Feature impact assessment: a new score to identify relevant metabolomics features in artificial neural networks using validated labels

INTRODUCTION

Artificial Neural Networks (ANN) are increasingly used in metabolomics but are hard to interpret.

OBJECTIVES

We aimed at developing a feature impact score that is model-agnostic, simple, and interpretable.

METHODS

Feature Impact Assessment (FIA) is calculated by varying combinations of features within their observed value range and checking for changes in prediction outcomes. FIA was implemented in R and tested on metabolomics datasets.

RESULTS

FIA exceeded LIME and SHAP in selecting biologically meaningful features. Values were comparable across different ANN architectures.

CONCLUSION

FIA is a novel score ranking feature impact, helping interpreting ANN in the metabolomics field.

A protein-free chemically defined medium for the cultivation of various micro-organisms with food safety significance

AIMS

To develop a broadly applicable medium free of proteins with well-defined and reproducible chemical composition for the cultivation of various micro-organisms with food safety significance.

METHODS AND RESULTS

The defined medium was designed as a buffered minimal salt medium supplemented with amino acids, vitamins, trace metals and other nutrients. Various strains commonly used for food safety research were selected to test the new defined medium. We investigated single growth factors needed by different strains and the growth performance of each strain cultivated in the defined medium. Results showed that the tested strains initially grew slower in the defined medium compared to tryptic soy broth, but after an overnight incubation cultures from the defined medium reached adequately high cell densities.

CONCLUSIONS

The newly designed defined medium can be widely applied in food safety studies that require media with well-defined chemical constituents.

SIGNIFICANCE AND IMPACT OF THE STUDY

Defined media are important in studies of microbial metabolites and physiological properties. A defined medium capable of cultivating different strains simultaneously is needed in the food safety area. The new defined medium has broader applications in comparing different strains directly and provides more reproducible results.

Maternal and Cord Blood Metabolite Associations with Gestational Weight Gain and Pregnancy Health Outcomes

Pre-pregnancy obesity and excessive gestational weight gain (GWG) are risk factors for future maternal and childhood obesity. Maternal obesity is potentially communicated to the fetus in part by the metabolome, altering the child's metabolic program in early development. Fasting maternal blood samples from 37 singleton pregnancies at 25-28 weeks of gestation were obtained from mothers with pre-pregnancy body mass indexes (BMIs) between 18 and 40 kg/m². Various health measures including GWG, diet, and physical activity were also assessed. At term (37-42 weeks), a venous umbilical cord sample was obtained. Serum metabolomic profiles were measured using nuclear magnetic resonance spectroscopy as well as a gut and metabolic hormone panel. Maternal and cord serum metabolites were tested for associations with pre-pregnancy BMI, GWG, health outcomes, and gut and metabolic hormones. While cord blood metabolites showed no significant correlation to maternal obesity status or other measured health outcomes, maternal serum metabolites showed distinct profiles for lean, overweight, and obese women. Additionally, four serum metabolites, namely, glutamate, lysine, pyruvate, and valine, allowed prediction of excessive GWG when pre-pregnancy BMI was controlled. Metabolic biomarkers predictive of GWG are reported and, if validated, could aid in the guidance of prenatal weight management plans as the majority of pregnancy weight gain occurs in the third trimester.

Determining the effects of nutrition on the reproductive physiology of male mosquitoes

Nutrition affects multiple aspects of insect physiology such as body size and fecundity, but we lack a detailed understanding of how nutrition influences the reproductive physiology of male insects such as mosquitoes. Given that female mosquitoes are vectors of many deadly diseases and can quickly proliferate, understanding how male nutrition impacts female fecundity could be of critical importance. To uncover the relationship between nutrition in adult male mosquitoes and its impacts on reproductive physiology, we reared larvae of the Northern house mosquito, Culex pipiens, on a standard lab diet and divided adult males among three different dietary treatments: low (3%), moderate (10%), and high (20%) sucrose. We found that although overall body size did not differ among treatments, one-week-old males raised on the 3% sucrose diet had significantly smaller male accessory glands (MAGs) compared to males that consumed the 10% and the 20% sucrose diets. Diet affected whole-body lipid content but did not affect whole-body protein content. Using nuclear magnetic resonance (NMR) spectroscopy, we found that diet altered the metabolic composition of the MAGs, including changes in lactic acid, formic acid, and glucose. We also observed changes in protein and lipid abundance and composition in MAGs. Females who mated with males on the 3% diet were found to produce significantly fewer larvae than females who had mated with males on the 10% diet. Taken together, our results demonstrate that the diet of adult male mosquitoes clearly affects male reproductive physiology and female fecundity.

Affine Transformation of Negative Values for NMR Metabolomics Using the mrbin R Package

Data from untargeted metabolomics studies employing nuclear magnetic resonance (NMR) spectroscopy oftentimes contain negative values. These negative values hamper data processing and analysis algorithms and prevent the use of such data in multiomics integration settings. New methods to deal with such negative values are thus an urgent need in the metabolomics community. This study presents affine transformation of negative values (ATNV), a novel algorithm for replacement of negative values in NMR data sets. ATNV was implemented in the R package mrbin, which features interactive menus for user-friendly application and is available for free for various operating systems within the free R statistical programming language. The novel algorithms were tested on a set of human urinary NMR spectra and were able to successfully identify relevant metabolites.

Caffeine-Containing Energy Shots Cause Acute Impaired Glucoregulation in Adolescents

Caffeine-containing, nutritionally fortified energy shots are consumed at high rates by adolescents, yet little is known about their metabolic impact. The purpose of this study was to examine the consequences of small format, caffeinated energy shots on glucose metabolism and gastrointestinal hormone secretion in adolescents. Twenty participants aged 13-19 years participated in a double-blind, randomized cross-over study consisting of two trials separated by 1-4 weeks. Participants consumed a volume-matched caffeinated energy shot (CAF, 5 mg/kg) or a decaffeinated energy shot (DECAF) followed by a 2 h oral glucose tolerance test. Blood samples were collected and area under the curve (AUC) calculated for glucose, insulin and gut and metabolic hormones. Consumption of CAF resulted in a 25% increase in glucose and a 26% increase in insulin area under the curve (AUC, p = 0.037; p < 0.0001) compared to DECAF. No impact on gut hormones was observed. To further characterize responses, individuals were classified as either slow or fast caffeine metabolizers based on an allele score. Glucose intolerance was greater in genetically fast vs. slow caffeine metabolizers and differences between groups were supported by distinct serum metabolomics separation. Consumption of caffeine-containing energy shots results in acute impaired glucoregulation in healthy adolescents as characterized by hyperinsulinemia following an oral glucose challenge.

Mesenchymal Stem Cells Shift Mitochondrial Dynamics and Enhance Oxidative Phosphorylation in Recipient Cells

Mesenchymal stem cells (MSCs) are the most commonly used cells in tissue engineering and regenerative medicine. MSCs can promote host tissue repair through several different mechanisms including donor cell engraftment, release of cell signaling factors, and the transfer of healthy organelles to the host. In the present study, we examine the specific impacts of MSCs on mitochondrial morphology and function in host tissues. Employing in vitro cell culture of inherited mitochondrial disease and an in vivo animal experimental model of low-grade inflammation (high fat feeding), we show human-derived MSCs to alter mitochondrial function. MSC co-culture with skin fibroblasts from mitochondrial disease patients rescued aberrant mitochondrial morphology from a fission state to a more fused appearance indicating an effect of MSC co-culture on host cell mitochondrial network formation. In vivo experiments confirmed mitochondrial abundance and mitochondrial oxygen consumption rates were elevated in host tissues following MSC treatment. Furthermore, microarray profiling identified 226 genes with differential expression in the liver of animals treated with MSC, with cellular signaling, and actin cytoskeleton regulation as key upregulated processes. Collectively, our data indicate that MSC therapy rescues impaired mitochondrial morphology, enhances host metabolic capacity, and induces widespread host gene shifting. These results highlight the potential of MSCs to modulate mitochondria in both inherited and pathological disease states.

nmrML: A Community Supported Open Data Standard for the Description, Storage, and Exchange of NMR Data

NMR is a widely used analytical technique with a growing number of repositories available. As a result, demands for a vendor-agnostic, open data format for long-term archiving of NMR data have emerged with the aim to ease and encourage sharing, comparison, and reuse of NMR data. Here we present nmrML, an open XML-based exchange and storage format for NMR spectral data. The nmrML format is intended to be fully compatible with existing NMR data for chemical, biochemical, and metabolomics experiments. nmrML can capture raw NMR data, spectral data acquisition parameters, and where available spectral metadata, such as chemical structures associated with spectral assignments. The nmrML format is compatible with pure-compound NMR data for reference spectral libraries as well as NMR data from complex biomixtures, i.e., metabolomics experiments. To facilitate format conversions, we provide nmrML converters for Bruker, JEOL and Agilent/Varian vendor formats. In addition, easy-to-use Web-based spectral viewing, processing, and spectral assignment tools that read and write nmrML have been developed. Software libraries and Web services for data validation are available for tool developers and end-users. The nmrML format has already been adopted for capturing and disseminating NMR data for small molecules by several open source data processing tools and metabolomics reference spectral libraries, e.g., serving as storage format for the MetaboLights data repository. The nmrML open access data standard has been endorsed by the Metabolomics Standards Initiative (MSI), and we here encourage user participation and feedback to increase usability and make it a successful standard.

Metabolite Measurement: Pitfalls to Avoid and Practices to Follow

Metabolites are the small biological molecules involved in energy conversion and biosynthesis. Studying metabolism is inherently challenging due to metabolites' reactivity, structural diversity, and broad concentration range. Herein, we review the common pitfalls encountered in metabolomics and provide concrete guidelines for obtaining accurate metabolite measurements, focusing on water-soluble primary metabolites. We show how seemingly straightforward sample preparation methods can introduce systematic errors (e.g., owing to interconversion among metabolites) and how proper selection of quenching solvent (e.g., acidic acetonitrile:methanol:water) can mitigate such problems. We discuss the specific strengths, pitfalls, and best practices for each common analytical platform: liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), and enzyme assays. Together this information provides a pragmatic knowledge base for carrying out biologically informative metabolite measurements.

Understanding Plant Nitrogen Metabolism through Metabolomics and Computational Approaches

A comprehensive understanding of plant metabolism could provide a direct mechanism for improving nitrogen use efficiency (NUE) in crops. One of the major barriers to achieving this outcome is our poor understanding of the complex metabolic networks, physiological factors, and signaling mechanisms that affect NUE in agricultural settings. However, an exciting collection of computational and experimental approaches has begun to elucidate whole-plant nitrogen usage and provides an avenue for connecting nitrogen-related phenotypes to genes. Herein, we describe how metabolomics, computational models of metabolism, and flux balance analysis have been harnessed to advance our understanding of plant nitrogen metabolism. We introduce a model describing the complex flow of nitrogen through crops in a real-world agricultural setting and describe how experimental metabolomics data, such as isotope labeling rates and analyses of nutrient uptake, can be used to refine these models. In summary, the metabolomics/computational approach offers an exciting mechanism for understanding NUE that may ultimately lead to more effective crop management and engineered plants with higher yields.

Metabolomics and Type 2 Diabetes: Translating Basic Research into Clinical Application

Type 2 diabetes (T2D) and its comorbidities have reached epidemic proportions, with more than half a billion cases expected by 2030. Metabolomics is a fairly new approach for studying metabolic changes connected to disease development and progression and for finding predictive biomarkers to enable early interventions, which are most effective against T2D and its comorbidities. In metabolomics, the abundance of a comprehensive set of small biomolecules (metabolites) is measured, thus giving insight into disease-related metabolic alterations. This review shall give an overview of basic metabolomics methods and will highlight current metabolomics research successes in the prediction and diagnosis of T2D. We summarized key metabolites changing in response to T2D. Despite large variations in predictive biomarkers, many studies have replicated elevated plasma levels of branched-chain amino acids and their derivatives, aromatic amino acids and α-hydroxybutyrate ahead of T2D manifestation. In contrast, glycine levels and lysophosphatidylcholine C18:2 are depressed in both predictive studies and with overt disease. The use of metabolomics for predicting T2D comorbidities is gaining momentum, as are our approaches for translating basic metabolomics research into clinical applications. As a result, metabolomics has the potential to enable informed decision-making in the realm of personalized medicine.

The ACTN3 R577X Polymorphism Is Associated with Cardiometabolic Fitness in Healthy Young Adults

Homozygosity for a premature stop codon (X) in the ACTN3 “sprinter” gene is common in humans despite the fact that it reduces muscle size, strength and power. Because of the close relationship between skeletal muscle function and cardiometabolic health we examined the influence of ACTN3 R577X polymorphism over cardiovascular and metabolic characteristics of young adults (n = 98 males, n = 102 females; 23 ± 4.2 years) from our Assessing Inherent Markers for Metabolic syndrome in the Young (AIMMY) study. Both males and females with the RR vs XX genotype achieved higher mean VO₂ peak scores (47.8 ± 1.5 vs 43.2 ±1.8 ml/O₂/min, p = 0.002) and exhibited higher resting systolic (115 ± 2 vs 105 ± mmHg, p = 0.027) and diastolic (69 ± 3 vs 59 ± 3 mmHg, p = 0.005) blood pressure suggesting a role for ACTN3 in the maintenance of vascular tone. We subsequently identified the expression of alpha-actinin 3 protein in pulmonary artery smooth muscle, which may explain the genotype-specific differences in cardiovascular adaptation to acute exercise. In addition, we utilized targeted serum metabolomics to distinguish between RR and XX genotypes, suggesting an additional role for the ACTN3 R577X polymorphism in human metabolism. Taken together, these results identify significant cardiometabolic effects associated with possessing one or more functional copies of the ACTN3 gene.

Polymorphisms within the APOBR gene are highly associated with milk levels of prognostic ketosis biomarkers in dairy cows

Essentially all high-yielding dairy cows experience a negative energy balance during early lactation leading to increased lipomobilization, which is a normal physiological response. However, a severe energy deficit may lead to high levels of ketone bodies and, subsequently, to subclinical or clinical ketosis. It has previously been reported that the ratio of glycerophosphocholine to phosphocholine in milk is a prognostic biomarker for the risk of ketosis in dairy cattle. It was hypothesized that this ratio reflects the ability to break down blood phosphatidylcholine as a fatty acid resource. In the current study, 248 animals from a previous study were genotyped with Illumina BovineSNP50 BeadChip, and genome-wide association studies were carried out for the milk levels of phosphocholine, glycerophosphocholine, and the ratio of both metabolites. It was demonstrated that the latter two traits are heritable with h2 = 0.43 and h2 = 0.34, respectively. A major quantitative trait locus was identified on cattle chromosome 25. The APOBR gene, coding for the apolipoprotein B receptor, is located within this region and was analyzed as a candidate gene. The analysis revealed highly significant associations of polymorphisms within the gene with glycerophosphocholine as well as the metabolite ratio. These findings support the hypothesis that differences in the ability to take up blood phosphatidylcholine from low-density lipoproteins play an important role in early lactation metabolic stability of dairy cows and indicate APOBR to contain a causative variant.

Short communication: Use of genomic and metabolic information as well as milk performance records for prediction of subclinical ketosis risk via artificial neural networks

Subclinical ketosis is one of the most prevalent metabolic disorders in high-producing dairy cows during early lactation. This renders its early detection and prevention important for both economical and animal-welfare reasons. Construction of reliable predictive models is challenging, because traits like ketosis are commonly affected by multiple factors. In this context, machine learning methods offer great advantages because of their universal learning ability and flexibility in integrating various sorts of data. Here, an artificial-neural-network approach was applied to investigate the utility of metabolic, genetic, and milk performance data for the prediction of milk levels of β-hydroxybutyrate within and across consecutive weeks postpartum. Data were collected from 218 dairy cows during their first 5wk in milk. All animals were genotyped with a 50,000 SNP panel, and weekly information on the concentrations of the milk metabolites glycerophosphocholine and phosphocholine as well as milk composition data (milk yield, fat and protein percentage) was available. The concentration of β-hydroxybutyric acid in milk was used as target variable in all prediction models. Average correlations between observed and predicted target values up to 0.643 could be obtained, if milk metabolite and routine milk recording data were combined for prediction at the same day within weeks. Predictive performance of metabolic as well as milk performance-based models was higher than that of models based on genetic information.

Metabolomics reveals the sex-specific effects of the SORT1 low-density lipoprotein cholesterol locus in healthy young adults

Metabolite profiles of individuals possessing either the cardiovascular risk or protective variants of the low-density lipoprotein cholesterol (LDL-C) associated 1p13.3 locus of the SORT1 gene (rs646776) were analyzed. Serum metabolites and lipids were assessed using LC-MS-based metabolomics in a healthy young population (n = 138: 95 males, 43 females). Although no significant differences were observed in the combined cohort, divergent sex effects were identified. Females carrying the protective allele showed increased phosphatidylcholines, very long chain fatty acids (>C20), and unsaturated fatty acids. Unsaturated fatty acids are considered to be protective against cardiovascular disease. In contrast, males carrying the protective allele exhibited decreased long-chain fatty acids (≤C20) and sphingomyelins, which is similarly considered to decrease cardiovascular disease risk. No significant changes in clinically assessed lipids such as LDL-C, high-density lipoprotein (HDL-C), total cholesterol, or triglycerides were observed in females, whereas only LDL-C was significantly changed in males. This indicates that, apart from reducing LDL-C, other mechanisms may contribute to the protective effect of the SORT1 locus. Thus, the analysis of metabolic biomarkers might reveal early disease development that may be overlooked by relying on standard clinical parameters.

Correlations between milk and plasma levels of amino and carboxylic acids in dairy cows

The objective of this study was to investigate the relationship between the concentrations of 19 amino acids, glucose, and seven carboxylic acids in the blood and milk of dairy cows and their correlations with established markers of ketosis. To that end, blood plasma and milk specimens were collected throughout lactation in two breeds of dairy cows of different milk yield. Plasma concentrations of glucose, pyruvate, lactate, α-aminobutyrate, β-hydroxybutyrate (BHBA), and most amino acids, except for glutamate and aspartate, were on average 9.9-fold higher than their respective milk levels. In contrast, glutamate, aspartate, and the Krebs cycle intermediates succinate, fumarate, malate, and citrate were on average 9.1-fold higher in milk than in plasma. For most metabolites, with the exception of BHBA and threonine, no significant correlations were observed between their levels in plasma and milk. Additionally, milk levels of acetone showed significant direct relationships with the glycine-to-alanine ratio and the BHBA concentration in plasma. The marked decline in plasma concentrations of glucose, pyruvate, lactate, and alanine in cows with plasma BHBA levels above the diagnostic cutoff point for subclinical ketosis suggests that these animals fail to meet their glucose demand and, as a consequence, rely increasingly on ketone bodies as a source of energy. The concomitant increase in plasma glycine may reflect not only the excessive depletion of protein reserves but also a potential deficiency of vitamin B6.

Early changes in the liver-soluble proteome from mice fed a nonalcoholic steatohepatitis inducing diet

Despite the increasing incidence of nonalcoholic steatohepatitis (NASH) with the rise in lifestyle-related diseases such as the metabolic syndrome, little is known about the changes in the liver proteome that precede the onset of inflammation and fibrosis. Here, we investigated early changes in the liver-soluble proteome of female C57BL/6N mice fed an NASH-inducing diet by 2D-DIGE and nano-HPLC-MS/MS. In parallel, histology and measurements of hepatic content of triglycerides, cholesterol and intermediates of the methionine cycle were performed. Hepatic steatosis manifested itself after 2 days of feeding, albeit significant changes in the liver-soluble proteome were not evident before day 10 in the absence of inflammatory or fibrotic signs. Proteomic alterations affected mainly energy and amino acid metabolism, detoxification processes, urea cycle, and the one-carbon/S-adenosylmethionine pathways. Additionally, intermediates of relevant affected pathways were quantified from liver tissue, confirming the findings from the proteomic analysis.

State-of-the art data normalization methods improve NMR-based metabolomic analysis

Extracting biomedical information from large metabolomic datasets by multivariate data analysis is of considerable complexity. Common challenges include among others screening for differentially produced metabolites, estimation of fold changes, and sample classification. Prior to these analysis steps, it is important to minimize contributions from unwanted biases and experimental variance. This is the goal of data preprocessing. In this work, different data normalization methods were compared systematically employing two different datasets generated by means of nuclear magnetic resonance (NMR) spectroscopy. To this end, two different types of normalization methods were used, one aiming to remove unwanted sample-to-sample variation while the other adjusts the variance of the different metabolites by variable scaling and variance stabilization methods. The impact of all methods tested on sample classification was evaluated on urinary NMR fingerprints obtained from healthy volunteers and patients suffering from autosomal polycystic kidney disease (ADPKD). Performance in terms of screening for differentially produced metabolites was investigated on a dataset following a Latin-square design, where varied amounts of 8 different metabolites were spiked into a human urine matrix while keeping the total spike-in amount constant. In addition, specific tests were conducted to systematically investigate the influence of the different preprocessing methods on the structure of the analyzed data. In conclusion, preprocessing methods originally developed for DNA microarray analysis, in particular, Quantile and Cubic-Spline Normalization, performed best in reducing bias, accurately detecting fold changes, and classifying samples. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0350-z) contains supplementary material, which is available to authorized users.

NMR metabolomic analysis of dairy cows reveals milk glycerophosphocholine to phosphocholine ratio as prognostic biomarker for risk of ketosis

Ketosis is a common metabolic disease in dairy cows. Diagnostic markers for ketosis such as acetone and beta-hydroxybutyric acid (BHBA) are known, but disease prediction remains an unsolved challenge. Milk is a steadily available biofluid and routinely collected on a daily basis. This high availability makes milk superior to blood or urine samples for diagnostic purposes. In this contribution, we show that high milk glycerophosphocholine (GPC) levels and high ratios of GPC to phosphocholine (PC) allow for the reliable selection of healthy and metabolically stable cows for breeding purposes. Throughout lactation, high GPC values are connected with a low ketosis incidence. During the first month of lactation, molar GPC/PC ratios equal or greater than 2.5 indicate a very low risk for developing ketosis. This threshold was validated for different breeds (Holstein-Friesian, Brown Swiss, and Simmental Fleckvieh) and for animals in different lactations, with observed odds ratios between 1.5 and 2.38. In contrast to acetone and BHBA, these measures are independent of the acute disease status. A possible explanation for the predictive effect is that GPC and PC are measures for the ability to break down phospholipids as a fatty acid source to meet the enhanced energy requirements of early lactation.

Detection of autosomal dominant polycystic kidney disease by NMR spectroscopic fingerprinting of urine

Autosomal dominant polycystic kidney disease (ADPKD) is a frequent cause of kidney failure; however, urinary biomarkers for the disease are lacking. In a step towards identifying such markers, we used multidimensional-multinuclear nuclear magnetic resonance (NMR) spectroscopy with support vector machine-based classification and analyzed urine specimens of 54 patients with ADPKD and slightly reduced estimated glomerular filtration rates. Within this cohort, 35 received medication for arterial hypertension and 19 did not. The results were compared with NMR profiles of 46 healthy volunteers, 10 ADPKD patients on hemodialysis with residual renal function, 16 kidney transplant patients, and 52 type 2 diabetic patients with chronic kidney disease. Based on the average of 51 out of 701 NMR features, we could reliably discriminate ADPKD patients with moderately advanced disease from ADPKD patients with end-stage renal disease, patients with chronic kidney disease of other etiologies, and healthy probands with an accuracy of >80%. Of the 35 patients with ADPKD receiving medication for hypertension, most showed increased excretion of proteins and also methanol. In contrast, elevated urinary methanol was not found in any of the control and other patient groups. Thus, we found that NMR fingerprinting of urine differentiates ADPKD from several other kidney diseases and individuals with normal kidney function. The diagnostic and prognostic potential of these profiles requires further evaluation.

Nuclear magnetic resonance and mass spectrometry-based milk metabolomics in dairy cows during early and late lactation

Milk production in dairy cows has dramatically increased over the past few decades. The selection for higher milk yield affects the partitioning of available nutrients, with more energy being allocated to milk synthesis and less to physiological processes essential to fertility and fitness. In this study, the abundance of numerous milk metabolites in early and late lactation was systematically investigated, with an emphasis on metabolites related to energy metabolism. The aim of the study was the identification and correlation of milk constituents to the metabolic status of the cows. To investigate the influence of lactation stage on physiological and metabolic variables, 2 breeds of different productivity were selected for investigation by high-resolution nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. We could reliably quantify 44 different milk metabolites. The results show that biomarkers such as acetone and beta-hydroxybutyrate are clearly correlated to the metabolic status of the individual cows during early lactation. Based on these data, the selection of cows that cope well with the metabolic stress of early lactation should become an option.

End-user searching: impetus for an expanding information management and technology role for the hospital librarian

Using the results of the 1993 Medical Library Association (MLA) Hospital Libraries Section survey of hospital-based end-user search services, this article describes how end-user search services can become an impetus for an expanded information management and technology role for the hospital librarian. An end-user services implementation plan is presented that focuses on software, hardware, finances, policies, staff allocations and responsibilities, educational program design, and program evaluation. Possibilities for extending end-user search services into information technology and informatics, specialized end-user search systems, and Internet access are described. Future opportunities are identified for expanding the hospital librarian's role in the face of changing health care management, advances in information technology, and increasing end-user expectations.

Effect of online literature searching on length of stay and patient care costs

PURPOSE

To examine the associations between (1) the economic indicators of hospital costs, charges, and length of stay (LOS) for inpatient cases and (2) the use of MEDLINE searches for such cases.

METHOD

An outcome-based, objective, prospective study with an economic evaluation was conducted from September 1989 to September 1990 at three metropolitan Detroit teaching hospitals representing both allopathic and osteopathic care. The study consisted of (1) 192 test cases, derived from a consecutive sample of inpatients of all ages for whom MEDLINE searches were requested at the participating medical libraries, and (2) 10,409 control cases, which were of the same diagnosis-related groups (DRGs) as the test cases but did not involve identified MEDLINE searches. Statistical analysis included the use of multivariate analyses of variance and correlation coefficients. Comparisons of cases were made on case-by-case and DRG bases regarding total patient costs, charges, and lengths of stay for cases with or without MEDLINE searches.

RESULTS

The test cases were found to have a higher severity of illness. Among test cases, statistically significant relationships existed between (1) hospital expenses and LOS and (2) hospital expenses and the timing of the search during hospitalization when controlling for LOS. When cases were matched for DRG and LOS, the cases with early searches (i.e., conducted during the first half of hospitalization) had significantly lower expenses.

CONCLUSION

Of the test-case patients (for whom MEDLINE searches were conducted during hospitalization), those whose searches were conducted earlier had statistically significantly lower costs, charges, and lengths of stay than those whose searches were conducted later.

Increasing access to clinical information on hospital wards

Medical library information resources can make a positive contribution to the clinical information needs of health care professionals. To increase availability of knowledge-based information and transfer information to its point of use, a CD-ROM resource library was networked and interfaced with the existing hospital information system at Children's Hospital of Michigan in Detroit, Michigan. Clinicians in 21 patient care areas now have access to the patient record, full-text pediatric journal information and the Micromedex CCIS database at one location.

Left ventricular pseudoaneurysm complicating mitral valve replacement: transesophageal echocardiographic diagnosis and impact on management

Left ventricular pseudoaneurysm formation after mitral valve replacement, although infrequent, is a serious complication with potential catastrophic results. We describe a case of an anterobasal pseudoaneurysm compressing all branches of the left coronary artery, which was missed by initial transthoracic echocardiography and was well characterized with the transesophageal approach. Although the pseudoaneurysm was detected at contrast ventriculography, the transesophageal study provided new specific details regarding the exact site of origin of the pseudoaneurysm and its relationship to the coronary arteries that significantly influenced planning the surgical procedure and patient management.

Behavioral thermoregulation in mice inoculated with influenza virus

Mice housed at 30 degrees C and inoculated with a mouse-adapted influenza virus show a fall in body temperature (Tb) and a decrease in food intake to almost 0 grams per day. This study tested whether the fall in Tb could be accounted for by the decreased food intake and whether the fall in Tb was due to a decrease of thermoregulatory set point or to an inability to maintain Tb at set point level. The fall in Tb of influenza-infected mice was greater than that of food-deprived mice. When food deprived, mice given access to a thermal gradient increased their preference for warmer areas in the gradient and, as a result, Tb did not fall as much as Tb of starved mice not given access to a thermal gradient. When infected with influenza virus, mice given a thermal gradient decreased Tb less and at a slower rate than mice not given a gradient. However, this fall in Tb of influenza-infected mice was greater than that of food-deprived mice given a thermal gradient. Mice given a thermal gradient increased their preference for the warmer temperatures after inoculation; this returned to preinoculation preference for cooler temperatures during the later days of infection despite a continuous fall in Tb. Influenza-infected mice given a thermal gradient survived significantly fewer days than infected mice not given a thermal gradient. We conclude that the influenza-induced fall of Tb in mice cannot be explained solely by the decrease in food intake, and is partially due to a decrease in thermoregulatory set point.

Self-tapping screw fixation of the Austin osteotomy

The authors present an alternative method of fixation for the Austin bunionectomy using the Richards self-tapping screw. A description of the screw and method of application is included. In more than 250 osteotomies fixated by this technique, no complications inherent to the self-tapping screw have been encountered.

Adapting IAIMS to a hospital library level

The Children's Hospital of Michigan Medical Library has adapted several of the Integrated Academic Information Management Systems (IAIMS) concepts and implemented them at a hospital library level. These have included features of network development, electronic interfacing and interlinking, and implementing an integrated information system in the library. The library has incorporated several information systems into library operations, including a variety of in-house, local, and national automated systems and telecommunication networks. Hospital libraries can incorporate IAIMS features and promote an institutional framework of interconnecting communication systems and electronic linkages.

Assessment of myocardial perfusion in humans by contrast echocardiography. I. Evaluation of regional coronary reserve by peak contrast intensity

Myocardial contrast echocardiography was performed during coronary angiography with 2 ml of sonicated meglumine diatrizoate sodium 76% (meglumine) in 40 patients (ranging in age from 25 to 79 years) before and 10 to 15 s after intracoronary injection of papaverine, 8 mg into the right coronary artery (n = 43) and 10 mg into the left (n = 46). The same protocol was repeated in 17 patients 5 to 10 min after completion of coronary angioplasty. In 13 patients with normal coronary angiograms, peak contrast intensity corrected for background myocardial intensity was measured in 36 regions and was found to increase after papaverine from 36 +/- 16 to 55 +/- 22 U (p less than 0.001). In contrast, in the 27 patients with angiographic evidence of coronary artery disease, peak intensity in 64 regions remained unchanged after papaverine (35 +/- 22 versus 36 +/- 23 U). An increase in peak intensity greater than or equal to 10 U was 80% sensitive and 92% specific for coronary artery disease. After successful coronary angioplasty, peak intensity in the involved regions improved significantly (p less than 0.001) during baseline contrast injections (from 32 +/- 16 to 50 +/- 25 U) as well as in the postpapaverine contrast injections (from 30 +/- 12 to 60 +/- 26 U). In conclusion, measurement of peak contrast intensity after intracoronary injections of sonicated meglumine provides a relative index of myocardial perfusion that allows assessment of regional coronary reserve in patients with coronary artery disease. This may be of particular value in evaluating the immediate effects of coronary angioplasty on myocardial perfusion.

Detection of myocardial ischemia before infarction, based on accumulation of labeled pyruvate

To determine whether ischemic, but not irreversibly injured myocardium, can be differentiated from normal tissue based on accumulation of labeled pyruvate, isolated hearts were perfused with buffer containing [14C]pyruvate under conditions of normal or low flow. Fifteen minutes after the hearts were exposed to labeled material, myocardial radioactivity was fourfold greater in ischemic compared to control hearts, due to accumulation of label in sequestered lactate produced from the pyruvate. Open-chest rabbits subjected to coronary occlusion exhibited a 1.73:1 ratio of radioactivity in ischemic compared with normal myocardium 15 min after systemic injection of [14C]pyruvate. The results obtained suggest that zones of myocardial ischemia should be detectable in vivo by positron tomography after systemic administration of [11C]pyruvate as well.

External assessment of myocardial metabolism with C-11 palmitate in vivo

The externally detected rate of clearance of C-11 palmitate ([11C]palmitic acid) from isolated hearts varies directly with CO2 production from neutral lipids and with physiological indexes of myocardial oxygen consumption. The present study was performed to determine whether myocardial metabolism could be quantified noninvasively in vivo in a fashion analogous to that in the isolated heart. Opened chest, male rabbits were injected with C-11 palmitate (100-200 muCi) and coincidence counts were detected externally with two NaI(TI) crystals so placed that their colinear field of view encompassed the heart. The monoexponential rate of clearance of tracer--obtained from the portion of the residue-detection curve reflecting metabolism of fatty acid incorporated into neutral lipids--correlated directly with induced changes in tension-time index after injections into the left atrium (r = 0.96, n = 12), right atrium (r = 0.86, n = 14), and ear vein (r = 0.93, n = 14). Clearance of labeled palmitate from the vascular pool within the field of detection (determined with both C-14 palmitate and red blood cells labeled with C15O-hemoglobin) was rapid and did not significantly affect measurements of palmitate clearance from the heart itself.

Abnormal technetium-99m pyrophosphate images in unstable angina: ischemia versus infarction?

There is controversy concerning the specificity of myocardial infarct imaging with technetium-99m pyrophosphate due to the high frequency of false positive images, especially in patients with unstable angina. In this study technetium-99m pyrophosphate images were compared with frequent determinations of plasma creatine kinase, MB isoenzyme (MB CK) activity in 116 patients admitted with the diagnosis of unstable angina. It was hypothesized that frequent measurement of MB CK activity, a sensitive and specific marker for myocardial necrosis, using sensitive assay techniques would detect small amounts of myocardial necrosis which might have been unrecognized by conventional clinical methods. The scintigraphic results and isoenzyme determinations agreed in 88 percent of patients; both tests were normal in 69 percent and both were abnormal, indicating acute myocardial infarcation, in 19 percent of patients. In the remaining 14 patients (12 percent), the scans were abnormal, but MB CK activity was normal. In five of these patients (4 percent), abnormal scintigrams presumably reflected persistent scan positivity after previous myocardial infarction. Only the remaining nine patients (8 percent) could be classified as having unexplained false positive scans, a frequency substantially less than that reported by other investigators who based the diagnosis of myocardial infarction on conventional clinical criteria. These results suggest that abnormal technetium-99m pyrophosphate images in patients with unstable angina generally indicate myocardial necrosis.

External assessment of myocardial metabolism with [11C]palmitate in rabbit hearts

To determine whether the rate of fatty acid utilization, reflecting myocardial oxygen consumption under steady-state conditions, can be assessed noninvasively, we assayed positron emission from [11C]palmitate (100 muCi) in isolated rabbit hearts and after intra-atrial injection in vivo. In 11 isolated hearts, clearance of 11C-radioactivity during a monoexponential portion of residue detection curves correlated with tension-time index (TTI)(r = 0.86) and peak dP/dt (r = 0.89). Among 9 hearts prelabeled with [14C]palmitate, 14CO2 production from neutral lipid stores correlated with TTI (r = 0.83). In vivo the decline of 11C-radioactivity was 1st order and constant when physiological conditions were maintained constant (slope of the semilog plot = 0.099 +/- 0.002 (SE) in counts/min) (n = 2 animals, 7 injections). Decline of activity changed predictably when oxygen requirements were increased by administration of methoxamine. Thus, residue detection of [11C]palmitate 1) permits external assessment of global myocardial metabolism in vitro, and 2) reflects effects of interventions that alter the rate of substrate utilization in vivo, and should, therefore, permit comparison of rates of regional myocardial metabolism in patients with detection of radioactivity by positron-emission transaxial tomography.

Traumatic epidural hematoma in shunt dependent patients: a report of two cases

Two patients are reported with congenital aqueductal stenosis and hydrocephalus, with functioning ventriculoperitoneal shunts, who developed posttraumatic epidural hematomas. Relative paucity of neurological signs in spite of large size of hematomas is discussed.