Recent advances in hepatitis A virus research and clinical practice guidelines for hepatitis A virus infection in Japan.

In 2018, there was a hepatitis A outbreak in Japan, and hepatitis A virus (HAV) infection is considered a sexually transmitted disease. In general, patients with hepatitis A should be given attention, and this disease should be prevented more than ever. The Japan Agency for Medical Research and Development (AMED) Hepatitis A and E viruses (HAV and HEV) Study Group has worked on the project to create "Recent Advances in Hepatitis A Virus (HAV) Research and Clinical Practice Guidelines for HAV Infection in Japan". The group consists of expert hepatologists and virologists who gathered at virtual meeting on August 5, 2023. Data about the pathogenesis, infection routes, diagnosis, complications, several factors for the severities, vaccination, and current and future treatments for hepatitis A were discussed and debated for a draft version. The participants assessed the quality of cited studies. The finalized recommendations are presented in this review. The recent advances in HAV research and clinical practice for HAV infection in Japan, have been reviewed by the AMED HAV and HEV Study Group.

Recent advances in hepatitis E virus research and the Japanese clinical practice guidelines for hepatitis E virus infection.

Acute hepatitis E was considered rare until reports emerged affirming the existence of hepatitis E virus (HEV) genotypes 3 and 4 infections in Japan in the early 2000s. Extensive studies by Japanese researchers have highlighted the pivotal role of pigs and wild animals, such as wild boars and deer, as reservoirs for HEV, linking them to zoonotic infections in Japan. Currently, when hepatitis occurs subsequent to the consumption of undercooked or grilled pork, wild boar meat, or offal (including pig liver and intestines), HEV infection should be considered. Following the approval of anti-HEV immunoglobulin A antibody as a diagnostic tool for hepatitis E by Japan's Health Insurance System in 2011, the annual number of diagnosed cases of HEV infection has surged. Notably, the occurrence of post-transfusion hepatitis E promoted nationwide screening of blood products for HEV using nucleic acid amplification tests since 2020. Furthermore, chronic hepatitis E has been observed in immunosuppressed individuals. Considering the significance of hepatitis E, heightened preventive measures are essential. The Japan Agency for Medical Research and Development Hepatitis A and E viruses (HAV and HEV) Study Group, which includes special virologists and hepatologists, held a virtual meeting on February 17, 2024. Discussions encompassed pathogenesis, transmission routes, diagnosis, complications, severity factors, and ongoing and prospective vaccination or treatments for hepatitis E. Rigorous assessment of referenced studies culminated in the formulation of recommendations, which are detailed within this review. This comprehensive review presents recent advancements in HEV research and Japanese clinical practice guidelines for HEV infection.

Usefulness of Prehospital 12-Lead Electrocardiography System in ST-Segment Elevation Myocardial Infarction Patients in Oita　- Comparison Between Urban and Rural Areas, Weekday Daytime and Weekday Nighttime/Holidays.

BACKGROUND: We have reported that a prehospital 12-lead electrocardiography system (P-ECG) contributed to transport of suspected acute coronary syndrome (ACS) patients to appropriate institutes and in this study, we compared its usefulness between urban and rural areas, and between weekday daytime and weekday nighttime/holiday.Methods and Results: Consecutive STEMI patients who underwent successful primary percutaneous coronary intervention after using P-ECG were assigned to the P-ECG group (n=123; 29 female, 70±13 years), and comparable STEMI patients without using P-ECG were assigned to the conventional group (n=117; 33 females, mean age 70±13 years). There was no significant difference in door-to-reperfusion times between the rural and urban cases (70±32 vs. 69±29 min, P=0.73). Door-to-reperfusion times in the urban P-ECG group were shorter than those in the urban conventional group for weekday nighttime/holiday (65±21 vs. 83±32 min, P=0.0005). However, there was no significance different between groups for weekday daytime. First medical contact to reperfusion time (90±22 vs. 105±37 min, P=0.0091) in the urban P-ECG group were significantly shorter than in the urban conventional groups for weekday nighttime/holiday, but were not significantly different between the groups for weekday daytime. CONCLUSIONS: P-ECG is useful even in urban areas, especially for patients who develop STEMI during weekday nighttime or while on a holiday.

Thirty-two years' experience of treating fulminant hepatitis in a Japanese single center.

AIM: The prognosis of patients with acute liver failure has improved dramatically in the past three decades due to advances in medical critical care and use of liver transplantation (LT) in Western countries, where the etiology of acute liver failure is different from that in Japan. We analyzed patients with fulminant hepatitis (FH) and late-onset hepatic failure (LOHF) admitted to our unit over a 32-year period to clarify the nature of Japanese patients with FH and LOHF. METHODS: A total of 137 Japanese patients with FH and LOHF between 1986 and 2017 were analyzed for etiologies, disease types, treatment protocols, and outcome. RESULTS: Of 137 patients, 124 were FH (53 acute type and 71 subacute type) and 13 LOHF. The major etiology was due to viral infections in 48% of patients. A total of 23.4% of patients recovered without LT, 7.3% received LT, and 69.3% died without LT. The number of patients showed rise and fall without an evident decrease during the period. Patients with autoimmune hepatitis increased after the establishment of autoimmune hepatitis criteria in 1999 (p < 0.001), and that with indeterminate cause decreased (p < 0.01). The mean age was older in the last decade than in the first decade (p = 0.036). Spontaneous and overall survival rates were not different during the period. CONCLUSIONS: The prognosis of our patients with FH and LOHF has not improved, probably because of aging and the increasing proportion of etiologies with poor prognosis and difficult-to-treat patients without response to medications regardless of advancement of clinical management, including artificial liver support devices and LT.

Diagnostic criteria for acute-on-chronic liver failure and related disease conditions in Japan.

The Intractable Hepato-Biliary Disease Study Group of Japan, sponsored by the Ministry of Health, Labor and Wealth, proposed in 2018 that patients with cirrhosis and a Child-Pugh score of 5-9 should be diagnosed as having acute-on-chronic liver failure (ACLF) when a deterioration of liver function ("serum bilirubin level of 5.0 mg/dl or more" and "prothrombin time value of 40% or less of the standardized values and/or international normalization rates of 1.5 or more") caused by severe liver damage develops within 28 days after an acute insult, including alcohol abuse, bacterial infection, gastrointestinal bleeding, and the exacerbation of underlying liver diseases. Disease severity can be classified into 4 grades depending on the extent of the deterioration in organ functions, including liver, kidney, cerebral, blood coagulation, circulatory and respiratory functions. The Study Group has since performed an annual nationwide survey of patients with ACLF diagnosed according to the proposed diagnostic criteria as well as those with disease conditions related to ACLF. A total of 501 patients, including 183 patients diagnosed as having ACLF, seen between 2017 and 2019 were enrolled, and univariate and multivariate analyses revealed that the proposed diagnostic criteria were useful for identifying cirrhotic patients with an unfavorable outcome following an acute insult. Consequently, the Study Group determined that the proposed diagnostic criteria should be used in both clinical practice and clinical research as formal diagnostic criteria.

Interhospital transportation of a COVID-19 patient undergoing veno-venous extracorporeal membrane oxygenation by helicopter.

Some coronavirus disease 2019 (COVID-19) patients develop rapidly progressive acute respiratory distress syndrome and require veno-venous extracorporeal membrane oxygenation (V-V ECMO). A previous study recommended the transfer of ECMO patients to ECMO centers. However, because of the pandemic, a limited number of ECMO centers are available for patient transfer. The safe long-distance interhospital transport of these patients is a concern. To minimize transportation time, helicopter use is a suitable choice. We report the first case of a COVID-19 patient on V-V ECMO, transferred to our ECMO center by helicopter. A 45-year-old man with rheumatoid arthritis history, treated with immunosuppressants, presented with fever and sore throat. He was diagnosed with COVID-19 following a positive severe acute respiratory syndrome coronavirus 2 polymerase chain reaction test result and was subsequently prescribed favipiravir. However, his respiratory failure progressively worsened. On day 10 of hospitalization at the previous hospital, he was intubated, and we received a request for ECMO transport on the next day. The ECMO team, who wore personal protective equipment (N95 respirators, gloves, gowns, and face shields), initiated V-V ECMO in the referring hospital and safely transported the patient by helicopter. The flight time was 7 min. He was admitted to the intensive care unit of our hospital and received tocilizumab. He was discharged on hospital day 31 with no significant sequelae. In this case report, we discuss important factors for the safe and appropriate interhospital transportation of COVID-19 patients on ECMO as well as staff and patient safety during helicopter transportation.

Estimation of Respiratory Rate from Thermography Using Respiratory Likelihood Index.

Respiration is a key vital sign used to monitor human health status. Monitoring respiratory rate (RR) under non-contact is particularly important for providing appropriate pre-hospital care in emergencies. We propose an RR estimation system using thermal imaging cameras, which are increasingly being used in the medical field, such as recently during the COVID-19 pandemic. By measuring temperature changes during exhalation and inhalation, we aim to track the respiration of the subject in a supine or seated position in real-time without any physical contact. The proposed method automatically selects the respiration-related regions from the detected facial regions and estimates the respiration rate. Most existing methods rely on signals from nostrils and require close-up or high-resolution images, while our method only requires the facial region to be captured. Facial region is detected using YOLO v3, an object detection model based on deep learning. The detected facial region is divided into subregions. By calculating the respiratory likelihood of each segmented region using the newly proposed index, called the Respiratory Quality Index, the respiratory region is automatically selected and the RR is estimated. An evaluation of the proposed RR estimation method was conducted on seven subjects in their early twenties, with four 15 s measurements being taken. The results showed a mean absolute error of 0.66 bpm. The proposed method can be useful as an RR estimation method.

Changes in acute blood purification therapy in critical care: republication of the article published in the Japanese Journal of Artificial Organs.

Acute blood purification therapy is an essential artificial organ in critical care. In the review article, looking back on the history, we describe our present knowledge and techniques of acute blood purification therapy in critical care. The topics include continuous hemodiafiltration (CHDF), online HDF as an artificial liver support, blood purification therapy aiming to remove pathogenic substances of sepsis, a procedure for connecting a CRRT device into an extra-corporeal membrane oxygenation circuit, and replacement fluid for CHDF. We also raise remaining issues and clarify the future direction of acute blood purification therapy in critical care. This review was created based on a translation of the Japanese review written in the Japanese Journal of Artificial Organs in 2017 (Vol. 46, No. 1, pp. 67-70), with adding some references.

Clinical course of a critically ill patient with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Although several studies have reported on the clinical and epidemiological characteristics of the patient with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), clinical course of the most severe cases requiring treatment in ICU have been insufficiently reported. A 73-year-old man traveling on a cruise ship with history of hypertension and dyslipidemia developed high fever, dyspnea and cough after 7 days of steroid treatment for sudden sensorineural hearing loss, and tested positive for SARS-CoV-2 in sputa polymerase chain reaction (PCR) examination. His respiratory function deteriorated despite treatments with lopinavir/ritonavir, oseltamivir, azithromycin and meropenem at a regional hospital. He was intubated and transferred to the ICU in the tertiary university hospital on day 10 (ICU day 1). Interferon beta-1b subcutaneous injection was initiated immediately to enhance anti-viral therapy, and favipiravir on ICU day 10 upon availability. Progression of organ dysfunctions necessitated inhalation of nitrogen oxide for respiratory dysfunction, noradrenaline for cardiovascular dysfunction and continuous renal replacement therapy for renal dysfunction. His blood samples PCR also tested positive for SARS-CoV-2, indicating viremia, concomitantly with elevated IL-6 levels. VV-ECMO was initiated after sudden exacerbation of respiratory dysfunction on ICU day 7 to maintain oxygenation. The sustained excessive inflammatory cytokines in the present case might have led to the exacerbation of the disease, requiring vigorous organ support therapies to allow for survival and recovery from the rapid progression of multiple organ dysfunctions and severe respiratory failure.

High recovery rate of consciousness by high-volume filtrate hemodiafiltration for fulminant hepatitis.

AIM: An artificial liver support (ALS) system sustaining patients with acute liver failure (ALF) in good condition until recovery of the native liver or performance of liver transplantation (LT), is essential for the improvement of the poor prognosis of ALF despite the lack of survival benefit. We aimed to investigate the efficacy of various ALS systems for fulminant hepatitis (FH) carried out in our liver unit so far, focusing on the restoration of consciousness from hepatic encephalopathy. METHODS: One hundred and ten consecutive adult Japanese patients with FH admitted to Chiba University Hospital (Chiba, Japan) between 1988 and 2016 who received ALS were analyzed. RESULTS: Recovery rate of consciousness improved with the increased dialysate flow rate and filtrate rate: 37.5% by plasma exchange (PE), 51.9% by PE + continuous hemodiafiltration (CHDF), 57.7% by slow PE (sPE) + high-flow CHDF (HFCHDF) (QD = 300 mL/min), 88.6% by HFCHDF (QD = 500 mL/min) (+ sPE), and 92.9% by on-line HDF (OLHDF) (+ sPE). All patients except one, who could not be fully treated because of circulatory failure, recovered consciousness by OLHDF, including those whose liver function were completely abolished. Superiority of HFCHDF (QD = 500 mL/min) and OLHDF was also shown in patients who died without LT or received LT. CONCLUSIONS: More effective ALS should be recognized considering the extremely high recovery rate of consciousness. In particular, OLHDF with predilution reduces the cost of substitution fluid by supplying an unlimited amount of dialysate as substitution fluid prepared using an on-line system, and simplifies the procedure for the management.

A safe procedure for connecting a continuous renal replacement therapy device into an extracorporeal membrane oxygenation circuit.

Patients receiving extracorporeal membrane oxygenation (ECMO) often require continuous renal replacement therapy (CRRT). The intra-circuit pressure of adult ECMO usually deviates from the physiological range. We investigated the use of CRRT connected to an ECMO circuit with physiological intra-circuit pressures (0-150 mmHg, defined as the "safety range") using an in vitro experiment involving a water-filled ECMO circuit. The intra-circuit pressure pre-pump, post-pump, and post-oxygenator were measured while varying the height of the pump or ECMO flow. The bypass conduit pressure and distance from the post-oxygenator port were measured to find the "safety point", where the bypass pressure remained within the safety range. Both drainage and return limbs of the CRRT machine were connected to the safety point and the inlet and outlet pressures of the hemofilter were recorded while varying the ECMO and CRRT flow. The pre-pump pressure only remained within the safety range for heights >75 cm (ECMO flow = 4 L/min) or ECMO flow <3.5 L min (height = 50 cm). The post-pump and post-oxygenator pressure was generally outside of the safety range. The bypass pressure decreased according to the distance from the post-oxygenator port and the safety point was found at 60 or 75 cm (in a 90-cm length conduit) regardless of ECMO flow. The hemofilter inlet and outlet pressures remained within the safety range for all conditions of ECMO and CRRT flow, findings validated in clinical cases. The bypass conduit within an ECMO circuit can be connected to a CRRT machine safely under physiological pressures in adult patients receiving ECMO.

Veno-arterial extracorporeal membrane oxygenation for Streptococcus pyogenes toxic shock syndrome in pregnancy.

Streptococcal toxic shock syndrome (STSS), an invasive Streptococcus pyogenes (Group A streptococcus) infection with hypotension and multiple organ failure, is quite rare in pregnancy but is characterized by rapid disease progression and high fatality rates. We present a case of STSS with infection-induced cardiac dysfunction in a pregnant woman who was treated with veno-arterial extracorporeal membrane oxygenation (VA-ECMO). A 24-year-old multiparous woman in the third trimester had early symptoms of high fever and diarrhea 1 day prior to admission to the hospital emergency department. On admission, she had multiple organ failure including circulatory failure. Due to fetal distress, emergency Cesarean section was carried out and transferred to intensive care units. She had refractory circulatory failure with depressed myocardial contractility with progressive multiple organ failure, despite receiving significant hemodynamic supports including high-dose catecholamine. Thus, VA-ECMO was initiated 18 h after intensive care unit admission. Consequently, ECMO provided extra time to recover from infection and myocardial depression. She was successfully weaned from VA-ECMO on day 7 and was discharged home on day 53. VA-ECMO can be a therapeutic option for refractory circulatory failure with significant myocardial depression in STSS.

Impact of the COVID-19 Pandemic on the Long-Term Prognosis of Acute Myocardial Infarction in Japan.

Background During the early phase of the coronavirus disease 2019 (COVID-19) pandemic, a global reduction in hospitalizations for acute myocardial infarction (AMI) was observed. Generally, patients experienced increased severity of AMI with delays in time from symptom onset to treatment during the pandemic. However, the impact of the COVID-19 pandemic on in-hospital mortality among patients with AMI remains unclear. This study aimed to compare the long-term prognosis of patients with AMI during the COVID-19 pandemic to that observed in the pre-pandemic period and to evaluate the influence of the COVID-19 pandemic on the prognosis of patients with AMI. Methods We reviewed the data of patients admitted to our hospital for AMI treatment between April 1, 2018, and March 31, 2021. The time from admission to major adverse cardiac events (MACE), as well as the time from admission to all-cause death, were examined between the pandemic period (April 1, 2020, to March 31, 2021) and the pre-pandemic period (April 1, 2018, to March 31, 2020). Results Eighty patients were included in the study, and those admitted during the pandemic exhibited a higher likelihood of advanced age, lower levels of LDL-cholesterol, and a reduced prevalence of hypertension. The 2.5-year MACE-free survival and overall survival rates between the patients during the pre-pandemic and pandemic periods were not significantly different. Conclusion The long-term prognosis of patients with AMI during the COVID-19 pandemic remains unclear. In this study, we reported that the 2.5-year MACE-free survival and overall survival rates of the patients with AMI admitted during the COVID-19 pandemic were not significantly different from those during the pre-pandemic period. The impact of the COVID-19 pandemic on the prognosis of patients with AMI appears to vary according to the study population.

Rapid Detection of Severe Fever with Thrombocytopenia Syndrome Virus in the Acute Phase of Infection by Direct Real-Time Reverse Transcription without RNA Extraction.

No specific treatment has been developed for severe fever with thrombocytopenia syndrome (SFTS). However, the prognosis can improve with early plasma exchange. Therefore, rapid and accurate detection of SFTS virus is important for diagnosis and prognosis. Direct real-time reverse transcription polymerase chain reaction (RT-PCR) testing is easier and more time-efficient than conventional real-time RT-PCR. Our study compared direct real-time RT-PCR efficiency without the RNA extraction and purification of conventional real-time RT-PCR. Samples were collected from 18 patients with SFTS and five without SFTS. A strong correlation (r = 0.774, 95% CI: 0.652-0.857, P <0.01) was found between conventional and direct real-time RT-PCR assays. Direct real-time RT-PCR showed 84.4% sensitivity and 92.0% specificity for viral detection. Direct real-time RT-PCR is an effective diagnostic tool for patients with acute phase SFTS, but further optimization is required for viral detection.

Differential pattern of cell-surface and soluble TREM-1 between sepsis and SIRS.

OBJECTIVE: Triggering receptor expressed on myeloid cells-1 (TREM-1) was reported to play a key roll in amplification of production of inflammatory cytokines. TREM-1 is suggested to be a specific biomarker for sepsis for this reason, but the clinical significance of TREM-1 has not been elucidated. We investigated TREM-1 expression on the cell-surface, and plasma levels of soluble TREM-1 (sTREM-1) in patients with non-infectious systemic inflammatory response syndrome (SIRS) and sepsis admitted to the ICU. METHODS: Thirty-five patients with SIRS and 21 patients with sepsis admitted to ICU were subjected to the study. TREM-1 expressions on the surfaces of monocytes and neutrophils were measured by flow cytometry. Plasma sTREM-1 level and serum interleukin (IL)-6 level were measured. RESULTS: Septic patients had decreased TREM-1 expression, clearly on neutrophils or to a lesser extent on monocyte compared to SIRS patients on ICU admission (neutrophils p<0.001, monocyte p<0.05). TREM-1 expression on neutrophils had a significant inverse correlation with serum IL-6 level (r=-0.64, p<0.0001). Plasma sTREM-1 level in septic patients was significantly higher than that in SIRS patients (p<0.05). Plasma sTREM-1 level positively correlated with severity score and non-survivors had increased plasma sTREM-1 level compared to survivors in all SIRS/sepsis patients (p<0.05). CONCLUSIONS: Patients with sepsis had increased soluble TREM-1 and decreased TREM-1 expression on neutrophil compared to SIRS patients. sTREM-1 may be useful to evaluate disease severity and outcome of patients with SIRS or sepsis.

Correlation between high blood IL-6 level, hyperglycemia, and glucose control in septic patients.

INTRODUCTION: The aim of the present study was to investigate the relationship between the blood IL-6 level, the blood glucose level, and glucose control in septic patients. METHODS: This retrospective observational study in a general ICU of a university hospital included a total of 153 patients with sepsis, severe sepsis, or septic shock who were admitted to the ICU between 2005 and 2010, stayed in the ICU for 7 days or longer, and did not receive steroid therapy prior to or after ICU admission. The severity of stress hyperglycemia, status of glucose control, and correlation between those two factors in these patients were investigated using the blood IL-6 level as an index of hypercytokinemia. RESULTS: A significant positive correlation between blood IL-6 level and blood glucose level on ICU admission was observed in the overall study population (n = 153; r = 0.24, P = 0.01), and was stronger in the nondiabetic subgroup (n = 112; r = 0.42, P < 0.01). The rate of successful glucose control (blood glucose level < 150 mg/dl maintained for 6 days or longer) decreased with increase in blood IL-6 level on ICU admission (P < 0.01). The blood IL-6 level after ICU admission remained significantly higher and the 60-day survival rate was significantly lower in the failed glucose control group than in the successful glucose control group (P < 0.01 and P < 0.01, respectively). CONCLUSIONS: High blood IL-6 level was correlated with hyperglycemia and with difficulties in glucose control in septic patients. These results suggest the possibility that hypercytokinemia might be involved in the development of hyperglycemia in sepsis, and thereby might affect the success of glucose control.

Prehospital diagnostic algorithm for acute coronary syndrome using machine learning: a prospective observational study.

Rapid and precise prehospital recognition of acute coronary syndrome (ACS) is key to improving clinical outcomes. The aim of this study was to investigate a predictive power for predicting ACS using the machine learning-based prehospital algorithm. We conducted a multicenter observational prospective study that included 10 participating facilities in an urban area of Japan. The data from consecutive adult patients, identified by emergency medical service personnel with suspected ACS, were analyzed. In this study, we used nested cross-validation to evaluate the predictive performance of the model. The primary outcomes were binary classification models for ACS prediction based on the nine machine learning algorithms. The voting classifier model for ACS using 43 features had the highest area under the receiver operating curve (AUC) (0.861 [95% CI 0.775-0.832]) in the test score. After validating the accuracy of the model using the external cohort, we repeated the analysis with a limited number of selected features. The performance of the algorithms using 17 features remained high AUC (voting classifier, 0.864 [95% CI 0.830-0.898], support vector machine (radial basis function), 0.864 [95% CI 0.829-0.887]) in the test score. We found that the machine learning-based prehospital algorithms showed a high predictive power for predicting ACS.

Pulsatile to-fro flow induces greater and sustained expression of tissue factor RNA in HUVEC than unidirectional laminar flow.

Tissue factor (TF) is expressed in atherosclerotic lesions. Since mechanical forces influence endothelial cell (EC) function and are thought to account for the unique distribution of atherosclerosis in areas exposed to disturbed flow, we hypothesized that disturbed to-fro flow (TFF) and unidirectional pulsatile forward flow (PFF) would have different effects on TF expression in EC. TF RNA expression in HUVEC exposed to mechanical stress in the presence or absence of chemical stimulation with thrombin was determined. TFF induced a significantly higher TF expression than PFF that was sustained for 8 h. Combination of mechanical and chemical stimuli induced significantly higher TF expression than only mechanical stresses, and this effect was synergistic in both TFF and PFF. The MAPK p38 inhibitor SB-203580 significantly inhibited TF expression induced by mechanical and chemical stimulations, but the MEK inhibitor PD-98059 did not inhibit TF induced by TFF. Immunoblotting revealed that ERK1/2 phosphorylation induced by TFF was sustained for 120 min, whereas that induced by PFF was not. We conclude that disturbed flow induced greater and sustained amplification of TF expression, and this synergistic effect may be regulated by p38 MAPK and ERK1/2. These results provide added insight into the mechanism of atherosclerosis in areas of disturbed flow.

Laminar shear, but not orbital shear, has a synergistic effect with thrombin stimulation on tissue factor expression in human umbilical vein endothelial cells.

INTRODUCTION: High levels of tissue factor (TF) have been associated with atherosclerotic plaques. The specific pathways linked to TF expression in endothelial cells (ECs) have not been well defined. This study compared TF expression in human umbilical vein ECs (HUVECs) exposed to laminar shear stress (LSS) using a parallel flow chamber and to orbital shear stress (OSS) using an orbital shaker. We also compared the effects of thrombin (TH) stimulation of ECs exposed to different shear forces on the expression of TF and investigated the role that second messengers, p38 and extracellular signal-regulated kinase 1 and 2 (ERK1/2), had in the EC response. METHODS: HUVECs were subjected to 2, 4, or 6 hours of LSS or OSS in the presence or absence of 4 U/mL of TH. Western blot analysis of ERK1/2 and p38 activation and polymerase chain reaction analysis of TF in the presence of inhibitors to these second messengers was performed in HUVECs subjected to OSS or LSS in the presence or absence of TH. RESULTS: TF expression was increased and peaked at 2 hours in all HUVECs exposed to LSS or TH. Stimulation of static HUVECs with TH resulted in an increase in TF expression of 5.68 ± 1.58-, 3.80 ± 1.21-, and 2.54 ± 0.38-fold at 2, 4, and 6 hours, respectively (n = 6 experiments). In the absence of TH, HUVECs exposed to LSS demonstrated a 9.51 ± 0.62-, 7.31 ± 1.43-, and 4.39 ± 1.32-fold increase in TF expression at 2, 4, and 6 hours, respectively (n = 6 experiments). TF was increased significantly more when exposed to LSS in the presence of TH (18.85 ± 1.43-, 15.05 ± 0.95-, and 8.91 ± 1.06-fold increases at 2, 4, and 6 hours, respectively [n = 6 experiments], P < .01). Between-group analysis showed a significant difference between groups (P < .001). OSS did not significantly increase TF expression in the presence or absence of TH. ERK1/2 and p38 activation was increased in LSS and LSS + TH but not in OSS or OSS + TH (n = 3 experiments). CONCLUSION: LSS and TH independently increased TF expression, but OSS did not. LSS + TH stimulation showed a synergistic effect, which suggests that these mechanical and chemical stimuli work through different pathways or that an intracellular interaction between TH and LSS may be present that does not occur in OSS.