Search

We hypothesize that thrombosis with thrombocytopenia syndrome recently described after administration of adenovirus‐vectored vaccines for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) occurs as a result of the unique properties of the adenovirus vectors, which can have widespread biodistribution throughout the body. The antigen is delivered to megakaryocyte cells, which act as part of the primary immune system and distribute the antigen within progeny platelets, also a key component of the immune system. The interaction of the antigen induces preformed antiplatelet factor 4 (PF4) antibodies to bind to PF4–heparan sulfate complexes in the absence of exogenous heparin, at sites where the heparan sulfate concentration in the vascular glycocalyx is optimal for complex formation, causing thrombosis and thrombocytopenia as observed clinically. This hypothesis is testable in cell culture and animal models, and potentially in vivo, and if proven correct has significant implications for vaccine development and our understanding of the links between the coagulation and immune systems., We hypothesize that thrombosis with thrombocytopenia syndrome recently described after administration of adenovirus‐vectored vaccines for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) occurs as a result of the unique properties of the adenovirus vectors, which can have widespread biodistribution throughout the body. The antigen is delivered to megakaryocyte cells, which act as part of the primary immune system and distribute the antigen within progeny platelets, also a key component of the immune system. The interaction of the antigen induces preformed antiplatelet factor 4 (PF4) antibodies to bind to PF4–heparan sulfate complexes in the absence of exogenous heparin, at sites where the heparan sulfate concentration in the vascular glycocalyx is optimal for complex formation, causing thrombosis and thrombocytopenia as observed clinically.

Platelets are a key component of the hemostatic system and their roles in inflammation via interactions with leukocytes have also gained attention in recent years. Changes in platelet phenotype and function can cause bleeding and/or thrombosis and, as such, monitoring platelet-specific changes is crucial to assessing hemostasis in the clinical setting. Currently, available platelet function tests such as platelet aggregometry and thromboelastography require a large volume of blood, which is a major limitation for the pediatric population. Whole blood flow cytometric analysis of platelets is increasingly utilized in recent years, primarily due to the sensitivity of this method, but also because it only requires a small amount of blood with minimal sample manipulation. We have developed a whole blood flow cytometry methodological approach that enables the assessment of platelet phenotype, function, and their interactions with monocytes and neutrophils.

Epidemiological studies have demonstrated that survivors of acute burn trauma are at long-term increased risk of developing a range of morbidities. The mechanisms underlying this increased risk remain unknown. This study aimed to determine whether burn injury leads to sustained immune dysfunction that may underpin long-term morbidity. Plasma and peripheral blood mononuclear cells were collected from 36 pediatric burn survivors >3 years after a non-severe burn injury (

Evidence-based guidelines recommend exercise therapy for patients with chronic heart failure (CHF). Such patients have increased atherothrombotic risk. Exercise can transiently increase platelet activation and reactivity and decrease vascular function in healthy participants, although data in CHF are scant. Eccentric (ECC) cycling is a novel exercise modality that may be particularly suited to patients with CHF, but the acute impacts of ECC cycling on platelet and vascular function are currently unknown. Our null hypothesis was that ECC and concentric (CON) cycling, performed at matched external workloads, would not induce changes in platelet or vascular function in patients with CHF. Eleven patients with heart failure with reduced ejection fraction (HFrEF) took part in discrete bouts of ECC and CON cycling. Before and immediately after exercise, vascular function was assessed by measuring diameter and flow-mediated dilation (FMD) of the brachial artery. Platelet function was measured by the flow cytometric determination of glycoprotein IIb/IIIa activation and granule exocytosis in the presence and absence of platelet agonists. ECC cycling increased baseline artery diameter (pre: 4.0 ± 0.8 mm vs. post: 4.2 ± 0.7 mm; P = 0.04) and decreased FMD%. When changes in baseline artery diameter were accounted for, the decrease in FMD post-ECC cycling was no longer significant. No changes were apparent after CON. Neither ECC nor CON cycling resulted in changes to any platelet-function measures (all P > 0.05). These results suggest that both ECC and CON cycling, at a moderate intensity and short duration, can be performed by patients with HFrEF without detrimental impacts on vascular or platelet function. NEW & NOTEWORTHY This is the first evidence to indicate that eccentric (ECC) cycling can be performed relatively safely by patients with chronic heart failure (CHF), as it did not result in impaired vascular or platelet function compared with conventional cycling. This is important, as acute exercise can transiently increase atherothrombotic risk, and ECC cycling is a novel exercise modality that may be particularly suited to patients with CHF.

Platelet activation, including the formation of monocyte platelet aggregates (MPAs), contributes to atherosclerosis, thrombus formation, and acute coronary syndromes. Regular participation in exercise can lower cardiovascular risk, but little is known regarding the impact of exercise training on platelet function. We investigated the effect of 6 mo of walking exercise on platelet function in sedentary older adults without significant cardiovascular disease. Twenty-seven participants were randomly allocated to 6 mo of either: no-exercise ( n = 13) or 3 × 50 min/wk of supervised center-based walking ( n = 14). Circulating and agonist-induced MPAs were assessed using flow cytometry before [ month 0 (0M)] and after [ month 6 (6M)] the intervention. Circulating MPAs increased from 0M (3.7 ± 1.0%) to 6M (4.7 ± 1.6%) in the no-exercise group ( P = 0.009), whereas a nonsignificant decrease was observed in the walking group (0M 4.3 ± 1.7 vs. 6M 3.7 ± 1.2 %, P = 0.052). The change in MPAs between groups was significant ( P = 0.001). There were no differences between groups in platelet responses to agonists across the interventions (all P > 0.05). Collectively, these data suggest that the absence of regular exercise may increase MPAs, which are cellular mediators involved in atherosclerosis, while regular walking inhibits such increases. The thrombotic function of platelets appears to be relatively unaltered by exercise training. This study provides novel data related to the cardioprotective effects associated with participation in exercise.NEW & NOTEWORTHY Monocyte-platelet aggregates contribute to atherosclerosis and exercise can lower cardiovascular risk. This is the first study to discover that a lack of regular physical activity is associated with increased monocyte-platelet aggregates over a 6-mo intervention period. In contrast, walking exercise inhibits increased monocyte-platelet aggregates in the circulation. This study highlights a novel pathway by which regular participation in exercise exerts its cardioprotective effects.

Polycystic ovarian syndrome (PCOS) affects 12 to 19% of women and has reproductive and metabolic features (endothelial dysfunction, increased diabetes, and cardiovascular risk factors). It also appears to have altered coagulation and fibrinolysis with a prothrombotic state with epidemiological evidence of increased venous thromboembolism. We aimed to comprehensively assess hemostasis in women with PCOS versus control women. In an established case-control cohort of lean, overweight, and obese women with (n = 107) and without PCOS (n = 67), with existing measures of plasminogen activator inhibitor 1 (PAI-1), asymmetric dimethylarginine (ADMA), hormonal, and metabolic markers, we also assessed prothrombin fragments 1 and 2 (PF1 & 2), plasminogen, tissue plasminogen activator (tPA), and thrombin generation (TG). Higher levels of ADMA (0.70 vs. 0.39 µmol/L, p

Diabetes is associated with increased cardiovascular risk. We have recently shown that the naturally occurring flavonol quercetin (Que) or the synthetic flavonol 3′,4′-dihydroxyflavonol (DiOHF) inhibits platelet function and delays thrombus formation in healthy mice. Therefore, the aim of this study was to investigate the effect of Que or DiOHF treatment on platelet function and ferric chloride–induced carotid artery thrombosis in a mouse model of type 1 diabetes. Diabetic mice treated with Que or DiOHF maintained blood flow at a significantly higher level than untreated diabetic mice at the end of the recording period. In addition, treatment with Que or DiOHF significantly reduced diabetes-induced platelet hyper-aggregability in response to platelet agonist stimulation. Furthermore, treatment with Que or DiOHF significantly inhibited dense, but not alpha, granule exocytosis in diabetic and control mice. Our demonstration that flavonols delay thrombus formation in diabetes suggests a potential clinical role for these compounds in anti-platelet therapy.

Background: Whilst resistance training has been proven to convey considerable benefits to olderpeople; immediately post-exercise there may be elevated transient risks for cardiac events and falls. Objectivesand Measurements:We assessed the acute effects of eccentrically-biased (EB) and conventional (CONV)resistance exercise on: platelet number, activation and granule exocytsosis; and mean velocity of centre ofpressure displacement (Vm). Design, Setting, Participants and Intervention:Ten older adults (7 males, 3females; 69 ± 4 years) participated in this randomised controlled cross-over study in which they performed EBand CONV training sessions that were matched for total work and a control condition. Results:Immediately post-exercise there was a statistically significant difference in platelet count between the control condition, in which ithad declined (pre 224 ± 35 109/L; post 211 ± 30 109/L: P < 0.05) and CONV in which it had increased (pre 236 ±55 109/L; post 242 ± 51 109/L: P > 0.05). There was no change in platelet activation and granule exocytsosis orVm following EB and CONV. Conclusions:Overall, while minor differences between regimens were observed,no major adverse effect on parameters of platelet function or centre of pressure displacement were observedacutely following either regimen. Eccentrically-biased and conventional resistance exercise training regimens donot appear to present an elevated acute risk in the context of changes to platelet function contributing to a cardiacevent or postural stability increasing falls risk for apparently healthy older adults.

Clinical Development Phases I-III Regulatory, Quality, Manufacturing Platelets are subcellular fragments in blood whose activation is central to atherothrombosis and cardiovascular events. Platelet activation is complex, with multiple pathways of initiation and amplification involved. Antiplatelet drugs may target any of these pathways to diminish the propensity of platelets to become activated. The most well-established antiplatelet drugs, aspirin and thienopyridines, target the thromboxane and adenosine diphosphate auto-amplification pathways of platelet activation, respectively. These are very effective medicines, but response varies and residual on-treatment platelet function is associated with poorer clinical outcomes. Alternative antiplatelet therapies are available and more are in development. Therefore, tailoring antiplatelet therapy to on-treatment platelet activation is an appealing strategy and the subject of investigation. There are many different approaches to measuring platelet activation and response to stimulation with antiplatelet therapy, but there is very little agreement between them regardless of the cutoffs used. Therefore, selection of the appropriate platelet function test is important in assessing on-treatment platelet activation for guided therapy. Recent research has shown that tailoring antiplatelet therapy can improve these laboratory measures of platelet activation, but clinical studies that assess cardiovascular benefit against potential for increased bleeding are required.

AB Purpose: Hyperactive platelets contribute to the thrombotic response in humans, and exercise transiently increases platelet function. Caffeine is routinely used by athletes as an ergogenic aid, but the combined effect of exercise and caffeine on platelet function has not been investigated. Methods: Twelve healthy males were randomly assigned to one of four groups and undertook four experimental trials of a high-intensity aerobic interval training (AIT) bout or rest with ingestion of caffeine (3 mg[middle dot]kg-1) or placebo. AIT was 8 x 5 min at approximately 75% peak power output (approximately 80% V[spacing dot above]O2peak) and 1-min recovery (approximately 40% peak power output, approximately 50% V[spacing dot above]O2peak) intervals. Blood/urine was collected before, 60, and 90 min after capsule ingestion and analyzed for platelet aggregation/activation. Results: AIT increased platelet reactivity to adenosine diphosphate (placebo 30.3%, caffeine 13.4%, P < 0.05) and collagen (placebo 10.8%, caffeine 5.1%, P < 0.05) compared with rest. Exercise placebo increased adenosine diphosphate-induced aggregation 90 min postingestion compared with baseline (40.5%, P < 0.05), but the increase when exercise was combined with caffeine was small (6.6%). During the resting caffeine protocol, collagen-induced aggregation was reduced (-4.3%, P < 0.05). AIT increased expression of platelet activation marker PAC-1 with exercise placebo (P < 0.05) but not when combined with caffeine. Conclusion: A single bout of AIT increases platelet function, but caffeine ingestion (3 mg[middle dot]kg-1) does not exacerbate platelet function at rest or in response to AIT. Our results provide new information showing caffeine at a dose that can elicit ergogenic effects on performance has no detrimental effect on platelet function and may have the potential to attenuate increases in platelet activation and aggregation when undertaking strenuous exercise.

Flavonols are polyphenolic compounds with broad-spectrum kinase inhibitory, as well as potent anti-oxidant and anti-inflammatory properties. Anti-platelet potential of quercetin (Que) and several related flavonoids have been reported; however, few studies have assessed the ability of flavonols to inhibit exocytosis of different platelet granules or to inhibit thrombus formation in vivo. 3',4'-Dihydroxyflavonol (DiOHF) is a flavonol which is structurally related to Que and has been shown to have greater anti-oxidant capacity and to improve the endothelial function in the context of diabetes and ischaemia/reperfusion injury. While the structural similarity to Que suggests DiOHF may have a potential to inhibit platelet function, no studies have assessed the anti-platelet potential of DiOHF. We therefore investigated platelet granule inhibition and potential to delay arterial thrombosis by Que and DiOHF. Both Que and DiOHF showed inhibition of collagen, adenosine diphosphate and arachidonic acid stimulated platelet aggregation, agonist-induced GPIIb/IIIa activation as demonstrated by PAC-1 and fibrinogen binding. While both flavonols inhibited agonist-induced granule exocytosis, greater inhibition of dense granule exocytosis occurred with DiOHF as measured by both ATP release and flow cytometry. In contrast, while Que inhibited agonist-induced P-selectin expression, as measured by both platelet surface P-selectin expression and upregulation of surface GPIIIa expression, inhibition by DiOHF was not significant for either parameter. C57BL/6 mice treated with 6 mg kg(-1) IV Que or DiOHF maintained greater blood flow following FeCl3-induced carotid artery injury when compared to the vehicle control. We provide evidence that Que and DiOHF improve blood flow following arterial injury in part by attenuating platelet granule exocytosis.

People with diabetes have an increased risk of life-threatening cardiovascular disease compared to the general population. Furthermore, people with diabetes are at greatly increased risk of not responding to standard anti-platelet therapy, such as aspirin, for the prevention of atherothrombotic events. This phenomenon is often referred to as treatment failure. Those who are at increased risk of such events despite aspirin therapy can be prospectively identified by a variety of laboratory measures of residual on-treatment platelet function, known as aspirin resistance. However, there is little agreement among laboratories on the approaches to these measurements, and insufficient data to guide the clinical management of people with diabetes-associated aspirin resistance if it is prospectively identified. This review provides a critical appraisal of the different approaches to the detection and evidence of mechanisms which contribute to this phenomenon, as well evidence for the potential effectiveness of different clinical approaches to overcoming aspirin treatment failure in diabetes. Potential mechanisms of aspirin resistance in diabetes include elevated platelet turnover that results in an immature platelet fraction able to synthesise the uninhibited therapeutic target of aspirin, cyclooxygenase-1 (COX-1); residual thromboxane production by both COX-1-dependent and COX-1-independent pathways; up-regulation of aspirin-insensitive pathways of platelet function, such as adenosine diphosphate signalling; and increased underlying atherosclerotic disease burden that results in elevated underlying platelet hyper-reactivity. High on-aspirin platelet reactivity in diabetes may be related to glycemic control. Potential approaches to treatment include controlling modifiable risk factors to achieve effective glycemic control, guided increases in aspirin dose or frequency of administration, or the use of additional antiplatelet therapies. While evidence suggests that altering antiplatelet therapy, particularly by increasing frequency of aspirin administration, can overcome incomplete inhibition of thromboxane synthesis, no clinical studies to date have assessed the effectiveness of these in preventing breakthrough atherothrombosis. While some clinicians currently alter therapy on the basis of theoretical potential benefit of these strategies following identification of aspirin resistance in the laboratory, this is not yet supported by clinical evidence of a benefit, and clear clinical guidelines for the management of aspirin resistance are lacking.

Taurine, 2-aminoethanesulphonic acid is a common ingredient of energy drinks which is very popular with young adults. Taurine in energy drinks is known to enhance muscular performance in athletes. However, caffeine in high concentrations as found in most energy drinks have also been implicated to play an adverse role leading to cardiovascular diseases (CVD). Hyper activation of platelets is one of the major risk factors of CVD. The aim of the study was to evaluate effect of taurine alone on platelet aggregation and activation of platelet surface antigens by flowcytometry. It is hypothe- sized that taurine's antioxidant property would inhibit platelet activity. Twelve healthy, male and female, volunteers aged 20-60 years were recruited for this study. A statistically significant inhibition of platelet aggregation was observed upon stimulation with agonists adenosine diphosphate (ADP), collagen and arachidonic acid (AA) (p

The term resistance has been applied to interindividual variability in platelet reactivity during antiplatelet therapy or to thrombosis despite appropriate therapy. In particular "aspirin resistance" and "clopidogrel resistance" have been the subject of intense investigation for their association with poor cardiovascular outcomes. Several mechanisms have been investigated including resistance arising from poor bioavailability, especially in clopidogrel therapy as resulting from a loss of function variant in hepatic metabolism required for prodrug activation. A limitation of studies linking on-treatment reactivity and clinical outcome is that they have been performed in high-risk patients with recent atherothrombotic disease. On-treatment platelet reactivity correlates with acuity of recent atherothrombosis, and variability in pretreatment platelet function predicts on-treatment platelet function for both aspirin and clopidogrel. It is therefore likely that high on-treatment platelet function at the time of testing may often result from underlying platelet hyperreactivity related to acute atherothrombosis, rather than true pharmacological resistance. The association of high on-treatment platelet reactivity with poor clinical outcomes may therefore be attributed to variability in underlying burden of disease instead of, or in addition to, pharmacological resistance to antiplatelet therapy.

Polycystic ovarian syndrome (PCOS), diagnosed based on hyperandrogenism, ovulatory dysfunction, and polycystic ovaries, is one of the most common disorders of reproductive-aged females. Etiology includes both genetic and environmental/lifestyle factors contributing to both insulin resistance and hyperandrogenism. Clinically, PCOS has reproductive, psychological, and metabolic features, the latter predisposing to cardiovascular disease (CVD). Hemostatic abnormalities have an association with and a demonstrated pathophysiological role in CVD in non-PCOS populations but have not been adequately explored in PCOS. This review focuses on the hemostatic system in PCOS, exploring also relationships to the metabolic and hormonal abnormalities of the syndrome, and aims to identify whether hemostatic abnormalities are present as potential contributors to increased cardiovascular risk. Ultimately, this area may reveal preventative and therapeutic opportunities, which could improve the cardiovascular health of women with PCOS.

Platelets are small, anucleate blood elements of critical importance in cardiovascular disease. The ability of platelets to activate and aggregate to form blood clots in response to endothelial injury, such as plaque rupture, is well established. These cells are therefore important contributors to ischaemia in atherothrombosis, and antiplatelet therapy is effective for this reason. However, growing evidence suggests that platelets are also important mediators of inflammation and play a central role in atherogenesis itself. Interactions between activated platelets, leukocytes and endothelial cells trigger autocrine and paracrine activation signals, resulting in leukocyte recruitment at and into the vascular wall. Direct physical interaction may contribute also, through platelet adhesion molecules assisting localization of monocytes to the site of atherogenesis and platelet granule release contributing to the chronic inflammatory milieu which leads to foam cell development and accelerated atherogenesis. Recent studies have shown that antiplatelet therapy in animal models of accelerated atherogenesis can lead to decreased plaque size and improve plaque stability. This review examines the complexity of platelet function and the nature of interactions between activated platelets, leukocytes and endothelial cells. We focus on the growing body of evidence that platelets play a critical role in atherogenesis and contribute to progression of atherosclerosis.

Release of serotonin and activation of serotonin 5HT2A receptors on platelet surfaces is a potent augmentative stimulus for platelet aggregation. However, earlier-generation serotonin receptor antagonists were not successfully exploited as antiplatelet agents, possibly owing to their lack of specificity for the 5HT2A receptor subtype.To assess whether targeted inhibition of the serotonin 5HT2A receptor attenuates recurrent thrombosis and improves coronary patency in an in vivo canine model mimicking unstable angina.In protocol 1, anesthetized dogs were pretreated with a novel, selective inverse agonist of the 5HT2A receptor (APD791) or saline. Recurrent coronary thrombosis was then initiated by coronary artery injury+stenosis, and coronary patency was monitored for 3 h. Protocol 2 was similar, except that: (i) treatment with APD791 or saline was begun 1 h after the onset of recurrent thrombosis; (ii) template bleeding time was measured; and (iii) blood samples were obtained for in vitro flow cytometric assessment of platelet responsiveness to serotonin.APD791 attenuated recurrent thrombosis, irrespective of the time of treatment: in both protocols, flow-time area (index of coronary patency; normalized to baseline coronary flow) averaged 58-59% (P0.01) following administration of APD791 vs. 21-28% in saline controls. Moreover, the in vivo antithrombotic effect of APD791 was not accompanied by increased bleeding, but was associated with significant and selective inhibition of serotonin-mediated platelet activation.5HT2A receptor inhibition with APD791, even when initiated after the onset of recurrent thrombosis, improves coronary patency in the in vivo canine model.

Background— Poor clinical outcome in aspirin-treated patients has been termed aspirin resistance and may result from inadequate inhibition of platelet cyclooxygenase-1 (COX-1) by aspirin. The objectives of this study were to determine prospectively whether COX-1-dependent and other platelet function assays correlate with clinical outcomes in aspirin-treated patients. Methods and Results— Blood was collected before percutaneous coronary intervention from 700 consecutive aspirin-treated (81 or 325 mg for ≥3 days) patients. Platelet function was tested by (1) serum thromboxane B 2 ; (2) arachidonic acid-stimulated platelet surface P-selectin and activated glycoprotein IIb/IIIa and leukocyte-platelet aggregates; and (3) platelet function analyzer (PFA)-100 collagen-epinephrine and collagen-ADP closure time (CT). Adverse clinical outcomes of all-cause death, cardiovascular death, and major adverse cardiovascular events (cardiovascular death, myocardial infarction, hospitalization for revascularization, or acute coronary syndrome) were assessed by telephone interview and/or medical record review. Clinical outcomes information was obtained at 24.8±0.3 months after platelet function testing. By univariate analysis, COX-1-dependent assays, including serum thromboxane B 2 level, were not associated with adverse clinical outcomes, whereas the COX-1-independent assay, PFA-100 collagen-ADP CT P =0.0149). After adjustment for covariables (including sex, aspirin dose, Thrombolysis in Myocardial Infarction risk score, clopidogrel use), both serum thromboxane B 2 >3.1 ng/mL and PFA-100 collagen-ADP CT Conclusions— In this prospective study of 700 aspirin-treated patients presenting for angiographic evaluation of coronary artery disease, residual platelet COX-1 function measured by serum thromboxane B 2 and COX-1-independent platelet function measured by PFA-100 collagen-ADP CT, but not indirect COX-1-dependent assays (arachidonic acid-stimulated platelet markers, shortened PFA-100 collagen-epinephrine CT), correlate with subsequent major adverse cardiovascular events. This study suggests that multiple mechanisms, including but not confined to inadequate inhibition of COX-1, are responsible for poor clinical outcomes in aspirin-treated patients, and therefore the term aspirin resistance is inappropriate.

Introduction Adenosine A2 agonists improve arterial patency in experimental models of recurrent thrombosis, an effect purportedly triggered by stimulation of platelet A2 receptors and subsequent down-regulation of platelet function. However: (i) there is no direct evidence to substantiate this premise; and (ii) given the recognized differences among species in platelet signaling, it is possible that the mechanisms of A2 receptor stimulation may be model-dependent. Accordingly, we applied an integrated in vivo and in vitro approach, using both canine and human models, to test the hypothesis that the anti-thrombotic effects of A2 agonist treatment are due in part to inhibition of platelet activation. Methods In Protocol 1, recurrent coronary thrombosis was triggered in anesthetized dogs by application of a stenosis at a site of arterial injury. Coronary patency and flow cytometric indices of platelet activation (P-selectin expression; formation of heterotypic aggregates) were compared in dogs pre-treated with the A2 agonist CGS 21680 versus controls. In Protocols 2 and 3, blood samples were obtained from dogs and human volunteers. In vitro aggregation and platelet activation (assessed by impedance aggregometry and flow cytometry, respectively) were quantified in paired aliquots pre-incubated with CGS versus vehicle. Results In the canine models, CGS improved in vivo coronary patency and attenuated in vitro aggregation but, contrary to our hypothesis, did not evoke a down-regulation in platelet activation. In contrast, in human blood samples, CGS attenuated both in vitro aggregation and flow cytometric markers of platelet activation–aggregation. Conclusion The mechanisms contributing to the anti-thrombotic effect of A2 agonist treatment are species-dependent: adenosine A2 receptor stimulation inhibits platelet activation in human, but not canine, models.

Introduction: We have previously demonstrated platelet hyperreactivity in cystic fibrosis (CF) patients. Carriers of one CF mutation (heterozygotes) have been shown to have abnormalities related to the presence of only one-half the normal amount of CF transmembrane conductance regulator protein. Platelet hyperreactivity in CF heterozygotes would be an important cardiovascular risk factor, since approximately 1 in 25 Caucasians is a CF carrier. Materials and methods: We used highly sensitive assays of platelet activation to assess the difference between 16 CF heterozygotes and 16 age- and sex-matched healthy controls without CF mutations. Results: We found no difference in platelet activation between CF heterozygotes and controls. Conclusions: The 50% reduction in the CF transmembrane conductance regulator protein in heterozygotes is insufficient to cause platelet activation.

Summary. Background: Clopidogrel is a widely used antithrombotic agent that inhibits the platelet P2Y12 adenosine diphosphate (ADP) receptor. There is increasing interest in ‘clopidogrel resistance’. Objectives: To determine whether ‘clopidogrel resistance’ is accounted for by a pre-existent variability in platelet response to ADP. Methods: Platelet response to 20 μm ADP was analyzed by four independent whole blood flow cytometric assays: platelet surface activated GPIIb-IIIa, platelet surface P-selectin, monocyte-platelet aggregates and neutrophil-platelet aggregates. In 25 consecutive, non-aspirin-treated healthy subjects, we studied platelet response before and after clopidogrel administration. In addition, we studied the platelet response in 613 consecutive aspirinated patients with or without coronary artery disease (CAD, as determined by angiography) who had or had not been treated with clopidogrel. In these patients, we tested for homogeneity of variance across all durations of clopidogrel exposure and severity of CAD by estimating the ‘goodness of fit’ of two independent models. Results: In the healthy subjects, pre-clopidogrel response to ADP predicted post-clopidogrel response to ADP. In the patients, clopidogrel, as expected, inhibited the platelet response to ADP. However, irrespective of the duration of clopidogrel administration, the severity of CAD, and the dose of aspirin, clopidogrel did not increase the variance in the platelet response to ADP in any of the four assays of platelet response. Conclusions: These studies provide evidence that ‘clopidogrel resistance’ is accounted for by a pre-existent variability in platelet response to ADP and this variability is not increased by clopidogrel administration.

Summary. Background: Previous studies have shown that ischemic preconditioning (PC) not only limits infarct size, but also improves arterial patency in models of recurrent thrombosis. We hypothesize that this enhanced patency is presumably because of a PC-induced attenuation of platelet-mediated thrombosis. However, there is, at present, no direct evidence that PC acts on the platelets per se and favorably down-regulates platelet reactivity. Objectives: Our goal was to test the concept that PC ischemia attenuates molecular indices of platelet activation-aggregation. Methods: Anesthetized dogs were randomly assigned to receive 10 min of PC ischemia followed by 10 min of reperfusion or a time-matched control period. Spontaneous recurrent coronary thrombosis was then initiated in all dogs by injury + stenosis of the left anterior descending coronary artery. Coronary flow was monitored for 3 h poststenosis, and molecular indices of platelet activation-aggregation were quantified by whole blood flow cytometry. Results: Coronary patency was, as expected, better-maintained following injury + stenosis in the PC group vs. controls (53% ± 5%* vs. 23% ± 5% of baseline flow, respectively; *P

Background— Thrombotic events still occur in aspirin-treated patients with coronary artery disease. Methods and Results— To better understand aspirin “resistance,” serum thromboxane B 2 (TXB 2 ) and flow cytometric measures of arachidonic acid–induced platelet activation (before and after the ex vivo addition of aspirin and indomethacin) were analyzed in 700 consecutive aspirin-treated patients undergoing cardiac catheterization. In 680 of 682 evaluable patients, serum TXB 2 concentrations were reduced compared with nonaspirinated healthy donors. Twelve patients had serum TXB 2 that was lower than nonaspirinated healthy donors but >10 ng/mL. Arachidonic acid stimulated greater platelet activation in patients with high serum TXB 2 (>10 ng/mL) than in patients with low serum TXB 2 . Addition of ex vivo aspirin reduced arachidonic acid–induced platelet activation to similar levels regardless of serum TXB 2 concentrations, which suggests that patients with high residual serum TXB 2 concentrations were either noncompliant or underdosed with aspirin. Among the remaining 98% of patients, ex vivo administration of either aspirin or indomethacin failed to prevent platelet activation across all degrees of arachidonic acid–induced platelet activation and aspirin doses. Although the patients were not randomized with respect to clopidogrel treatment, multivariate analysis showed that arachidonic acid–induced platelet activation was less in patients receiving clopidogrel. Conclusions— There is a residual arachidonic acid–induced platelet activation in aspirin-treated patients that (1) is caused by underdosing and/or noncompliance in only &2% of patients and (2) in the remaining patients, occurs via a cyclooxygenase-1 and cyclooxygenase-2 independent pathway, in direct proportion to the degree of baseline platelet activation, and is mediated in part by adenosine diphosphate–induced platelet activation.

Aspirin, the most widely used antiplatelet agent, irreversibly acetylates the enzyme cyclooxygenase 1 (COX-1), thereby inhibiting platelet thromboxane synthesis and subsequent platelet aggregation. Although aspirin has been demonstrated to reduce the odds of serious atherothrombotic events and death in high-risk patients by 25%, subsets of patients fail to respond to therapy and continue to suffer atherothrombotic events. This aspirin treatment failure may be due to sub-optimal bioavailability (e.g. because of non-compliance or under-dosing) or may be a consequence of the as yet poorly understood phenomenon of aspirin resistance. In this review, we summarize the current laboratory methods used to identify aspirin-resistant patients, outline the cellular mechanisms that may contribute to aspirin resistance, and discuss the clinical implications of this important issue.

Objectives The purpose of this study was to examine the effects of glycoprotein (GP) IIb/IIIa antagonists (abciximab, eptifibatide, and tirofiban) and other inhibitors on translocation of CD40L from intraplatelet stores to the platelet surface and on the release of soluble CD40L (sCD40L) from platelets. Background CD40L is a proinflammatory and prothrombotic ligand in the tumor necrosis factor family. Methods Platelet surface CD40L was measured by flow cytometry, and sCD40L was measured by enzyme-linked immunosorbent assay. Results Translocation of CD40L from intraplatelet stores to the platelet surface was not inhibited by GP IIb/IIIa antagonists. However, release of sCD40L from the surface of activated platelets was inhibited by GP IIb/IIIa antagonists in a dose-dependent manner, in concert with inhibition of PAC1 binding to platelets (a surrogate marker for fibrinogen binding). Release of sCD40L from activated platelets was also markedly reduced in Glanzmann platelets (deficient in GP IIb/IIIa). Ethylenediaminetetraacetic acid was an effective inhibitor of sCD40L release, but only when added before platelet activation. Both cytochalasin D (an inhibitor of actin polymerization) and GM6001 (an inhibitor of matrix metalloproteinases [MMPs]) inhibited the release of sCD40L from platelets when added before, as well as 3 min after, platelet activation. However, neither cytochalasin D nor GM6001 affected translocation of CD40L to the platelet surface. Conclusions The GP IIb/IIIa antagonists inhibit release of sCD40L from activated platelets. Release of sCD40L from platelets is regulated, at least in part, by GP IIb/IIIa, actin polymerization, and an MMP inhibitor-sensitive pathway. In addition to their well-characterized inhibition of platelet aggregation, GP IIb/IIIa antagonists may obviate the proinflammatory and prothrombotic effects of sCD40L.

Cardiac surgery involving cardiopulmonary bypass is a common yet complex procedure that results in considerable disruption of hemostasis during and following surgery. Despite the relatively common and widespread use of this procedure, there remains a significant peri-operative risk of both thrombosis and hemorrhage in some patients. This is known as the hemostatic defect of cardiopulmonary bypass. Strategies including the use of pharmacological agents, hemodilution, autologous blood transfusion, rapid in-theatre monitoring of hemostatic potential with fine-tuning of the degree of heparinization, minimally invasive surgery and the use of biologically coated cardiopulmonary bypass equipment have been employed to ameliorate the effects of cardiopulmonary bypass on hemostasis. However there exists a fine line between preventing hemorrhage and promoting thrombosis. Likewise attempts to prevent thrombosis may result in increased hemorrhage. Research into many strategies for minimizing the hemostatic defect of cardiopulmonary bypass is incomplete, with safety and efficacy the subjects of intensive investigation.

Background A single bout of strenuous running exercise results in perturbations to numerous biomarkers. An understanding of these is important when analysing samples from individuals who have recently performed such exercise. Methods A literature search was undertaken using the search terms, exercise, marathon and delayed onset of muscle soreness. The search was then refined using the terms for key biomarkers known to be altered by exercise. Results The magnitude of changes to biomarkers is proportional to the severity of the running bout. Familiar, moderate intensity running exercise produces brief transient changes in common biomarkers such as lactate, whereas more severe bouts of running exercise, such as marathons and ultra-marathon events can produce changes to biomarkers that are normally associated with pathology of the muscles, liver and heart. Examples being changes to concentrations and/or activity of myoglobin, leucocytes, creatine kinase, bilirubin, cardiac troponins, lactate dehydrogenase, alanine aminotransferase and aspartate aminotransferase. While persisting for longer, these changes are also transient and full recovery occurs within days, without any apparent long-term adverse consequences. Additionally, unfamiliar exercise involving forceful eccentric muscle contractions, such as running downhill, can cause increases in creatine kinase and delayed onset of muscle soreness that peaks 36–72 h after the exercise bout. Conclusions Strenuous running exercise can produce changes to biomarkers that are normally associated with disease and injury, but these do not necessarily reflect chronic pathology.

It has been suggested that aprotinin results in significantly increased risk for perioperative thrombotic complications in patients with Factor VLEIDEN (F5L) due to its ability to competitively inhibit activated protein C (APC) function in vitro. No clinical studies have been performed to assess the effect of aprotinin on APC function of F5L in vivo. We developed an ex vivo model to mimic the effects of cardiopulmonary bypass with the exclusion of the patient in order to assess APC function. Blood from normal ( n = 2) and F5L heterozygous donors ( n = 2) was treated with aprotinin or placebo (saline). The blood was heparinized, added to the prime and circulated at 2 l/min through a modified cardiopulmonary bypass circuit. After 60 min of circulation, the heparin was neutralized with protamine sulfate. Blood samples, drawn at specific time points, were analysed for APC ratio. Results showed a decrease in APC ratio for both F5L and normal bloods with the addition of aprotinin (18% and 40%, respectively). APC ratios also decreased with the commencement of extracorporeal circulation for all bloods, resulting in an APC ratio of 1.35 in normal placebo-treated blood and 0.67 in F5L placebo-treated blood. The combined effect of aprotinin and extracorporeal circulation resulted in APC ratios of 0.90 for normal blood and 0.63 for F5L blood, corresponding to a severe dysfunction of APC intraoperatively (reference range 1.9-4.0). The data from this model predict an increased risk of perioperative thrombosis due to inhibition of APC function in cardiac surgical patients heterozygous for the F5L mutation. Aprotinin further compounds the severity of APC dysfunction, though the effect is more severe in normal blood. The ex vivo model employed was an effective tool for the investigation of the haemostatic effect of aprotinin. This model may be exploited for other applications such as the investigation of novel or emerging haemostatic agents prior to clinical trial.

Diabetes is associated with substantially poorer cardiovascular outcomes. Furthermore, people with diabetes are at greatly increased risk of not responding to standard antiplatelet therapy for acute coronary syndromes, leading to higher mortality and stent thrombosis [1]. Poor glucose control likely contributes to these cardiovascular events through changes in platelet membrane fluidity and signalling, increased production of platelets leading to a greater fraction of younger and more reactive platelets not yet exposed to antiplatelet therapy, and increased triggering of platelet activation arising from an underlying thromboinflammatory milieu [2]. While patients with higher thrombotic risk may be prospectively identified through laboratory identification of elevated blood glucose or HbA1c [3], the approach to treatment for diabetic platelet hyper-responsiveness remains unclear. Options such as increasing frequency of antiplatelet therapy, additional and more aggressive antiplatelet therapy or more intensive glucose control have been suggested (Fig. 1). However, the data to support these are limited and, particularly where more aggressive antiplatelet therapy is proposed, must be measured against the potential for increased bleeding risk in patients with hyperglycemia. In patients with type-2 diabetes, Capodanno et al. [4] demonstrated enhanced inhibition of platelet function when patients took 81 mg of aspirin twice per day compared with 81 mg daily. Spectre et al. [5] showed greater inhibition of platelet function with 75 mg twice per day when compared to 75 mg daily in patients with type-2 diabetes and vascular complications. In a recent study Rocca et al. [6] showed that increasing frequency of dose better attenuated platelet activation over 24 h in both diabetic and non-diabetic patients. Therefore increasing the frequency of antiplatelet therapy dosing represents an appealing strategy in patients with diabetes and poor glycemic control. However, the clinical effectiveness of this approach on cardiovascular outcome, as well as the net benefit against increased bleeding risk remains to be investigated. Similarly, the addition of more aggressive antiplatelet therapy, such as newer ADP receptor antagonists with greater potency and bioavailability, or emerging thrombin receptor antagonists have been suggested [2]. The use of these must be weighed against the potentially increased risk of bleeding. While altering antiplatelet therapy strategies in patients with diabetes and poor glycemic control is an appealing avenue for further clinical investigation, a potential alternative or complimentary approach might be to achieve improved glycemic control in order to attenuate platelet activation. Several studies have assessed the ability of infused insulin in patients with diabetes to attenuate platelet function and improve cardiovascular outcome in acute coronary syndromes [7]. While evidence of improvement in cardiovascular outcome is variable, intensive treatment with insulin in patients with diabetes may attenuate platelet activation relative to conventional approaches to glycemic control [8]. In this issue of the Journal of Thrombosis and Thrombolysis, Vivas et al. [9] explore whether tight glycemic control with insulin infusion attenuates platelet reactivity in patients with an acute coronary syndrome and hyperglycemia at admission. In a post hoc analysis of the prospective, randomized, open-label CHIPs study, 67 patients with poor glycemic control (as measured by HbA1c [ 6.5 %) were M. D. Linden (&) Centre for Microscopy, Characterisation and Analysis, M510, University of Western Australia, 35 Stirling Highway, Nedlands, WA 6009, Australia e-mail: matthew.linden@uwa.edu.au

Flavonols are polyphenolic compounds with reported cardiovascular benefits and have been shown to exhibit antiplatelet properties in vitro. While some studies have shown inhibition of platelet aggregation following dietary supplementation with flavonol rich foods, few studies have assessed the ability of flavonols to inhibit platelet mediated thrombus generation in vivo. Furthermore, the duration of benefit and the influence of different dosing regimens remain unclear. In this study we investigate the ability of two structurally related flavonols; quercetin (Que) and 3′,4′-dihydroxyflavonol (DiOHF) to inhibit platelet aggregation, platelet granule exocytosis and vessel occlusion in a well characterized mouse model of platelet mediated arterial thrombosis. We investigated the effect of a single 6 mg/kg intravenous bolus and daily 6 mg/kg intraperitoneal doses over seven consecutive days. Carotid artery blood flow after injury was better maintained in mice treated with both Que and DiOHF when compared to the vehicle for both dosage regimens. This improved blood flow corresponded to inhibition of platelet aggregation and platelet dense granule exocytosis following chemical stimulation of PAR4. We therefore provide evidence of inhibition of platelet-mediated arterial thrombosis by flavonols in vivo, and demonstrate that this effect persists for at least 24 h after the last intraperitoneal dose. These data suggest a potential clinical role for flavonols as anti-platelet therapy.

The effects of eltrombopag, a thrombopoietin-receptor agonist, on platelet function in immune thrombocytopenia (ITP) are not fully characterized. This study used whole blood flow cytometry to examine platelet function in 20 patients receiving eltrombopag treatment at days 0, 7, and 28. Platelet surface expression of activated GPIIb/IIIa, P-selectin, and GPIb was measured with and without low and high adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP) concentrations. Before eltrombopag treatment with no ex vivo agonist, platelet activation was higher in ITP patients than controls. Platelet GPIb and activated GPIIb/IIIa expression without added agonist was unchanged following eltrombopag treatment, whereas a slight increase in P-selectin was observed. Expression of P-selectin and activated GPIIb/IIIa in response to high-dose ADP was lower during eltrombopag treatment than at baseline. Eltrombopag led to a slight increase in platelet reactivity to TRAP only in responders to eltrombopag but not to levels above those in controls; whole blood experiments demonstrated that this increase was probably because of higher platelet counts rather than higher platelet reactivity. In conclusion, although thrombocytopenic ITP patients have higher baseline platelet activation than controls, eltrombopag did not cause platelet activation or hyper-reactivity, irrespective of whether the platelet count increased.

Severe thrombocytopenia is a major risk factor for hemorrhage, but platelet function and bleeding risk at low platelet counts are poorly understood, because of the limitations of platelet function testing at very low platelet counts.To examine and compare platelet function in severely thrombocytopenic patients with acute myeloid leukemia (AML) or myelodysplasia (MDS) with that in patients with immune thrombocytopenia (ITP).Whole blood flow cytometric measurement of platelet activation and platelet reactivity to agonists was correlated with the immature platelet fraction (IPF) and bleeding symptoms.Patients with AML/MDS had smaller platelets, lower IPF and substantially lower platelet surface expression of activated glycoprotein (GP)IIb-IIIa and GPIb, both with and without addition of ex vivo ADP or thrombin receptor-activating peptide, than patients with ITP. In both ITP and AML/MDS patients, increased platelet surface GPIb on circulating platelets and expression of activated GPIIb-IIIa and GPIb on ex vivo activated platelets correlated with a higher IPF. Whereas platelet reactivity was higher for AML/MDS patients with bleeding than for those with no bleeding, platelet reactivity was lower for ITP patients with bleeding than for those with no bleeding.AML/MDS patients have lower in vivo platelet activation and ex vivo platelet reactivity than patients with ITP. The proportion of newly produced platelets correlates with the expression of platelet surface markers of activation. These differences might contribute to differences in bleeding tendency between AML/MDS and ITP patients. This study is the first to define differences in platelet function between AML/MDS patients and ITP patients with equivalent degrees of thrombocytopenia.

Our conclusion that “poor clinical outcomes of aspirin-treated patients is due in part to incomplete cyclooxygenase-1 (COX-1) inhibition, but is also due in part to COX-1–independent platelet hyperreactivity” is based on the independent association of both high residual serum thromboxane B2 (TXB2) and shortened platelet function analyzer (PFA-100) collagen/ADP closure time (CADP CT; indicative of COX-1–independent platelet hyperreactivity) with adverse outcomes in aspirin-treated patients.1 These findings help define factors that contribute to the risk for adverse events in …

Bouts of strenuous exercise in sedentary individuals acutely increses cardiovascular risk with a 100 fold increased risk of myocardial infarction immediately following exercise and 40% of all patient who experience myocardial infaction reporting repoting physical activity as the trigger.

Summary. Background: Aspirin ‘resistance’ is a widely used term for hyporesponsiveness to aspirin in a platelet function test. Serum thromboxane (TX) B2 is the most specific test of aspirin’s effect on platelets. Objectives: (i) To examine the role of pre-existent platelet hyperreactivity in aspirin ‘resistance’. (ii) To determine the correlation between aspirin resistance defined by serum TXB2 and other assays of platelet function. Methods: To enable pre-aspirin samples to be drawn, platelet function was measured in normal subjects (n = 165) before and after aspirin 81 mg daily for seven days. Results: The proportion of the post-aspirin platelet function predicted by the pre-aspirin platelet function was 28.3 ± 7.5% (mean ± asymptotic standard error) for serum TXB2, 39.3 ± 6.8% for urinary 11-dehydro TXB2, 4.4 ± 7.7% for arachidonic acid-induced platelet aggregation, 40.4 ± 7.1% for adenosine diphosphate-induced platelet aggregation, 26.3 ± 9.2% for the VerifyNow Aspirin Assay®, and 45.0 ± 10.9% for the TEG® PlateletMapping™ System with arachidonic acid. There was poor agreement between aspirin-resistant subjects identified by serum TXB2 vs. aspirin-resistant subjects identified by the other five assays, irrespective of whether the analysis was based on categorical or continuous variables. Platelet count correlated with pre-aspirin serum TXB2 and VerifyNow Aspirin Assay, but not with any post-aspirin platelet function test. Conclusions: (i) Aspirin ‘resistance’ (i.e. hyporesponsiveness to aspirin in a laboratory test) is in part unrelated to aspirin but is the result of underlying platelet hyperreactivity prior to the institution of aspirin therapy. (ii) Aspirin resistance defined by serum TXB2 shows a poor correlation with aspirin resistance defined by other commonly used assays.

Aim: To determine whether indices of platelet activation are associated with the stability of coronary artery disease (CAD). Methods: Platelet function was examined in 677 consecutive aspirin-treated patients presenting for cardiac catheterization. Patients were grouped into recent myocardial infarction (MI), no MI but angiographically documented CAD (non-MI CAD) and no angiographically detectible CAD (no CAD), as well as additional subgroups. Results: Compared with non-MI CAD or no CAD patients, more patients with recent MI had a shortened platelet function analyzer (PFA)-100 collagen-epinephrine closure time (CT) and increased circulating monocyte-platelet aggregates, neutrophil-platelet aggregates, activated platelet surface GPIIb-IIIa and plasma soluble CD40 ligand (sCD40L). More patients with non-MI CAD had shortened PFA-100 CTs and increased monocyte-platelet aggregates compared with patients with no CAD. Platelet surface P-selectin did not differ among the groups. Subgroup analysis revealed that decreasing PFA-100 CT correlated with the stability of CAD. Conclusions: Indices of platelet activation, especially the PFA-100 CT, are associated with the stability of CAD, and may reflect plaque instability, an ongoing thrombotic state and/or reduced responsiveness to aspirin

We thank Dr Kronish and his colleagues for their interest in our work.1 Kronish et al suggest that because of the patient population we studied, our work underestimates the role of noncompliance in aspirin resistance if applied to all patients taking aspirin.1 However, we did not suggest that …

Platelets are a central cellular interface of the thrombotic and inflammatory processes of coronary atherosclerosis and modulate this interface by binding to leukocytes and altering their function. In addition, platelet activation; formation of leukocyte- platelet aggregates (monocyte-platelet aggregates and neutrophil-platelet aggregates); and platelet secretion of inflammatory modulators that affect leukocyte function, such as CD40 ligand, are associated with progression of disease across the entire spectrum of atherothrombosis. Monocyte-platelet aggregates are elevated in stable coronary artery disease and further elevate with plaque rupture, characteristic of percutaneous coronary intervention, acute coronary syndromes, and myocardial infarction. Through this interaction, activated platelets may contribute to the pathogensis of ischemic heart disease by localizing and activating monocytes to the site of the atherosclerotic lesion. These heterotypic aggregates have potential for a number of clinical applications, including measurement as an early marker for plaque rupture, evaluation of the efficacy of antiplatelet therapy, and as a potential target for therapeutic intervention. Additional investigations evaluating these applications as well as the relationship between monocyte-platelet aggregates and outcome are needed.

The effect of haemodilution on antithrombin concentration was investigated in 73 patients undergoing elective cardiac surgery with and without cardiopulmonary bypass. In patients who required cardiopulmonary bypass (n=45), the antithrombin concentration fell to 52% of baseline during surgery (24.2 mg.dl−1to 12.6 mg.dl−1), and the haemoglobin level fell to 55% (136 g.l−1to 75 g.l−1). In patients who did not require cardiopulmonary bypass (n=28), the antithrombin concentration fell to 82% of baseline (23.7 mg.dl−1to 19.5mg.dl−1), and the haemoglobin concentration fell to 78% (141 g.l−1to 109 g.l−1). The overall correlation coefficient (r) for changes in antithrombin and haemoglobin concentrations was 0.76. The results indicate that most of the decrease in concentration of antithrombin during cardiac surgery is a consequence of cardiopulmonary bypass and is due to haemodilution. This data demonstrates that the percentage decrease in haemoglobin concentration can be used to estimate the percentage decrease in antithrombin concentration that occurs during cardiac surgery, if blood products that might effect the results are not administered between measurements.

Summary. Objective: To investigate the effects of abciximab, eptifibatide and no GPIIb–IIIa antagonist (control) on soluble CD40 ligand (sCD40L) and the formation of leukocyte-platelet aggregates (LPA) in 98 ACS patients undergoing percutaneous coronary intervention (PCI). Background: sCD40L and LPA are increased in patients with ACS. Methods: sCD40L was measured by enzyme-linked immunosorbent assay (ELISA) and LPA by whole blood flow cytometry. Results: There were no baseline differences between the three groups in sCD40L and LPA. At the end of PCI, sCD40L was unchanged in the controls, decreased by 30% (P

Flow cytometry is a powerful and versatile tool that can be used to yield definitive information regarding the phenotypic status of platelets. The method provides a quantitative assessment of the physical and antigenic properties of platelets (e.g., surface expression of receptors, bound ligands, components of granules, or interactions of platelets with other platelets, other blood cells, or components of the plasma coagulation system), thereby facilitating the diagnosis of inherited or acquired platelet disorders (e.g., Bernard-Soulier syndrome, Glanzmann thrombasthenia, storage pool disease), the pathological activation of platelets (e.g., in the setting of acute coronary syndromes, cerebrovascular ischemia, peripheral vascular disease, cardiopulmonary bypass), and changes in the ability of platelets to activate via specific stimuli (e.g., efficacy of antiplatelet therapies). Accordingly, this review summarizes the key technical and methodologic components of flow cytometric analysis of platelets, as well as specific examples of its application to diagnosis and patient care.

Acute normovolemic hemodilution (ANH) is used to reduce allogeneic blood transfusion with cardiac surgery. This procedure involves pre-operatively removing and storing a volume of whole blood and replacing the volume with crystalloid. The stored blood is then available for transfusion, if required. Hemodilution associated with ANH may reduce the effectiveness of heparin anticoagulation due to dilution of antithrombin. The aim of this study was to determine if antithrombin concentrations are reduced in patients who undergo one unit of ANH during cardiac surgery.Patients scheduled for cardiac surgery (n = 71) were grouped according to whether they did or did not undergo ANH pre-operatively. Antithrombin concentrations were measured before and after ANH. This study had 80% power to detect a difference in reduction of antithrombin concentration of 6% between groups following ANH with an alpha error of0.05. The effect of one unit ANH was expected to cause a difference of 12% or greater.No significant difference in the concentration of antithrombin between ANH patients and those that did not have ANH, nor was there a difference in the decrease in antithrombin between groups.The results indicate that one unit of ANH does not significantly reduce the concentration of antithrombin prior to cardiac surgery. Thus patients who undergo one unit of ANH are not at increased risk due to dilution of antithrombin.