictive change in arterioles. Changes of intracellular Ca2+ mobilization after treatment with ET-1 were investigated in vitro using a cell line (A-10 cell) derived from rat arterial smooth muscle cells. ET-1 caused a prompt rise in the fura-2-associated fluorescence intensity in the individual A-10 cell and it fell to a lower plateau level that was still higher than the baseline value. CV-6209-pretreated cells did not show the rapid-phase mobilization of Ca2+, but showed the slow late phase of Ca2+ activation. The present study demonstrates that PAF may be involved in endothelin-induced microvascular constriction by mediating the mobilization of Ca2+ in vascular smooth muscle cells.

Arterioles supply oxygen to capillaries by diffusion as well as by convection

In the early part of this century, August Krogh proposed a model of oxygen transport in capillaries that assumes that all oxygen is delivered to the capillaries by convection from small terminal arterioles and lost from these capillaries by diffusion. This model and its consequences have been used extensively to interpret whole organ oxygen transport data in terms of diffusion between capillaries and tissues and to relate changes in microvascular hemodynamics to alterations in oxygen transport. We evaluated the appropriateness of such extrapolation by measuring oxygen saturation at discrete locations along the lengths of individual capillaries in the hamster cheek pouch retractor muscle. Our results indicate that the amount of oxygen lost from individual capillaries can be markedly affected by the presence of larger microvessels that frequently cross the capillary path. These larger vessels act either as a diffusive supply of oxygen for the red blood cells within the capillary or as an additional sink for the oxygen depending on the direction of the oxygen tension gradient. This transfer of oxygen between larger microvessels and capillaries attenuates the importance of capillary hemodynamics in oxygen exchange. Therefore, conclusions about local oxygen exchange that utilize only hemodynamic data from whole organ or microvascular experiments and the Krogh model will generally be invalid and should be viewed with caution.

Transcapillary protein leakage and fluid movement: Effect of venous pressure

The effect of elevating venous pressure ( ΔP v) on the transcapillary escape of albumin ( Q T) in control and papverinized gracilis muscles perfused at constant flow was determined by means of direct monitoring of the rate of accumulation of tissue 125I-labeled albumin radioactivity. Simultaneously, transcapillary fluid movement (FM) was assessed volumetrically. Under control isovolumetric conditions, Q T = 2.25 mg/min · 100 g. In addition to causing an FM of 0.03 ml/min · 100 g · mm Hg, increasing P v enhanced Q T by 0.06 mg/min · 100 g · mm Hg. Papverinization itself decreased Q T to 2.0 mg/min · 100 g and affected FM only slightly. However, the superposition of P v elevation caused a FM of 0.008 ml/min · 100 g · mm Hg and resulted in Q T increasing by 0.29 mg/min · 100 g · mm Hg. The results of this study indicate that Q T is sensitive to changes in microvascular hemodynamics, and thus changes in microvascular pressure may affect FM in two ways, first by increasing the transcapillary pressure gradient and second by augmenting Q T which may superimpose an oncotic adjunct to FM.