Whole Blood Aggregometer Research Articles

Haemostatic abnormalities in treatment-naïve patients with Type 1 Gaucher's disease

There is a paucity of data on the effects of enzyme replacement therapy (ERT) on the coagulation abnormalities and platelet function of patients with Gaucher's disease (GDPs) and much of this data are controversial. This study investigates the haemostatic parameters in treatment-naïve GDPs and the effects of ERT. 31 Serbian treatment-naïve type 1 GDPs (M/F 17/14; median age 49 years, splenectomized 9/31) were studied. The complete blood count, prothrombin time (PT), activated partial tromboplastin time (aPTT) and coagulation factors were measured using the standard methods. Platelet aggregation was assessed with a whole-blood aggregometer. Splenic volumes were assessed using computer tomography. Twenty-one patients were treated with ERT (Imiglucerase). The haemostatic parameters were assessed after 6, 12 and 24 months (ERT6, 12, 24). Initially bleeding episodes were registered in 10/31 GDPs. Median platelet count was 108 × 109/L; 22/31 GDPs were thrombocytopenic. The PT and aPTT values were abnormal in 16/31 and 13/31 GDPs, respectively. Platelet aggregation abnormalities were recorded in 19/31GDPs. Median platelet aggregation was reduced in response to adenosine-diphosphate 5 µmol/L (ADP5 0.46) and collagen 5 µmol/L (Col5 0.47). Splenic volume inversely correlated with the platelet count and a reduced response to arachidonic acid (AA), Col5 and ADP5 (p < 0.05). The splenectomized GDPs had a significantly lower platelet aggregation to Col10 (p < 0.05). Bleeding GDPs had a significantly lower platelet count, higher chitotriosidase levels and a greater splenic volume compared to non-bleeding patients (p < 0.01). ERT: The number of bleeding GDPs had significantly decreased by ERT6 (1/10; p < 0.01). The platelet count had significantly increased by ERT6 (ERT6 180 × 109/L, p < 0.01). The PT increased significantly from ERT0 to ERT24 (PT0 65%, PT24 81%; p < 0.05). The von Willebrand factor had increased significantly by ERT6 and ERT24 (ERT0 56%, ERT6 70%, ERT12 70%, ERT24 86%; p < 0.01). The number of GDPs with abnormal platelet aggregation had decreased significantly by ERT6 (10/19; p < 0.05). Platelet aggregation on ADP10 and AA significantly increased by ERT6 (ADP10: ERT0 0.75, ERT6 0.8 p < 0.01; AA: ERT0 0.7, ERT6 0.8 p < 0.05). In conclusion, platelet dysfunction and coagulation abnormalities were found in a considerable number of our GDPs. The absence of severe bleeding episodes suggests that the haemostatic system is sufficiently balanced and therefore the exact mechanism of the etiology of these abnormalities need to be fully clarified. ERT resulted in the cessation of bleeding and marked increase in platelet count, PT, vWF and platelet aggregation.

Measuring Platelet Aggregation in Dialysis Patients With a Whole Blood Aggregometer by the Screen Filtration Pressure Method

A semi-automatic, whole-blood aggregometer based on the screen filtration pressure (SFP) method is now widely used clinically and in research, but has not been used with hemodialysis (HD) patients. We measured whole-blood platelet aggregation in HD patients by the SFP method. This retrospective cross-sectional study included 62 HD patients, of whom 47 were non-diabetic and 15 were diabetic; we also included a control group of healthy, non-uremic subjects. With the t-test, we examined differences in the platelet aggregation threshold index (PATI) in meaningful sub-groupings of the HD patients, depending on whether or not they had diabetes, and whether or not they had been given antiplatelet agents. Considering the non-diabetic HD patients first, their PATI values were significantly higher than those values in the control subjects (3.1 [1.0-5.2] vs. 1.8 [1.3-2.3] µM, P<0.001). The non-diabetic HD patients taking antiplatelet agents showed significantly (1.9 times) higher PATI values than the non-diabetic HD patients without antiplatelet agents (4.4 [1.8-7.0] vs. 2.3 [1.3-3.3] µM, P=0.003). We observed similar trends among diabetic HD patients. Whole-blood analysis by the SPF method seems to be a promising way of monitoring platelet function for HD patients.

COX-2 Inhibition by Use of Rofecoxib or High Dose Aspirin Enhances ADP-Induced Platelet Aggregation in Fresh Blood

Aim:Increased cardiovascular risk after use of selective or nonselective cyclooxygenase-2 (COX-2)-inhibitors might partly be caused by enhanced platelet aggregability. However, an effect of COX-2 inhibition on platelets has so far not been observed in humans.Methods:We tested in healthy volunteers the effect of COX-2-inhibition nearly in-vivo, i.e. immediately after and even during blood sampling.Results:Measurement within 2 minutes after venipuncture, but not 60 minutes later, showed that 50 mg of rofecoxib (n=12) or 500 (n=8) or 1000 (n=8) mg of aspirin increased ADP-induced platelet aggregation in a whole-blood aggregometer to, respectively, 152, 176 and 204 % of basal level (p<0.01). No significant differences in aggregability were observed after ingestion of 80 mg of aspirin (n=16), or placebo (n=8). Plasma 6-keto-PGF1α was decreased to 74 % after rofecoxib and to 76 and 70 % after 500 and 1000 mg of aspirin but did not change after low dose aspirin. Continuous photometrical measurement of aggregation in blood flowing from a cannulated vein revealed that high dose aspirin did not elicit aggregation by itself, but increased ADP-induced aggregation in proportion to the decrease in prostacyclin formation (r=0.68, p = 0.004). Since in these experiments thromboxane production was virtually absent, the enhanced aggregation after partial COX-2 inhibition was not caused by unopposed thromboxane formation.Conclusions:We conclude that both selective and nonselective COX-2 inhibition enhances ADP-induced platelet aggregation in humans. This effect can only be detected during or immediately after venipuncture, possibly because of the short half-life of prostacyclin.

Low responsiveness to thienopyridine in hemodialysis patients

We sought to evaluate whether thienopyridine low responsiveness, a predictor of stent thrombosis, is found in hemodialysis patients. We measured platelet aggregation at the site of implantation of drug-eluting stents in 333 patients with angina pectoris undergoing dual anti-platelet therapy. Thirty-one patients were on hemodialysis (HD group), and 302 were not (N-HD group). We used a novel whole-blood aggregometer. The aggregometer used the screen filtration method, with adenosine diphosphate as an agonist. The concentration of agonist required to induce 50% of the maximum pressure rate was calculated and indicated as the platelet aggregatory threshold index (PATI). Low responsiveness for thienopyridine was defined if the PATI levels were <4μmol/l. PATI levels (μmol/l) were significantly lower in the HD group than in the N-HD group (6.8±4.8 vs. 9.1±5.4, P=0.023), and the rate of low responsiveness for thienopyridine was significantly higher in the HD group than in the N-HD group (45.7 vs. 26.8%, P=0.019). Non-fatal myocardial infarction and stent thrombosis occurred in three of the HD group and in nine of the N-HD group (P=0.122). Late stent thrombosis occurred at a significantly higher rate in the HD group than in the N-HD group (P=0.002). The rate of target lesion revascularization was significantly higher in the HD group than in the N-HD group (38 vs. 11.8%, P=0.0001). In conclusion, low responsiveness to thienopyridine, as an indicator of platelet reactivity, is found more frequently in hemodialysis patients.

Comparison of four laboratory methods to assess aspirin sensitivity

The purpose of this study was to compare the ability of four commercial platelet function assays to detect aspirin response in normal individuals taking 81 or 325 mg aspirin in a single-dose response and then in a 7-day dosing regimen. We employed the Chronolog 570VS whole-blood aggregometer with agonists 1.0 microgram/ml collagen and 0.5 mmol/l arachidonic acid, the PFA-100 epinephrine/collagen cartridge closure time, the Accumetrics Verify/Now arachidonic acid cartridge, and the urine 11-dehydrothromboxane immunoassay normalized to urine creatinine. Fifty normal individuals who met the inclusion criteria were consented in the single-dose study. Blood and urine were collected at baseline, and then each participant was given a 81 mg enteric-coated aspirin tablet. Blood and urine were collected after 24 h. After a minimum of 14 days the process was repeated with a 325 mg aspirin dose. Forty-five individuals were enrolled in the 7-day study. Blood and urine were collected at baseline. Then each participant was given an 81 mg dose of aspirin daily for 7 days. After 7 days, blood and urine specimens were obtained and tested. After a minimum washout period of 14 days the process was repeated using a 7-day regimen of 325 mg enteric-coated aspirin tablet. Student's t-test indicated statistical significance between baseline and post responses in both dosing regimens (P < 0.05). Individuals were not consistently identified as aspirin responsive across all platforms. All assays discriminated between platelet response and nonresponse to aspirin at both dosages. It may be necessary to employ multiple assays to detect individual platelet response.

RETRACTED: Evaluation of a New Platelet Function Analyzer in Cardiac Surgery: A Comparison of Modified Thromboelastography and Whole-Blood Aggregometry

Impaired hemostasis of multiple etiologies are often present in patients undergoing cardiopulmonary bypass (CPB) surgery. Platelet dysfunction is considered to be important in the early postoperative period. Therefore, a new whole-blood platelet function analyzer was compared with thromboelastography in predicting postoperative hemostatic outcomes as measured by blood loss and blood product use. Prospective study. Teaching hospital. The study enrolled 54 patients scheduled for coronary artery bypass surgery with CPB. Coagulation and platelet function were assessed preoperatively, after CPB, at 3 hours, and at 24 hours after surgery by using thromboelastography and impedance aggregometry. Patients were divided into a transfused and nontransfused group on the basis of postoperative transfusion requirements. Postoperative blood loss and requirements of blood transfusions were documented until 24 hours postoperatively. Twenty-five patients (46%) received postoperative blood transfusions. Impaired hemostasis occurred after CPB detected by thromboelastography (p < 0.01) and impedance aggregometry (p < 0.01). In contrast to thromboelastography, preoperative adenosine diphosphate-mediated aggregometry correlated with postoperative requirements for blood transfusion (Spearman r = -0.302, p < 0.05) and was significantly lower in patients receiving allogeneic blood transfusion compared with nontransfused patients (p < 0.05). Neither aggregometry nor thromboelastography was correlated with postoperative blood loss. Impedance aggregometry as well as thromboelastography are able to detect impaired hemostasis after CPB. In contrast to thromboelastography, aggregometry using a new whole-blood aggregometer identified patients with a reduced risk for postoperative transfusion requirements.

Platelet Dysfunction During Cardiopulmonary Bypass Assessed by a Novel Whole-Blood Aggregometer

The purpose of this study was to assess perioperative platelet function with 2 types of monitors (a whole-blood aggregometer [WBA analyzer; Mebanix, Tokyo, Japan]) and the Sonoclot monitor [Sienco, Wheat Ridge, CO]) in patients undergoing hypothermic cardiopulmonary bypass (CPB). Prospective, observational study. Single-center study at a university hospital. Twenty-six patients who underwent coronary artery bypass grafting or valve replacement under hypothermic CPB without platelet transfusion or fresh frozen plasma administration. Blood sampling was performed at the following time periods: after anesthetic induction, after CPB, and on the first postoperative day. These samples were assessed with the WBA analyzer and the Sonoclot. Significant attenuation of adenosine diphosphate-induced platelet aggregation was detected shortly after CPB by 2 WBA analyzer-derived parameters: a decrease in the filtration pressure rate and an increase in the platelet aggregatory threshold index. Platelet aggregation returned to the preoperative level on the next day. There was no correlation between the amount of postoperative mediastinal drainage and defects in platelet aggregation. On the other hand, time to peak obtained by the Sonoclot did not show any significant changes. Whole-blood aggregation measured with the WBA analyzer detected transient platelet dysfunction shortly after CPB, whereas the Sonoclot was less sensitive to this change.

The effects of desflurane on human platelet aggregation in vitro.

In view of the possible antiplatelet effects of general anesthetics, we investigated the in vitro effects of desflurane, a new inhalation agent, on platelet aggregation. For 15 patients who underwent elective operations, blood was sampled with desflurane induction before and after anesthesia but prior to surgery so that platelet aggregation in the drawn blood could be tested before desflurane anesthesia and again after exposure to the anesthetic. Platelet aggregation was measured with a whole-blood aggregometer. Adenosine diphosphate (ADP), collagen, and ristocetin were used as aggregating agents. Our results showed that aggregation in response to ADP, collagen, or ristocetin was not inhibited in patients who received desflurane anesthesia. This study with an in vitro model showed that desflurane had no influence on platelets in clinically relevant doses.

Electrical impedance measurement as an endpoint detection method for routine coagulation tests

A whole-blood platelet aggregometer is adapted to measure electrical impedance changes in plasma during prothrombin time (PT) estimations. The impedance curve shows an acceleration phase, which is comparable to the absorbance curve acceleration phase associated with the onset of coagulation. The amplitude of the impedance change correlates with the fibrinogen concentration of the plasma. Statistical analysis of PT derived by absorbance and impedance changes shows a significant difference between the two methods but a good correlation. The method is reproducible but laborious and requires attention to technique. Further investigation of the method utilising a more sensitive instrument and redesigned electrodes is indicated. It may also be possible to modify reagent systems to optimise impedance changes.

Effect of Laparoscopic Cholecystectomy on Platelet Aggregation

The purpose of this study was to investigate the effect of laparoscopic cholecystectomy on platelet function. We operated on 40 women with symptomatic gallbladder stone, 20 of whom (study group) underwent laparoscopic cholecystectomy and 20 of whom (control group) open cholecystectomy. Patients with a history of bleeding, abnormal platelet count, or systemic disorders and those who were on salicylates, heparin, or oral anticoagulants were excluded. Blood parameters were checked at the beginning and the end of the operation, including platelet aggregation using adenosine 5'-diphosphate (ADP), collagen, and ristocetin in a whole-blood aggregometer. Platelet aggregation was evaluated by percent aggregation. Platelet aggregation due to collagen and ristocetin increased significantly at the end of the operation in the study group (p < 0.001). Aggregation due to ADP did not differ significantly from the start to the end of the operation. Control group results did not show any differences. Although the clinical findings of aggregated platelet are not frequently observed in practice, we suggest that laparoscopy increases platelet aggregation.

Whole-blood platelet aggregation, buccal mucosa bleeding time, and serum cephalothin concentration in dogs receiving a presurgical antibiotic protocol

Summary Whole-blood platelet aggregation (using the impedance method) and adenosine triphosphate (atp) release, buccal mucosal bleeding time (bt), and serum cephalothin concentration were measured in 21 adult female Beagles before (pre) and 1 hour (1hr) after iv administration of cephalothin (22 mg/kg). A second injection of cephalothin (22 mg/kg) was given 3 hours after the first, and blood samples were obtained 1 hour (4 hr, 4 hours after the first injection) and 3 hours (6 hr, 6 hours after the first injection) after the second injection. Samples of jugular blood were obtained from each dog, using citrate as an anticoagulant. A platelet count was obtained for each sample. Platelet aggregation and atp released from the aggregating platelets were measured within 1 hour of sample collection, using a whole-blood aggregometer. Adenosine diphosphate (ADP) and collagen were used as aggregating agents. Aggregation was measured over 6 minutes for each aggregating agent; atp release in response to collagen, but not to ADP, was measured over the same period. For 1 hr samples, there was a significant (P &lt; 0.01) reduction from pre values in the ability of platelets to aggregate in response to ADP. Bleeding time was determined, using a published procedure, with each dog as its own control. Bleeding time during the same period was found to be significantly increased over pre values for 1 hr (P &lt; 0.01) and 6 hr (P &lt; 0.02) samples. There was no significant difference between bt for 1 hr and 4 hr samples. Median serum cephalothin concentrations in pre, 1 hr,4hr, and 6 hr samples did not correlate significantly to platelet aggregation, atp release, platelet count, or bt at any time during the study. Because serum cephalothin concentration was so low, and because there are few reports of the kinetics of cephalothin after iv administration, serum cephalothin was measured in 2 dogs over 2 hours after single iv administration of cephalothin. Values reached a peak at 2 minutes after drug administration, then decreased rapidly over 10 to 15 minutes, and were low by 2 hours.

Platelet aggregation in dogs after sedation with acepromazine and atropine and during subsequent general anesthesia and surgery

Summary Platelet aggregation and adenosine triphosphate (atp) release were measured by use of the impedance method in blood samples obtained from 25 adult female Beagles before and after sedation with acepromazine (0.13 mg/kg of body weight) and atropine (0.05 mg/kg), and during general anesthesia. General anesthesia was induced by iv administration of thiamylal (average dosage, 2.1 mg/kg; range, 1.2 to 4.2 mg/kg) and was maintained with halothane in oxygen. Samples of jugular venous blood were obtained from each dog, using citrate as anticoagulant. Platelet count was done on each sample. Platelet aggregation and atp released from the aggregating platelets were measured within 2.5 hours of sample collection, using a whole-blood aggregometer. Adenosine diphosphate (adp) or collagen was used as aggregating agent. For each aggregating agent, platelet aggregation and atp release were measured over 6 minutes. After sedation with acepromazine and atropine, significant (P &lt; 0.01) reduction was observed in platelet count (from median values of 341,000 cells/μl to 283,000 cells/μl) and in the ability of platelets to aggregate in response to adp (from 14.0 to 7.0 Ω). During the same period, maximal release of atp in response to collagen also was reduced (from 5.56 μmol to 4.57 μmol; P &lt; 0.01); however, this difference ceased to be significant when atp release was normalized for platelet count. During general anesthesia and surgery (200 minutes after sedation), platelet count and aggregation responses to adp and collagen had returned to presedation values. None of the dogs in this study appeared to have hemostasis problems during surgery. In conclusion, sedation with acepromazine and atropine induces measurable inhibition of adp-induced platelet aggregation that resolves during subsequent general anesthesia and surgery. Transient inhibition of platelet aggregation is not manifested by a change in gross hemostasis during surgery.

Dipyridamole Potentiates Platelet Inhibition by Nitric Oxide

In a placebo-controlled double blind cross-over experiment the adenosine uptake inhibitor dipyridamole (400 mg/day) did not affect ex vivo platelet aggregation induced by collagen or adenosine-diphosphate (ADP) in an electronic whole blood aggregometer (WBA). Dipyridamole was also inactive in vitro, unless red blood cell injury was deliberately enhanced, thereby increasing the level of free adenine nucleotides. Since dipyridamole also inhibits cyclic guanosine monophosphate (GMP) phosphodiesterase (PDE), we used platelet rich plasma (PRP) to study its interaction with authentic and endothelium-derived nitric oxide (NO). The latter inhibits platelets by increasing cyclic GMP. Dipyridamole (1 to 30 microM), either alone or in combination with a subthreshold concentration of prostacyclin (PGI2), was inactive. However, when combined with a subthreshold concentration of NO, dipyridamole caused a concentration-dependent platelet suppression, which became more pronounced when PGI2 was present as well. It is concluded that dipyridamole could reduce the threshold for platelet suppression by NO through inhibition of cyclic GMP PDE.

Enhanced erythrocyte aggregability in occlusive cerebrovascular disease.

We measured the rate of erythrocyte aggregation using our whole-blood aggregometer in 80 patients with occlusive cerebrovascular disease during the acute and chronic phases. We compared the data with values for 38 age-matched healthy controls. Mean +/- SD erythrocyte aggregability of the patients during both the acute phase (0.145 +/- 0.21/sec, n = 35) and the chronic phase (0.139 +/- 0.21/sec, n = 45) was higher than that in the controls (0.123 +/- 0.21/sec, n = 38; p less than 0.01). Erythrocyte aggregability was positively correlated with the plasma concentration of globulin and fibrinogen and inversely correlated with the albumin:globulin ratio. However, these correlations did not necessarily exclude the possibility that some unknown substance(s) released from ischemic tissue might enhance erythrocyte aggregability.

Whole-blood red blood cell aggregometer for human and feline blood.

A whole-blood aggregometer of red blood cells (RBC) is described. It consists of a transparent 0.26-cm ID vinyl tube of approximately 30 cm in length containing freshly drawn heparinized blood and a densitometer head that is attached to the tube. The densitometer head consists of an infrared light source of gallium arsenide and a light detector (silicon photodiode) to monitor changes in optical density of the blood in the tube. The tube and densitometer head were installed in a temperature-controlled box at 37 degrees C. The blood in the tube was first subjected to rapid flow with a solenoid so that the wall shear rate of the blood was approximately 500 s-1. The shear gave rise to a rapid increase in optical density of the blood due to dispersion of the blood corpuscles. The blood was then brought abruptly to a full stop. After the flow had stopped the densitometer head revealed a gradual decrease in optical density in association with RBC aggregate formation. The resultant pattern was termed by us an "RBC aggregogram." The RBC aggregogram exhibited an exponential decay in its initial part, which was followed by an asymptotic decrease. A simple mathematical procedure was employed to calculate the rate constant of the initial decrease from the two values on the RBC aggregogram at 10 and 20 s. The rate constant k10 was 0.192 +/- 0.028 (5.2 s as time constant; 3.6 s as half time) for feline blood and 0.129 +/- 0.012 (7.7 s as time constant; 5.3 s as half time) for human blood. The RBC aggregation rate varied linearly with the hematocrit below 40%.

Use of the whole-blood aggregometer to study the aggregation of “giant” platelets

Use of the whole-blood aggregometer to study the aggregation of “giant” platelets