Influence of feeding hematocrit and perfusion pressure on hematocrit reduction (Fåhraeus effect) in an artificial microvascular network.

OBJECTIVE: Hct in narrow vessels is reduced due to concentration of fast-flowing RBCs in the center, and of slower flowing plasma along the wall of the vessel, which in combination with plasma skimming at bifurcations leads to the striking heterogeneity of local Hct in branching capillary networks known as the network Fåhraeus effect. We analyzed the influence of feeding Hct and perfusion pressure on the Fåhraeus effect in an AMVN. METHODS: RBC suspensions in plasma with Hcts between 20% and 70% were perfused at pressures of 5-60 cm H2 O through the AMVN. A microscope and high-speed camera were used to measure RBC velocity and Hct in microchannels of height of 5 µm and widths of 5-19 µm. RESULTS: Channel Hcts were reduced compared with Hctfeeding in 5 and 7 µm microchannels, but not in larger microchannels. The magnitude of Hct reduction increased with decreasing Hctfeeding and decreasing ΔP (flow velocity), showing an about sevenfold higher effect for 40% Hctfeeding and low pressure/flow velocity than for 60% Hctfeeding and high pressure/flow velocity. CONCLUSIONS: The magnitude of the network Fåhraeus effect in an AMVN is inversely related to Hctfeeding and ΔP.

Optimal hematocrit in an artificial microvascular network.

BACKGROUND: Higher hematocrit increases the oxygen-carrying capacity of blood but also increases blood viscosity, thus decreasing blood flow through the microvasculature and reducing the oxygen delivery to tissues. Therefore, an optimal value of hematocrit that maximizes tissue oxygenation must exist. STUDY DESIGN AND METHODS: We used viscometry and an artificial microvascular network device to determine the optimal hematocrit in vitro. Suspensions of fresh red blood cells (RBCs) in plasma, normal saline, or a protein-containing buffer and suspensions of stored red blood cells (at Week 6 of standard hypothermic storage) in plasma with hematocrits ranging from 10 to 80% were evaluated. RESULTS: For viscometry, optimal hematocrits were 10, 25.2, 31.9, 37.1, and 37.5% for fresh RBCs in plasma at shear rates of 3.2 or less, 11.0, 27.7, 69.5, and 128.5 inverse seconds. For the artificial microvascular network, optimal hematocrits were 51.1, 55.6, 59.2, 60.9, 62.3, and 64.6% for fresh RBCs in plasma and 46.4, 48.1, 54.8, 61.4, 65.7, and 66.5% for stored RBCs in plasma at pressures of 2.5, 5, 10, 20, 40, and 60 cm H2 O. CONCLUSION: Although exact optimal hematocrit values may depend on specific microvascular architecture, our results suggest that the optimal hematocrit for oxygen delivery in the microvasculature depends on perfusion pressure. Therefore, anemia in chronic disorders may represent a beneficial physiological response to reduced perfusion pressure resulting from decreased heart function and/or vascular stenosis. Our results may help explain why a therapeutically increasing hematocrit in such conditions with RBC transfusion frequently leads to worse clinical outcomes.

Influence of red blood cell aggregation on perfusion of an artificial microvascular network.

OBJECTIVE: RBCs suspended in plasma form multicellular aggregates under low-flow conditions, increasing apparent blood viscosity at low shear rates. It has previously been unclear, however, if RBC aggregation affects microvascular perfusion. Here, we analyzed the impact of RBC aggregation on perfusion and 'capillary' hematocrit in an AMVN at driving pressures ranging from 5 to 60 cm H2 O to determine if aggregation could improve tissue oxygenation. METHODS: RBCs were suspended at 30% hematocrit in either 46.5 g/L dextran 40 (D40, non-aggregating medium) or 35 g/L dextran 70 (D70, aggregating medium) solutions with equal viscosity. RESULTS: Aggregation was readily observed in the AMVN for RBCs suspended in D70 at driving pressures ≤40 cm H2 O. The AMVN perfusion rate was the same for RBCs suspended in aggregating and non-aggregating medium, at both 'venular' and 'capillary' level. Estimated 'capillary' hematocrit was higher for D70 suspensions than for D40 suspensions at intermediate driving pressures (5-40 cm H2 O). CONCLUSIONS: We conclude that although RBC aggregation did not affect the AMVN perfusion rate independently of the driving pressure, a higher hematocrit in the 'capillaries' of the network for D70 suspensions suggested a better oxygen transport capacity in the presence of RBC aggregation.

The optimum hematocrit.

The hematocrit (Hct) determines the oxygen carrying capacity of blood, but also increases blood viscosity and thus flow resistance. From this dual role the concept of an optimum Hct for tissue oxygenation has been derived. Viscometric studies using the ratio Hct/blood viscosity at high shear rate showed an optimum Hct of 50-60% for red blood cell (RBC) suspensions in plasma. For the perfusion of an artificial microvascular network with 5-70µm channels the optimum Hct was 60-70% for high driving pressures. With lower shear rates or driving pressures the optimum Hct shifted towards lower values. In healthy, well trained athletes an increase of the Hct to supra-normal levels can increase exercise performance. These data with healthy individuals suggest that the optimum Hct for oxygen transport may be higher than the physiological range (35-40% in women, 39-50% in men). This is in contrast to clinical observations. Large clinical studies have repeatedly shown that a correction of anemia in a variety of disorders such as chronic kidney disease, heart failure, coronary syndrome, oncology, acute gastrointestinal bleeding, critical care, or surgery have better clinical outcomes when restrictive transfusion strategies are applied. Actual guidelines, therefore, recommend a transfusion threshold of 7-8 g/dL hemoglobin (Hct 20-24%) in stable, hospitalized patients. The discrepancy between the optimum Hct in health and disease may be due to factors such as decreased perfusion pressures (low cardiac output, vascular stenoses, change in vascular tone), endothelial cell dysfunction, leukocyte adhesion and others.

Shape matters: the effect of red blood cell shape on perfusion of an artificial microvascular network.

BACKGROUND: The shape of human red blood cells (RBCs) deteriorates progressively throughout hypothermic storage, with echinocytosis being the most prevalent pathway of this morphologic lesion. As a result, each unit of stored blood contains a heterogeneous mixture of cells in various stages of echinocytosis and normal discocytes. Here we studied how the change in shape of RBCs following along the path of the echinocytic transformation affects perfusion of an artificial microvascular network (AMVN). STUDY DESIGN AND METHODS: Blood samples were obtained from healthy consenting volunteers. RBCs were leukoreduced, resuspended in saline, and treated with various concentrations of sodium salicylate to induce shape changes approximating the stages of echinocytosis experienced by RBCs during hypothermic storage (e.g., discocyte, echinocyte I, echinocyte II, echinocyte III, spheroechinocyte, and spherocyte). The AMVN perfusion rate was measured for 40% hematocrit suspensions of RBCs with different shapes. RESULTS: The AMVN perfusion rates for RBCs with discocyte and echinocyte I shapes were similar, but there was a significant decline in the AMVN perfusion rate between RBCs with shapes approximating each subsequent stage of echinocytosis. The difference in AMVN perfusion between discocytes and spherocytes (the last stage of the echinocytic transformation) was 34%. CONCLUSION: The change in shape of RBCs from normal discocytes progressively through various stages of echinocytosis to spherocytes produced a substantial decline in the ability of these cells to perfuse an AMVN. Echinocytosis induced by hypothermic storage could therefore be responsible for a similarly substantial impairment of deformability previously observed for stored RBCs.

Washing stored red blood cells in an albumin solution improves their morphologic and hemorheologic properties.

BACKGROUND: Prolonged storage of red blood cells (RBCs) leads to storage lesions, which may impair clinical outcomes after transfusion. A hallmark of storage lesions is progressive echinocytic shape transformation, which can be partially reversed by washing in albumin solutions. Here we have investigated the impact of this shape recovery on biorheologic variables. STUDY DESIGN AND METHODS: RBCs stored hypothermically for 6 to 7 weeks were washed in a 1% human serum albumin (HSA) solution. RBC deformability was measured with osmotic gradient ektacytometry. The viscosity of RBC suspensions was measured with a Couette-type viscometer. The flow behavior of RBCs suspended at 40% hematocrit was tested with an artificial microvascular network (AMVN). RESULTS: Washing in 1% albumin reduced higher degrees of echinocytes and increased the frequency of discocytes, thereby shifting the morphologic index toward discocytosis. Washing also reduced RBC swelling. This shape recovery was not seen after washing in saline, buffer, or plasma. RBC shape normalization did not improve cell deformability measured by ektacytometry, but it tended to decrease suspension viscosities at low shear rates and improved the perfusion of an AMVN. CONCLUSIONS: Washing of stored RBCs in a 1% HSA solution specifically reduces echinocytosis, and this shape recovery has a beneficial effect on microvascular perfusion in vitro. Washing in 1% albumin may represent a new approach to improving the quality of stored RBCs and thus potentially reducing the likelihood of adverse clinical outcomes associated with transfusion of blood stored for longer periods of time.

Effect of osmolality on erythrocyte rheology and perfusion of an artificial microvascular network.

Plasma sodium concentration is normally held within a narrow range. It may however vary greatly under pathophysiological conditions. Changes in osmolality lead to either swelling or shrinkage of red blood cells (RBCs). Here we investigated the influence of suspension osmolality on biophysical properties of RBCs and their ability to perfuse an artificial microvascular network (AMVN). Blood was drawn from healthy volunteers. RBC deformability was measured by osmotic gradient ektacytometry over a continuous range of osmolalities. Packed RBCs were suspended in NaCl solutions (0.45, 0.6, 0.9, 1.2, and 1.5 g/dL), resulting in supernatant osmolalities of 179 ± 4, 213 ± 1, 283 ± 2, 354 ± 3, and 423 ± 5 mOsm/kg H2O. Mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) were determined using centrifuged microhematocrit. RBC suspensions at constant cell numbers were used to measure viscosity at shear rates ranging from 0.11 to 69.5s(-1) and the perfusion rate of the AMVN. MCV was inversely and MCHC directly proportional to osmolality. RBC deformability was maximized at isosmotic conditions (290 mOsm/kg H2O) and markedly decreased by either hypo- or hyperosmolality. The optimum osmolality for RBC suspension viscosity was shifted toward hyperosmolality, while lower osmolalities increased suspension viscosity exponentially. However, the AMVN perfusion rate was maximized at 290 mOsm/kg H2O and changed by less than 10% over a wide range of osmolalities. These findings contribute to the basic understanding of blood flow in health and disease and may have significant implications for the management of osmotic homeostasis in clinical practice.

Albumin reverses the echinocytic shape transformation of stored erythrocytes.

The storage of red blood cells (RBCs) leads to storage lesions, which have a negative impact on the clinical outcome after transfusion. A hallmark of storage lesions is echinocytosis. Albumin may reverse this shape transformation, which was the topic of this study. Echinocytosis was generated by incubation of blood for 48 h at room temperature or in RBC units stored 48 days at 5°C. Human serum albumin was diluted in phosphate-buffered saline. RBCs were fixed in 1% glutaraldehyde and examined by light and scanning electron microscopy. The degree of echinocytosis was quantified by calculating the morphological index. Incubation and storage of RBCs led to an echinocytic shape transformation, which was reversible upon incubation in albumin solutions. This process was time-, concentration- and hematocrit-dependent. Treating RBC units at the end of their shelf-life by adding 20% albumin or washing them in 0.2% albumin reversed all degrees of echinocytosis towards discocytosis. In conclusion, albumin has the capacity to reverse echinocytosis generated by RBC storage. This observation may improve the quality of RBC units stored for longer periods of time.

Interaction of injectable neurotropic drugs with the red cell membrane.

The normal red blood cell (RBC) shape is a biconcave discocyte. An intercalation of a drug in the outer half of the membrane lipid bilayer leads to echinocytosis, an intercalation in the inner half to stomatocytosis. We have used the shape transforming capacity of RBCs as a model to analyse the membrane interaction potential of various neurotropic drugs. Chlorpromazine, clomipramine, citalopram, clonazepam, and diazepam induced a reversible stomatocytosis, phenytoin induced echinocytosis, while the anticonvulsants levetiracetam, valproic acid and phenobarbital had no effect. This diversity of RBC shape transformations suggests that the pharmacological action is not linked to the membrane interaction. We conclude that this simple RBC shape transformation assay could be a useful tool to screen for potential drug interactions with cell membranes.

[What is the spleen needed for?]. / Wozu braucht es die Milz?

Although the spleen is not essential for survival, it has important functions such as immune defence, blood filtration, retention and on demand extramedullary hematopoiesis. The white pulp with its T-lymphocytes in perarteriolar lymphoid sheaths and B-lymphocytes in lymphoid follicules is responsible for the detection and removal of circulating pathogens. After splenectomy, this immune defence is missing, which may lead to overwhelming post- splenectomy sepsis by encapsulated bacteria, which has a high mortality rate. In the red pulp, the blood is filtered through narrow slits in the sinusoidal endothelium, which abnormal and senescent erythrocytes can not pass and are eliminated by macrophages. The spleen is, therefore, not a "spleen" of nature, but a sophisticated organ.

Incidence and time frame of life-threatening arrhythmias in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention.

BACKGROUND: Life-threatening arrhythmias may complicate the hospital course of patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). The optimal duration of electrocardiographic monitoring in such patients is not well established. We aimed to determine the incidence and the time of occurrence of life-threatening arrhythmias in STEMI patients undergoing PPCI. METHODS: Data of 382 consecutive patients with STEMI undergoing PPCI were analysed regarding the occurrence of ventricular fibrillation (VF), sustained ventricular tachycardia (sVT) or bradycardia necessitating temporary or permanent pacing. RESULTS: Of these patients, 55% had inferior STEMI, 41% anterior and 4% lateral STEMI. The infarct-related arteries were the right in 41%, the left anterior descending in 41%, the left circumflex in 16%, the left main stem in 1% and a vein graft in <1%. During hospitalisation, 27 (7.0%) patients developed 29 life-threatening arrhythmias (incidence 7.6%): 19 episodes occurred during PPCI (VF n = 11, bradycardia n = 8), 9 episodes during the first 24 hours after PPCI (VF n = 7, sVT n = 2), and 1 sVT episode in a hypokalemic patient on the 4th post-procedural day. A total of 17 patients (4.5%) died within the first 30 days, and 3 of these died during the PPCI procedure. CONCLUSIONS: Life-threatening arrhythmias occur in a considerable proportion of STEMI patients undergoing PPCI during hospitalisation. Most of these arrhythmias occur during the PPCI procedure. Post-procedural life-threatening arrhythmias are virtually limited to the first 24 hours after PPCI. Thus, routine electrocardiographic monitoring beyond the first 24 hours after PPCI might not be required in most patients with uncomplicated STEMI.

Hypereosinophilia driven by GM-CSF in large-cell carcinoma of the lung.

In contrast to leukocytosis, paraneoplastic hypereosinophilia is uncommon in lung cancer. We present a patient with large-cell carcinoma of the lung, in which cancer cells generate large amounts of GM-CSF leading to a leukemoid reaction with prominent hypereosinophilia and potentially involved in autocrine tumor stimulation.

Incidence of acute myocardial infarction after implementation of a public smoking ban in Graubünden, Switzerland: two year follow-up.

QUESTION UNDER STUDY: In the first year after implementation of a public smoking ban a significant decrease in the incidence of acute myocardial infarction (AMI) was observed in Graubünden. In the present study we analyzed the incidence of AMI in the second year of the ban. In addition, we investigated the contribution of smoking ban-unrelated factors to the reduced incidence of AMI incidence observed after enactment of the ban. METHODS: Data of all AMI patients who underwent coronary angiography at the Kantonsspital Graubünden, the only tertiary care hospital with a cardiac catheterization laboratory in Graubünden, between March 1st, 2009 and February 28th, 2010 were collected prospectively. Data were compared with those of the three preceding 12-month periods. We also estimated AMI incidence during the corresponding time period in Lucerne, a region with no smoke-free legislation, using data of the AMIS Plus registry. The influence of outdoor air pollution was analyzed with the help of official measurements of PM(10)- and NO(2)-concentrations in Graubünden. The prescription of lipid-lowering drugs was estimated by using sales figures in Graubünden and Lucerne. RESULTS: In Graubünden, the number of patients with AMI in the second year after adoption of the smoking ban was similar to that in the first year of the ban (188 vs. 183; P = ns) and significantly lower than in each of the two years preceding the ban (229 and 242, respectively; P <0.05 vs. each of the 12-month periods after the ban). Overall, the number of AMI patients in the two post-ban years was 21% lower than in the two pre-ban years. The reduction in the number of patients with AMI was most pronounced in non-smokers and individuals with known coronary artery disease. During the corresponding time period, no similar decrease in the incidence of AMI was observed in Lucerne. No association was found between the magnitude of outdoor air pollution and the incidence of AMI. During the observation period, the use of lipid-lowering drugs increased similarly in Graubünden and Lucerne. CONCLUSIONS: Compared with the two years preceding the implementation of a smoking ban, the incidence of AMI remained significantly reduced in the second year of the ban in Graubünden, whereas no similar reduction was seen in a comparable area without smoke-free legislation. Changes in outdoor air pollution or the use of lipid-lowering drugs did not substantially contribute to the decrease in the incidence of AMI that occurred after adoption of the ban in Graubünden.

Effect of brief secondhand smoke exposure on endothelial function and circulating markers of inflammation.

OBJECTIVE: In contrast to the well defined detrimental consequences of long-term secondhand smoke (SHS) exposure, little is known about the acute effects of passive smoking on endothelial function and inflammation. The aim of the present study was to assess the acute effects of short-term SHS exposure on endothelial function and circulating markers of inflammation. METHODS: Peripheral microvascular endothelial function assessed by reactive hyperemia peripheral arterial tonometry (RH-PAT) index, circulating markers of endothelial function (von Willebrand factor antigen, Thrombomodulin, E-selectin) and circulating inflammatory markers (high sensitivity C-reactive protein (hsCRP), Interleukin-6 (IL-6)) were measured in eighteen male, non-smoking volunteers before and 12h after a 1-h SHS exposure. RESULTS: Twelve hours after passive smoking, average RH-PAT index was significantly lower than before SHS exposure (1.54±0.49 vs 2.01±0.55 (mean±SD), p=0.01) indicating deterioration of peripheral microvascular endothelial function. von Willebrand factor antigen as a marker of endothelial activation was significantly increased after SHS exposure (93.0±25.5% vs 78.4±17.9%, p=0.03). Levels of Thrombomodulin, E-selectin, hsCRP, and IL-6 were unaffected by SHS exposure. CONCLUSION: Short-term SHS exposure leads to a measurable disturbance of endothelial function. However, 1h of passive smoking appears to be too short to elicit a significant inflammatory response.

Complement inhibition to treat myocardial infarction?

The authors describe the case of a middle-aged women who presented with an acute myocardial infarction due to thrombotic occlusion of angiographically normal coronary arteries. Coronary thrombosis was caused by a hypercoagulable state related to a haemolytic crisis of paroxysmal nocturnal haemoglobinuria and the patient was treated conservatively with antithrombotic agents. The clinical course was complicated by both severe bleeding and thrombotic complications and the patient eventually died of a massive intracerebral haemorrhage. The rapid occurrence of complications inhibited a timely administration of a specific treatment for complement-mediated haemolysis (eculizumab).

[Between thrombosis and bleeding - a case of paroxysmal nocturnal hemoglobinuria]. / Auf dem schmalen Grat zwischen Thrombosen und Verbluten.

A 67-year-old lady was admitted with a myocardial infarction. Coronarography revealed thrombotic material within coronary arteries. The underlying disease was paroxysmal nocturnal hemoglobinuria (PNH), a stem cell defect characterized by episodes of complement-induced hemolysis and thromboembolic events. Anticoagulation and antiaggregation were initiated. Subsequently, massive cerebral bleeding developed, to which the patient finally succumbed despite neurosurgical craniectomy. This tragic case illustrates that an antithrombotic treatment is always a balancing act with an unsecure outcome.