[Automatic load-distributing band CPR (AutoPulse™) in prone position, feasible?] / Mechanische CPR (AutoPulse™) in Bauchlage, machbar?

BACKGROUND: Due to SARS-CoV­2 respiratory failure, prone positioning of patients with respiratory and hemodynamic instability has become a frequent intervention in intensive care units (ICUs), and even in patients undergoing transfer in an ambulance or helicopter. It has become increasingly important how to perform safe and effective CPR in prone position, achieving both an optimal outcome for the patient and optimal protection of staff from infection. MATERIALS AND METHODS: We conducted feasibility tests to assess the effects of CPR with an automatic load-distributing band (AutoPulse™) in prone position and discussed different aspects of mechanical chest compression (mCPR) in prone position. RESULTS: In supine position, AutoPulse™ generated a constant pressure depth of 3cm at a frequency of 84/min. In prone position, AutoPulse™ generated a constant pressure depth of 2.6cm at a frequency of 84/min. CONCLUSION: We found mCPR to be feasible in manikins in both prone and supine positions.

Optimisation of the dosage of tranexamic acid in trauma patients with population pharmacokinetic analysis.

Tranexamic acid is used both pre-hospital and in-hospital as an antifibrinolytic drug to treat or prevent hyperfibrinolysis in trauma patients; dosing, however, remains empirical. We aimed to measure plasma levels of tranexamic acid in patients receiving pre-hospital anti-hyperfibrinolytic therapy and to build a population pharmacokinetic model to propose an optimised dosing regimen. Seventy-three trauma patients were enrolled and each received tranexamic acid 1 g intravenously pre-hospital. A blood sample was drawn after arrival in the emergency department, and we measured the plasma tranexamic acid concentration using liquid chromatography-mass spectrometry, and modelled the data using non-linear mixed effect modelling. Tranexamic acid was administered at a median (IQR [range]) time of 43 (30-55 [5-135]) min after trauma. Plasma tranexamic acid levels were determined on arrival at hospital, 57 (43-70 [20-148]) min after pre-hospital administration of the drug. The measured concentration was 28.7 (21.5-38.5 [8.7-89.0]) µg.ml-1 . Our subjects had sustained severe trauma; injury severity score 20 (16-29 [5-75]), including penetrating injury in 2.8% and isolated traumatic brain injury in 19.7%. The pharmacokinetics were ascribed a two-compartment open model with body-weight as the main covariate. As tranexamic acid concentrations may fall below therapeutic levels during initial hospital treatment, we propose additional dosing schemes to maintain a specific target blood concentration for as long as required. This is the first study to investigate plasma level and pharmacokinetics of tranexamic acid after pre-hospital administration in trauma patients. Our proposed dosing regimen could be used in subsequent clinical trials to better study efficacy and tolerance profiles with controlled blood concentrations.

[Sealing of the hepatic resection area using hemostat devices does not improve results of adequate surgery]. / Versiegelung der Leberresektionsfläche mit Gewebsklebematerialien bewirkt keine weitere Verbesserung adäquater Chirurgie.

PURPOSE: In hepatic resections, there has been a high quality demand. The aim of this systematic clinical, prospective, unblinded unicenter observational study with two arms in an unselected patient cohort was to investigate whether hemostat device can significantly improve outcome in resective liver surgery, in particular, in high risk patients. METHODS: All consecutive patients (mean age, 60.5 [range, 17 - 96] years) who underwent hepatic resection (ntotal = 770) were prospectively documented in a computer-based registry at a university hospital (tertiary center) over a time period of 10 years and retrospectively evaluated specifically with regard to the use (-/+; in daily practice and intraoperative decision-making) of hemostat device (Tissucol(®), n = 59/Tachocomb(®), n = 202/combination, n = 55) indicated (among others) by drainage volume, inflammatory parameters and rate of specific complications (nvalidated = 541 [100 %]). RESULTS: Most frequently, (a-)/typical segmental resections were used: n = 192/90 (3-segment resection, only n = 38). 1) For the assignment of patients to the two different groups (-/+ hemostat device), weight loss and type of resection were found as significant factors (trend: ASA, cirrhosis), for the amount of drainage volume, ASA, sex, Karnofsky Performance Scale and also type of resections using independent distributed statistical tests (such as χ(2), U test [Mann/Whitney]; H test [Kruskal-Willis]; correlation coefficient by Spearman) - no impact: smoking, diabetes, BMI, ethanol. 2) Not taking into account these parameters, the use of hemostat device was characterized by an increased drainage volume (negative control < Tissucol = Tachocomb < combination). 3) Using multifactorial analysis of variance, it was found even under correction by the factors with significant impact elucidated in the single test that the application of hemostat device onto the hepatic resection area resulted unexpectedly rather in an increase than a decrease of the drainage volume but 4) under accompanying more pronounced increase of the white blood cell count (leucocytosis). 5) General and specific complications such as postoperative bleeding, biliary fistula and subhepatic abscess were not further lowered in a significant manner using hemostat device. CONCLUSION: Adequate surgery in the operative management of hepatic resection area cannot further be improved or optimized using hemostat device. In this context, drainage volume may not be considered a sufficient rather an orienting parameter. However, there is an inflammatory response detectable most likely indicated by a(n un-)specific effusion and increase of white blood cell count, which can be interpreted as a) being characteristic for the problematic group of patients, in whom hemostat device was decided to be useful and was finally used in daily prectice, or b) reactive inflammation to foreign material.

[Prospective Evaluation of Risk Factors Concerning Intraoperative Conversion from Laparoscopic to Open Cholecystectomy]. / Prospektive Evaluation von Risikofaktoren bezüglich intraoperativer Konversion von laparoskopischer zu offener Cholezystektomie.

BACKGROUND: The surgical approach of choice in the treatment of symptomatic cholecystolithiasis is considered to be elective laparoscopic cholecystectomy (CCE) as the established gold standard. Today, approximately 80-90% of CCE are performed using a laparoscopic approach whereas the remaining portion undergoes primary conventional CCE, however, in 6% conversion is necessary. AIM: Since pathological aspects found intraoperatively and finally requiring conversion are correlated to an increased risk for complications, it appears reasonable to assess the risk factors prior to operation. PATIENTS AND METHODS: Through a well defined study period of 9 years, all consecutive patients who underwent CCE for cholecystolithiasis at the Municipal Hospital "HELIOS Klinikum Aue" were enrolled in a registry comparing laparoscopic and conversion CCE. Diverse parameters were tested as to whether they increase significantly the risk for conversion. The intensity of each factor-associated impact on a possible conversion was determined. RESULTS: From 2001 to 2009 1477 patients underwent CCE at the Municipal Hospital "Helios Klinikum Aue", out of them 131 (8.9%) cases were primarily treated by conventional CCE whereas in the vast majority (1346 subjects [91.1%]), laparoscopic CCE was the initial approach. However, conversion became necessary in 106 individuals resulting in a conversion rate of 7.9%. Comparing data obtained from laparoscopic CCE with those from open procedure after conversion, there were significant differences in operating time, complication rate and postoperative hospital stay (p = 0.01). Over the study period, there were 5 cases (0.37%) with iatrogenic injuries of the biliary system. Hospital mortality was 0.08% in the laparoscopic and 2.8% in the conversion group. The following parameters were found to have a significant impact on the risk for conversion (univariate analysis): elevation of CRP, preoperative ERCP, renal insufficiency, previous laparotomy, histological grade M3 (ulcerous, haemorrhagic necrotising cholecystitis, perforation of the gall bladder) and M4 (carcinoma of the gall bladder). While in the spectrum of preoperative factors former ERCP, elevation of CRP and terminal renal insufficiency were most relevant (2- to 3-fold each), histological grade M3 and M4, 7- and 14-fold, respectively, showed the greatest impact on conversion rate highlighting the profile of postoperative parameters. CONCLUSION: The main focus is directed to keep the conversion rate low. In case of diagnosing a severely inflamed gall bladder, a primarily open procedure or an early decision for conversion should be considered.

[Deployment and efficacy of ground versus helicopter emergency service for severely injured patients. Analysis of a nationwide Swiss trauma center]. / Status quo der Boden- und Luftrettung schwerverletzter Patienten. Analyse eines überregionalen Schweizer Traumazentrums.

The influence of the transport mode, i.e. Helicopter Emergency Medical Service (HEMS) versus ground-based Emergency Medical Service (EMS) on the mortality of multiple trauma patients is still controversially discussed in the literature. In this study a total of 333 multiple trauma patients treated over a 1-year period in a level I trauma center in Switzerland were analyzed. Using the newly established revised injury severity classification (RISC) score there was a tendency towards a better outcome for patients transported by HEMS (standardized mortality ratio 1.06 for HEMS versus 1.29 for EMS). Overall a short preclinical time and the presence of an emergency physician (EP) were associated with a better outcome.

Hemagglutinin stalk-based universal vaccine constructs protect against group 2 influenza A viruses.

Current influenza virus vaccines contain H1N1 (phylogenetic group 1 hemagglutinin), H3N2 (phylogenetic group 2 hemagglutinin), and influenza B virus components. These vaccines induce good protection against closely matched strains by predominantly eliciting antibodies against the membrane distal globular head domain of their respective viral hemagglutinins. This domain, however, undergoes rapid antigenic drift, allowing the virus to escape neutralizing antibody responses. The membrane proximal stalk domain of the hemagglutinin is much more conserved compared to the head domain. In recent years, a growing collection of antibodies that neutralize a broad range of influenza virus strains and subtypes by binding to this domain has been isolated. Here, we demonstrate that a vaccination strategy based on the stalk domain of the H3 hemagglutinin (group 2) induces in mice broadly neutralizing anti-stalk antibodies that are highly cross-reactive to heterologous H3, H10, H14, H15, and H7 (derived from the novel Chinese H7N9 virus) hemagglutinins. Furthermore, we demonstrate that these antibodies confer broad protection against influenza viruses expressing various group 2 hemagglutinins, including an H7 subtype. Through passive transfer experiments, we show that the protection is mediated mainly by neutralizing antibodies against the stalk domain. Our data suggest that, in mice, a vaccine strategy based on the hemagglutinin stalk domain can protect against viruses expressing divergent group 2 hemagglutinins.

Model of influenza A virus infection: dynamics of viral antagonism and innate immune response.

Viral antagonism of host responses is an essential component of virus pathogenicity. The study of the interplay between immune response and viral antagonism is challenging due to the involvement of many processes acting at multiple time scales. Here we develop an ordinary differential equation model to investigate the early, experimentally measured, responses of human monocyte-derived dendritic cells to infection by two H1N1 influenza A viruses of different clinical outcomes: pandemic A/California/4/2009 and seasonal A/New Caledonia/20/1999. Our results reveal how the strength of virus antagonism, and the time scale over which it acts to thwart the innate immune response, differs significantly between the two viruses, as is made clear by their impact on the temporal behavior of a number of measured genes. The model thus sheds light on the mechanisms that underlie the variability of innate immune responses to different H1N1 viruses.

Summary of FDA workshop on ischemia reperfusion injury in kidney transplantation.

The Food and Drug Administration (FDA) held an open public workshop in September 2011 to discuss the current state of science related to the effects of ischemia reperfusion injury (IRI) on outcomes in kidney transplantation. Topics included the development of IRI and delayed graft function (DGF), histology and biomarkers, donor factors, recipient factors, organ quality and organ preservation by means of cold storage solutions or machine perfusion. Various mechanisms of injury and maladaptive response to IRI were discussed as potential targets of intervention. Animal models evaluating specific pathophysiological pathways were presented, as were the limitations of extrapolating animal results to humans. Clinical trials of various drug products administered in the peri-transplant period were summarized; a few demonstrated early improvements in DGF, but none demonstrated an improvement in late graft function. Clinical trial design for IRI and DGF were also discussed.

[Matched-pair analysis comparing laparoscopic (LA) vs. single-port appendectomy (SP) for initial assessment of a new surgical approach during its inauguration]. / "Matched-Pair"-Analyse der laparoskopischen (LA) vs. Single-Port-Appendektomie (SP) zur initialen Evaluation im Rahmen der Etablierung einer neuen Operationsmethode.

INTRODUCTION: By minimising the invasiveness of a surgical intervention, a reduction of operative trauma can be achieved. AIM AND METHODS: The aim of this study was based on a theoretical approach to investigate (i) the feasibility of the SP approach and its overall costs, and, furthermore, (ii) the patients' outcome based on simple perioperative parameters available in daily clinical practice. Therefore, single-port (SP) and laparoscopic appendectomies (LA) were compared using a matched-pair analysis. As a prediction, an absolute match between the criteria histology, sex and ASA stage was required. RESULTS: From 01/01/2009 to 12/31/2010, 196 (60 % were females) consecutive patients underwent appendectomy. Out of them, in 23 patients with either SP or LA appendectomy the predictions for matched-pair analysis (congruence in histopathological finding, sex and ASA criteria) were fulfilled. The operating time was the target criterion for the feasibility of the new surgical method (SP), which could be shortened as seen by comparing SP No. 1-10 with 11-23 (54.6 ± 19.8 min vs. 28.5 ± 18.9 min) expressing the typical effect of a learning curve. The times were similar to those for LA. The postoperative hospital stay and complication rate used to appropriately assess patient outcome did not show a significant difference if comparing SP and LA. Based on the use of single ports, which can be re-used (which has been also a further target) in SP (34.8 %) at the end of the investigation period, SP and LA can be considered comparable surgical techniques with regard to operating times, middle-term outcome and general costs. CONCLUSION: SP is (in case of well-developed laparoscopic expertise) a surgical method that can be easily inaugurated and considered as a feasible approach in daily surgical practice; it is comparable to LA with regard to outcome and general costs. Based on this, SP can be gradually added to the spectrum of surgical procedures in clinical practice and can be performed in suitable cases. A further systematic institutional or even country-wide case register appears to be recommendable to recruit a larger case number and, thus, to achieve a better knowledge on the perioperative management as well as the especially interesting long-term outcome for an appropriate assessment of treatment quality.

[Hybrid NOS appendectomy (NA): clinical assessment of a new surgical technique]. / Hybrid-NOS-Appendektomie (NA), eine neue Operationsmethode - eine klinische Evaluation.

UNLABELLED: INTRODUCTION, AIM AND METHOD: Consecutive female patients undergoing hybrid NOS appendectomy (NA - with prospectively collected data) and laparoscopic appendectomy (LA - with retrospectively registered data) were compared by means of a matched-pair analysis according to selected criteria such as patient age, BMI, ASA and previous operations showing a near-perfect congruence with the following aims to: 1) demonstrate the feasibility of NA and to estimate its general costs, and 2) elucidate the outcome of the two techniques using available perioperative parameters from daily clinical practice. In particular, operating time, complications, histopathological findings, postoperative hospital stay and analgesic scores were used for comparison. A gynaecological follow-up investigation was carried out on the day of discharge and after a medium-term time period of 4 weeks in the NA group, and 6 months postoperatively, patients of both groups were interviewed using a standardised questionnaire. RESULTS: From 05/01/2008 to 02/28/2010, transvaginal NA (n = 30) was compared with the results of the conventional LA (n = 30) in 60 female patients with regard to the operative outcome. Overall, matched-pair analysis of LA with NA, the novel technique resulted in the assessment of basically comparable surgical procedures with regard to perioperative routine parameters and outcome. There were no intraoperative complications in either of the two approaches; conversion was not required in both techniques. In addition, there were no significant differences in operating time (p = 0.099), postoperative complications (p = 0.72) and analgesic scores (p = 0.33/0.46). Postoperative hospital stay was even slightly shorter in the NA group (p = 0.02). The costs of the two methods are almost identical if the same instruments are used. Patient interviews suggested a slightly faster recovery, greater satisfaction with the better cosmetic outcome as well as a reduced pain intensity in favour of transvaginal NA. CONCLUSION: Provided that a well developed laparoscopic expertise exists, it turned out i) that there are no serious reasons to resist a quick inauguration and establishment of NA for selected cases as well as ii) even to facilitate further clinical distribution of NA. Further systematic data collection appears to be indicated to analyse long-term outcome as parameters of an appropriate quality assurance.

Summary of the US FDA approval of belatacept.

Elements of the Food and Drug Administration (FDA) review of the clinical data that supported the approval of the Biologics License Application (BLA) for belatacept for prophylaxis of organ rejection in adult patients receiving a kidney transplant are summarized. The article is not intended as a comprehensive summary of the entire belatacept data submission. Rather, the discussion is meant to illustrate aspects of the FDA's process for evaluating efficacy and safety, using belatacept as an example.

[Life-saving air supported avalanche mission at night in high alpine terrain]. / Lebensrettender luftgestützter lawineneinsatz bei nacht im hochalpinen gelände.

This is a case report about a helicopter emergency medical service (HEMS) operation during the night in response to an avalanche accident with two completely buried victims. One of the victims was rescued alive after 9.2 h presenting with a patent airway and an air pocket and was successfully rewarmed with forced air from 23°C core temperature without any neurological deficits. After the rescue the patient developed lung edema which resolved spontaneously within 2 days. The second victim was found dead presenting with an air pocket but solid frozen thorax. The special circumstances of the rescue operation and treatment are presented and discussed. The impact of a frozen chest on resuscitation decisions is presented and discussed with an emphasis on the triage of multiple victims.

Clinical characteristics and haemodynamic state of patients undergoing interhospital transfer for postpartum haemorrhage: A study of a single-centre helicopter emergency medical service.

OBJECTIVE: Uterine artery embolization is an attractive option for the management of postpartum haemorrhage, however it is not available in every hospital. We compared the clinical characteristics and haemodynamic state of patients with postpartum haemorrhage, before and after helicopter transfer to a tertiary hospital for possible uterine artery embolization. We also analysed whether the type of treatment could modify the outcome. STUDY DESIGN: Between 1999 and 2019 in Switzerland, we retrospectively found 82 consecutive patients with postpartum haemorrhage who were transferred by a physician-staffed helicopter emergency medical service to the tertiary hospital for potential uterine artery embolization. The collected data included the type of delivery, estimated blood loss, shock index and blood lactate levels before transfer and at destination, uterine artery embolization rate and hospital mortality rate. Our primary outcome was to describe the clinical characteristics, outcomes and haemodynamic state of the patients with postpartum haemorrhage before and after helicopter transfer. Our secondary outcome was to report the treatments performed at the tertiary hospital. The collected data were analysed with Stata version 14 (Stata Corporation, College Station, TX, USA). Continuous data are compared by using the Student's t-test or the Mann-Whitney U test, as appropriate. RESULTS: We included 69 patients. Postpartum haemorrhage occurred after vaginal delivery in 38 cases (55%). Blood loss prior to transfer exceeded 2 L in 34% of cases. The median shock index was 1 (IQR 0.8-1.1) before transfer and 0.9 (IQR 0.8-1.1) after transfer (p = 0.41). The median lactate level was 2.9 mmol/L (IQR 2.1-6.8) before, and 2.1 mmol/L (IQR 1.55-3.5) after transfer (p = 0.90). Forty-four patients underwent uterine artery embolization (64%), with an overall success rate of 93%. One patient died (1.4%), from a haemorrhagic shock of abdominal origin. CONCLUSIONS: Interhospital helicopter transfer of patients with postpartum haemorrhage to a tertiary hospital seems to be safe in our setting, despite a significant proportion of patients exhibiting signs of haemodynamic instability. Decision criteria would be helpful to better guide choices regarding the transfer of patients with postpartum haemorrhage.

Summary of FDA antibody-mediated rejection workshop.

The Food and Drug Administration (FDA) held an open public workshop in June 2010 to discuss the current state of science related to antibody-mediated rejection (AMR) in kidney transplantation. Desensitization, acute AMR and chronic AMR (CAMR) were considered in the context of clinical trial design. Participants discussed experiences with HLA antibody detection and quantitation and the utility of monitoring donor-specific antibodies (DSAs) to inform the management of patients with AMR. The role for animal models was discussed. Diagnostic and prognostic features of histology were presented, followed by discussion of sensitivity and specificity of various criteria. The published literature on treatment of acute AMR was summarized, which consisted of case series and limited data from controlled clinical trials. Considerations for future clinical trials were presented, including endpoints and statistical evaluations of outcome. Although many issues need further consideration, the meeting enabled an important exchange of ideas between experts in the field.

Laparoscopic sigmoid resection for diverticular disease has no advantages over open approach: midterm results of a randomized controlled trial.

PURPOSE: Elective laparoscopic sigmoid resection (LSR) for symptomatic diverticular disease is supposed to have significant short-term advantages compared to open surgery (open sigmoid resection (OSR)). This opinion is rather based on inferences from trials on colonic resections for malignant diseases or minor laparoscopic surgery. This randomized controlled trial was conducted to compare quality of life as well as morbidity and clinical outcome after LSR vs. OSR following a midterm follow-up period. METHODS: Patients presenting with a symptomatic sigmoid diverticular disease stage II/III (Stock/Hansen) were randomly allocated to LSR or OSR in a prospective multicenter trial. Endpoints included the quality of life assessed with a standardized questionnaire, postoperative mortality, and complications within the follow-up of 12 months after operation. RESULTS: A total of 143 patients randomized between 2005 and 2008 in 12 centers could be analyzed. The recruitment was aborted for nonachievement of the planned sample size. Seventy-five patients were allocated to LSR, and 68 received OSR. Nine operations were converted to OSR (9%) and analyzed as intention to treat. Groups were comparable for age, gender, body mass index, comorbidity, and indication for surgery. Operation time was longer for LSR (p < 0.001). Quality of life did not differ between LSR and OSR, either during the early postoperative course or after 12 months (p = 0.172). Also, mortality and morbidity, including subgroups of major and minor morbidity, were compared. CONCLUSION: LSR was not superior to OSR regarding postoperative quality of life and incidence of complications in this trial.

[Is it possible to perform a laparoscopic assisted Hartmann's procedure and a subsequent laparoscopically assisted reversal in complicated diverticulitis?]. / Sind eine laparoskopische Diskontinuitätsresektion und eine spätere laparoskopische Rekonstruktion bei der komplizierten Sigmadivertikulitis möglich?

Surgery of complicated sigmoid diverticulitis should be as gentle as possible. Serious time pressure, unpredictable operation fields and unprepared bowel determine the surgical strategy. Hence, we examine whether minimal invasive surgery (MIS) (i. e., Hartmann procedure) is suited for emergency conditions in selected patients. Furthermore, the objective of the study was to -assess the feasibility of the reversal of Hartmann procedure in appropriate patients after a preceding classical or laparoscopic intervention. -Between 2005 and 2009 128 patients with sigma diverticulitis were operated, 72 patients of them with complicated sigmoid diverticulitis (peritonitis, haemorrhage, ileus, perforation), The classical Hartmann procedure was performed in 45 (35 %) patients, 39 of them being treated within 24 hours. The laparoscopically assisted Hartmann procedure was realised in 15 patients and could be successfully completed in 13 cases. The cor-responding mortality rate was 0 %. A Hartmann reversal could be performed in 26 patients (58 %). A laparoscopic approach was chosen in 16 patients and could be successfully completed in 14 cases. 12 patients were operated with classical Hartmann reversal. The respective mortality rates in both groups were 0 %. We therefore conclude that in cases of peritonitis due to sigmoid diverticulitis laparoscopic surgery, like laparoscopically assisted Hartmann procedure and a subsequent laparoscopically assisted reversal could be recommended in selected patients.

Extrapulmonary tissue responses in cynomolgus macaques (Macaca fascicularis) infected with highly pathogenic avian influenza A (H5N1) virus.

The mechanisms responsible for virulence of influenza viruses in humans remain poorly understood. A prevailing hypothesis is that the highly pathogenic virus isolates cause a severe cytokinemia precipitating acute respiratory distress syndrome and multiple organ dysfunction syndrome. Cynomolgus macaques (Macaca fascicularis) infected with a human highly pathogenic avian influenza (HPAI) H5N1 virus isolate (A/Vietnam/1203/2004) or reassortants of human influenza virus A/Texas/36/91 (H1N1) containing genes from the 1918 pandemic influenza A (H1N1) virus developed severe pneumonia within 24 h postinfection. However, virus spread beyond the lungs was only detected in the H5N1 group, and signs of extrapulmonary tissue reactions, including microglia activation and sustained up-regulation of inflammatory markers, most notably hypoxia inducible factor-1alpha (HIF-1alpha), were largely limited to this group. Extrapulmonary pathology may thus contribute to the morbidities induced by H5N1 viruses.

Redistribution of the fibrinogen receptor of human platelets after surface activation.

We investigated the whole cell distribution of the platelet membrane receptor for fibrinogen in surface-activated human platelets. Fibrinogen-labeled colloidal gold was used in conjunction with platelet whole mount preparations to visualize directly the fibrinogen receptor. Unstimulated platelets fail to bind fibrinogen, and binding was minimal in the stages of activation immediately following adhesion. The amount of fibrinogen bound per platelet increased rapidly during the shape changes associated with surface activation until 7,600 +/- 500 labels were present at saturation. Maximal binding of fibrinogen was followed by receptor redistribution. During the early stages of spreading, fibrinogen labels were uniformly distributed over the entire platelet surface, including pseudopodia, but the labels become progressively centralized as the spreading process continued. In well spread platelets, labels were found over the central regions, whereas peripheral areas were cleared of receptors. Receptor redistribution during spreading was accompanied by cytoskeletal reorganization such that a direct correlation was seen between the development of specific ultrastructural zones and the distribution of surface receptor sites suggesting a link between the surface receptors and the cytoskeleton. The association of fibrinogen receptors with contractile elements of the cytoskeleton, which permits coordinated receptor centralization, is important to the understanding of the role of fibrinogen in normal platelet aggregation and clot retraction.

Platelet activation and cytoskeletal reorganization: high voltage electron microscopic examination of intact and Triton-extracted whole mounts.

The sequential changes in the three-dimensional organization of the filamentous components of human platelets following surface activation were investigated in whole-mount preparations. Examination of intact and Triton-extracted platelets by high voltage electron microscopy provides morphological evidence of increased polymerization of actin into the filamentous form and an increased organization of the cytoskeletal elements after activation. The structure of resting platelets consists of the circumferential band of microtubules and a small number of microfilaments randomly arranged throughout a dense cytoplasmic matrix. Increased spreading is accompanied by cytoskeletal reorganization resulting in the development of distinct ultrastructural zones including the peripheral web, the outer filamentous zone, the "trabecular-like" inner filamentous zone, and the granulomere . These zones are present only in well-spread platelets during the late stages of surface activation and are retained following Triton extraction. Extraction of the less stable cytoplasmic components provides additional information about the underlying structure and filament interactions within each zone.