School formation characteristics and stimuli based modeling of tetra fish

Self-organizing motion is an important yet inadequately understood phenomena in the field of collective behavior. For birds flocks, insect swarms, and fish schools, group behavior can provide a mechanism for defense against predators, better foraging and mating capabilities and increased hydro/aerodynamic efficiency in long-distance migration events. Although collective motion has received much scientific attention, more work is required to model and understand the mechanisms responsible for school initiation and formation, and information transfer within these groups. Here we investigate schooling of black tetra (Gymnocorymbus ternetzi) fish triggered by startle stimuli in the form of approaching objects. High-speed video and tagging techniques were used to track the school and individual members. We then measured several variables including reaction times, group formation shapes, fish velocity, group density, and leadership within the group. These data reveal three things: (1) information propagates through the group as a wave, indicating that each fish is not reacting individually to the stimulus, (2) the time taken for information to transfer across the group is independent of group density, and (3) information propagates across large groups faster than would be expected if the fish were simply responding to the motion of their nearest neighbor. A model was then built wherein simulated fish have a simple 'stimuli/escape' vector based on a hypothetical field of vision. The model was used to simulate a group of individual fish with initial conditions, size, and stimuli similar to the biological experiments. The model revealed similar behavior to the biological experiments and provide insights into the observed patterns, response times, and wave speeds.

How vision governs the collective behaviour of dense cycling pelotons

In densely packed groups demonstrating collective behaviour, such as bird flocks, fish schools or packs of bicycle racers (cycling pelotons), information propagates over a network, with individuals sensing and reacting to stimuli over relatively short space and time scales. What remains elusive is a robust, mechanistic understanding of how sensory system properties affect interactions, information propagation and emergent behaviour. Here, we show through direct observation how the spatio-temporal limits of the human visual sensory system govern local interactions and set the network structure in large, dense collections of cyclists. We found that cyclists align in patterns within a ± 30° arc corresponding to the human near-peripheral visual field, in order to safely accommodate motion perturbations. Furthermore, the group structure changes near the end of the race, suggesting a narrowing of the used field of vision. This change is consistent with established theory in psychology linking increased physical exertion to the decreased field of perception. Our results show how vision, modulated by arousal-dependent neurological effects, sets the local arrangement of cyclists, the mechanisms of interaction and the implicit communication across the group. We furthermore describe information propagation phenomena with an analogous elastic solid mechanics model. We anticipate our mechanistic description will enable a more detailed understanding of the interaction principles for collective behaviour in a variety of animals.

Evaluating a federated medical search engine: tailoring the methodology and reporting the evaluation outcomes

BACKGROUND

Federated medical search engines are health information systems that provide a single access point to different types of information. Their efficiency as clinical decision support tools has been demonstrated through numerous evaluations. Despite their rigor, very few of these studies report holistic evaluations of medical search engines and even fewer base their evaluations on existing evaluation frameworks.

OBJECTIVES

To evaluate a federated medical search engine, MedSocket, for its potential net benefits in an established clinical setting.

METHODS

This study applied the Human, Organization, and Technology (HOT-fit) evaluation framework in order to evaluate MedSocket. The hierarchical structure of the HOT-factors allowed for identification of a combination of efficiency metrics. Human fit was evaluated through user satisfaction and patterns of system use; technology fit was evaluated through the measurements of time-on-task and the accuracy of the found answers; and organization fit was evaluated from the perspective of system fit to the existing organizational structure.

RESULTS

Evaluations produced mixed results and suggested several opportunities for system improvement. On average, participants were satisfied with MedSocket searches and confident in the accuracy of retrieved answers. However, MedSocket did not meet participants' expectations in terms of download speed, access to information, and relevance of the search results. These mixed results made it necessary to conclude that in the case of MedSocket, technology fit had a significant influence on the human and organization fit. Hence, improving technological capabilities of the system is critical before its net benefits can become noticeable.

CONCLUSIONS

The HOT-fit evaluation framework was instrumental in tailoring the methodology for conducting a comprehensive evaluation of the search engine. Such multidimensional evaluation of the search engine resulted in recommendations for system improvement.

A randomized, controlled trial of remacemide for motor fluctuations in Parkinson's disease

BACKGROUND

Preclinical studies suggest that glutamate antagonists help ameliorate motor fluctuations in patients with PD treated with levodopa.

METHODS

In a multicenter, randomized, double-blind, placebo-controlled, parallel-group, dose-ranging study, the authors assessed the safety, tolerability, and efficacy of the glutamate receptor blocker remacemide hydrochloride in 279 patients with motor fluctuations treated with levodopa. The primary objective was to assess the short-term tolerability and safety of four dosage levels of remacemide during 7 weeks of treatment. Patients were also monitored with home diaries and the Unified PD Rating Scale (UPDRS) to collect preliminary data on treatment efficacy.

RESULTS

Remacemide was well tolerated up to a dosage of 300 mg/d on a twice daily schedule and 600 mg/d on a four times daily schedule. The most common dosage-related adverse events were dizziness and nausea, as observed in previous studies of remacemide. The percent "on" time and motor UPDRS scores showed trends toward improvement in the patients treated with 150 and 300 mg/d remacemide compared with placebo-treated patients, although these improvements were not significant.

CONCLUSION

Remacemide is a safe and tolerable adjunct to dopaminergic therapy for patients with PD and motor fluctuations. Although this study had limited power to detect therapeutic effects, the observed improvement is consistent with studies of non-human primates with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian signs and symptoms. Additional studies are warranted to confirm these results over an extended period of observation, and to explore the potential neuroprotective effects of remacemide in slowing the progression of PD.

Effects of injectate volume on thermodilution measurements of cardiac output in patients with low ventricular ejection fraction

OBJECTIVE: To determine the effect of 5-mL injectate on cardiac output measurements in critically ill patients with low ventricular ejection fraction (< 35%). METHODS: Thermodilution cardiac output measurements obtained with three 5-mL and three 10-mL (randomly ordered) iced injectates in 50 patients with low ejection fraction were averaged if the measurements were within 10% of the median. If the 3 measurements were not within those limits, additional measurements were obtained. RESULTS: Cardiac output measured with the 5-mL injectate (mean, 4.63 L/min) and cardiac output measured with the 10-mL injectate (mean, 4.52 L/min) were not significantly different (P = .64). Lower and upper limits of agreement were -1.7 L/min to +1.6 L/min. The bias (mean difference between 10- and 5-mL measurements) of all measurements was -0.09, and the precision was 1.43 L/min, with a 95% confidence limit (mean difference +/- 2 SD) of -1.7 to +1.6 L/min. An additional measurement was necessary in 77% of patients in the 5-mL group but in only 48% of the 10-mL group (P = .006). CONCLUSIONS: Cardiac outputs measured with 5- and 10-mL injectates do not differ significantly. The greater variability of measurements obtained with a 5-mL injectate suggests that more measurements, and thus more time, are needed to measure cardiac output accurately. Clinicians must weigh the benefit of minimizing fluid volume used against the potential decreased reliability of cardiac output measurements.

Effects of injectate volume on thermodilution measurements of cardiac output in patients with low ventricular ejection fraction

OBJECTIVE

To determine the effect of 5-mL injectate on cardiac output measurements in critically ill patients with low ventricular ejection fraction (< 35%).

METHODS

Thermodilution cardiac output measurements obtained with three 5-mL and three 10-mL (randomly ordered) iced injectates in 50 patients with low ejection fraction were averaged if the measurements were within 10% of the median. If the 3 measurements were not within those limits, additional measurements were obtained.

RESULTS

Cardiac output measured with the 5-mL injectate (mean, 4.63 L/min) and cardiac output measured with the 10-mL injectate (mean, 4.52 L/min) were not significantly different (P = .64). Lower and upper limits of agreement were -1.7 L/min to +1.6 L/min. The bias (mean difference between 10- and 5-mL measurements) of all measurements was -0.09, and the precision was 1.43 L/min, with a 95% confidence limit (mean difference +/- 2 SD) of -1.7 to +1.6 L/min. An additional measurement was necessary in 77% of patients in the 5-mL group but in only 48% of the 10-mL group (P = .006).

CONCLUSIONS

Cardiac outputs measured with 5- and 10-mL injectates do not differ significantly. The greater variability of measurements obtained with a 5-mL injectate suggests that more measurements, and thus more time, are needed to measure cardiac output accurately. Clinicians must weigh the benefit of minimizing fluid volume used against the potential decreased reliability of cardiac output measurements.

Thrombus in vertebrobasilar dolichoectatic artery treated with intravenous urokinase

BACKGROUND

Vertebrobasilar dolichoectasia is often found in patients with posterior circulation ischemia. Brain ischemia is caused by abnormal flow in the dilated artery and obstruction of paramedian arteries or intraluminal thrombus with artery-to-artery embolism. We report a patient with vertebrobasilar dolichoectasia and luminal thrombus treated with intravenous urokinase who did well but died 2 months later of subarachnoid hemorrhage.

CASE DESCRIPTION

A 60-year-old man developed right-hand clumsiness, dysarthria and ataxia. Computed tomography showed vertebrobasilar dolichoectasia and thrombus in the basilar artery. Symptoms quickly resolved on heparin but recurred on warfarin and again resolved on heparin. Two weeks later, while on warfarin and aspirin 325 mg, he developed hand numbness, oscillopsia and ataxia. Symptoms again resolved on heparin. Angiography showed severe dolichoectasia of the distal right vertebral artery and basilar artery. A large mural thrombus was detected in the ventral part of the distal basilar artery narrowing the lumen by 50%. He was treated with intravenous urokinase 4,400 units/kg as a bolus followed by 4,400 units/kg/h for 12 h. Repeat angiography showed almost complete recanalization and improved filling of basilar artery branches. He was maintained on warfarin and aspirin 81 mg and had no further ischemic episodes. He died 2 months later of rupture of the basilar artery and subarachnoid hemorrhage.

CONCLUSION

Some patients with thrombosis of vertebrobasilar dolichoectactic arteries continue to have ischemic symptoms despite adequate anticoagulation. Intravenous thrombolysis may be effective in reducing the risk of stroke, but the risk/benefit ratio needs to be assessed in each patient.

Multifocal motor neuropathy presenting as ophthalmoplegia

A 45-year-old man developed ophthalmoplegia and subsequently multiple cranial nerve palsies in association with bibrachial paresis. Investigations revealed evidence of conduction block occurring at a very proximal location (i.e., the spinal roots) and seemingly sparing sensory fibers. Other causes were ruled out and a diagnosis of multifocal motor neuropathy with conduction block (MMN) was suggested. The patient responded to cyclophosphamide. Differentiating features between MMN and chronic inflammatory demyelinating polyradioneuropathy (CIDP) are discussed. This case demonstrates that MMN may rarely present with ophthalmoparesis and also demonstrates that features of MMN and CIDP may overlap.