Case Report: Phenazopyridine-Induced Sulfhemoglobinemia in an 83-Year-Old Presenting with Dyspnea

BACKGROUND

Sulfhemoglobinemia is a rare dyshemoglobinemia that presents similarly to methemoglobinemia.

CASE REPORT

An 83-year-old woman with stage IV ovarian cancer presented to the Emergency Department after a near syncopal spell and was found to be cyanotic with a pulse oximetry reading of 71%. Pulse oximetry improved to only the mid-80s range with administration of high-flow oxygen. Her arterial blood gas on supplemental high-flow oxygen demonstrated a PaO₂ of 413 mm Hg and methemoglobin of 1.2%, but also noted the interference of the co-oximetry with sulfhemoglobinemia. Further history revealed that the patient had recently been started on phenazopyridine. The phenazopyridine was stopped, an exchange transfusion was offered but declined, and the patient was discharged to home hospice. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The diagnosis of sulfhemoglobinemia can be challenging given that routine co-oximetry does not identify it. The clue to the diagnosis is that the cyanotic-appearing patient has a normal or elevated PaO₂ and seems to be less ill than expected, given the degree of cyanosis. Sulfhemoglobinemia does not reverse with the administration of methylene blue.

O5: THE CLIFF AND CONOR STUDIES NOVEL ASSESSMENT TOOLS IN COLORECTAL LIVER METASTASES (CLIFF STUDY - CHANGE IN LIVER FUNCTION AND FAT IN PRE-OPERATIVE CHEMOTHERAPY FOR COLORECTAL LIVER METASTASES, CONOR STUDY

Introduction

Hepatic resection is the only potentially curative treatment for patients with colorectal liver metastases (CLM). Patient selection is key, but there is wide variation in practice. Pre-operative chemotherapy can improve oncological outcomes, however chemotherapy-associated liver injury (CALI) may hinder liver regenerative capacity. Standard pre-operative assessments fail to accurately capture factors such as CALI and future liver remnant (FLR) function. The CLiFF and CoNoR studies utilise two novel assessment techniques, aiming to improve patient outcomes.

Method

The CLiFF study prospectively assesses two primary outcomes in 35 patients undergoing pre-operative chemotherapy for CLM: 1) change in liver function (via LiMAx test: direct assessment of hepatic functional capacity), and 2) change in liver fat (via advanced MR imaging (in-house spectroscopy and modified Dixon technique, scaled up via Perspectum LiverMultiScan)). The CoNoR study assesses potential added benefit of these novel tools in CLM resectability decision-making via sequential workstreams: a systematic review and international hepatobiliary expert interviews inform the online survey, assessing added benefit via online MDT scenarios.

Result

Preliminary CLiFF analysis suggests that CALI changes in liver fat and function are unrelated. Liver fat analysis techniques are compared and correlated with digital histological analysis. The CoNoR systematic review identifies key factors influencing CLM resectability decision-making and informs the international expert interviews, scheduled to occur during a February 2020 international hepatobiliary conference.

Conclusion

These studies are the first to assess where these novel tools might be utilised to maximal patient benefit within the Hepatobiliary MDT, and the first systematic review in CLM resectability decision-making.

Take-home message

These two linked studies evaluate the use of two novel assessment tools in the treatment of colorectal liver metastases, with the potential to improve patient selection for curative resection and patient outcomes.

PATEY PRIZE SESSION

High-precision calibration of MRS thermometry using validated temperature standards: effects of ionic strength and protein content on the calibration

Currently, there is very limited ability to measure the temperature of the brain, but a direct technique for its estimation in vivo could improve the detection of patients at risk of temperature-related brain damage, help in the diagnosis of stroke and tumour, and provide useful information on the mechanisms of thermoregulation of the brain. In this article, new calibrations in vitro of MRS thermometry using temperature-stabilised reference phantoms are reported. The phantoms comprise two concentric glass spheres: the inner sphere contains the phantom material to be measured by MRS, and the outer sphere contains a substance with a known temperature stable to within 0.2 °C. The substances were freezing organic fixed-point compounds (diphenyl ether and ethylene carbonate, freezing at 26.3 and 35.8 °C, respectively) or temperature-controlled circulating water. The phantom temperature was continuously monitored with a fluoroptic probe calibrated at the National Physical Laboratory with traceability to the International Temperature Scale 1990 (ITS-90). The MRS temperature calibration was obtained by measuring the chemical shift of water relative to N-acetylaspartate (NAA) in a single voxel as a function of temperature using a 1.5-T Philips Intera scanner. Measurements were made for several phantom materials to assess the effect of tissue composition on the water-NAA chemical shift against temperature calibration. The phantom mixtures contained 25 mm of NAA buffered to pH 6.5 or 7.5 and several ionic salts or bovine serum albumin (BSA). Spectra were acquired from 25 to 45 °C. The correlation between frequency differences and phantom temperature was very linear with small residuals. However, the linear fitting parameters varied with ionic composition and BSA concentration. The 'apparent' temperature (calibrated using the water-NAA frequency differences) decreased by approximately 1 °C for every 100 mm increase in ionic concentration and increased proportionally to the concentration of BSA.

Effects of Alzheimer's disease transgenes on neurochemical expression in the mouse brain determined by ¹H MRS in vitro

Transgenic models of human disease can be used to understand pathology and to discover biomarkers of disease presence, progression and response to therapy. Here we report a study of longitudinal metabolic differences between TASTPM transgenic Alzheimer's disease (AD) mice and their wild type counterparts using (1)H magnetic resonance spectroscopy (MRS) to look for potential biomarkers for use in AD research and drug discovery. Chloroform methanol extractions were performed on the brains of mice aged between 3 and 18 months. (1)H MR spectra were recorded from the aqueous fractions. Absolute metabolite concentrations, determined from resonance integrals relative to an internal standard, were analysed by 2-way ANOVA (genotype x age). Significant effects of age alone were identified for creatine, glutamine and total choline-containing compounds. There was a marked increase in creatine in the oldest (15-18 mo) TASTPM mice. The increase in creatine was unexpected and may be caused by osmotic stress in older animals as plaque load increases. Care should be taken when using creatine as a reference metabolite during scans of these animals in vivo. A significant effect of genotype alone was identified for myo-inositol (MI), which was higher in TASTPM mice at all ages. Succinate, glycerophosphocholine and choline all showed significant effects of age and genotype. No significant effects were detected in N-acetylaspartate (NAA) levels. Increased MI could be a marker of gliosis or microglial activation in TASTPM mice, but the absence of an age dependence for MI levels means it may be a biomarker of disease, but not of disease progression. Decreased succinate is indicative of disrupted neuronal energy metabolism, an effect that has been seen in human AD.

Wear and surface analysis of 38 mm ceramic-on-metal total hip replacements under standard and severe wear testing conditions

The purpose of this study was to compare the wear of zirconia-toughened alumina (ZTA) and alumina femoral heads tested against as-cast CoCrMo alloy acetabular cups under both standard and severe wear conditions. A new severe test, which included medio-lateral displacement of the head and rim impact upon relocation, was developed. This resulted in an area of metal transfer and an area of increased wear on the superior-anterior segment of the head that were thought to be due to dislocation and rim impact respectively. While the wear of all ceramic heads was immeasurable using the gravimetric method, the wear rates for the metallic cups from each test were readily calculated. An average steady state wear rate of 0.023 ± 0.005 mm3/106 cycles was found for the cups articulating against ZTA under standard wear conditions. A similar result had previously been obtained for the wear of cups articulated against alumina heads of the same size (within the same laboratory). Under severe wear conditions an increase in the metallic cup steady state wear rate was found with the ZTA and alumina tests giving 0.623 ± 0.252 and 1.35 ± 0.154 mm3/106 cycles respectively. Wear of the ceramic heads was detected using atomic force microscopy which showed, under severe wear conditions, a decrease in polishing marks and occasional grain removal. The surfaces of the ZTA heads tested under standard conditions were virtually unchanged from the unworn samples. Friction tests showed low friction factors for all components, pre and post wear.

Tribological and surface analysis of 38mm alumina–as-cast Co–Cr–Mo total hip arthroplasties

There is currently much discussion over the use of ceramic femoral components against metal acetabular cups, for use in total hip arthroplasty. The current study investigates six hot isostatically pressed alumina femoral heads of 38 mm diameter articulating against six as-cast Co—Cr—Mo metallic acetabular cups. Standard walking-cycle simulator wear testing was carried out to 5×106 cycles using the Durham Mark II hip wear simulator, and wear was determined gravimetrically. In addition, surface topography, using a non-contacting profilometer, an atomic force microscope, and an optical microscope, was monitored throughout the wear test. The wear of the ceramic heads was found to be undetectable using the current gravimetric method; however, a change in the surface topography was seen, as grain removal on the pole was observed through atomic force microscopy analysis. A biphasic wear pattern was found for the metallic cups, with low wear rates of 1.04 ± 0.293 mm3/106 cycles (mean, ±95 per cent confidence interval) and 0.0209 ± 0.004 mm3/106 cycles (mean, ±95 per cent confidence interval) for running-in and steady state wear phases respectively. Frictional measurement revealed that the joints were tending towards full fluid-film lubrication in parts of the walking cycle. The results show that the combination of hot isostatically pressed alumina and as-cast Co—Cr—Mo is a promising alternative for total hip arthroplasties.

Assessing human 5-HT function in vivo with pharmacoMRI

A number of novel ways of using magnetic resonance imaging (MRI) to visualise the action of drugs on animal and human brain (pharmacoMRI or phMRI) are becoming established tools in translational psychopharmacology. Using drugs with known pharmacology it is possible to investigate how neurotransmitter systems are involved in neural systems engaged by other processes, such as cognitive challenge (modulation phMRI) or to examine the acute effects of the drug itself in the brain (challenge phMRI). In this article we discuss the principles behind phMRI and review studies investigating the effect of serotonin (5-HT) manipulations. 5-HT modulation phMRI studies show the involvement of 5-HT in a broad range of neural processes ranging from motor function through 'cold' cognition, such as memory and response inhibition, to emotional processing. We highlight findings in brain areas that show some consistency or complementarity across studies, such as the ventrolateral orbitofrontal cortex where modulation by 5-HT is task-specific, and the amygdala in emotional processing where 5-HT is predominantly inhibitory. 5-HT challenge phMRI is promising but as yet few studies have been carried out. New ways of analysing phMRI data include connectivity analysis which holds the promise of going beyond identifying isolated areas of activation/modulation to understanding functional circuits and their neurochemistry. 5-HT phMRI now needs to be taken into patient populations and methods of investigating treatment effects need to be developed. If this is successful then phMRI will provide a genuinely exciting opportunity for the rapid development of better treatments for psychiatric conditions.

Rattlesnake envenomation with neurotoxicity refractory to treatment with crotaline Fab antivenom

INTRODUCTION

Neurotoxicity following rattlesnake envenomation is reported with certain crotaline species. In some instances, crotaline Fab antivenom therapy that effectively halts progression of local tissue edema and hemotoxicity fails to reverse neurologic venom effects.

CASE SERIES

A 50-year-old man presented following a rattlesnake envenomation to the left ring finger. He had swelling and pain in the affected hand and complained of dyspnea and dysphonia. Significant fasciculations were seen in the face, tongue, neck, trunk, and arms. The patient received crotaline Fab antivenom but continued to develop worsening respiratory distress. His respiratory insufficiency requiring ventilatory support appeared related to respiratory muscle incoordination as extremity motor function remained intact. Initial control of local edema progression and hematologic parameters was achieved with antivenom, but diffuse fasciculations involving the entire body worsened despite aggressive antivenom treatment. In another case, a 9-year-old boy was envenomated by a rattlesnake on the left thenar eminence. He presented with pain and swelling up to the forearm and fasciculations of the tongue, face, and upper extremities. The progression of edema was halted at the mid-bicep level and hematologic parameters normalized with crotaline Fab antivenom. However, fasciculations continued for two days despite antivenom treatment.

CONCLUSION

We describe two cases of neurotoxicity following rattlesnake envenomation in which treatment with crotaline Fab antivenom adequately obtained initial control of local swelling and hematologic effects, but neurotoxic venom effects remained refractory to antivenom therapy. This phenomenon is anecdotally recognized following certain crotaline species envenomations.

A Prospective Evaluation of Shortened Course Oral N-Acetylcysteine for the Treatment of Acute Acetaminophen Poisoning

STUDY OBJECTIVE

Treatment with a shortened duration of oral N-acetylcysteine (20 to 48 hours) after acute acetaminophen poisoning is effective in the prevention of subsequent hepatic failure and death when administered to individuals meeting appropriate laboratory criteria.

METHODS

Individuals with a potentially toxic acetaminophen ingestion according to serum acetaminophen levels were identified prospectively using a large statewide poison control system database throughout a 12-month period. N-acetylcysteine was administered for a minimum of 6 doses (20 hours), after which laboratory studies were obtained. Discontinuation of N-acetylcysteine was recommended by the poison center when 2 criteria were met: serum acetaminophen was undetectable (<10 microg/mL) and liver test results were normal (serum aminotransferase, international normalized ratio). A follow-up questionnaire was administered to individuals treated with N-acetylcysteine for 48 hours or less to ascertain the presence of symptoms consistent with progressive hepatotoxicity.

RESULTS

Of 205 acutely poisoned individuals treated with N-acetylcysteine for 48 hours or less, 195 were successfully contacted after discharge, and 187 of 195 (95.9%) reported no symptoms consistent with hepatic failure. Eight individuals (4.1%) reported abdominal pain or vomiting; however, none received further N-acetylcysteine treatment or additional hospitalization.

CONCLUSION

A shortened duration of treatment with N-acetylcysteine (20 to 48 hours) may be an effective treatment option in individuals considered to be at no further risk of developing liver toxicity according to the fulfillment of appropriate laboratory criteria before N-acetylcysteine discontinuation.

Vasopressin treatment for cyclic antidepressant overdose

Due to neurotransmitter reuptake inhibition, peripheral alpha receptor blocking effects, and sodium channel blockade, severe cyclic antidepressant poisoning may lead to intractable hypotension. We report a case of severe amitriptyline toxicity, with hypotension unresponsive to direct alpha receptor agonists after pH manipulation, but improved with intravenous vasopressin. Vasopressin use in the setting of cyclic antidepressant toxicity has not been previously reported. Vasopressin may be a beneficial agent in the treatment of recalcitrant hypotension associated with poisoning or overdose. The anecdotal nature of this report must be emphasized and the use of vasopressin requires further research to define efficacy, dose, and potential side effects.

Crotalidae polyvalent immune Fab (ovine) antivenom is effective in the neutralization of South American viperidae venoms in a murine model

STUDY OBJECTIVE

Crotalidae polyvalent immune Fab (ovine) (CroFab; FabAV) is used in the treatment of symptomatic crotaline envenomations in North America. Unlike Antivenin (Crotalidae) Polyvalent, which is approved for treatment of crotaline envenomation in North and South America, FabAV is manufactured using only venoms from crotaline snakes native to the United States. This study was designed to evaluate the efficacy of FabAV in the neutralization of venom from 2 South American crotaline snakes: Crotalus durissus terrificus (tropical rattlesnake) and Bothrops atrox (fer-de-lance).

METHODS

A randomized, blinded, placebo-controlled murine model of intraperitoneal venom injection was used. Venom potency was determined in preliminary median lethal dose (LD 50) dosing studies. Study animals were then divided into 7 groups: (1) C durissus terrificus venom (Sigma-Aldrich Co.)+FabAV, (2) C durissus terrificus venom (Sigma-Aldrich Co.)+0.9% normal saline solution, (3) C durissus terrificus venom (Biotoxins Inc.)+FabAV, (4) C durissus terrificus venom (Biotoxins Inc.)+normal saline solution, (5) B atrox venom+FabAV, (6) B atrox venom+normal saline solution, and (7) FabAV+normal saline solution. Twice the estimated LD 50 was the chosen venom dose, and the amount of FabAV injected was 10 times the amount needed for venom neutralization. Statistical analysis included Fisher's exact test and log-rank testing to compare survival rates and times.

RESULTS

The venom LD 50 was found in preliminary studies to be 0.9 mg/kg and 1.35 mg/kg for the C durissus terrificus venom obtained from Sigma-Aldrich Co. and Biotoxins Inc., respectively. The LD 50 for B atrox venom was 5.0 mg/kg. All animals receiving venom only and saline solution died. Animals receiving FabAV together with either venom survived to the end of the 24-hour observation period ( P <.001). Comparison of survival times between groups demonstrated a significant difference in time to death between venom-only control groups and the FabAV+venom groups (P <.001). All animals in the FabAV+normal saline solution group survived to the conclusion of the study.

CONCLUSION

FabAV, when premixed with venom, decreases lethality in a murine model of intraperitoneal venom injection of the South American pit vipers, C durissus terrificus and B atrox .

North American coral snake antivenin for the neutralization of non-native elapid venoms in a murine model

OBJECTIVES

North American coral snake antivenin (CSAV; Wyeth Antivenin [Micrurus fulvius], equine origin) is approved for the treatment of coral snake envenomations in the United States. The coral snake is the only elapid that is native to North America, but envenomations from non-native elapids are occurring more commonly in this country. This study was designed to evaluate the efficacy of CSAV in the neutralization of two exotic elapid envenomations: Naja naja (Indian cobra) and Dendroaspis polylepsis (black mamba).

METHODS

A randomized, blinded, placebo-controlled murine model of intraperitoneal venom injection was employed. Venom potency was determined in preliminary dosing studies. Study animals then were divided into five groups: 1) N. naja venom + CSAV, 2) N. naja venom + 0.9% normal saline (NS), 3) D. polylepsis venom + CSAV, 4) D. polylepsis venom + NS, and 5) CSAV + NS. The venom dose was chosen to be twice the estimated LD50. The amount of CSAV injected was ten times the amount necessary for neutralization of a 2 x LD50 dose of M. f. fulvius venom in a murine model. Statistical analysis included Fisher's exact and log-rank testing to compare survival rates and times.

RESULTS

Preliminary studies estimated the venom LD50 to be 2.58 mg/kg and 0.45 mg/kg, respectively, for the N. naja and D. polylepsis. A significant difference was shown in comparison of survival times between CSAV-venom groups and normal saline-venom groups despite all animals in both treatment and control arms dying. Animals receiving CSAV and N. naja venom survived (mean +/- SD) 24.4 +/- 3.0 minutes, versus 17.8 +/- 1.3 minutes in the control group (p < 0.001), whereas those receiving CSAV and D. polylepsis venom survived 203.8 +/- 37.0 minutes versus 130.0 +/- 42.6 minutes in the control group (p < 0.001). All animals in the CSAV + NS group survived to the conclusion of the study.

CONCLUSIONS

When premixed with venom, CSAV increased survival time in a murine model of intraperitoneal N. naja and D. polylepsis venom injection. The clinical implications of this are unclear, given unchanged mortality rates.

Fatal unintentional overdose of diltiazem with antemortem and postmortem values

BACKGROUND

Therapeutic errors involving calcium channel antagonists (CCA) resulting in death rarely have been reported in detail. We report a fatality from an unintentional overdose of sustained-release (SR) diltiazem including antemortem and postmortem blood concentrations.

CASE REPORT

A 65-year-old man with aortic stenosis mistakenly took six tablets of diltiazem 360 mg SR. He developed symptoms of toxicity by 7 hours after ingestion. By 10 hours, he went to the emergency department. Despite a prolonged resuscitative attempt, the patient died 17 hours postingestion. An antemortem blood sample drawn 11.5 hours after ingestion was 2.9 mcg/mL. Postmortem gas chromatography of central blood revealed a diltiazem level of 6 mcg/mL and the peripheral blood sample measured 5 mcg/ mL.

CONCLUSION

This case suggests that an unintentional overdose with a CCA may be lethal if the patient's cardiovascular ability to compensate for the toxic effects is compromised.

Overdose of aripiprazole, a new type of antipsychotic

Aripiprazole is the first member of a new class of antipsychotic medications. Unlike other antipsychotics, it acts as a partial agonist at dopamine D(2) and 5-HT(1A) receptors, thereby mitigating most of the adverse reactions such as extrapyramidal side effects and hyperprolactinemia. Additionally, most research to date has suggested a low incidence of QTc prolongation and orthostatic hypotension at therapeutic doses. Experience in the setting of intentional overdose, however, is limited. We present a case of a 27-year-old woman who intentionally ingested 330 mg of aripiprazole in a suicide attempt. Clinical effects were limited to mild sedation. Serum levels performed by the drug's manufacturer confirmed a total level (parent drug and active metabolite) of 716 ng/mL, nearly six times the upper limit of accepted therapeutic levels. This suggests that aripiprazole's therapeutic index is quite high and reinforces the drug's known safety profile.

The assessment of antiangiogenic and antivascular therapies in early-stage clinical trials using magnetic resonance imaging: issues and recommendations

Vascular and angiogenic processes provide an important target for novel cancer therapeutics. Dynamic contrast-enhanced magnetic resonance imaging is being used increasingly to noninvasively monitor the action of these therapeutics in early-stage clinical trials. This publication reports the outcome of a workshop that considered the methodology and design of magnetic resonance studies, recommending how this new tool might best be used.

Rattlesnake envenomation to the face of an infant

BACKGROUND

Mortality from rattlesnake envenomation in the United States is rare. Despite approximately 8000 crotaline (pit vipers) bites annually, it is estimated that only 10 to 15 deaths occur. Besides direct intravascular envenomation and anaphylaxis, bites to the head and neck may account for some of these rare fatalities. We report a pediatric case of severe facial envenomation requiring emergent intubation and antivenom administration.

CASE REPORT

A 14-month-old female toddler was envenomated by a Southern Pacific rattlesnake (Crotalus viridis helleri) above the right upper lip while playing in her backyard. Rapid swelling and ecchymosis developed, and the patient was airlifted to a pediatric tertiary care hospital. Within 3 hours, stridorous respirations complicated by significant facial and oropharyngeal edema necessitated emergent orotracheal intubation. A total of 16 vials of FabAV [Crotalidae Polyvalent Immune Fab (ovine) antivenom] were administered over the next 24 hours. The child gradually improved and was successfully extubated 5 days later. A 3-month follow-up demonstrated no significant cosmetic facial abnormalities.

CONCLUSION

Crotaline bites to the head and neck have the potential for significant swelling and airway compromise. Facial bites, anaphylaxis, and rare intravascular envenomation may account for many of the fatalities from rattlesnake envenomation. Early intubation may be required to maintain airway patency.

The development of functional imaging in the diagnosis, management and understanding of childhood brain tumours

Imaging plays a fundamental role in the management of children with brain tumours. A series of new techniques, commonly grouped under the heading functional imaging, promise to give information on the properties and biological characteristics of tissues thereby adding to the structural information available from current imaging. The EPSRC funded a workshop to bring together clinicians from the UK Children's Cancer Study Group and scientific experts in the field to identify clinical problems in childhood brain tumours that may be addressed by functional imaging and to develop a clinical test bed for applying, evaluating and developing this new technology. The presentations and discussion sessions from the workshop are summarised and a review of the current 'state of the art' for this rapidly developing area provided. A key output of the workshop was agreement on a series of hypotheses which can be tested in carefully designed clinical studies.

A Case of Type F Botulism in Southern California

BACKGROUND

Botulism caused by type F botulinum toxin accounts for less than 0.1% of all human botulism cases and is rarely reported in the literature.

CASE REPORT

A 45-year-old woman presented to an emergency department complaining of blurred vision, difficulty focusing, and dysphagia. The treating physician initially considered the possibility of paralytic shellfish poisoning due to a report of shellfish ingestion, which was later determined to be frozen shrimp and a can of tuna, but no gastroenteritis or paresthesias were present. During the emergency department observation, the patient developed respiratory distress with hypercapnea and required intubation and mechanical ventilation. Within hours, ptosis, mydriasis, and weakness in the arms and legs developed. Bivalent (A, B) botulinum antitoxin was administered approximately 24 h from the onset of initial symptoms, but over the next two days complete paralysis progressed to the upper and lower extremities. Shortly thereafter a stool toxin assay demonstrated the presence of type F botulinum toxin. The patient subsequently received an experimental heptavalent botulinum antitoxin on hospital day 7 but paralysis was already complete. Her three-week hospital course was complicated by nosocomial pneumonia and a urinary tract infection, but she gradually improved and was discharged to a rehabilitation facility. Anaerobic cultures and toxin assays have yet to elucidate the source of exposure.

CONCLUSION

We report a rare case of type F botulism believed to be foodborne in etiology. Administration of bivalent botulinum antitoxin did not halt progression of paralysis.

The 100-day PSA: usefulness as surrogate end point for biochemical disease-free survival after definitive radiotherapy of prostate cancer

Overall and biochemical disease-free (bNED) survival data after definitive radiotherapy (RT) for prostate cancer (CaP) requires decades of patient follow-up. Surrogates involving dynamics of prostate-specific antigen (PSA) decline, PSA nadir and time thereto have been unrewarding. This study investigated the metric of the PSA value 100 days after RT (PSA(100)), analyzed with respect to 8-y bNED survival. A total of 214 patients with T1-3 CaP were treated with definitive RT (defined as dose >66 Gy) in our institution between 1/1/1988 and 12/31/2000. All were subject to continuous follow-up with routine PSA levels. Biochemical failure (77 patients) was defined by the ASTRO criteria (n=67) or by the date of first hormonal therapy for a rising PSA, which did not meet the ASTRO criteria (n=10). No patients were included if they received postoperative radiation, or if hormones were administered prior to bNED recurrence, if any. Patients were stratified by PSA(100) values </= or >4.0 ng/ml, and </= or <2.5 ng/ml. Median follow-up was 64.3 months: follow-up data were calculated as of time to last PSA, with data collection as of 12/31/02. Patients with PSA(100)</=4.0 ng/ml had 62% 8-y bNED survival, and those with PSA(100)>4.0 ng/ml had 20% 8-y bNED survival (P<0.001). Use of a PSA(100) cutoff of 2.5 ng/ml yielded no significant difference in 8-y bNED survival (P=0.229). Cox proportional analysis revealed that initial PSA (P=0.006), stage (P=0.001) and PSA(100)</=4.0 ng/ml (P=0.002) were significantly related to bNED survival, but that age (P=0.887), race (P=0.500), RT dose (P=0.669), Gleason sum (P=0.091), and PSA(100)</=2.5 ng/ml (P=0.128) were not. In conclusion, PSA(100) using a cutoff of 4 ng/ml is a valuable and reliable surrogate for bNED survival after definitive RT, requiring less follow-up than other metrics. Patients with less values will have only about a 1 in 3 chance of bNED failure at 8 y.

Development of vigabatrin-induced lesions in the rat brain studied by magnetic resonance imaging, histology, and immunocytochemistry

Vigabatrin, the gamma-aminobutyric acid transaminase (GABA-T)-inhibiting anticonvulsant drug, was given orally at a dose of 275 mg/kg/day to rats (n = 6) in their feed for a period of 12 weeks, during which T2-weighted magnetic resonance images (MRIs) and diffusion-weighted MRIs (DWIs) were collected at weeks 1, 3, 6, 9, and 12. Half the rats (n = 3; and half their age-matched littermate controls; n = 3) were then killed for histopathological confirmation of the observed VGB-induced cerebellar and cortical white-matter lesions. VGB was removed from the diet and additional MRIs of the remaining rats taken at weeks 14, 17, 20, and 24, at which time they (n = 3), along with remaining controls (n = 3), were also killed for histopathology. The T2-weighted MRIs acquired were used to compute T2 relaxation time maps. Statistically significant VGB-induced T2 increases were observed in the frontal and occipital cortices and in the cerebellar white matter (CWM). The cerebellar lesions were more clearly discerned by eye in the DWIs than by T2-contrast alone. During the recovery period the VGB-treatment group CWM-T2 and CWM-DWI hyperintensity greatly decreased as the reversible lesion disappeared. As expected, histological and immunocytochemical examinations demonstrated the presence of intra-myelinic edema, microvacuolation, and reactive astrocytosis in the CWM and cortex after 12 weeks VGB-treatment. In the remaining animals microvacuolation of the white matter had not completely resolved during the 12-week recovery phase. The data show that quantitative MRI T2-relaxometry can be used to detect VGB-induced CNS pathology, and also suggest that DWI is particularly sensitive to the cerebellar lesion. The reversible neurotoxicity of global GABA-elevation in experimental animals is discussed.

Prevalence of autonomic signs and symptoms in antimuscarinic drug poisonings

Classically described antimuscarinic poisoning signs and symptoms include mydriasis, decreased secretions, ileus, urinary retention, hyperthermia, tachycardia, and altered mental status. These features may be used clinically to assist in the diagnosis of patients with unknown poisonings. We sought to analyze the prevalence of antimuscarinic physical examination findings in evaluating patients presenting with acute poisoning from antimuscarinic agents. We conducted a retrospective, medical record review at two urban tertiary care teaching hospitals. The study population consisted of patients presenting to the Emergency Department with a diagnosis of acute poisoning secondary to medications with known antimuscarinic side effects during a 78-month period between January 1994 and July 2001. Cases were excluded for incomplete medical records or unreliable histories of ingestion, and when concomitant ethanol intoxication was present on laboratory analysis. Clinical information obtained from each patient included vital signs, pupillary size, electrocardiogram abnormalities, the presence of mucous membrane and axillary secretions, initial urine output after bladder catheterization, quality of bowel sounds, mental status changes, the occurrence of seizures and coma, need for orotracheal intubation, and time required for clinical resolution. Diagnostic and therapeutic information including laboratory tests, administration of sodium bicarbonate, and usage of physostigmine was also collected. We identified a total of 345 cases, 213 of which met inclusion criteria. Of these cases, the most common documented findings included decreased secretions in 75.1%, tachycardia in 68.1%, confusion in 49.3%, drowsiness in 48.2%, and hypoactive or absent bowel sounds in 44.6%. Combining signs and symptoms to predict this toxic syndrome was not very reliable. Tachycardia, decreased oral or axillary secretions, and mydriasis proved to be the most predictive trio of clinical signs, but were found in only 28.2% of cases. At least one of these three signs was documented in 94% of our patients. The combination of tachycardia and decreased secretions was the most common pair of findings, recorded in 55.4% of cases. We conclude that the clinical presentation of antimuscarinic syndrome is variable.

The Kawasaki identity and the Fluctuation Theorem

In this paper we show that the Fluctuation Theorem of Evans and Searles [D. J. Evans, D. J. Searles, Phys. Rev. E 50, 1645 (1994)] implies that the Kawasaki function exp(-Omega(t)) is unity for all time t. We confirm this relationship using experimental data obtained using optical tweezers, and show that the Kawasaki function is a valuable diagnostic tool.

Complications of diagnostic physostigmine administration to emergency department patients

STUDY OBJECTIVES

Literature exists describing the complications associated with therapeutic physostigmine administration. No series exists detailing strictly diagnostic use. Our objective was to document the complications associated with diagnostic physostigmine administration in emergency department (ED) patients suspected of having antimuscarinic delirium.

METHODS

Two reviewers blinded to the study purpose performed a retrospective chart review on all adult patients administered physostigmine diagnostically over a 79-month period at a tertiary-care hospital. Twenty percent of charts were reviewed by both abstractors. The data abstracted from the chart included total dose of physostigmine, effect on mental status, any subsequent complications, or any use of atropine. Discharge summaries, toxicology consultations, and urine drug screens were used to determine the cause of the altered mental status.

RESULTS

Thirty-nine adult patients were administered varying doses of physostigmine (range 0.5 to 2 mg). The reviewers were able to determine the cause of the altered mental status in 35 patients. The cause was purely antimuscarinic in 19 patients, purely nonantimuscarinic in 10 patients, mixed antimuscarinic and nonantimuscarinic in 2 patients, psychiatric in 4 patients, and unknown in 4 patients. A total of 22 patients had full reversal of delirium, and this group comprised all 19 patients with a purely antimuscarinic cause and 3 patients in whom a cause was never determined. One (2.6%) in 39 patients had a brief convulsion without adverse sequelae. This patient was poisoned with an antimuscarinic drug. No patient had dysrhythmias, had signs of cholinergic excess, or was administered atropine.

CONCLUSION

Diagnostic physostigmine administration was without significant complication when given to ED patients suspected of having antimuscarinic delirium. Although a relatively small series, it contributes to the safety profile of physostigmine.

Dendrotoxin poisoning in a neurobiochemist

BACKGROUND

Dendrotoxin is a highly potent blocker of KV1.1, KV1.2, and KV1.6 potassium channels that is derived from the venom of the green mamba (Dendroaspis angusticeps). It is commonly used to inhibit the function of whole nerve preparations in vitro. Despite the widespread use and potency of this compound, neurotoxicity in humans has not been described from refined toxin. We report a case of dendrotoxin toxicity from dermal exposure.

CASE REPORT

A healthy 40-year-old female neurobiochemist presented with complaints of progressive numbness of the left malar region and lateral orbit that progressed to include the medial orbit and tongue. One hour prior to presentation she used her bare hands to remove residual petroleum jelly from a dish that had previously contained 500 nanoliters of 500 nanomolar dendrotoxin. She recalled rubbing her left eye prior to the onset of symptoms. Before touching the dish, she had washed it with running water and then 70% ethanol while using latex gloves. Physical examination was remarkable only for weakness to superior gaze and some mild tongue fasciculations. Within 12 hours of exposure, she was completely asymptomatic.

CONCLUSION

Dendrotoxin is a highly potent neurotoxin that can cause localized impairment of nerve function after mucous membrane exposure.

Random packings of spheres and spherocylinders simulated by mechanical contraction

We introduce a simulation technique for creating dense random packings of hard particles. The technique is particularly suited to handle particles of different shapes. Dense amorphous packings of spheres have been formed, which are consistent with the existing work on random sphere packings. Packings of spherocylinders have also been simulated out to the large aspect ratio of alpha=160.0. Our method packs randomly oriented spherocylinders to densities that reproduce experimental results on anisotropic powders and colloids very well. Interestingly, the highest packing density of phi=0.70 is achieved for very short spherocylinders rather than spheres. This suggests that slightly changing the shapes of the particles forming a hard sphere glass could cause it to melt. Comparisons between the equilibrium phase diagram for hard spherocylinders and the densest possible amorphous packings have interesting implications on the crystallization of spherocylinders as a function of aspect ratio.

How hard is a colloidal "hard-sphere" interaction?

Poly-12-hydroxystearic acid (PHSA) is widely used as a coating on colloidal spheres to provide a "hard-sphere-type" interaction. These hard spheres have been widely used in fundamental studies of nucleation, crystallization, and glass formation. Most authors describe the interaction as "nearly" hard sphere. In this paper we directly measure this interaction, using layers of PHSA adsorbed onto mica sheets in a surfaces force apparatus. We find that the layers, in appropriate solvents, have no long-range interaction. When the solvent is decahydronaphthalene (decalin), the repulsion rises from zero to the maximum measurable over a distance range of 15-20 nm. The data is converted to equivalent forces between spheres of different diameters, and modeled using a hard core potential. Using zeroth-order perturbation theory and computer simulation, we demonstrate that the equation of state does not deviate from that of a perfect hard-sphere system under any relevant experimental conditions.

Massive OxyContin ingestion refractory to naloxone therapy

OxyContin (oxycodone hydrochloride controlled release) is a long-acting preparation of oxycodone that is used as an opioid analgesic to treat chronic pain conditions. We report a patient who ingested a massive quantity of OxyContin and had altered mental status, noncardiogenic pulmonary edema, and hypoventilation that proved refractory to naloxone administration. She required mechanical ventilation for 3 days before recovering completely. The severity and length of poisoning was likely related both to the quantity and formulation of the oxycodone ingested.

5-HT(2C) receptor activation by m-chlorophenylpiperazine detected in humans with fMRI

Functional brain imaging using selective drug probes offers the opportunity to investigate regional neuronal activation linked to receptor stimulation or inhibition. In a placebo-controlled, balanced order design in eight male volunteers, the 5-HT(2c) agonist, m-chlorophenylpiperazine (mCPP) increased blood oxygen level dependent (BOLD) signal in the hypothalamus, caudate, pallidum, amygdala and pyriform cortex, anterior cingulate gyrus and choroid plexus (p < 0.001 uncorrected), areas with high density of 5-HT(2c) receptors. Activation in the hypothalamus correlated significantly with the prolactin response (p < 0.05 small volume corrected). In a subsequent Go/NoGo task, mCPP enhanced activation in right lateral orbitofrontal cortex (p < 0.05 small volume corrected). These findings suggest that pharmacoMRI is a potentially powerful tool for investigating neurotransmitter function in humans.

In vivo GABA+ measurement at 1.5T using a PRESS-localized double quantum filter

A point-resolved spectroscopy (PRESS)-localized double quantum filter was implemented on a 1.5T clinical scanner for the estimation of gamma-amino butyric acid (GABA) concentrations in vivo. Several calibrations were found to be necessary for consistent results to be obtained. The apparent filter yield was approximately 38%; filter strength was sufficient to reduce the singlet metabolite peaks in vivo to below the level of the noise. Metabolite-nulled experiments were performed, which confirmed that significant overlap occurred between macromolecule signals and the GABA resonance at 3.1 ppm. Although the multiplet arm at 2.9 ppm was confirmed to be relatively free of contamination with macromolecules, some contribution from these and from peptides is likely to remain; therefore, the term GABA+ is used. GABA+ concentrations were estimated relative to creatine (Cr) at the same echo time (TE) in a group of controls, studied on two occasions. The GABA+ concentration in 35-ml regions of interest (ROIs) in the occipital lobe was found to be 1.4 +/- 0.2 mM, with scan-rescan repeatability of 38%.

A prospective study of acute, unintentional, pediatric superwarfarin ingestions managed without decontamination

STUDY OBJECTIVE

We determine the incidence of clinically important bleeding in children with superwarfarin rodenticide ingestions not treated with gastrointestinal decontamination or prophylactic vitamin K.

METHODS

We prospectively studied patients younger than 6 years of age who reported to our poison center with acute unintentional superwarfarin ingestions. Patients who received gastrointestinal decontamination or prophylactic vitamin K were excluded. Forty-eight- to 96-hour prothrombin time or international normalized ratio (INR) blood tests were recommended, and telephone contact was attempted at least 3 days after ingestion.

RESULTS

A total of 595 consecutive patients were enrolled during the 16-month study period. Fifty patients were excluded: 8 who were known to have ingested 1 pellet or less; 25 who received activated charcoal; 15 who were treated with induced emesis; and 2 who received prophylactic vitamin K. The resulting study group contained 545 patients. Eighty-two patients were lost to follow-up. Follow-up was obtained for 463 patients, including 222 by telephone contact alone, 62 by 48- to 96-hour INR, and 179 by both methods. None of the patients had clinically important coagulopathy. Two patients had an INR of 1.5 or greater (1.5 and 1.8) without symptoms. Single nosebleeds were reported in another 2 patients with normal 48-hour INRs. Another child had a small amount of blood crusted in the nose with no other symptoms and no laboratory work available. One child with a normal 48-hour INR had blood-streaked stools that were thought to be caused by an anal fissure.

CONCLUSION

Children with acute unintentional superwarfarin ingestions of less than 1 box may be managed without gastric decontamination or prophylactic vitamin K. Laboratory testing for coagulopathy should be reserved for cases involving clinically evident bleeding abnormalities.

Delayed valproic acid toxicity: a retrospective case series

STUDY OBJECTIVE

We estimate how often an initially undetectable or nontoxic valproic acid (VPA) concentration misrepresents the potential toxicity of an acute VPA overdose.

METHODS

All patients followed up by the San Diego and San Francisco Divisions of the California Poison Control System between January 1997 and June 1999 with a documented serum VPA concentration of 120 microg/mL or greater at any time were identified through a search of poison center databases. Cases involving patients who had serial VPA concentrations and an initial VPA concentration that was unmeasurable or less than 100 microg/mL were also identified. The methods of decontamination, clinical outcomes, highest measured concentration, and times after ingestion of the initial and highest measured concentration of VPA were determined by means of chart review for these cases.

RESULTS

Of the 173 patients identified with VPA concentrations of 120 microg/mL or greater, 21 (12.1%) had a detectable initial concentration not in the toxic range, and 5 (2.9%) had initial concentrations of less than the limit of detection. These 26 cases involved acute ingestion of VPA preparations. Four of these 26 patients were discharged to home or to a psychiatric facility after the initial results were obtained.

CONCLUSION

Delayed toxicity might occur in patients after an acute overdose of enteric-coated VPA. Initial serum VPA concentrations might be misleading. Serial measurements documenting declining VPA concentrations or prolonged observation are recommended to determine whether a patient is medically safe for discharge or psychiatric placement.

Mercuric oxide poisoning treated with whole-bowel irrigation and chelation therapy

Most reported cases of inorganic mercury poisoning are from mercuric chloride. We report a case of mercuric oxide (HgO) powder ingestion. A 31-year-old man presented to an emergency department after ingestion of approximately 40 g of HgO. Soon after ingestion, he developed nausea, vomiting, and abdominal cramping. Abdominal radiograph revealed densely radiopaque material in the stomach. Gastrointestinal decontamination was accomplished with activated charcoal and whole-bowel irrigation with polyethylene glycol solution (Golytely) for 24 hours until repeat abdominal radiographs no longer demonstrated the substance in the gastrointestinal tract. He was also chelated with British anti-Lewisite for 5 days, followed by succimer for 10 days. He had markedly elevated urine and blood mercury levels after ingestion, but except for a mildly depressed serum bicarbonate (19 mEq/L), his chemistry results remained normal including blood urea nitrogen and creatinine. He had an uncomplicated hospital course and remained asymptomatic at 6 months postingestion. Despite elevated urine and blood mercury levels after ingestion of HgO, our patient did not develop the end-organ toxicity typical of inorganic mercury poisoning.

A comparison of cell and tissue extraction techniques using high-resolution 1H-NMR spectroscopy

Analysis of brain metabolites by a wide range of analytical techniques is typically achieved using biochemical extraction methodologies that require either two separate samples or two separate extraction steps to prepare both aqueous and organic metabolite fractions. However there are a number of brain pathologies in which both aqueous metabolite and lipid changes occur so that a simultaneous extraction of both fractions would be valuable. The methanol-chloroform (M/C) technique enables extraction of both aqueous metabolites and lipids simultaneously. It is already well established for lipid extraction of cells and tissue but its efficiency and reproducibility for extraction of aqueous metabolites is unknown. Therefore, we compared the aqueous metabolite yield and the reproducibility of the M/C method to the commonly used perchloric acid (PCA) method, using 1H-NMR spectroscopy of adult rat brain and purified rat astrocyte culture extracts. The results indicate that M/C is a superior technique for aqueous metabolite extraction from both brain tissue and cells when compared to the PCA method. The M/C extraction technique enables the simultaneous extraction of both lipids and aqueous metabolites from a single sample using small solvent-volumes, making it well suited for NMR investigations of both tissues and cells.

Motions in binary mixtures of hard colloidal spheres: melting of the glass

Dynamic light-scattering experiments are performed on binary mixtures of hard-sphere-like colloidal suspensions with a size ratio of 0.6. The optical properties of the particles are such that the relative contrast of the two species is very sensitive to temperature, a feature that is exploited to obtain the three partial coherent intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or arrest of the alpha process, on the time scale of the experiment. This is observed in a one-component suspension at a packing fraction of 0.575. The intermediate scattering functions measured on the mixtures quantify how, on introduction of the smaller spheres, the alpha process is released, i.e., how the glass melts. Increasing the fraction of smaller particles causes the alpha process to speed up but, at a given wave vector, also incurs a change to its amplitude in proportion to the change in the (partial) structure factor.

Molecular dynamics study of the stability of the hard sphere glass

Glassy states have been observed in hard-spherelike colloidal suspensions; however, some recent work suggests that a stable, one-component hard-sphere glass doesn't exist. A possible resolution of this dilemma is that colloidal glass formation results from a small degree of particle polydispersity. In order to investigate this further, we used the molecular-dynamics method to explore the phase behavior of both one- and two-component hard-sphere systems. It was found that the metastable fluid branch of the one-component system ceased to exist at a volume fraction marginally above melting, instead this system always crystallized within a relatively short period of time. Binary systems with a size ratio gamma=0.9 were then used as the simplest approximation to model a polydisperse hard-sphere colloidal system. Here the crystallization process was slowed down dramatically for all volume fractions and the fluid state was maintained for many relaxation times. Indeed, at the lowest volume fraction straight phi=0.55 no sign of crystallization was seen on the simulation time scale. The systems at intermediate volume fractions did eventually crystallize but at the highest volume fraction of straight phi=0.58, a dramatic slowing down in the crystallization process was observed. This is qualitatively in agreement with the experimental results on colloidal suspensions. Using the insight gained from this paper, the reasons behind a polydisperse system forming a stable glass, in contrast to the one-component system, are elucidated.

Elevated plasma cholecystokinin at high altitude: metabolic implications for the anorexia of acute mountain sickness

The aims of the present study were to measure the satiety neuropeptide cholecystokinin (CCK) in humans at terrestrial high altitude to investigate its possible role in the pathophysiology of anorexia, cachexia, and acute mountain sickness (AMS). Nineteen male mountaineers aged 38 +/- 12 years participated in a 20 +/- 5 day trek to Mt. Kanchenjunga basecamp (BC) located at 5,100 m, where they remained for 7 +/- 5 days. Subjects were examined at rest and during a maximal exercise test at sea-level before/after the expedition (SL1/SL2) and during the BC sojourn. There was a mild increase in Lake Louise AMS score from 1.1 +/- 1.2 points at SL1 to 2.3 +/- 2.3 points by the end of the first day at BC (P < 0.05). A marked increase in resting plasma CCK was observed on the morning of the second day at BC relative to sea-level control values (62.9 +/- 42.2 pmol/L(-1) vs. SL1: 4.3 +/- 8.3 pmol/L(-1), P < 0.05 vs. SL2: 26.5 +/- 25.2 pmol/L(-1), P < 0.05). Maximal exercise increased CCK by 78.5 +/- 24.8 pmol/L(-1), (P < 0.05 vs. resting value) during the SL1 test and increased the plasma concentration of non-esterified fatty acids and glycerol at BC (P < 0.05 vs. SL1/SL2). The CCK response was not different in five subjects who presented with anorexia on Day 2 compared with those with a normal appetite. While there was no relationship between the increase in CCK and AMS score at BC, a more pronounced increase in resting CCK was observed in subjects with AMS (> or =3 points at the end of Day 1 at BC) compared with those without (+98.9 +/- 1.4 pmol/L(-1) vs. +67.6 +/- 37.2 pmol/L(-1), P < 0.05). Caloric intake remained remarkably low during the stay at BC (8.9 +/- 1.4 MJ.d(-1)) despite a progressive decrease in total body mass (-4.5 +/- 2.1 kg after 31 +/- 13 h at BC, P < 0.05 vs. SL1/SL2), which appeared to be due to a selective loss of torso adipose tissue. These findings suggest that the satiogenic effects of CCK may have contributed to the observed caloric deficit and subsequent cachexia at high altitude despite adequate availability of palatable foods. The metabolic implications of elevated CCK in AMS remain to be elucidated.

Moderate hypothermia ameliorates liver energy failure after intestinal ischaemia-reperfusion in anaesthetised rats

BACKGROUND/PURPOSE

Intestinal ischaemia-reperfusion (IR) can cause liver failure. The aims of this work were to study the effects of intestinal IR on liver energy metabolism and to evaluate the effects of moderate hypothermia.

METHODS

Intestinal IR (90-minute intestinal ischaemia plus 60-minute or 240-minute reperfusion) was achieved by clamping and unclamping the superior mesenteric artery in rats. Normothermia or moderate hypothermia (30 degrees to 33 degrees C) was maintained by adjusting the environmental temperature. The ratio of hepatic inorganic phosphate to adenosine triphosphate (ATP) was monitored continuously during intestinal IR using in vivo phosphorus ((31)P) magnetic resonance spectroscopy. Phosphorus metabolites also were measured in extracts prepared from freeze-clamped liver and intestine.

RESULTS

Mortality occurred exclusively during normothermic intestinal IR. A progressive increase in the hepatic inorganic phosphate to ATP ratio after normothermic intestinal IR was observed. Moderate hypothermia delayed this effect. Analysis of liver extracts confirmed above findings. However, there was no difference in intestinal phosphocreatine or ATP between normothermic and hypothermic rats undergoing intestinal IR.

CONCLUSIONS

Intestinal IR at normothermia was associated with liver energy failure and high mortality rate. Moderate hypothermia ameliorated liver energy failure but did not attenuate intestinal energy failure after intestinal IR. Hypothermia may prove to be useful in the management of patients with intestinal IR injuries in the future.

Cerebrovascular reactivity following focal brain ischemia in the rat: a functional magnetic resonance imaging study

An essential goal of stroke research is to identify potentially salvageable regions of brain that may respond to therapy. However, current imaging methods are inadequate for this purpose. We therefore used dynamic magnetic resonance imaging of vascular reactivity following focal occlusion in the rat to determine whether measurement of perfusion reserve would help resolve this problem. We used the increase in blood-oxygen-level-dependent (BOLD) signal that occurs in normal brain following a CO2 challenge, to map vascular reactivity over the brain at 30-min intervals for 3.5 h after complete (CO) or partial (PO) focal ischemia. We assessed the regional correspondence between reactivity changes and areas of lowered apparent diffusion coefficient (ADC) and initial perfusion deficit. The area of lowered ADC was significantly smaller in the PO group compared to the CO group despite similar areas of perfusion deficit (P < 0.05). We identified four distinct areas within hypoperfused brain: a core area with low/absent reactivity and low ADC; borderzone areas with normal reactivity and either reduced ADC (CO group) or normal ADC (PO group); and an area with normal ADC and reduced/absent reactivity. In all ischemic regions, the BOLD peak arrival time in the brain was delayed or absent. There was a negative correlation between BOLD peak latency time and ADC (r = -0.42, P < 0.001), although latency alone did not differentiate individual ischemic regions. In conclusion, combining perfusion, ADC, and vascular reactivity mapping of the ischemic brain enables improved discrimination of core and borderzone regions.

Backpropagation of physiological spike trains in neocortical pyramidal neurons: implications for temporal coding in dendrites

In vivo neocortical neurons fire apparently random trains of action potentials in response to sensory stimuli. Does this randomness represent a signal or noise around a mean firing rate? Here we use the timing of action potential trains recorded in vivo to explore the dendritic consequences of physiological patterns of action potential firing in neocortical pyramidal neurons in vitro. We find that action potentials evoked by physiological patterns of firing backpropagate threefold to fourfold more effectively into the distal apical dendrites (>600 microm from the soma) than action potential trains reflecting their mean firing rate. This amplification of backpropagation was maximal during high-frequency components of physiological spike trains (80-300 Hz). The disparity between backpropagation during physiological and mean firing patterns was dramatically reduced by dendritic hyperpolarization. Consistent with this voltage dependence, dendritic depolarization amplified single action potentials by fourfold to sevenfold, with a spatial profile strikingly similar to the amplification of physiological spike trains. Local blockade of distal dendritic sodium channels substantially reduced amplification of physiological spike trains, but did not significantly alter action potential trains reflecting their mean firing rate. Dendritic electrogenesis during physiological spike trains was also reduced by the blockade of calcium channels. We conclude that amplification of backpropagating action potentials during physiological spike trains is mediated by frequency-dependent supralinear temporal summation, generated by the recruitment of distal dendritic sodium and calcium channels. Together these data indicate that the temporal nature of physiological patterns of action potential firing contains a signal that is transmitted effectively throughout the dendritic tree.