Two-event Model Research Articles

Problematic non-double-couple mechanism of the 2002 Amfilochia Mw5 earthquake, Western Greece

Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%, by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms, carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values. However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data, that the Amfilochia earthquake was an almost pure-shear event.

Pathophysiology of TRALI: current concepts

Transfusion-related acute lung injury (TRALI) is a life-threatening adverse event in blood transfusion and is considered the most common cause of transfusion-related fatalities in the United States and the United Kingdom. TRALI and acute respiratory distress syndrome (ARDS) share a common clinical definition except that TRALI is temporally and mechanistically related to blood transfusion. Two different mechanisms have been proposed. The first is leuko-agglutination due to infusion of leukocyte Antibodies with the blood product transfused. The second proposes a two-event model where the first event is the clinical condition of the patient, and the second the infusion of lipids that accumulate in blood products during storage. An emerging common pathway of granulocyte activation is discussed, as is the relevance of immune and non-immune TRALI from a practical point of view. Some unresolved questions in TRALI pathophysiology, including the relevance of Antibodies to HLA class-II antigens and the participation of the endothelium, are examined, as are the suggested preventive measures for both immune and non-immune TRALI. It is concluded that further clinical and experimental data are necessary before any recommendations can be made regarding non-immune TRALI. In contrast, in immune TRALI, preventive measures to avoid transfusion of blood products that contain leukocyte Antibodies should be taken now.

Donor antibodies to HNA-3a implicated in TRALI reactions prime neutrophils and cause PMN-mediated damage to human pulmonary microvascular endothelial cells in a two-event in vitro model

AbstractTransfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related mortality. Antibodies to HNA-3a are commonly implicated in TRALI. We hypothesized that HNA-3a antibodies prime neutrophils (PMNs) and cause PMN-mediated cytotoxicity through a two-event pathogenesis. Isolated HNA-3a+ or HNA-3a− PMNs were incubated with plasma containing HNA-3a antibodies implicated in TRALI, and their ability to prime the oxidase was measured. Human pulmonary microvascular endothelial cells (HMVECs) were activated with endotoxin or buffer, HNA-3a+ or HNA-3a− PMNs were added, and the coculture was incubated with plasma ± antibodies to HNA-3a. PMN-mediated damage was measured by counting viable HMVECs/mm2. Plasma containing HNA-3a antibodies primed the fMLP-activated respiratory burst of HNA-3a+, but not HNA-3a−, PMNs and elicited PMN-mediated damage of LPS-activated HMVECs when HNA-3a+, but not HNA-3a−, PMNs were used. Thus, antibodies to HNA-3a primed PMNs and caused PMN-mediated HMVEC cytotoxicity in a two-event model identical to biologic response modifiers implicated in TRALI.

The two-event model of transfusion-related acute lung injury

The objective of this review is to present the two-event model of transfusion-related acute lung injury (TRALI), a life-threatening complication of transfusions that has been the most common cause of transfusion-related death over the past 2 yrs in the United States. The two-event model of TRALI, which is identical to the pathogenesis of the acute respiratory distress syndrome (ARDS), is reviewed and contrasted to antibody-mediated TRALI. Laboratory studies, both in vitro and in vivo, are discussed as well as human studies of TRALI. Methods to avoid patient exposure to blood components that may cause TRALI are also discussed.

Transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a life-threatening adverse event of transfusion, which has an increasing incidence in the United States and is the leading cause of transfusion-related death. TRALI and acute lung injury (ALI) share a common clinical definition except that TRALI is temporally- and mechanistically-related to transfusion of blood or blood components. A number of different models have been proposed to explain the pathogenesis. The first is an antibody-mediated event whereby transfusion of anti-HLA, class I or class II, or anti-granulocyte antibodies into patients whose leukocytes express the cognate antigens. The antibody:antigen interaction causes complement-mediated pulmonary sequestration and activation of neutrophils (PMNs) resulting in TRALI. The second is a two-event model: the first event is the clinical condition of the patient resulting in pulmonary endothelial activation and PMN sequestration, and the second event is the transfusion of a biologic response modifier (including anti-granulocyte antibodies, lipids, and CD40 ligand) that activates these adherent PMNs resulting in endothelial damage, capillary leak, and TRALI. These hypotheses are discussed with respect to animal models and human studies that provide the experimental and clinical relevance. The definition of TRALI, patient predisposition, treatment, prevention and reporting guidelines are also examined.

THE TWO-EVENT CONSTRUCT OF POSTINJURY MULTIPLE ORGAN FAILURE

THE TWO-EVENT CONSTRUCT OF POSTINJURY MULTIPLE ORGAN FAILURE

The Two-Event Model of Transfusion-Related Acute Lung Injury: Antibodies to HNA-3a Cause PMN Cytotoxicity.

Transfusion related acute lung injury (TRALI) is a serious complication of blood administration. TRALI is neutrophil (PMN)-mediated and the pathogenesis is due to the infusion of antibodies directed against specific HLA (class I or II) or granulocyte antigens and may also be the result of two events: 1) a predisposing clinical condition of the patient resulting in PMN pulmonary sequestration followed by 2) the infusion of biologic response modifiers (BRMs), e.g. lipids from stored blood. These BRMs prime PMNs in vitro and cause PMN cytotoxicity in vivo resulting in endothelial damage, capillary leak and TRALI. We hypothesize that antibodies directed against specific PMN antigens cause rapid PMN priming and cytotoxicity in a two-event model, specific to the antigen they recognize. PMNs were isolated from healthy donors and 5b− (HNA-3a−) donors by standard techniques and were incubated for 3 min with 10% fresh plasma (FP) from healthy donors, plasma from three donors who had antibodies against HNA-3a and were implicated in TRALI, or 10% immune complexes (ICs) made from sera (+ control). Selected wells had Fab′2 fragments against the Fc receptors (CD16, CD32 & CD64). The maximal rate of O2− production was measured as cytochrome c reduction at 550 nm. Priming is defined as augmentation of the fMLP-activated respiratory burst (Table 1). We used an in vitro model of TRALI (Wyman AJP Cell 283: C1592, 2002) in which Human plumonary microvascular endothelial cells (HMVECs) were grown to 90% confluence and incubated with buffer or endotoxin (LPS) [200 ng/ml] for 6 hours. HNA-3a+ PMNs were added ± Fab′2 fragments, allowed to settle, and incubated for 30 min with FP or HNA-3a+ plasma. The plates were forcibly decanted and the viable HMVECs per mm2 were counted (Table 2). HNA-3a+ plasma significantly primed the PMN oxidase as compared to FP-treated controls (Table 1). Pre-treatment of PMNs with Fab′2 inhibited IC priming but did not affect other groups, and HNA-3a+ plasma did not prime HNA-3a− PMNs (data not shown). HNA-3a+ plasma ± LPS without PMNs did not affect HMVEC viability (data not shown), and HMVECs activated with LPS caused widespread PMN adherence. HNA-3a+ plasma plus HNA-3a+ PMNs caused destruction of LPS-activated HMVECs that was partially inhibited by Fab′2 fragments (Table 2). We conclude that HNA-3a+ plasma rapidly, effectively, and specifically primes HNA3+ PMNs. HNA-3a+ plasma can also serve as the second event in a two-event model of PMN-mediated HMVEC damage. Thus, antibodies directed against specific granulocyte antigens and lipids from stored blood may cause TRALI through a common final pathway of PMN activation.HNA-3a+ (5b+) plasma priming of HNA-3a+ PMNsPre-tx/GroupControlICsFFPDonor 1Donor 2Donor 3Buffer2.7±0.58.8±0.7†2.5±0.45.7±1.8†6.5±†5.0±1.0†Fab′22.1±0.83.2±0.4*3.6±0.93.8±0.74.6±1.54.0±1.0Units=nmol O2−/min; †=P<0.05 versus FFP controls; *=p<0.05 versus ICs.HNA-3a+ (5b+) plasma causes PMN cytotoxicityPre-tx/GroupControlLPS/PMNsLPS/PMNs/FFPLPS/PMNs/5b plasmaBuffer245±1234±8229±9151±7†Fab′2no datano data240±9190±*Units=viable HMVECs/mm2; †=p<0.05 versus Controls and LPS/PMNs/FFP; *=p<0.05 versus LPS/PMN/5b+ plasma.

Transfusion Medicine

In the vein-to-vein flow of blood from donor to patient, the role of the transfusion medicine specialist has become increasingly centered at the bedside. Three clinically centered issues in blood safety and in blood conservation are presented in this chapter. In Section I, Dr. Patricia Hewitt presents the epidemiologic and clinical evidence regarding new variant Creutzfeldt-Jakob disease (nvCJD) in the UK and its relevance to transfusion medicine. Lessons learned from the responses by the National Blood Service to this crisis are discussed, particularly in the context of recent evidence of a case of vCJD transmission by blood transfusion and a second case of apparent transmission of abnormal prion protein without development of clinical illness. In Section II, Dr. Christopher Silliman and his colleagues summarize recent knowledge gained regarding transfusion-related acute lung injury (TRALI), which is now the leading cause of transfusion-related mortality. Two different etiologies have been proposed: a single antibody-medicated event, involving anti-HLA Class I and Class II, or anti-granulocyte antibodies; and a two-event model, which includes the clinical condition of the patient resulting in pulmonary endothelial activation and neutrophil sequestration. The second event is the transfusion of a biologic response modifier (lipids or antibodies) in the blood component that activates primed neutrophils. Prevention, clinical treatment, and proposed definition of TRALI are discussed. In Section III, Dr. Lawrence Goodnough and colleagues present a transfusion medicine service approach to the utilization of recombinant factor VIIa (rFVIIa) in non-approved clinical settings. rFVIIa has a potential role as a hemostatic intervention in a variety of clinical settings, yet few clinical trials have been completed to date to guide indications for its use. The policies presented here are those in place at the authors' medical center, and will undergo periodic review and revision as relevant new information and data are generated.

The abdominal compartment syndrome as a second insult during systemic neutrophil priming provokes multiple organ injury.

In our recent clinical study of damage control laparotomy, the abdominal compartment syndrome (ACS) emerged as an independent risk factor for postinjury multiple organ failure (MOF). We and others have shown previously that the ACS promotes the systemic production of proinflammatory cytokines. Our study objective was to develop a clinically relevant two-event animal model of postinjury MOF using the ACS as a second insult during systemic neutrophil priming to provoke organ dysfunction. Male adult rats underwent hemorrhagic shock (30 mmHg x 45 min) and were resuscitated with crystalloids and shed blood. The timing of postshock systemic neutrophil (PMN) priming was determined by the surface expression of CD11b via flow cytometry. Finding maximal PMN priming at 8 h, but no priming at 2 h (early) and 18 h (late), the ACS (25 mmHg x 60 min) was introduced at these time points. At 24 h postshock, lung injury was assessed by lung elastase concentration and Evans blue dye extravasation in bronchoalveolar lavage. Liver and renal injuries were determined by serum alanine aminotransferase, serum creatinine, and blood urea nitrogen. The ACS during the time of maximal systemic PMN priming (8 h) provoked lung and liver injury, but did not if introduced at 2 or 18 h postshock when there was no evidence of systemic PMN priming. The 24-h mortality of this two-event model was 33%. These findings corroborate the potential for the ACS to promote multiple organ injury when occurring at the time of systemic PMN priming. This clinically relevant two-event animal model of PMN organ injury may be useful in elucidating therapy strategies to prevent postinjury MOF.

Post-hemorrhagic shock mesenteric lymph activates human pulmonary microvascular endothelium for in vitro neutrophil-mediated injury: the role of intercellular adhesion molecule-1.

Splanchnic hypoperfusion is believed to be central in the pathogenesis of hemorrhagic shock-induced acute respiratory distress syndrome and multiple organ failure. Our previous work focused on the portal circulation as the conduit for gut-derived mediators of acute respiratory distress syndrome. Our current focus is the proinflammatory effects of postshock mesenteric lymph. We hypothesize that postshock lymph induces neutrophil (PMN)-mediated endothelial cell damage in an intercellular adhesion molecule-1 (ICAM-1)-dependent fashion, and devised a two-insult model to test this hypothesis. Rats (n > or = 5) underwent hemorrhagic shock (mean arterial pressure, 40 mm Hg for 30 minutes) and resuscitation (shed blood plus two times crystalloid) with lymph collection. Human pulmonary microvascular endothelial cells (HMVECs) were divided into three groups and grown to near confluence. Group 1 was incubated for 6 hours in 1% preshock or postshock lymph and ICAM-1 was measured by flow cytometry. Group 2 consisted of coculture of HMVECs and PMNs after endothelial cell activation to determine whether postshock lymph would stimulate PMN adherence. Group 3 was incubated under identical conditions, but PMNs were added for 30 minutes, and then activated with 4.5 micromol/L lysophosphatidylcholine (lyso-PC) for 1 hour to ascertain cytotoxicity. HMVEC density was measured using microscopy and recorded as HMVECs per millimeter squared. ICAM-1-blocking antibody and isotype control were used to assess the effects of ICAM-1 on PMN cytotoxicity. A buffer control was used for comparison using analysis of variance with Tukey's correction. Postshock lymph activated HMVECs for increased surface expression of ICAM-1 and stimulated PMNs to adhere to endothelial cell monolayers. Activation of PMNs with lyso-PC in the presence of postshock lymph resulted in marked HMVEC death. The addition of an ICAM-1-blocking antibody abrogated this effect. Neither postshock lymph alone (758 +/- 35 HMVECs/mm(2)), nor postshock lymph in the presence of quiescent PMNs alone (734 +/- 28 HMVECs/mm(2)), nor lymph plus lyso-PC (834 +/- 21 HMVECs/mm(2)) provoked endothelial cell damage. Postshock mesenteric lymph activates endothelial cells for increased ICAM-1 expression and PMN adherence. Furthermore, postshock lymph acts as an inciting event in a two-event in vitro model of PMN-mediated endothelial cell injury. These findings further substantiate the key mechanistic role of mesenteric lymph in hemorrhagic shock-induced acute lung injury and suggest that ICAM-1 expression is pivotal in the two-event model of multiple organ failure.

"Primed" human neutrophils on a standard peripheral blood smear.

In the two-event model of end organ injury the first event is the priming of circulating neutrophils (PMNs); the second stressor activates these primed PMNs with subsequent indiscriminate release of cytotoxic reactive oxygen metabolites and proteases into the PMNendothelial microenvironment. After both trauma and cardiopulmonary bypass, circulating PMNs are primed for superoxide release. The first “priming” event in the development of multiple organ failure can be detected with standard light microscopic (100 ) evaluation of routine peripheral blood smears (Wright-Giemsa stain). The resting neutrophil (A) exhibits a smooth, round cell shape with uniform cytoplasmic granularity. After priming (B), with 2 M platelet activating factor, PMNs lose their resting morphology and exhibit an irregular cell shape and membrane, toxic granulation with polarized granularity (white arrowhead), and cytoplasmic vacuolization (black arrowhead).

A Method for Parametric Estimation of the Number and Size Distribution of Cell Clusters from Observations in a Section Plane

The problem of finding the number and size distribution of cell clusters that grow in an organ or tissue from observations of the number and sizes of transections of such cell clusters in a planar section is considered. This problem is closely related to the well-known corpuscle or Wicksell problem in stereology, which deals with transections of spherical objects. However, for most biological applications, it is unrealistic to assume that cell clusters have spherical shapes since they may grow in various ways. We therefore propose a method that allows for more general spatial configurations of the clusters. Under the assumption that a parametric growth model is available for the number and sizes of the cell clusters, expressions are obtained for the probability distributions of the number and sizes of transections of the clusters in a section plane for each point in time. These expressions contain coefficients that are independent of the parametric growth model and time but depend on which model is chosen for the configuration of the cell clusters in space. These results enable us to perform estimation of the parameters of the growth model by maximum likelihood directly on the data instead of having to deal with the inverse problem of estimation of three-dimensional quantities based on two-dimensional data. For realistic choices of the configuration model, it will not be possible to obtain the exact values of the coefficients, but they can easily be approximated by means of computer simulations of the spatial configuration. Monte Carlo simulations were performed to approximate the coefficients for two particular spatial configuration models. For these two configuration models, the proposed method is applied to data on preneoplastic minifoci in rat liver under the assumption of a two-event model of carcinogenesis as the parametric growth model.

Targeted mutation at cytosine-containing pyrimidine dimers: studies of Escherichia coli B/r with acetophenone and 313-nm light.

We have tested the two-event model for UV mutagenesis producing class 2 suppressor mutations at glutamine tRNA genes in Escherichia coli. In the model used, the induction/indexing lesion is any type of pyrimidine dimer and the premutational photoproduct at the target site is a cytosine-containing dimer. Specific mutation-frequency responses were analyzed under conditions in which the ratio of thymine-thymine dimers to cytosine-containing dimers was modified by using 313-nm light and 0.0%, 0.1%, or 0.2% acetophenone. Changes observed in the production of class 2 suppressor mutations were consistent with the model and suggested that the G X C leads to A X T transitions responsible for class 2 suppressor mutations are targeted by cytosine-containing pyrimidine dimers at the mutational sites.

The visual perception of accelerated motion.

The present research is an investigation of how changes in the rate of motion are percieved. Five separate experiments were performed with the use of filmed stimulus material and a variety of response measures, including both categorical judgments and reporduction techniques. It was found that (a) the smaller the ratio of terminal to initial velocity, the less frequent the judgments of acceleration or deceleration, (b) deceleration was significantly easier to perceive than acceleration, (c) the perception of acceleration was facilitated when the velocity of a lead-in segment was the same as the velocity at onset of motion, (d) a short tunnel centered in the motion path facilitated the perception of acceleration and deceleration, and (e) instantaneous changes in velocity were much more easily perceived than gradual changes. A one-event model for the perception of motion change in which there is a continuous interplay between earlier, later, and interpolated motion segments is favored over a two-event model in which earlier and later segments of velocity are compared.