Inter operator variability of machine learning researchers predicting all-cause mortality in patients admitted to intensive care unit

Background

The number of publications using machine learning (ML) to predict cardiovascular outcomes and identify clusters of patients at greater risk has risen dramatically in recent years. However, research papers which use ML often fail to provide sufficient information about their algorithms to enable results to be replicated by others in the same or different datasets.

Aim

To test the reproducibility of results from ML algorithms given three different levels of information commonly found in publications: model type alone, a description of the model, and complete algorithm.

Methods

MIMIC-III is a healthcare dataset comprising detailed information from over 60,000 intensive care unit (ICU) admissions from the Beth Israel Deaconess Medical Centre between 2001 and 2012. Access is available to everyone pending approval and completion of a short training course.

Using this dataset, three models for predicting all-cause in-hospital mortality were created, two from a PhD student working in ML, and one from an existing research paper which used the same dataset and provided complete model information. A second researcher (a PhD student in ML and cardiology) was given the same dataset and was tasked with reproducing their results. Initially, this second researcher was told what type of model was created in each case, followed by a brief description of the algorithms. Finally, the complete algorithms from each participant were provided. In all three scenarios, recreated models were compared to original models using Area Under the Receiver Operating Characteristic Curve (AUC).

Results

After excluding those younger than 18 years and events with missing or invalid entries, 21,139 ICU admissions remained from 18,094 patients between 2001 and 2012, including 2,797 in-hospital deaths. Three models were produced: two Recurrent Neural Networks (RNNs) which differed significantly in internal weights and variables, and a Boosted Tree Classifier (BTC). The AUC of the first reproduced RNN matched that of the original RNN (Figure 1), however the second RNN and the BTC could not be reproduced given model type alone. As more information was provided about these algorithms, the results from the reproduced models matched the original results more closely.

Conclusions

In order to create clinically useful ML tools with results that are reproducible and consistent, it is vital that researchers share enough detail about their models. Model type alone is not enough to guarantee reproducibility. Although some models can be recreated with limited information, this is not always the case, and the best results are found when the complete algorithm is shared. These findings have huge relevance when trying to apply ML in clinical practice.

Funding Acknowledgement

Type of funding sources: None.

A comparison of machine learning models for predicting rehospitalisation and death after a first hospitalisation with heart failure

Background

Many machine learning models exist, including Multilayer Perceptron (MLP), Random Forest algorithm (RF), Support Vector Machine (SVM), and Gradient Boosted Machine (GBM), but their value for predicting outcome in patients with heart failure has not been compared.

Aim

To predict rehospitalisation (all-cause) and death (all-cause) at 1-, 3- and 12 months after discharge from a first hospitalisation for heart failure using four machine learning models.

Methods

The National Health Service Greater Glasgow and Clyde Health Board serves a population of ∼1.1 million. We obtained de-identified administrative data, including investigations, diagnosis and prescriptions, linked to hospital admissions and deaths for anyone with a diagnosis of vascular disease or heart failure or prescribed loop diuretics, statins or neuro-endocrine antagonists at any time between 1st January 2010 and 1st June 2018. Patients who were under 18 or had no prior hospitalisation for heart failure were excluded. Four ML algorithms using 46 variables were applied.

Results

Of 360,000 people who met the above criteria between 2010–2018, 6,372 had a hospitalisation for heart failure prior to 1st January 2010 and 8,304 had a first hospitalisation for heart failure thereafter. Between 2010 and 2018 there were 3,086 re-hospitalisations over 24 hours and 3,706 patients died, with 5,070 patients experiencing the composite outcome.

GBM and RF consistently outperformed MLP and SVM when comparing AUC, sensitivity and specificity combined, with GBM performing best in all scenarios. Since GBM and RF are both tree-based models, and with SVM and MLP regularly reporting very poor sensitivity or specificity despite a similar AUC to the others, this suggests that SVM and MLP may be suffering from overfitting and might perform better in larger data-sets.

Both GBM and RF work by ordering variables, so the final model can be used to determine the most important prediction variables. Age, number of times a blood sample was taken out of hospital, length of stay, social deprivation index and haemoglobin concentration consistently ranked amongst the most important variables. Models predicted all 1-month events better than later events.

Conclusions

Some, but not all, ML models applied to this data-set predicted rehospitalisation and death with great accuracy for up to 3 months after a first hospitalisation for heart failure. The models identified several important prognostic variables that are currently seldom collected in clinical research registries but perhaps should be.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Medical Research Council

Leveraging the Outpatient Pharmacy to Reduce Medication Waste in Pediatric Asthma Hospitalizations

BACKGROUND AND OBJECTIVE

Previous local quality improvement focused on discharging patients with inhaled corticosteroids (ICS) "in-hand" decreased healthcare reutilization after hospitalization for an asthma exacerbation. However, as a result of these new processes, some patients admitted for an asthma exacerbation received more than one ICS inhaler during their admission, contributing to medication waste and potential patient confusion regarding their discharge medication regimen. We sought to decrease this waste.

METHODS

We conducted a quality improvement project to reduce the prescribing of multiple ICS inhalers to patients at a large academic children's hospital. Our primary outcome measure was the monthly percentage of patients admitted with an asthma exacerbation who were administered more than one ICS inhaler. A secondary outcome measure evaluated the reliability of the new process of using the hospital-based outpatient pharmacy to supply ICS "in-hand" and verify insurance coverage. After the process map review, we hypothesized a delay in the initial ICS treatment decision would allow for both a finalized discharge medication plan and a standardized process to verify outpatient insurance coverage.

RESULTS

The mean percentage of patients receiving more than one ICS inhaler decreased from our baseline of 7.4% to 0.7%. Verification of outpatient prescription insurance coverage via the outpatient pharmacy increased from 0.7% to 50%. The average inpatient cost (average wholesale price) for ICS decreased by 62% to $90.25.

CONCLUSIONS

Our process change to use the outpatient pharmacy to dispense and verify insurance coverage for ICS medication was associated with a reduction in medication waste during admission for an asthma exacerbation.

Teaching High-Value Care: Case Vignettes for Pediatric Practice

INTRODUCTION

As health care systems recognize the importance of high-value care (HVC), physicians must focus on individualized patient outcomes using economically responsible and evidence-based medicine. The best ways to teach medical trainees HVC principles that can result in meaningful practice and behavior changes are unknown.

METHODS

We designed a case-based curriculum mapping six common pediatric clinical scenarios to HVC principles. Each scenario included learning objectives, small-group activities, educational resources, a facilitator guide, and participant evaluations. After internal and external review, the scenarios were piloted at four teaching institutions (Children's Hospital Los Angeles, Johns Hopkins All Children's Hospital, Seattle Children's Hospital, and Texas Children's Hospital). Facilitators were encouraged to adapt each vignette to learner needs and site-specific conference characteristics. All participants were asked to complete anonymous case-specific evaluations at the end of each session.

RESULTS

Approximately 331 individuals (students, residents, attendings) participated, with an evaluation response rate of 76% (n = 253). Participants across all sites acknowledged the sessions as a valuable use of time (range: 4.2-4.6 on a 5-point Likert scale) and identified HVC principles that could be applied daily in clinical practice (range: 4.4-4.6).

DISCUSSION

Implementation of six case-based HVC vignettes at four pilot institutions was both feasible and well received by a diverse group of learners. The curriculum was perceived as valuable and applicable to learners' clinical practice. Next steps include longitudinal assessments of learners and the development of tools measuring HVC-related behaviors to understand better the impact of the curriculum on clinical practice.

Gender and Feedback in Medical Education

This article was migrated. The article was not marked as recommended. Background: More women are entering medical school and faculty positions, creating increased opportunities for interactions across gender during medical education. Little is known about how gender affects attitudes towards and preferences around feedback. Objective: To explore differences in giving and receiving feedback between men and women in clinical education. Methods: An anonymous survey was distributed to 3rd and 4th year medical students, residents, and clinical faculty at West Virginia University School of Medicine at the start of the 2014-2015 academic year. Participants were surveyed about their attitudes, expectations, and knowledge about feedback in the clinical educational setting. Responses were mostly on a 5-point Likert scale. The authors used Fisher's exact test (FET) and binary logistic regression to identify differences in responses by gender. Results: Of 762 potential respondents, 155 (20%) completed the survey. More women preferred to receive constructive feedback in written form (FET p = .05, OR = 4.18, p = .009). They also preferred to give feedback in written form (FET p = .04, OR 4.98, p = 0.003). However, a greater proportion of men preferred to give constructive feedback face-to-face (FET p = 0.003, OR NS), reported liking to give constructive feedback (OR = 4.40, p = 0.04), and felt comfortable giving constructive feedback (FET p = .03, OR = 10.21, p = 0.003). Conclusions: These findings suggest there are differences in the preferences and comfort men and women have for giving and receiving feedback. This has implications for approaches to clinical preceptor training around feedback.

Uveal Spindle Cell Tumor of Blue-Eyed Dogs: An Immunohistochemical Study

Immunohistochemical techniques were used to investigate the origin of a spindle cell tumor in the anterior uveal tract of dogs and the influence of ultraviolet radiation on the development of this tumor. Thirteen tumors were identified from the 4,007 canine ocular samples examined at the Comparative Ocular Pathology Laboratory of Wisconsin between 1978 and 2005. Siberian Husky and Siberian Husky mix dogs were overrepresented (10/13 dogs, overall median age 10 years). Light microscopic evaluation (all dogs) and electron microscopy (2 dogs) were performed. Immunohistochemical staining included alpha-smooth muscle actin (SMA), vimentin, S-100, desmin, glial fibrillary acidic protein (GFAP), Melan A, microphthalmic transcription factor (MITF-1), protein gene product 9.5 (PGP 9.5), laminin, gadd45, p53, proliferating cell nuclear antigen (PCNA), anti-UVssDNA (antibody for detection of (6–4)-dipyrimidine photoproducts), and telomerase reverse transcriptase (TERT). All tumors occurred in the iris with or without ciliary body involvement and were composed of spindle cells arranged in fascicles and whorls (variable Antoni A and B behavior). All tumors were positive when immunostained for vimentin and S-100. Nine of 13 tumors exhibited GFAP immunopositivity. All tumors were negative for SMA, desmin, Melan A, and MITF-1. Tumors were variably positive for PGP 9.5, laminin, gadd45, p53, PCNA, anti-UVssDNA, and TERT. Electron microscopy revealed intermittent basal laminae between cells. These tumors are morphologically and immunohistochemically most consistent with schwannoma. The relationship between spindle cell tumors of the anterior uvea of dogs, altered neural crest, blue iris color, and ultraviolet radiation has not yet been fully elucidated.

Mandibular incisal edge demineralization and caries associated with Twin Block appliance design

Demineralization and caries are well documented and unwanted complications of orthodontic therapy. These are most commonly reported in relation to fixed appliance therapy. Five cases are presented of patients undergoing Twin Block appliance therapy with the appliances incorporating lower labial segment capping, illustrating a pattern of demineralization and caries of the incisal tips of the mandibular labial segment, influenced by the incisal capping and the frequent intake of carbonated soft drinks.

[Factors related to suicide attempts in a Tunisian sample of patients with schizophrenia]

INTRODUCTION

The mortality rate in schizophrenia is 4.5 times higher than in the general population. Suicide is one of the main causes of premature death in this affection. Life time prevalence of this behavior ranges from 10 to 15%, which represents a risk 20 to 50 times higher than in the general population. In addition, 40 to 93% of patients who committed suicide had attempted suicide previously. Thus, assessment of correlated variables with suicide attempts is a fundamental issue for developing preventive and therapeutic strategies in suicidal behavior. To the best of our knowledge, no systematic study has yet investigated suicide attempts in an Arabic Muslim population with schizophrenia, although many authors have demonstrated cultural differences in socio-demographic and clinical variables related to suicide attempts within many geographic areas around the world.

OBJECTIVES

The objectives of this study were to assess the frequency and characteristics of lifetime suicide attempts in Tunisian schizophrenic outpatients and to determine the correlated socio-demographic, clinical and therapeutic variables.

METHODS

A total of 134 patients with a DSM-IV diagnosis of schizophrenia who attended the outpatient department of the university psychiatric hospital of Tunis were included. The main demographic and lifetime clinical variables considered were: gender, marital status, family history of psychiatric disorders and suicide attempts, age at time of recruitment, age at onset of illness, duration of untreated psychosis defined as the interval between the onset of the illness and the first antipsychotic treatment, the type and dose of current treatment, dose of antipsychotic drugs converted to chlorpromazine equivalents, extrapyramidal side effects assessed with the Simpson Angus rating scale, number of hospitalizations, comorbid substance abuse, cigarette smoking, severity of psychopathology measured with the Positive And Negative Syndrome Scale (PANSS), and history of at least one suicide attempt. A suicide attempt was defined as a self-destructive act carried out with at least some intent to end one's life. We also assessed the number, the used methods and the causes of suicide attempts. We subdivided the sample into two sub samples according to the presence or absence of suicidal attempts. We analyzed and compared the demographic, clinical and therapeutic variables.

RESULTS

Out of the 134 patients, 45 (32%) had attempted suicide at least once. Half of them (49%) had attempted suicide more than once. The number of suicide attempts varied from one to five with an average of 1.8. The most used methods were medication overdose (n=18, 23.4%), followed by organophosphate poisoning (n=11, 14.3%), defenestration (n=9, 11.7%) and hanging or using sharp objects (n=7, 9.1% for each of them). The main reported reasons of suicide attempts were depressive symptoms (n=46, 60%) including depressed mood and hopelessness, stressful life events (bereavement, divorce, separation) (n=35, 46%) and presence of delusions and/or auditory hallucinations (n=25, 32.5%). No differences were found between the two groups regarding the different socio-demographic variables. Significant differences were found with respect to a duration of untreated psychosis equal to or more than one year (P<0.001), smoking in men (P=0.03), positive symptoms score on the PANSS (P<0.001), scores of Simpson-Angus scale (P=0.029) and poor medication compliance (P=0.02).

CONCLUSION

Demographic variables as suggested by other studies are less valuable predictors of suicide attempts in patients with schizophrenia. Interventions for reducing such behavior should focus on clinical variables and integrate an early diagnosis of the disease, reduce positive psychotic symptoms and tobacco consumption, correct extrapyramidal signs and improve medication compliance.

Peliod hepatocellular carcinoma in a domesticated ferret (Mustela putorius furo)

Peliod hepatocellular carcinoma was diagnosed in a domesticated ferret (Mustela putorius furo). The diagnosis was made using immunohistochemical analysis, histologic examination, and the accepted classification schemes based on histomorphologic features. Bilateral, adrenocortical hyperplasia also was evident. Speculation about a possible association between the variant of hepatocellular neoplasia diagnosed in this animal and its adrenal pathologic changes was done.

Carriage of group B streptococcus in pregnant women from Oxford, UK

OBJECTIVE

To investigate asymptomatic vagino-rectal carriage of group B streptococcus (GBS) in pregnant women.

METHODS

Women in the final trimester of pregnancy were recruited. A single vagino-rectal swab was taken, with consent, for culture of GBS. Two microbiological methods for isolation of GBS from vagino-rectal swabs were compared. The distribution of capsular serotypes of the GBS identified was determined. Epidemiological data for a subset (n = 167) of the pregnant women participating were examined.

RESULTS

21.3% were colonised vagino-rectally with GBS. Risk factors for neonatal GBS disease (maternal fever, prolonged rupture of membranes, and preterm delivery) were present in 34 of 167 women (20.4%), and the presence of these factors correlated poorly with GBS carriage. Capsular serotypes III (26.4%), IA (25.8%), V (18.9%), and IB (15.7%) were prevalent in the GBS isolates. Selective broth culture of vagino-rectal swabs was superior to selective plate culture, but the combination of both methods was associated with increased detection of GBS (7.5%). An algorithm for the identification of GBS from vagino-rectal swabs was developed.

CONCLUSIONS

GBS carriage is prevalent in pregnant women in Oxfordshire, UK. The poor correlation between risk factors and GBS carriage requires further investigation in larger groups, given that the identification of these surrogate markers is recommended to guide administration of intrapartum antibiotic prophylaxis by the Royal College of Obstetricians of the UK. A selective broth culture detected more GBS carriers than a selective plate culture.

Epidemiology and characterization of animal Salmonella enterica subspecies Enterica serotype typhimurium DT104 in Hungary

Reports on the internationally emerging significance of multiresistant zoonotic Salmonella in animals and man prompted studies to estimate the significance of multiresistant Salmonella enterica subspecies enterica serotype Typhimurium (S. Typhimurium) phage type DT104 of animal origin in Hungary. A collection of 231 strains (primarily of goose, turkey, poultry and porcine origin from the years 1997-1998) was tested for resistance against 7 selected antibiotics (ampicillin, chloramphenicol, enrofloxacin, nalidixic acid, streptomycin, tetracycline and sulphamethoxazole). Strains with resistance against 3 or more were defined as multiresistant. All strains were phage typed using Felix-Callow's S. Typhimurium phage typing system, and 91 of them (suspect DT104) were also typed according to Anderson's definitive typing (DT) system. In this study, 14% of animal strains from 1997-1998 was classified as DT104, for which turkey, pig and duck seemed to be the main carriers, and the multiresistant non-DT104 strains represented a further 6% of this collection. The prevalence of DT104 was highest among strains of turkey origin (50%), followed by strains of pig (29%), chicken (25%), duck (19%), and goose (3%) origin. The other DT104 related phage types (DT12 and U302) were only detected in the case of 4 strains (2 of porcine, and one each of turkey and of goose origin). The DT104 corresponded to the Felix-Callow types 2/3 or 2c/3 in each case, except in the case of 3 turkey strains where they corresponded to type 35/3. Nalidixic acid resistance was detected in all multiresistant turkey strains and in some of other animal origin but none of these strains were resistant to enrofloxacin. A retrospective analysis (based on the above relationship) indicated that S. Typhimurium strains corresponding to DT104 could be present and increase in the Hungarian farm animal population from about 2% to 20% between 1985 and 1990, in a manner similar to the emergence of human DT104, as reported elsewhere (Pászti et al., 2000). The 91 suspect DT104 strains were also tested for plasmid profile and for spvC gene indicating the presence of the large serotype specific plasmid (Ssp). No characteristic plasmid profile could be attributed to S. Typhimurium DT104. The serovar-specific large plasmid was detected by PCR for spvC in 100% of DT104 strains and in 77% of the non-DT104 strains. The virulence of two DT104 strains was tested in orally infected day-old chicks and compared with virulence of 4 non-DT104 strains. Higher colonizing virulence of DT104 strains could be established as compared to the other strains.

Prehospital blood transfusion versus crystalloid alone in the air medical transport of trauma patients

INTRODUCTION

Differences in prehospital resuscitation measures and outcomes of trauma patients transported by two air medical programs were assessed comparing the prehospital administration of crystalloid only (Group A) with the administration of 2 liters of crystalloid followed by blood (Group B).

METHODS

A 1-year retrospective review of flight and hospital records of patients taken to Level I trauma centers by two separate air medical programs was completed. Physiologic variables, total fluids infused, and flight times were compared.

RESULTS

Thirty-one patients (Group A) received crystalloids in flight, and 17 patients received in-flight blood (Group B). No statistical differences were found between the two groups when comparing age, ISS, PS, RTS, GCS, survival, and total fluid volume. Group B had statistically greater mean flight times compared with Group A (P < .05). A difference was demonstrated between groups A and B in pH and HCO3 measurements (P < .05), with Group B presenting in a more acidotic state on admission to the hospital.

CONCLUSION

Patients with lengthy flight times, despite the administration of blood products, presented to the trauma center more acidotic than trauma patients receiving only crystalloid. The true impact of blood products on outcome could not be demonstrated because of statistical differences in flight times between the groups. A multicenter study matching flight times, head injury status, and flight type of assess benefit of prehospital utilization of blood products is warranted.

Subcellular localization and PKC-dependent regulation of the human lysophospholipase A/acyl-protein thioesterase in WISH cells

Lysophospholipases play essential roles in keeping their multi-functional substrates, the lysophospholipids, at safe levels. Recently, a 25 kDa human lysophospholipase A (hLysoPLA I) that is highly conserved among rat, mouse, human and rabbit has been cloned, expressed and characterized and appears to hydrolyze only lysophospholipids among the various lipid substrates. Interestingly, this enzyme also displays acyl-protein thioesterase activity towards a G protein alpha subunit. To target the subcellular location of this hLysoPLA I, we have carried out immunocytochemical studies and report here that hLysoPLA I appears to be associated with the endoplasmic reticulum (ER) and nuclear envelope in human amnionic WISH cells and not the plasma membrane. In addition, we found that the hLysoPLA I can be up-regulated by phorbol 12-myristate 13-acetate (PMA) stimulation, a process in which phospholipase A(2) is activated and lysophospholipids are generated in WISH cells. Furthermore, the PMA-induced hLysoPLA I expression can be blocked by the protein kinase C (PKC) inhibitor Gö6976. The regulated expression of the LysoPLA/acyl-protein thioesterase by PKC may have important implications for signal transduction processes.

Is electroconvulsive therapy unsuitable for children and adolescents?

Electroconvulsive therapy (ECT) as a treatment option for adults with affective disorders has a long history. ECT with children and adolescents, however, has not been widely used, and no empirical studies or controlled evaluations have been conducted. A review of the literature on ECT with minors reveals that it has an unknown mechanism of action, with a domain of applicability diminished yearly by legislation, litigation, and a wide range of intervention alternatives.

Specific interaction of HTLV tax protein and a human type IV neuronal intermediate filament protein

The human T-cell leukemia virus (HTLV) is associated with adult T cell leukemia and neurological disorders (TSP/HAM). The HTLV transcriptional transactivator, Tax, is known to exert its effect through protein-protein interaction with several transcription factors that activate genes in T cell proliferation. The pathogenic mechanism in the CNS is less defined. Using the yeast two-hybrid system, we have identified a specific Tax-binding protein as the neuronal specific intermediate filament protein, alpha-internexin. Tax binds to the domain corresponding to the rod region of alpha-internexin, which is essential for neurofilament assembly. The Tax domains involved in binding are separable from those involved in transactivation. TxBP-1/alpha-internexin and Tax are expressed in the cytoplasm and nucleus, respectively, when expressed alone, but in coexpressing cells, colocalization of both proteins was observed in a perinuclear, punctate distribution. This in vivo interaction also resulted in a dramatic reduction in Tax transactivation and the network formation by alpha-internexin. The specific interaction of Tax and a neuronal specific intermediate filament protein may provide a clue to the pathogenesis of TSP/HAM.

The structure of HIV-1 reverse transcriptase complexed with 9-chloro-TIBO: lessons for inhibitor design

BACKGROUND

HIV reverse transcriptase (RT) is a key target of anti-AIDS therapies. Structural studies of HIV-1 RT, unliganded and complexed with different non-nucleoside inhibitors (NNIs), have pointed to a common mode of binding and inactivation through distortion of the polymerase catalytic site by NNIs containing two hinged rings. The mode of binding of the TIBO family of inhibitors is of interest because these compounds do not fit the two-hinged-ring model.

RESULTS

The structure of HIV-1 RT complexed with 9-chloro-TIBO (R82913) has been determined at 2.6 A resolution. As reported for the lower resolution analysis of another TIBO compound, this inhibitor binds at the same site as other NNIs, but our higher resolution study reveals the Cl-TIBO is distorted from the conformation seen in crystals of the inhibitor alone. This allows Cl-TIBO to mimic the binding of NNIs containing two hinged rings. Inhibitor-protein interactions are again predominantly hydrophobic and the protein conformation corresponds to that seen in complexes with other tight-binding NNIs.

CONCLUSIONS

Although Cl-TIBO is chemically very different from other NNIs, it achieves remarkable spatial equivalence and shape complementarity with other NNIs on binding to RT. Comparison of the different RT-NNI complexes suggests modifications to the TIBO group of inhibitors which might enhance their binding and hence, potentially, their therapeutic efficacy.

High resolution structures of HIV-1 RT from four RT-inhibitor complexes

We have determined the structures of four complexes of HIV-1 reverse transcriptase with non-nucleoside inhibitors, three fully refined at high resolution. The highest resolution structure is of the RT-nevirapine complex which has an R-factor of 0.186 and a root-mean-square bond length deviation of 0.015 A for all data to 2.2 A. The structures reveal a common mode of binding for these chemically diverse compounds. The common features of binding are largely hydrophobic interactions and arise from induced shape complementarity achieved by conformational rearrangement of the enzyme and conformational/configurational rearrangement of the compounds.

Mechanism of inhibition of HIV-1 reverse transcriptase by non-nucleoside inhibitors

The structure of unliganded HIV-1 reverse transcriptase has been determined at 2.35 A resolution and refined to an R-factor of 0.219 (for all data) with good stereochemistry. The unliganded structure was produced by soaking out a weak binding non-nucleoside inhibitor, HEPT, from pregrown crystals. Comparison with the structures of four different RT and non-nucleoside inhibitor complexes reveals that only minor domain rearrangements occur, but there is a significant repositioning of a three-stranded beta-sheet in the p66 subunit (containing the catalytic aspartic acid residues 110, 185 and 186) with respect to the rest of the polymerase site. This suggests that NNIs inhibit RT by locking the polymerase active site in an inactive conformation, reminiscent of the conformation observed in the inactive p51 subunit.

Studies on plaque fluoride after use of F-containing dentifrices

Increased fluoride levels in plaque and saliva have been associated with improved protection against dental caries for dentifrices which contained sodium monofluorophosphate (Duckworth et al., 1992). The main aim of the present work was to test whether oral fluoride retention depended on F source after use of dentifrices containing either NaF or Na2FPO3. In study 1, plaque samples were collected from 474 subjects who had been using one of six test dentifrices for two years, and analyzed by F extraction with water. The dentifrices contained 1000 or 1500 micrograms F/g as either NaF or Na2FPO3. Significantly more fluoride was found in plaque from subjects who were using the NaF dentifrices than in plaque from subjects who were using Na2FPO3 dentifrices of the same F content. Subsets of plaque samples were large enough to divide into two parts for extraction by both acid and water. No significant difference was found between mean fluoride contents, indicating that the majority of fluoride retained in plaque from these conventional dentifrices appears to be relatively labile. The results of two small-scale human enamel studies showed that NaF dentifrices gave elevated F concentrations in plaque and saliva, respectively, compared with Na2FPO3 dentifrices of equivalent F content, consistent with the main plaque study 1. These findings demonstrate that oral F retention from dentifrices is dependent on the source of ionic fluoride and support the view that NaF dentifrices may be more clinically effective than dentifrices which contain the same amount of F as Na2FPO3.

Crystallization and X-ray diffraction study of recombinant platelet-derived endothelial cell growth factor

Crystals of recombinant platelet-derived endothelial cell growth factor (PD-ECGF) were obtained by the hanging drop vapour diffusion technique. The crystals belong to the space group P2(1)2(1)2(1) with unit cell dimensions a = 63.7 A, b = 70.4 A, c = 219.6, alpha = beta = gamma = 90 degrees, and probably contain a single dimer in the asymmetric unit. Diffraction to a minimum Bragg spacing of 3.5 A has been obtained using a synchrotron X-ray source.

A mask to modify inspired air temperature and humidity and its effect on exercise induced asthma

BACKGROUND

Heat and moisture loss from the respiratory tract during exercise are important triggers of exercise induced asthma.

METHODS

A new heat and moisture exchange mask has been developed which both recovers exhaled heat and water and has a sufficiently low resistance for use during exercise. The effect of the mask on inspired air temperature was studied in four normal subjects. Eight asthmatic subjects performed identical exercise protocols on three separate days, breathing room air through a conventional mouthpiece, a dummy mask, and the new heat and moisture exchange mask. Seven different asthmatic subjects exercised while breathing cold air at -13 degrees C through a dummy or active mask.

RESULTS

All subjects found the new mask comfortable to wear. The mean inspired temperature when the mask was used rose to 32.5 (1.4) degrees C when normal subjects breathed room air at 24 degrees C and to 19.1 (2.7) degrees C when they inhaled subfreezing air at -13 degrees C. The heat and moisture exchange mask significantly reduced the median fall in forced expiratory volume in one second (FEV1) after exercise to 13% (range 0-49%) when asthmatic subjects breathed room air compared with 33% (10-65%) with the dummy mask and 28% (21-70%) with the mouthpiece. The fall in FEV1 when the asthmatic subjects breathed cold air was 10% (0-26%) with the heat and moisture exchange mask compared with 22% (13-51%) with the dummy mask.

CONCLUSION

Use of a heat and moisture exchange mask can raise the inspired temperature and humidity and ameliorate the severity of exercise induced asthma. The mask may be of practical value in non-contact sport or for people working in subzero temperatures.

Hormones regulating lipid and carbohydrate metabolism in premenopausal women: modulation by dietary lipids

The effect of high- and low-fat diets with different levels of fatty acid unsaturation on plasma hormones involved in lipid metabolism was studied during different phases of the menstrual cycle in 31 premenopausal women. Subjects were divided into two groups and were fed controlled diets containing 39% fat with a ratio of polyunsaturated to saturated fatty acids (P:S) of either 0.3 or 1.0 for four menstrual cycles and then switched to a 19% fat diet with the same P:S for another four cycles. Blood samples were analyzed during both the follicular and luteal phases. A significant direct effect of level of dietary fat was observed on plasma cortisol and dehydroepiandrosterone-sulphate whereas an inverse relationship was seen for plasma insulin. Both plasma insulin and growth hormone levels were higher during the luteal compared with the follicular phase of the menstrual cycle. None of the hormones was affected by the level of unsaturation of dietary fats.