Speed skills: measuring the visual speed analyzing properties of primate MT neurons.

Knowing the direction and speed of moving objects is often critical for survival. However, it is poorly understood how cortical neurons process the speed of image movement. Here we tested MT neurons using moving sine-wave gratings of different spatial and temporal frequencies, and mapped out the neurons' spatiotemporal frequency response profiles. The maps typically had oriented ridges of peak sensitivity as expected for speed-tuned neurons. The preferred speed estimate, derived from the orientation of the maps, corresponded well to the preferred speed when moving bars were presented. Thus, our data demonstrate that MT neurons are truly sensitive to the object speed. These findings indicate that MT is not only a key structure in the analysis of direction of motion and depth perception, but also in the analysis of object speed.

Effects of wheat germ agglutinin and concanavalin A on parameters of highly purified sodium-potassium adenosine triphosphatases from Squalus acanthias and Electrophorus electricus.

The effects of two lectins, wheat germ agglutinin and concanavalin A, were studied on a variety of parameters of two highly purified (Na+ + K+)-ATPases (ATP phosphohydrolase, EC 3.6.1.3), from the rectal salt gland of Squalus acanthias and from the electroplax of Electrophorus electricus. Both lectins agglutinated the rectal gland enzyme equally, but wheat germ agglutinin inhibited (Na+ + K+)-ATPase activity much more. The electroplax enzyme was only marginally agglutinated and inhibited by the lectins. Neuraminidase treatment of the rectal gland (Na+ + K+)-ATPase had no effect on germ agglutinin inhibition. The inhibition of the rectal gland (Na+ + K+)-ATPase by wheat germ agglutinin could be reversed by N,N'-diacetylchitobiose, which has a high affinity for wheat germ agglutinin. Neither ouabain inhibition nor ouabain binding to the rectal gland enzyme was affected by wheat germ agglutinin. The p-nitrophenylphosphatase activity of the rectal gland enzyme was not inhibited by wheat germ agglutinin. Na+-ATPase activity, which reflects ATP binding and phosphorylation at the substrate site was inhibited by wheat germ agglutinin and this inhibition was reversed by potassium. Evidence is cited (Pennington, J. and Hokin, L.E., in preparation) that the inhibition of the (Na+ + K+)-ATPase by wheat germ agglutinin is due to binding to the glycoprotein subunit.

Evaluation of surgical performance with standard rigid and flexible-tip laparoscopes.

BACKGROUND: Flexible-tip laparoscopes have recently been introduced into clinical practice, with the goal of improving surgeon performance during complex laparoscopic procedures. We used objective and subjective performance parameters to compare standard rigid 0 degrees and 30 degrees lens laparoscopes two flexible-tip laparoscopes in an in vitro model. METHODS: Twenty-nine subjects with varied levels of surgical experience performed complex laparoscopic tasks in three different models simulating (a) prostate dissection from the rectum, (b) cystic duct clipping, and (c) distal posterior rectum dissection. Each task was performed using two Storz rigid laparoscopes (0 degrees and 30 degrees) and two flexible-tip laparoscopes, the Olympus LTF-V3 and the Fujinon EL2-TF310. The sequence of application of the two flexible-tip laparoscopes was randomized. In each case, an experienced laparoscopic camera driver controlled the field of vision. Time to complete each task, operative precision, and subjective surgeon rating scores were compared. Statistical analysis was performed with analysis of variance (ANOVA) and a two-sided fisher's exact test. RESULTS: In all three models, the flexible laparoscopes offered no advantage in terms of procedure time, surgical precision, or subjective surgeon rating score when compared with the 30 degrees lens rigid laparoscope. The 30 degrees rigid lens laparoscope and the two flexible-tip laparoscopes were superior to the 0 degrees lens rigid laparoscope for all parameters evaluated, with the exception of subjective rating in the cystic duct model and procedure time in the colorectal model. CONCLUSION: In this in vitro experimental model, the flexible-tip laparoscopes found to have no advantage over the standard rigid 30 degrees lens laparoscope. These models were validated, as the 0 degrees lens rigid laparoscope was surpassed by the 30 degrees lens rigid laparoscope and the flexible-tip laparoscopes. Both flexible-tip laparoscopes produced similar results and excellent image quality, but some experience is required before their smooth application can be achieved.

Chronic salicylism resulting in noncardiogenic pulmonary edema requiring hemodialysis.

Salicylate intoxication is frequently overlooked as a cause of noncardiogenic pulmonary edema and altered mental status in adult patients. We describe a 42-year-old woman who presented with two episodes of recurrent noncardiogenic pulmonary edema requiring intubation. The first admission to hospital triggered an extensive initial workup that did not indicate a cause for the pulmonary edema. At the second presentation, recognition of the clinical syndrome in the emergency department led to the correct diagnosis of salicylate intoxication. The patient was successfully treated with hemodialysis and urinary alkalinization, leading to rapid resolution of pulmonary edema and extubation. Several aspects of the clinical presentation suggest that the patient suffers from chronic salicylism, probably complicated by episodic superimposed acute intoxication, a condition often misdiagnosed or diagnosed late in the course of disease, contributing to substantial morbidity and mortality in these patients. Maintenance of a high index of suspicion and rapid institution of appropriate therapy including hemodialysis once the diagnosis is established is an important determinant of outcome in this serious but underdiagnosed disorder.

Cervical spinal cord injury in the adult rat: assessment of forelimb dysfunction.

Traumatic injury to the adult human spinal cord most frequently occurs at the mid-to-low cervical segments and produces tetraplegia. To investigate treatments for improving upper extremity function after cervical spinal cord injury (SCI), three behavioral tests were examined for their potential usefulness in evaluating forelimb function in an adult rat model that mimics human low cervical SCI. Testing was conducted pre- and up to 4 weeks post-operation in adult female rats subjected to either contusion injury at the C7 spinal cord segment or sham-surgery. Modified Forelimb Tarlov scales revealed significant proximal and distal forelimb extension dysfunction in lesion rats at l-to-4 weeks post-cervical SCI. The Forelimb Grip Strength Test showed a significant decrease in forelimb grip strength of lesion rats throughout the 4 weeks post-cervical SCI. Significant deficits in reach and pellet retrieval by lesion rats were measured at l-to-4 weeks post-cervical SCI with the conditioned pellet retrieval Staircase Test. The results demonstrate that these qualitative and quantitative forelimb behavioral tests can be used to evaluate forelimb function following low cervical SCI and may be useful to investigate treatments for improving forelimb function in these lesions.

Rapid in vivo detection of chloroquine resistance by the Quantitative Buffy Coat Malaria Diagnosis System.

The use of the Giemsa-stained thick blood smear for the diagnosis of malaria has not been supplanted since the discovery of the parasite by A. Laveran in 1880. Recently, a new direct diagnosis technique, the Quantitative Buffy Coat (QBC)* Malaria Diagnosis System, has been developed. We compared this technique with the thick blood smear diagnosis in a study of the efficacy of chloroquine therapy in Zaire. A total of 815 subjects were screened; 71 participated in the trial. They were given chloroquine at a dose of 25 mg/kg of body weight over three days and were examined for parasitemia two and seven days after treatment. Chloroquine resistance was detected in 38% of the subjects by thick blood smear and in 45% by the QBC test. Of greater interest was the time required for each diagnosis: an average of 17 min was required to examine microscopic fields with 1,000 leukocytes by thick blood smear analysis compared with less than one min by the QBC system. In addition, we did not observe diminished attention from fatigue by microscopists using the QBC system despite the large number of tests conducted. We conclude that the QBC system is an important tool for studies of drug resistance.

Malaria diagnosis by direct observation of centrifuged samples of blood.

We compared the effectiveness of malaria diagnosis by means of direct observation of centrifuged blood with that by conventional examination of Giemsa stained blood-films in a malaria clinic in Ethiopia. A commercially available, modified hematological apparatus (the QBC tube) was used for centrifugation. Red blood cells infected with diverse stages of Plasmodium falciparum and P. vivax are lighter than noninfected cells and somewhat heavier than granulocytes; thus they can readily be detected by direct inspection of UV-illuminated tubes. About 10% of infections diagnosed by direct centrifugal microscopy in a clinical setting were not detected by conventional examination of stained thick films. Diagnosis by direct centrifugation appears to be at least 8 times as sensitive as conventional microscopy when applied to serially diluted samples of malaria-infected blood. Superior sensitivity, together with the one step, solid state nature of the direct centrifugal procedure, provides important advantages for malaria diagnosis.

Human heading estimation during visually simulated curvilinear motion.

Recent studies have suggested that humans cannot estimate their direction of forward translation (heading) from the resulting retinal motion (flow field) alone when rotation rates are higher than approximately 1 deg/sec. It has been argued that either oculomotor or static depth cues are necessary to disambiguate the rotational and translational components of the flow field and, thus, to support accurate heading estimation. We have re-examined this issue using visually simulated motion along a curved path towards a layout of random points as the stimulus. Our data show that, in this curvilinear motion paradigm, five of six observers could estimate their heading relatively accurately and precisely (error and uncertainty < approximately 4 deg), even for rotation rates as high as 16 deg/sec, without the benefit of either oculomotor or static depth cues signaling rotation rate. Such performance is inconsistent with models of human self-motion estimation that require rotation information from sources other than the flow field to cancel the rotational flow.

A model of self-motion estimation within primate extrastriate visual cortex.

Perrone [(1992) Journal of the Optical Society of America A, 9, 177-194] recently proposed a template-based model of self-motion estimation which uses direction- and speed-tuned input sensors similar to neurons in area MT of primate visual cortex. Such an approach would generally require an unrealistically large number of templates (five continuous dimensions). However, because primates, including humans, have a number of oculomotor mechanisms which stabilize gaze during locomotion, we can greatly reduce the number of templates required (two continuous dimensions and one compressed and bounded dimension). We therefore refined the model to deal with the gaze-stabilization case and extended it to extract heading and relative depth simultaneously. The new model is consistent with previous human psychophysics and has the emergent property that its output detectors have similar response properties to neurons in area MST.

Toxic ingestions in pregnancy: abortifacient use in a case series of pregnant overdose patients.

OBJECTIVES: To profile young, pregnant patients with an overdose reported to an urban poison center; and to characterize the ingestions and short-term outcomes of these overdose patients. METHODS: A prospective, observational study of female overdose patients was performed from November 1, 1994, through March 31, 1995. Consecutive cases were identified from all calls to the regional poison center (annual call volume = 70,000) regarding intentional overdose in women between the ages of 12 and 30 years. Pregnancy tests were recommended by the poison center during the study period in female patients aged 12-30 years who presented to a health care facility (usually an urban ED) with an intentional overdose. Pregnant patients were then followed during their hospitalizations, and the results of toxicology studies and maternal and short-term fetal outcomes were recorded. RESULTS: Pregnancy tests were obtained for 371 (32%) of 1,142 eligible patients. Of patients with pregnancy tests, 43 (11.6%) were pregnant. Although most cases were comparable to general adult intentional ingestions, 5 of the 43 pregnant patients ingested known abortifacients. Most pregnant patients (35/43, 81%) had toxicity at or below American Association of Poison Control Centers (AAPCC) criteria for minimal toxicity, and all patients recovered completely. CONCLUSION: Pregnancy was a common finding in this sample of young, female, intentional overdose patients reported to our regional poison control center. Frequent use of abortifacients for toxic ingestions has not been previously reported. A pregnancy test should be obtained for all female patients of childbearing age with an intentional ingestion to address the potential association of the ingestion with an unanticipated or undesired pregnancy.

Randomized, double-blind, placebo-controlled trial of diazepam, nitroglycerin, or both for treatment of patients with potential cocaine-associated acute coronary syndromes.

INTRODUCTION: To the authors' knowledge, treatment of patients with cocaine-associated acute coronary syndromes has not been rigorously investigated in symptomatic patients. OBJECTIVE: To perform a randomized double-blind trial of diazepam, nitroglycerin, or both for treatment of patients with potential cocaine-associated acute coronary syndromes. METHODS: Patients with potential cocaine-associated acute coronary syndromes were randomized to treatment with either diazepam, nitroglycerin, or both every 5 minutes or until symptom resolution. Outcomes were chest pain resolution (measured by visual analog scale), and changes in blood pressure, pulse rate, cardiac output (L/min), cardiac index (L/min/m2), stroke volume (mL/beat), and stroke index (mL/beat/m2) over the 15-minute treatment period. To adjust for seven outcomes using the Bonferroni correction, alpha was set at 0.007. RESULTS: Forty patients were enrolled (diazepam, 12; nitroglycerin, 13; both, 15). Patients had a mean age (+/-SD) of 35.4 (+/-7.5) years; 75% were male. They presented a mean of 5 hours and 37 minutes after cocaine use. Baseline demographics, cocaine use patterns, chest pain characteristics, and initial electrocardiograms were similar for all groups. Chest pain severity improved similarly in the three groups [-33.3 mm (+/-8.0); -30.7 mm (+/-7.1); -33.0 mm (+/-7.9); p = 0.6]. The stroke index decreased during the 15-minute treatment period for all groups (diazepam, -8.7 (+/-3.3); nitroglycerin, -3.1 +/- 2.8; both, -1.8 (+/-3.1) mL/beat/m2; p = 0.03). After adjustment for differences between baseline hemodynamic and cardiac profiles and multiple comparisons, there was no difference in any response to therapy over time for the different treatments. CONCLUSIONS: For treatment of patients with potential cocaine-associated acute coronary syndromes, chest pain resolutions and changes in cardiac performance are not different in patients treated with diazepam or nitroglycerin. In this study, the use of both agents did not offer any advantage over either agent alone.

Results of laparoscopic Heller-Toupet operation for achalasia.

BACKGROUND: Laparoscopic myotomy has become the preferred treatment for achalasia. Controversy persists on the need for fundoplication and/or its type; when used, most series have utilized the Dor fundoplication. We report a large series of laparoscopic Heller-Toupet procedures. METHODS: All patients operated for achalasia were entered into a prospective database. Pre and postoperative esophageal symptoms, satisfaction scores, and SF-36 variables were compared. Surgical failures were defined as recurrent or persistent dysphagia leading to secondary treatment. Data are expressed as mean +/- S.D. RESULTS: One hundred consecutive cases were analyzed (61 men, 39 women, age 47 +/- 17 yr). Heller-Toupet was performed in 94, whereas six patients had a Dor fundoplication because of mucosal perforation (three) or technical difficulties performing a posterior wrap (three). Operative time was 148 +/- 21 min. There were 13 intraoperative adverse events managed laparoscopically, and no conversions. Minor postoperative complications were noted in two cases, whereas there were no major complications or deaths. Mean hospital stay was 1.2 +/- 0.5 days, (range 1-4). Follow-up was complete in 92% at 26 +/- 17 months. Failures leading to further treatment occurred in 4%. All symptom scores were significantly improved (p < 0.0001). Solid dysphagia score went from 6.4 to 1.0 postoperatively; regurgitation score went from 4.5 to 0.2 (combined frequency and severity, range 0-8). Postoperative global esophageal symptoms scale revealed improvement in 97%, and all domains of the SF-36 were improved. CONCLUSIONS: Although the best surgical approach to achalasia is yet to be determined, laparoscopic Heller-Toupet operation in experienced hands is a safe and effective procedure with low rates of morbidity and failure and high patient satisfaction.

Microfilarial perforation of the midgut of a mosquito.

To determine whether the midgut envelope of mosquitoes is disrupted by the passage of microfilariae, ultrastructural changes induced by microfilariae of Brugia malayi were observed in midguts of Aedes aegypti mosquitoes. Basal and apical plasma membranes were destroyed, disrupting the full depth of the midgut wall. Ingested ferritin lay against the gut wall, suggesting absence of the peritrophic membrane during penetration. Exsheathment of microfilariae appears to be enhanced by movement against the constricting midgut wall. It was concluded that particles present in the lumen of the gut may be disseminated passively to the hemocoel.

Herbal and alternative medicine.

An extensive range of herbal and dietary supplements is now available, and use of these products by ED patients is fairly common. Emergency physicians should be familiar with some of the products used more frequently for common complaints. Emergency personnel also should be vigilant for toxic syndromes resulting from ingestion of certain of these products and be wary of possible toxicity from any of these supplements owing to their minimal quality control and absence of FDA regulation.

Special considerations in gastrointestinal decontamination.

Many considerations factor into selecting the most appropriate method of gastrointestinal decontamination used in the poisoned patient. A thorough knowledge of the indications and efficacy as well as contraindications and complications of each modality is critical to the clinician's assessment. This article examines the current utility of syrup of ipecac-induced emesis, orogastric lavage, activated charcoal, cathartics, and whole bowel irrigation. In addition, the role of multiple dose activated charcoal and the controversial issue of the N-acetylcysteine and activated charcoal interaction are discussed.

Twenty-foot fall averts fatality from massive hydrogen sulfide exposure.

Hydrogen sulfide is a colorless irritant and asphyxiant gas with a noxious odor of "rotten eggs." Acute hydrogen sulfide exposure may cause, depending on the level and duration of toxicity, symptoms ranging from mild mucous membrane irritation to permanent neurologic impairment and cardiopulmonary arrest. We present a case of an oil refinery worker exposed to a typically fatal concentration of hydrogen sulfide gas (>1000 ppm) while working on top of a 20-foot ladder. The "knockdown" effect of exposure to high concentrations of hydrogen sulfide caused him to lose consciousness and fall from the top of the ladder. He was transported to the Emergency Department as a major trauma victim. Ironically, this 20-foot fall saved his life and possibly those of the rescuers by immediately removing him from the source of the hydrogen sulfide. Treatment of hazardous materials incidents and the pathophysiology and treatment options for hydrogen sulfide poisoning are discussed.

Visual slant misperception and the 'black-hole' landing situation.

A theory is presented which explains the often quoted tendency for dangerously low approaches during night-landing situations. The two-dimensional information at the pilot's eye contains sufficient information for the visual system to estimate correctly the angle of slant of the runway relative to the approach path. An algorithm is developed which can perform this angle estimation. It is dependent upon perspective information being available a certain lateral distance out from the aimpoint, to either side of the runway edgelights. However, under 'black-hole' landing conditions this information is not available, and it is proposed that the visual system uses instead the only available information--namely the perspective gradient of the runway edgelights. An equation is developed which predicts what the perceived approach angle will be when this incorrect perspective is used. The predictions are in close agreement with existing experimental data.

Adolescents with cancer: are they at risk for suicide?

When the threat of cancer is imposed during a period of intense developmental changes, it is difficult to envision that an adolescent has a strong enough sense of self to survive. Yet, adolescents with cancer tend to fight to live rather than succumb to death naturally or by suicide. Possible reasons for this fight to survive can be derived from Orbach, Grass, and Glaubman's (1981) model of children's attitudes toward life and death.