Speed can go up as well as down at low contrast: implications for models of motion perception

It is well-known that reducing the contrast of a slow moving stimulus reduces its apparent speed. [Thompson, P. (1982). Perceived rate of movement depends on contrast. Vision Research, 22, 377-380.] report of this finding also suggested that at speeds above 8 cycles/s reducing contrast increased perceived speed. However in a later report, Stone and Thompson (1992), using a more rigorous, forced-choice procedure, failed to collect reliable data at these higher speeds. Here, we confirm that faster moving stimuli can appear to move faster than their true speed at low contrasts and we propose a physiologically plausible ratio model that unlike recent Bayesian models (e.g. Weiss, Y., Simoncelli, E. P., & Adelson, E. H. (2002). Motion illusions as optimal percepts. Nature Neuroscience, 5, 598-604) can account well for the results.     

Hematologic effects of recombinant factor VIIa combined with hemoglobin-based oxygen carrier-201 for prehospital resuscitation of swine with severe uncontrolled hemorrhage due to liver injury

The combination of traumatic injury, hemorrhage, and fluid resuscitation results in consumption and dilution of coagulation factors, adversely impacting hematology outcome in trauma patients. The hemostatic effects of escalating doses of recombinant factor VIIa added to hemoglobin-based oxygen carrier-201 were assessed as prehospital fluid resuscitation in swine with severe uncontrolled hemorrhage. Swine underwent liver injury causing severe uncontrolled hemorrhage and shock. During a 4-h prehospital phase, either hypotensive or tachycardic, or both, animals were resuscitated with hemoglobin-based oxygen carrier-201 without (0x) or with escalating doses of recombinant factor VIIa [90 microg/kg (1x), 180 microg/kg (2x), or 360 microg/kg (4x)]. The animals received one initial full dose of 10 ml/kg at 15 min and up to four doses of 5 ml/kg thereafter. From 4 to 72 h (hospital phase), animals received either transfusions or isotonic saline or both as needed. Hematology profile (complete blood count), thromboelastography, in-vitro bleeding (platelet function analyzer), and coagulation (prothrombin time) were measured and the results were compared using mixed statistical models. In all groups, dilutional coagulopathy was evidenced by reduced hematocrit, platelets, and thromboelastography-maximum amplitude, and increased platelet function analyzer closure time and thromboelastography-reaction time. During the prehospital phase, hemoglobin-based oxygen carrier-201 restored hemoglobin in all groups. Recombinant factor VIIa decreased prothrombin time in recombinant factor VIIa groups compared with the hemoglobin-based oxygen carrier-201 group (P < 0.01). Unexpectedly, increasing recombinant factor VIIa dosage tended to increase fluid requirement (P > 0.05). Compared with hemoglobin-based oxygen carrier, 1x recombinant factor VIIa tended to decrease blood loss, lactate and thromboelastography-reaction time at 24 h but the 4x group increased these parameters. Platelets and thromboelastography-maximum amplitude decreased (P < 0.01) with the 4x group. In swine with severe uncontrolled hemorrhage, prehospital resuscitation with escalating doses of recombinant factor VIIa in combination with hemoglobin-based oxygen carrier-201 did not change survival or hemostasis. However, there were trends toward possible benefits of low recombinant factor VIIa doses, whereas high recombinant factor VIIa doses adversely affected hemostasis.     

Coagulation patterns following haemoglobin-based oxygen carrier resuscitation in severe uncontrolled haemorrhagic shock in swine

Massive blood loss due to penetrating trauma and internal organ damage can cause severe haemorrhagic shock (HS), leading to a severely compromised haemostatic balance. This study evaluated the effect of bovine polymerized haemoglobin (Hb) (Hb-based oxygen carrier, HBOC) resuscitation on haemostasis in a swine model of uncontrolled HS. Following liver injury/HS, swine received HBOC (n= 8), Hextend (HEX) (n= 8) or no resuscitation (NON) (n= 8). Fluids were infused to increase mean arterial pressure above 60 mmHg and to reduce heart rate to baseline. At 4 h, the animals were eligible for blood transfusions. Prothrombin time (PT), activated partial thromboplastin time, fibrinogen, thromboelastography (TEG) and platelet function analyser closure time (PFA-CT) were compared by using mixed statistical model. At 4 h, blood loss (% estimated blood volume) was comparable for HBOC (65.5 +/- 18.5%) and HEX (80.8 +/- 14.4%) and less for NON (58.7 +/- 10.1%; P < 0.05). Resuscitation-induced dilutional coagulopathy was observed with HBOC and HEX, as indicated by reduced haematocrit, platelets and fibrinogen (P < 0.05). At 4 h, PT was higher in HEX than in HBOC groups (P < 0.01). In the early hospital phase, a trend to increased TEG reaction time and PFA-CT indicates that dilutional effects persist in HBOC and HEX groups. PFA-CT returned to baseline later with HBOC than with HEX (48 vs. 24 h) following blood transfusion. At 4 h, all surviving HEX animals (n= 3) required transfusion, in contrast to no HBOC (n= 7) or NON (n= 1) animals. In this severe uncontrolled HS model, successful resuscitation with HBOC produced haemodilutional coagulopathy less than or similar to that produced by resuscitation with HEX.     

'Social evils' and harm reduction: the evolving policy environment for human immunodeficiency virus prevention among injection drug users in China and Vietnam

AIMS: This paper reviews the evolution of government policies in China and Vietnam regarding harm reduction interventions for human immunodeficiency virus (HIV) prevention, such as needle/syringe provision and opioid substitution treatment. METHODS: The work is based upon the authors' experiences in and observations of these policy developments, as well as relevant government policy documents and legislation. RESULTS: Both countries are experiencing HIV epidemics driven by injection drug use and have maintained generally severe policies towards injection drug users (IDUs). In recent years, however, they have also officially endorsed harm reduction. We sought to understand how and why this apparently surprising policy evolution took place. Factors associated with growing support for harm reduction were similar but not identical in China and Vietnam. These included the emergence of effective 'champions' for such policies, an ethos of pragmatism and receptivity to evidence, growing collaboration across public health, police and other sectors, the influence of contingent events such as the severe acute respiratory syndrome (SARS) epidemic and pressure from donors and international organizations to adopt best practice in HIV prevention. CONCLUSIONS: Ongoing challenges and lessons learned include the persistence of tensions between drug control and harm reduction that may have negative effects on programs until a fully harmonized policy environment is established. Excessive reliance on law enforcement and forced detoxification will not solve the problems of substance abuse or of HIV among drug users. Ongoing evaluation of harm reduction programs, as well as increased levels of multi-sectoral training, collaboration and support are also needed.