Loss of high-molecular-weight von Willebrand factor multimers mainly affects platelet aggregation in patients with aortic stenosis

Severe aortic stenosis is associated with a haemostatic abnormality that resembles acquired von Willebrand syndrome type 2. It is assumed that high shear conditions render large von Willebrand factor (VWF) multimers accessible to cleavage by ADAMTS-13. However, whether loss of these large multimers affects platelet function by impairing adhesion, aggregate formation, or both has not been evaluated in clinical studies. We prospectively enrolled 47 patients with severe aortic stenosis, and studied them prior to aortic valve surgery and at a median of six months after valve replacement. We investigated levels of large VWF multimers, platelet function under high shear conditions, and residual response to suboptimal concentrations of ADP to express P-selectin. As expected, there was a significant reduction of VWF large multimers before surgery that resolved thereafter in most patients (p<0.0001). The closure time of the ADP cartridge of the PFA-100 was also corrected in most patients after the operation (p<0.0001). We used the cone and plate(let) analyser Impact-R to differentiate between adhesion and aggregation. Both adhesion (p=0.03) and ADP-inducible platelet aggregation (p=0.002) improved considerably after valve replacement. Consequently, ADP-inducible expression of P-selectin was higher after valve replacement (p=0.001). We conclude that reduced levels of large VWF multimers associated with aortic stenosis lead to impairment of both adhesion and, especially, ADP-inducible platelet aggregation.

Asymmetric effector transfer of complex movement sequences

An experiment was designed to determine if the addition of a load altered the effector transfer profile observed in earlier experiments using multi-element movement sequences. The acquisition task required participants to move a horizontal lever (with 0.567kg load) to 16 sequentially projected targets. One group practiced the movement sequence with their right (dominant) limb and another group practiced with their left (non-dominant) limb. Approximately 24h after completion of the acquisition session both groups were administered test blocks (0kg, 0.567kg, and 1.134kg) using their practiced and unpracticed limbs. Decreased and increased loads had minimal effect on test performance. The results indicated that the group trained with their left limb were able to perform the right limb tests as well as the group that trained with the right limb. However, the group that trained with their right limb were significantly slower performing the tests with the left limb than the group that practiced with their left limb. Importantly, the left acquisition limb group maintained the pattern of element durations used during practice on the various tests including transfer to the dominant limb. However, the pattern of element durations for the right acquisition limb group on the left limb transfer tests was altered such that the production of only the fastest produced elements were disrupted. These results suggest that one of the reasons for poor sequence performance when transferring from the right to left is because the sequence structure developed during acquisition and used on the tests lacked access to the appropriate commands or the controller lacked the ability to implement codes that effectively manage the movement dynamics.

Monitoring anticoagulation of primary haemostasis--estimation of platelet function in whole blood assays

This article provides an overview on current commercially available methods to determine primary haemostasis as a target of drug-mediated anticoagulation. It focuses on whole blood methods only, and references the currently major achievements that have been reported with each method in respect to its clinical use. Advantages and disadvantages of the various methods are presented, based on considerations of platelet physiology, and on feasibility of the procedures.

Short article: Effects of interlimb practice on coding and learning of movement sequences

An interlimb practice paradigm was designed to determine the role that visual–spatial (Cartesian) and motor (joint angles, activation patterns) coordinates play in the coding and learning of complex movement sequences. Participants practised a 16-element movement sequence by moving a lever to sequentially presented targets with one limb on Day 1 and the contralateral limb on Day 2. Practice involved the same sequence with either the same visual–spatial or motor coordinates on the two days. A unilateral practice condition (control) was also tested where both coordinate systems were changed but the same limb was used. Retention tests were conducted on Day 3. Regardless of the order in which the limbs were used during practice, results indicated that keeping the visual–spatial coordinates the same during acquisition resulted in superior retention. This provides strong evidence that the visual–spatial code plays a dominant role in complex movement sequences, and this code is represented in an effector-independent manner.

Inter-manual transfer and practice: coding of simple motor sequences

Previous research suggests that movements are represented early in practice in visual-spatial coordinates/codes, which are effector independent, and later in practice in motor coordinates/codes (e.g., joint angles, activation patterns), which are effector dependent. In the present experiments, the task was to reproduce 1.3 s patterns of elbow flexions and extensions. An inter-manual transfer paradigm was used in Experiment 1 and an inter-manual practice paradigm was used in Experiment 2. The present results clearly indicated a strong advantage of effector transfer when the motor coordinates available during acquisition were reinstated (Experiment 1) and demonstrate that inter-manual practice with the same motor coordinates results in enhanced retention performance relative to transfer and practice where the same visual-spatial coordinates are used. These results demonstrate that the more effective movement code (motor or visual-spatial) is dependent on the movement sequence characteristics (e.g., difficulty, number of elements, and mode of control [preplanned or on-line]). These results are also interesting because they indicate, contrary to previous findings with more complex movement sequences, that an effective motor code can be developed relatively early in practice for rapid movement sequences.

The effects of sequence difficulty and practice on proportional and nonproportional transfer

Two experiments were designed to determine participants' ability to transfer a learned movement sequence to new spatial locations. A 16-element dynamic arm movement sequence was used in both experiments. The task required participants to move a horizontal lever to sequentially projected targets. Experiment 1 included two groups. One group practised a relatively easy 16-element movement sequence (easy long). The other group practised a more difficult 16-element movement sequence (difficult long). Approximately 24 hours after practice with their respective sequence both groups were administered a retention and two transfer tests. The only difference between the retention and transfer tests was the location of the targets. The short transfer target configuration was considered a proportional transfer because all the amplitudes between targets were reduced by the same proportion. The mixed transfer configuration was considered a nonproportional transfer because the targets did not have the same proportional distances between targets as the sequence they practised. The results indicated that participants could effectively transfer the difficult long sequence to the new target configurations regardless of whether the transfer required proportional and nonproportional spatial changes to the movement pattern. However, the easy long sequence was only effectively transferred in the proportional transfer condition. Experiment 2 assessed the effects of extended practice of the easy long sequence on proportional and nonproportional spatial transfer. The data indicated that participants could again effectively transfer the easy long sequence to proportional but not the nonproportional spatial transfer conditions regardless of the amount of practice (1 or 4 days). The results are discussed in terms of the mechanism by which response sequences become increasingly specific over extended practice in an attempt to optimize movement production and how this process interacts with the difficulty of the sequence.

Monoclonal platelet antigen capture assays (MAIPA) and reagents: a statement

This statement concerning the monoclonal-specific immobilization of platelet antigens (MAIPA) has been written on behalf of the International Society of Blood Transfusion--Working Party on Platelet Immunology. The MAIPA technique is considered as the gold standard reference technique in platelet immunology. The assay performed with reagents labelled for 'research only' is acceptable as long as it is regularly evaluated by participation of laboratories in national or international workshops held with reference laboratories.

New therapeutic options for adult chronic immune thrombocytopenic purpura: a brief review

BACKGROUND

Patients with chronic immune thrombocytopenic purpura (ITP) only require treatment if they are bleeding, or prior to scheduled operations. Patients are also treated if platelet counts are very low. Some patients become refractory, relapse or do not respond to treatment with steroids. Splenectomy is effective in raising the platelet count in most patients, but as spontaneous remission may occur even after 1 year or more, it is justified to defer splenectomy. Furthermore, splenectomy and/or first-line treatment modalities may not suit all patients. Therefore, alternatives are desirable.

MATERIALS

This review will focus on anti-B cell therapy with rituximab, and two thrombopoietin mimetic agents that have entered clinical trials, AMG 531 and eltrombopag. These therapeutics have been studied in patients who were refractory to first-line treatment and/or splenectomy, and to defer splenectomy.

RESULTS

There are no controlled trials with rituximab, but clinical experience has shown a success rate of 40% to 60%. Encouraging phase 1 and 2 data have been published for both thrombopoietin mimetics; preliminary data from an open-label extension trial with AMG 531 and from phase 3 studies with eltrombopag further confirm their efficacy.

CONCLUSION

Clinical experience will ultimately determine the appropriate indications of these new treatments for ITP.

Platelet function to estimate the bleeding risk in autoimmune thrombocytopenia

BACKGROUND

Knowledge of platelet function may assist in patient care in chronic autoimmune thrombocytopenia (cAITP).

MATERIALS AND METHODS

We evaluated the association of platelet function with haemorrhage in 41 patients, median age 41 years (range 14-82 years, 24 females) with chronic autoimmune thrombocytopenia (cAITP). Samples were investigated for platelet P-selectin, and adhesion and aggregate formation under high shear conditions. Data were compared to those from 28 healthy controls (median age 39 years, range 23-70 years, 17 females) and correlated with a bleeding score of 0 (no bleeding) to 3 (overt mucosal bleedings).

RESULTS

P-selectin levels were higher in patients than in controls (P < 0.0004). Compared to controls, the patients' samples responded to high shear with decreased adhesion to the polystyrene surface (P < 0.0001), but formed aggregates of normal size. P-selectin expression was neither correlated with platelet counts, nor platelet adhesion, nor the bleeding score. Only the size of formed aggregates correlated with P-selectin (P = 0.01). Platelet counts (odds ratio 0.5, 95% confidence interval 0.22-0.88; P = 0.04) and adhesion (odds ratio 0.45, 95% confidence interval 0.17-0.87; P = 0.04) were independently inversely correlated with bleeding symptoms.

CONCLUSION

Platelet adhesion correlates with bleeding symptoms, while the size of aggregates that are formed under high shear correlates with in vivo platelet activation. The determination of these parameters may assist in estimating an individual bleeding risk and thus a decision for treatment.

Research Notes

Zusammenfassung. Für das Lernen von Bewegungssequenzen wird postuliert, dass die Codierung einer entsprechenden Repräsentation parallel in zwei unterschiedlichen Koordinatensystemen erfolgt, einem visuellen System (visuell-räumlicher Code) und einem motorischen System (motorischer Code). Dabei wird zusätzlich angenommen, dass sich der visuell-räumliche Code schneller entwickelt als der motorische Code und in einer frühen Lernphase eine ausführungsleitende Funktion hat. Bei einer Störung der visuell-räumlichen Codierung werden Einbußen in der Leistungsentwicklung bei der zu lernenden Bewegungssequenz erwartet. In zwei konsekutiven Versuchssitzungen wurden der visuell-räumliche Code und/oder der motorische Code beim Lernen einer Bewegungssequenz in einem intermanuellen Transferdesign systematisch manipuliert. In einer dritten Versuchssitzung wurden Behaltens- und Transferleistungen für die rechte und linke Hand untersucht. Die Befunde zeigen, dass bei einer Veränderung der visuell-räumlichen Codierung Leistungsdekremente im Behaltens- und Transfertest auftreten. Hingegen zeigen sich bei einem Handwechsel von der zuerst trainierten rechten auf die linke Hand bei einer Beibehaltung der visuell-räumlichen Codierung Leistungsvorteile für die zu lernende Bewegungssequenz. Die Ergebnisse bestätigen die Annahme, dass beim Lernen von Bewegungssequenzen der visuell-räumliche Code in der frühen Lernphase eine dominante, d. h. ausführungsleitende Funktion besitzt.

The transfer of movement sequences: effects of decreased and increased load

A number of recent experiments have demonstrated that a movement structure develops during the course of learning a movement sequence that provides the basis for transfer. After learning a movement sequence participants have been shown to be able to effectively produce the sequence when movement demands require that the sequence be rescaled in amplitude or produced with an unpractised set of effectors. The purpose of the present experiment was to determine whether participants, after learning a complex 16-element movement sequence with a 0.567-kg load, could also effectively produce the sequence when the load was decreased (0.0 kg) or increased (1.134 kg). The results indicated that participants were able to effectively compensate for decreased and increased load with virtually no changes in performance characteristics (displacement, velocity, acceleration, and pattern of element durations) while electromyographic (EMG) signals demonstrated that smaller (reduced load) or larger forces (increased load) were spontaneously generated to compensate for the change in load. The muscle activation patterns of the biceps and triceps as well as the level of coactivation appeared to be generally upscaled to generate and dissipate the changes in force requirement needed to compensate for the increased load.

Late spontaneous remissions in severe adult autoimmune thrombocytopenia

We report on four cases (three women, one man, age at diagnosis 26-61 years) with severe autoimmune thrombocytopenia (AITP) who were refractory to initial steroid therapy (n = 4), to subsequent splenectomy (n = 2), azathioprine (n = 1), and cyclosporine (n = 1). Over years they received low-dose continuous or intermittent steroid therapy. After 6 to 31 years these patients achieved a "spontaneous" complete remission (CR) (n = 3) or partial remission (PR) (n = 1) unrelated to any specific second or third line treatment; CR/PR are sustained for 0.5+ to 9+ years. These data indicate that spontaneous remissions may occur in AITP even after a long duration of the disease.

Monitoring survival and function of transfused platelets in Glanzmann thrombasthenia by flow cytometry and thrombelastography

Patients with Glanzmann thrombasthenia (GT) may form isoantibodies which induce refractoriness or inhibition of function of transfused platelets. We monitored the survival and function of transfused platelets by flow cytometry and thrombelastography in a patient with GT. Gating on CD42a+ allowed identification of even a few transfused platelets. Only by gating on these CD41+ CD42a+ cells were we able to demonstrate their capability to bind fibrinogen and PAC-1 upon activation. Platelets were rapidly cleared from the circulation as a result of boosted isoantibodies. The contribution of transfused platelets to clot formation was also demonstrated by thrombelastography by blocking their function with abciximab.

Influence of clinical factors on the haemolysis marker haptoglobin

BACKGROUND

Plasma haptoglobin determination is clinically used as parameter for haemolysis. To date, however, the influence of the mode of haemolysis (extravascular vs. intravascular) and of nonhaemolytic conditions on haptoglobin concentration and its reliability as a haemolysis marker remain poorly defined.

MATERIALS AND METHODS

In a total of 479 individuals, the influence of haemolytic and nonhaemolytic conditions on plasma haptoglobin levels was investigated.

RESULTS

All studied types of haemolytic disease (n = 16) were associated with markedly decreased plasma haptoglobin levels, without significant differences between intravascular vs. predominantly extravascular haemolysis. Diminished haptoglobin values were also observed in patients with liver cirrhosis, which normalized after liver transplantation. In contrast, markedly increased haptoglobin levels were found in patients with inflammation. In patients with haemolysis and a concomitant acute-phase response, however, haemolysis-dependent haptoglobin depletion was not attenuated. Interestingly, patients with a strongly positive direct antiglobulin test or high cold agglutinin titre but no further evidence for haemolysis had normal haptoglobin values. Likewise, anaemia owing to bone marrow failure, acute gastrointestinal or chronic diffuse blood loss, and end-stage kidney disease were associated with normal haptoglobin levels.

CONCLUSIONS

Plasma haptoglobin depletion is a reliable marker for the instant diagnosis of accelerated red cell destruction irrespective of the site of haemolysis or the presence of inflammation. The capacity of this parameter to predict haemolysis appears to be limited in patients with liver cirrhosis and decreased haptoglobin production only.

Learning of Similar Complex Movement Sequences: Proactive and Retroactive Effects on Learning

The authors used an interference paradigm to determine the extent to which the learning of 2 similar movement sequences influences the learning of each other. Participants (N=30) produced the sequences by moving a lever with their right arm and hand to sequentially presented target locations. They practiced 2 similar 16-element movement sequences (S1 and S2), 1 sequence on each of 2 consecutive days of practice. Control groups received only 1 day of practice on 1 of the sequences. Early in S2 practice, the experimental group demonstrated a relatively strong level of proactive facilitation arising from previous practice with S1. The advantage was not evident at the end of S2 practice or on the S2 retention test. No advantage of practicing the 1st sequence on the learning of the 2nd sequence (proactive effect) was found in the analysis of element duration in the retention and transfer tests, even though 14 of the 16 elements were common to both sequences. A strong retroactive interference on the switched elements was detected, however. Thus, the memories underpinning S1 seemed to be "overwritten" or adapted in response to the learning of S2.