Cocaine Use Prediction With Tensor-Based Machine Learning on Multimodal MRI Connectome Data

This letter considers the use of machine learning algorithms for predicting cocaine use based on magnetic resonance imaging (MRI) connectomic data. The study used functional MRI (fMRI) and diffusion MRI (dMRI) data collected from 275 individuals, which was then parcellated into 246 regions of interest (ROIs) using the Brainnetome atlas. After data preprocessing, the data sets were transformed into tensor form. We developed a tensor-based unsupervised machine learning algorithm to reduce the size of the data tensor from 275 (individuals) × 2 (fMRI and dMRI) × 246 (ROIs) × 246 (ROIs) to 275 (individuals) × 2 (fMRI and dMRI) × 6 (clusters) × 6 (clusters). This was achieved by applying the high-order Lloyd algorithm to group the ROI data into six clusters. Features were extracted from the reduced tensor and combined with demographic features (age, gender, race, and HIV status). The resulting data set was used to train a Catboost model using subsampling and nested cross-validation techniques, which achieved a prediction accuracy of 0.857 for identifying cocaine users. The model was also compared with other models, and the feature importance of the model was presented. Overall, this study highlights the potential for using tensor-based machine learning algorithms to predict cocaine use based on MRI connectomic data and presents a promising approach for identifying individuals at risk of substance abuse.

Assessing the Efficacy and Safety of a Digital Therapeutic for Symptoms of Depression in Adolescents: Protocol for a Randomized Controlled Trial

BACKGROUND

Depression is a serious, prevalent, recurrent, and undertreated disorder in adolescents. Low levels of treatment seeking and treatment adherence in this age group, combined with a growing national crisis in access to mental health care, have increased efforts to identify effective treatment alternatives for this demographic. Digital health interventions for mental illness can provide cost-effective, engaging, and accessible means of delivering psychotherapy to adolescents.

OBJECTIVE

This protocol describes a virtual randomized controlled trial designed to evaluate the efficacy and safety of a self-guided, mobile app-based implementation of behavioral activation therapy, SparkRx, for the adjunct treatment of symptoms of depression in adolescents.

METHODS

Participants are recruited directly through web-based and print advertisements. Following eligibility screening and consenting, participants are randomly assigned to a treatment arm (SparkRx) or a control arm (assessment-enhanced usual care) for 5 weeks. The primary efficacy outcome, total score on the 8-item Patient Health Questionnaire (PHQ-8), is assessed at the end of the 5-week intervention period. Additional participant-reported outcomes are assessed at baseline, the postintervention time point, and 1-month follow-up. The safety of the intervention is assessed by participant report (and legal guardian report, if the participant is younger than 18 years) and by patterns of symptom deterioration on the PHQ-8, as part of a larger clinical safety monitoring protocol. The primary efficacy outcome, total PHQ-8 score at the postintervention time point, will be compared between SparkRx and enhanced usual care arms using mixed effect modeling, with baseline PHQ-8 and current antidepressant medication status included as covariates. Secondary efficacy outcomes, including the proportion of participants exhibiting treatment response, remission, and minimal clinically significant improvement (all derived from total PHQ-8 scores), will be compared between groups using chi-square tests. Symptom severity at 1-month follow-up will also be compared between arms. Planned subgroup analyses will examine the robustness of treatment effects to differences in baseline symptom severity (PHQ-8 score <15 or ≥ 15) and age (younger than 18 years and older than 18 years). The primary safety outcome, the number of psychiatric serious adverse events, will be compared between trial arms using the Fisher exact test. All other adverse events will be presented descriptively.

RESULTS

As of May 2023, enrollment into the study has concluded; 223 participants were randomized. The analysis of the efficacy and safety data is expected to be completed by Fall 2023.

CONCLUSIONS

We hypothesize that the results of this trial will support the efficacy and safety of SparkRx in attenuating symptoms of depression in adolescents. Positive results would more broadly support the prospect of using accessible, scientifically validated, digital therapeutics in the adjunct treatment of mental health disorders in this age range.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05462652; https://clinicaltrials.gov/study/NCT05462652.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/48740.

A CBT-based mobile intervention as an adjunct treatment for adolescents with symptoms of depression: a virtual randomized controlled feasibility trial

Background

High rates of adolescent depression demand for more effective, accessible treatment options. A virtual randomized controlled trial was used to assess the feasibility and acceptability of a 5-week, self-guided, cognitive behavioral therapy (CBT)-based mobile application, Spark, compared to a psychoeducational mobile application (Active Control) as an adjunct treatment for adolescents with depression during the COVID-19 pandemic.

Methods

A community sample aged 13-21, with self-reported symptoms of depression, was recruited nationwide. Participants were randomly assigned to use either Spark or Active Control (N_Spark = 35; N_{Active Control} = 25). Questionnaires, including the PHQ-8 measuring depression symptoms, completed before, during, and immediately following completion of the intervention, evaluated depressive symptoms, usability, engagement, and participant safety. App engagement data were also analyzed.

Results

60 eligible adolescents (female = 47) were enrolled in 2 months. 35.6% of those expressing interest were consented and all enrolled. Study retention was high (85%). Spark users rated the app as usable (System Usability Scale_mean = 80.67) and engaging (User Engagement Scale-Short Form_mean = 3.62). Median daily use was 29%, and 23% completed all levels. There was a significant negative relationship between behavioral activations completed and change in PHQ-8. Efficacy analyses revealed a significant main effect of time, F = 40.60, p < .001, associated with decreased PHQ-8 scores over time. There was no significant Group × Time interaction (F = 0.13, p = .72) though the numeric decrease in PHQ-8 was greater for Spark (4.69 vs. 3.56). No serious adverse events or adverse device effects were reported for Spark users. Two serious adverse events reported in the Active Control group were addressed per our safety protocol.

Conclusion

Recruitment, enrollment, and retention rates demonstrated study feasibility by being comparable or better than other mental health apps. Spark was highly acceptable relative to published norms. The study's novel safety protocol efficiently detected and managed adverse events. The lack of significant difference in depression symptom reduction between Spark and Active Control may be explained by study design and study design factors. Procedures established during this feasibility study will be leveraged for subsequent powered clinical trials evaluating app efficacy and safety.

Clinical Trial Registration

https://clinicaltrials.gov/ct2/show/NCT04524598.

Neuroimaging and immunological features of neurocognitive function related to substance use in people with HIV

This study sought to identify neuroimaging and immunological factors associated with substance use and that contribute to neurocognitive impairment (NCI) in people with HIV (PWH). We performed cross-sectional immunological phenotyping, neuroimaging, and neurocognitive testing on virally suppressed PWH in four substance groups: cocaine only users (COC), marijuana only users (MJ), dual users (Dual), and Non-users. Participants completed substance use assessments, multimodal MRI brain scan, neuropsychological testing, and blood and CSF sampling. We employed a two-stage analysis of 305 possible biomarkers of cognitive function associated with substance use. Feature reduction (Kruskal Wallis p-value < 0.05) identified 53 biomarkers associated with substance use (22 MRI and 31 immunological) for model inclusion along with clinical and demographic variables. We employed eXtreme Gradient Boosting (XGBoost) with these markers to predict cognitive function (global T-score). SHapley Additive exPlanations (SHAP) values were calculated to rank features for impact on model output and NCI. Participants were 110 PWH with sustained HIV viral suppression (33 MJ, 12 COC, 22 Dual, and 43 Non-users). The ten highest ranking biomarkers for predicting global T-score were 4 neuroimaging biomarkers including functional connectivity, gray matter volume, and white matter integrity; 5 soluble biomarkers (plasma glycine, alanine, lyso-phosphatidylcholine (lysoPC) aC17.0, hydroxy-sphingomyelin (SM.OH) C14.1, and phosphatidylcholinediacyl (PC aa) C28.1); and 1 clinical variable (nadir CD4 count). The results of our machine learning model suggest that substance use may indirectly contribute to NCI in PWH through both metabolomic and neuropathological mechanisms.

The Individualized Prediction of Neurocognitive Function in People Living with HIV Based on Clinical and Multimodal Connectome Data

Neurocognitive impairment continues to be common comorbidity for people living with HIV (PLWH). Given the chronic nature of HIV disease, identifying reliable biomarkers of these impairments is essential to advance our understanding of the underlying neural foundation and facilitate screening and diagnosis in clinical care. While neuroimaging provides immense potential for such biomarkers, to date, investigations in PLWH have been mostly limited to either univariate mass techniques or a single neuroimaging modality. In the present study, connectome-based predictive modeling (CPM) was proposed to predict individual differences of cognitive functioning in PLWH, using resting-state functional connectivity (FC), white matter structural connectivity (SC), and clinical relevant measures. We also adopted an efficient feature selection approach to identify the most predictive features, which achieved an optimal prediction accuracy of r = 0.61 in the discovery dataset (n = 102) and r = 0.45 in an independent validation HIV cohort (n = 88). Two brain templates and nine distinct prediction models were also tested for better modeling generalizability. Results show that combining multimodal FC and SC features enabled higher prediction accuracy of cognitive scores in PLWH, while adding clinical and demographic metrics may further improve the prediction by introducing complementary information, which may help better evaluate the individual-level cognitive performance in PLWH.

Strengthened and posterior-shifted structural rich-club organization in people who use cocaine

BACKGROUND

People with cocaine use disorder (CUD) often have abnormal cognitive function and brain structure. Cognition is supported by brain networks that typically have characteristics like rich-club organization, which is a group of regions that are highly connected across the brain and to each other, and small worldness, which is a balance between local and long-distance connections. However, it is unknown whether there are abnormalities in structural brain network connectivity of CUD.

METHODS

Using diffusion-weighted imaging, we measured structural connectivity in 37 people with CUD and 38 age-matched controls. We identified differences in rich-club organization and whether such differences related to small worldness and behavior. We also tested whether rich-club reorganization was associated with caudate and putamen structural connectivity due to the relevance of the dopamine system to cocaine use.

RESULTS

People with CUD had a higher normalized rich-club coefficient than controls, more edges connecting rich-club nodes to each other and to non-rich-club nodes, and fewer edges connecting non-rich-club nodes. Rich-club nodes were shifted posterior and lateral. Rich-club reorganization was related to lower clustered connectivity around individual nodes found in CUD, to increased impulsivity, and to a decrease in caudate connectivity.

CONCLUSIONS

These findings are consistent with previous work showing increased rich-club connectivity in conditions associated with a hypofunctional dopamine system. The posterior shift in rich-club nodes in CUD suggests that the structural connectivity of posterior regions may be more impacted than previously recognized in models based on brain function and morphology.

Principal component analysis denoising improves sensitivity of MR diffusion to detect white matter injury in neuroHIV

BACKGROUND AND PURPOSE

Diffusion-weighted imaging is able to capture important information about cerebral white matter (WM) structure. However, diffusion data can suffer from MRI and biological noise that degrades the quality of the images and makes finding important features difficult. We investigated how effectively local and nonlocal denoising increased the sensitivity to detect differences in cerebral WM in neuroHIV.

METHODS

We utilized principal component analysis (PCA) denoising to detect WM differences using fractional anisotropy. Local and nonlocal PCA denoising paradigms were implemented that varied in search area and number of components. We examined different-sized WM tracts that consistently show differences between people living with Human Immunodeficiency Virus (HIV) (PWH) and HIV-negative individuals (corpus callosum, forceps minor, and right uncinate fasciculus), and size-matched tracts not typically associated with HIV-related differences (spinothalamic, right medial lemniscus, and left occipitopontine). We first conducted a full sample comparison of WM differences between groups, and then randomly reduced the sample to the point where we still found differences in WM.

RESULTS

Nonlocal PCA denoising allowed us to detect differences after a sample reduction of 35% in the forceps minor, 17% in the right uncinate fasciculus, and 6% in the corpus callosum.

CONCLUSIONS

PCA denoising had a beneficial effect on detecting significant differences in PWH after sample size reduction. The smaller forceps minor tract and right uncinate fasciculus showed greater sensitivity to PCA denoising than the larger corpus callosum. These results show the importance of identifying the most effective PCA denoising strategy when investigating WM in PWH.

Human immunodeficiency virus-related decreases in corpus callosal integrity and corresponding increases in functional connectivity

People living with human immunodeficiency virus (PLWH) often have neurocognitive impairment. However, findings on HIV-related differences in brain network function underlying these impairments are inconsistent. One principle frequently absent from these reports is that brain function is largely emergent from brain structure. PLWH commonly have degraded white matter; we hypothesized that functional communities connected by degraded white matter tracts would show abnormal functional connectivity. We measured white matter integrity in 69 PLWH and 67 controls using fractional anisotropy (FA) in 24 intracerebral white matter tracts. Then, among tracts with degraded FA, we identified gray matter regions connected to these tracts and measured their functional connectivity during rest. Finally, we identified cognitive impairment related to these structural and functional connectivity systems. We found HIV-related decreased FA in the corpus callosum body (CCb), which coordinates activity between the left and right hemispheres, and corresponding increases in functional connectivity. Finally, we found that individuals with impaired cognitive functioning have lower CCb FA and higher CCb functional connectivity. This result clarifies the functional relevance of the corpus callosum in HIV and provides a framework in which abnormal brain function can be understood in the context of abnormal brain structure, which may both contribute to cognitive impairment.

Increased alpha suppression with age during involuntary memory retrieval

Recent work suggests that while voluntary episodic memory declines with age, involuntary episodic memory, which comes to mind spontaneously without intention, remains relatively intact. However, the neurophysiology underlying these differences has yet to be established. The current study used electroencephalography (EEG) to investigate voluntary and involuntary retrieval in older and younger adults. Participants first encoded sounds, half of which were paired with pictures, the other half unpaired. EEG was then recorded as they listened to the sounds, with participants in the involuntary group performing a sound localization cover task, and those in the voluntary group additionally attempting to recall the associated pictures. Participants later reported which sounds brought the paired picture to mind during the localization task. Reaction times on the localization task were slower for voluntary than involuntary retrieval and for paired than unpaired sounds, possibly reflecting increased attentional demands of voluntary retrieval and interference from reactivation of the associated pictures respectively. For the EEG analyses, young adults showed greater alpha event-related desynchronization (ERD) during voluntary than involuntary retrieval at frontal and occipital sites, while older adults showed pronounced alpha ERD regardless of intention. Additionally, older adults showed greater ERD for paired than unpaired sounds at occipital sites, likely reflecting visual reactivation of the associated pictures. Young adults did not show this alpha ERD memory effect. Taken together, these data suggest that involuntary memory is largely preserved with age, but this may be due to older adults' greater recruitment of top-down control even when demand for such control is limited.

Hypoactivation in the precuneus and posterior cingulate cortex during ambiguous decision making in individuals with HIV

People with human immunodeficiency virus (HIV) often have neurocognitive impairment. People with HIV make riskier decisions when the outcome probabilities are known, and have abnormal neural architecture underlying risky decision making. However, ambiguous decision making, when the outcome probabilities are unknown, is more common in daily life, but the neural architecture underlying ambiguous decision making in people with HIV is unknown. Eighteen people with HIV and 20 controls completed a decision making task while undergoing functional magnetic resonance imaging scanning. Participants chose between a certain reward and uncertain reward with a known (risky) or unknown (ambiguous) probability of winning. There were three levels of risk: high, medium, and low. Ambiguous > risky brain activity was compared between groups. Ambiguous > risky brain activity was correlated with emotional/psychiatric functioning in people with HIV. Both groups were similarly ambiguity-averse. People with HIV were more risk-averse than controls and chose the high-risk uncertain option less often. People with HIV had hypoactivity in the precuneus, posterior cingulate cortex (PCC), and fusiform gyrus during ambiguous > medium risk decision making. Ambiguous > medium risk brain activity was negatively correlated with emotional/psychiatric functioning in individuals with HIV. To make ambiguous decisions, people with HIV underrecruit key regions of the default mode network, which are thought to integrate internally and externally derived information to come to a decision. These regions and related cognitive processes may be candidates for interventions to improve decision-making outcomes in people with HIV.

Synergistic effects of HIV and marijuana use on functional brain network organization

HIV is associated with disruptions in cognition and brain function. Marijuana use is highly prevalent in HIV but its effects on resting brain function in HIV are unknown. Brain function can be characterized by brain activity that is correlated between regions over time, called functional connectivity. Neuropsychiatric disorders are increasingly being characterized by disruptions in such connectivity. We examined the synergistic effects of HIV and marijuana use on functional whole-brain network organization during resting state. Our sample included 78 adults who differed on HIV and marijuana status (19 with co-occurring HIV and marijuana use, 20 HIV-only, 17 marijuana-only, and 22 controls). We examined differences in local and long-range brain network organization using eight graph theoretical metrics: transitivity, local efficiency, within-module degree, modularity, global efficiency, strength, betweenness, and participation coefficient. Local and long-range connectivity were similar between the co-occurring HIV and marijuana use and control groups. In contrast, the HIV-only and marijuana-only groups were both associated with disruptions in brain network organization. These results suggest that marijuana use in HIV may normalize disruptions in brain network organization observed in persons with HIV. However, future work is needed to determine whether this normalization is suggestive of a beneficial or detrimental effect of marijuana on cognitive functioning in HIV.

Cocaine-related alterations in fronto-parietal gray matter volume correlate with trait and behavioral impulsivity

BACKGROUND

Chronic cocaine use is associated with structural brain abnormalities within prefrontal regions implicated in impulsivity. Despite high levels of impulsivity among persons who use cocaine, it is not known how reductions in gray matter volume (GMV) may relate to trait and behavioral measures of impulsivity.

METHODS

The sample included 39 active cocaine users (COC+) and 40 controls with no history of cocaine use (COC-). Participants had a brain scan on a 3 T MRI machine and completed out-of-scanner measures of trait impulsivity and delayed reward discounting. Whole-brain voxel-based morphometry was used to compare GMV between COC+ and COC-. Within regions that differed between groups, voxelwise correlations were conducted to examine the relationship between GMV and impulsivity.

RESULTS

In a whole-brain analysis, COC+ had broad reductions in GMV compared to COC- in bilateral frontal, parietal, occipital, and cerebellar regions. Lower GMV correlated with trait impulsivity in lateral prefrontal regions and with delayed reward discounting in medial prefrontal regions, while lower GMV correlated with both measures in the posterior parietal cortex. COC+ demonstrated significantly higher impulsivity than COC- on all measures, but the nature of the correlation with GMV was similar in both groups.

CONCLUSIONS

Reflecting the multi-faceted nature of impulsivity, these results show that trait and behavioral measures of impulsivity map differentially onto altered brain morphology. While the brain-behavior patterns were similar in COC+ and COC-, suggesting that impulsivity varies on a continuous spectrum, cocaine-related abnormalities in frontal-parietal brain systems may contribute to heightened impulsivity.

Development and validation of a multiplex fluorescent microsphere immunoassay assay for detection of porcine cytokines

Cytokines are cell signalling proteins that mediate a number of different physiological responses. The accurate measurement of cytokine profiles is important for a variety of diagnostic and prognostic scenarios in relation to animal health and welfare. Simultaneous quantification of cytokine profiles in a single sample is now possible using fluorescent microsphere immunoassays (FMIA). We describe the development and validation of a novel multiplex assay using the Bio-Plex® 200 system to quantify cytokines in five different porcine tissues (brain, placenta, synovial tissue and fluid, plasma). The cytokine profiles are both tissue, and research hypothesis, -dependent but include Interleukin-1beta (IL-1β), Interleukin-4 (IL-4), Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10) and Tumor necrosis factor (TNF-α).

This methods paper is reported in two parts: the development of a FMIA for porcine tissues and validation of pre-treatment for optimal cytokine recovery in porcine brain, placenta, synovial tissue and plasma. Validation steps are critical in ensuring an assay is suitable for novel sample types.

This technique advances traditional ELISAs by:

•

FMIA provides insight into the profiles of multiple porcine cytokines in certain situations (e.g. disease, parturition).

•

Use of the Bio-Plex® 200 system to investigate novel sample types, including brain, placenta and synovial tissue.

•

Multiplexing utilises a fraction of the sample volume compared with multiple ELISAs.

Neural responses to emotional involuntary memories in posttraumatic stress disorder: Differences in timing and activity

Background

Involuntary memories are a hallmark symptom of posttraumatic stress disorder (PTSD), but studies of the neural basis of involuntary memory retrieval in posttraumatic stress disorder (PTSD) are sparse. The study of the neural correlates of involuntary memories of stressful events in PTSD focuses on the voluntary retrieval of memories that are sometimes recalled as intrusive involuntary memories, not on involuntary retrieval while being scanned. Involuntary memory retrieval in controls has been shown to elicit activity in the parahippocampal gyrus, precuneus, inferior parietal cortex, and posterior midline regions. However, it is unknown whether involuntary memories are supported by the same mechanisms in PTSD. Because previous work has shown that both behavioral and neural responsivity is slowed in PTSD, we examined the spatiotemporal dynamics of the neural activity underlying negative and neutral involuntary memory retrieval.

Methods

Twenty-one individuals with PTSD and 21 non-PTSD, trauma-exposed controls performed an involuntary memory task, while undergoing a functional magnetic resonance imaging scan. Environmental sounds served as cues for well-associated pictures of negative and neutral scenes. We used a finite impulse response model to analyze temporal differences between groups in neural responses.

Results

Compared with controls, participants with PTSD reported more involuntary memories, which were more emotional and more vivid, but which activated a similar network of regions. However, compared to controls, individuals with PTSD showed delayed neural responsivity in this network and increased vmPFC/ACC activity for negative > neutral stimuli.

Conclusions

The similarity between PTSD and controls in neural substrates underlying involuntary memories suggests that, unlike voluntary memories, involuntary memories elicit similar activity in regions critical for memory retrieval. Further, the delayed neural responsivity for involuntary memories in PTSD suggests that factors affecting cognition in PTSD, like increased fatigue, or avoidance behaviors could do so by delaying activity in regions necessary for cognitive processing. Finally, compared to neutral memories, negative involuntary memories elicit hyperactivity in the vmPFC, whereas the vmPFC is typically shown to be hypoactive in PTSD during voluntary memory retrieval. These patterns suggest that considering both the temporal dynamics of cognitive processes as well as involuntary cognitive processes would improve existing neurobiological models of PTSD.

Taking tests in the magnet: Brain mapping standardized tests

Standardized psychometric tests are sophisticated, well-developed, and consequential instruments; test outcomes are taken as facts about people that impact their lives in important ways. As part of an initial demonstration that human brain mapping techniques can add converging neural-level evidence to understanding standardized tests, our participants completed items from standardized tests during an fMRI scan. We compared tests for diagnosing posttraumatic stress disorder (PTSD) and the correlated measures of Neuroticism, Attachment, and Centrality of Event to a general-knowledge baseline test. Twenty-three trauma-exposed participants answered 20 items for each of our five tests in each of the three runs for a total of 60 items per test. The tests engaged different neural processes; which test a participant was taking was accurately predicted from other participants' brain activity. The novelty of the application precluded specific anatomical predictions; however, the interpretation of activated regions using meta-analyses produced encouraging results. For instance, items on the Attachment test engaged regions shown to be more active for tasks involving judgments of others than judgments of the self. The results are an initial demonstration of a theoretically and practically important test-taking neuroimaging paradigm and suggest specific neural processes in answering PTSD-related tests. Hum Brain Mapp 38:5706-5725, 2017. © 2017 Wiley Periodicals, Inc.

Quantifying Interparticle Forces and Heterogeneity in 3D Granular Materials

Interparticle forces in granular materials are intimately linked to mechanical properties and are known to self-organize into heterogeneous structures, or force chains, under external load. Despite progress in understanding the statistics and spatial distribution of interparticle forces in recent decades, a systematic method for measuring forces in opaque, three-dimensional (3D), frictional, stiff granular media has yet to emerge. In this Letter, we present results from an experiment that combines 3D x-ray diffraction, x-ray tomography, and a numerical force inference technique to quantify interparticle forces and their heterogeneity in an assembly of quartz grains undergoing a one-dimensional compression cycle. Forces exhibit an exponential decay above the mean and partition into strong and weak networks. We find a surprising inverse relationship between macroscopic load and the heterogeneity of interparticle forces, despite the clear emergence of two force chains that span the system.

The neural basis of involuntary episodic memories

Voluntary episodic memories require an intentional memory search, whereas involuntary episodic memories come to mind spontaneously without conscious effort. Cognitive neuroscience has largely focused on voluntary memory, leaving the neural mechanisms of involuntary memory largely unknown. We hypothesized that, because the main difference between voluntary and involuntary memory is the controlled retrieval processes required by the former, there would be greater frontal activity for voluntary than involuntary memories. Conversely, we predicted that other components of the episodic retrieval network would be similarly engaged in the two types of memory. During encoding, all participants heard sounds, half paired with pictures of complex scenes and half presented alone. During retrieval, paired and unpaired sounds were presented, panned to the left or to the right. Participants in the involuntary group were instructed to indicate the spatial location of the sound, whereas participants in the voluntary group were asked to additionally recall the pictures that had been paired with the sounds. All participants reported the incidence of their memories in a postscan session. Consistent with our predictions, voluntary memories elicited greater activity in dorsal frontal regions than involuntary memories, whereas other components of the retrieval network, including medial-temporal, ventral occipitotemporal, and ventral parietal regions were similarly engaged by both types of memories. These results clarify the distinct role of dorsal frontal and ventral occipitotemporal regions in predicting strategic retrieval and recalled information, respectively, and suggest that, although there are neural differences in retrieval, involuntary memories share neural components with established voluntary memory systems.

Progression and remission of urologic symptoms in the community: results of a longitudinal cluster analysis approach

OBJECTIVE

To investigate the natural history of urologic symptom progression and remission by means of cluster analysis in a large, well-characterized cohort of men and women.

METHODS

Cluster analysis was used to assign men and women to symptom clusters on the basis of the prevalence of 14 self-reported urologic symptoms. Data were analyzed from the Boston Area Community Health study at baseline (T1) and 5-year follow-up (T2). Cluster progression was defined as any change from a less symptomatic to a more symptomatic cluster; conversely, cluster remission was defined as movement from more symptomatic to less symptomatic clusters. Logistic regression models examined the association of sociodemographic, psychosocial, and health outcome measures with cluster progression and remission.

RESULTS

Follow-up data were available from 4145 participants (1610 men; 2535 women). More than two thirds of men (69.2%) and women (68.2%) had stable symptom cluster assignments. Cluster progression occurred in 280 of 1610 (15.2%) men and 390 of 2535 (14.6%) women; cluster remission in 280 of 1610 (15.6%) men and 409 of 2535 (17.4%) women. In multivariate analyses, cluster progression was twice as common in men with incident depression (odds ratio = 2.43, 95% confidence interval 1.26-4.67) and 3 times more likely in men with ≥ 3 comorbidities at baseline. Urologic surgeries were uncommon in men and women and were not consistently related to cluster progression or remission.

CONCLUSION

Urologic symptom clusters were relatively stable over a 5-year follow-up period for more than two thirds of men and women in our sample. Specific risk factors for progression were identified in men and women.

High versus low level of response to alcohol: evidence of differential reactivity to emotional stimuli

BACKGROUND

The low level of response (LR) or sensitivity to alcohol is genetically influenced and predicts heavy drinking and alcohol problems. Functional magnetic resonance imaging (fMRI) studies using cognitive tasks suggest that subjects with a low-LR process cognitive information differently after placebo and alcohol than those with a high LR, but no studies have evaluated whether similar LR group differences are seen during an emotional processing task.

METHODS

The fMRI data were gathered from 116 nonalcoholic subjects (60 women) after oral placebo or approximately .7 mL/kg of ethanol while performing a modified emotional faces processing task. These included 58 low- and high-LR pairs matched on demography and aspects of substance use.

RESULTS

Blood alcohol levels and task performance were similar across LR groups, but low-LR subjects consumed approximately .8 drinks more/occasion. Thirteen brain regions (mostly the middle and inferior frontal gyri, cingulate, and insula) showed significant LR group or LR × placebo/alcohol condition interactions for emotional (mostly happy) faces relative to non-face trials. Low-LR subjects generally showed decreasing blood-oxygen level-dependent response contrasts across placebo to alcohol, whereas high LR showed increasing contrasts from placebo to alcohol, even after controlling for drinking quantities and alcohol-related changes in cerebral blood flow.

CONCLUSIONS

Thus, LR group fMRI differences are as prominent during an emotional face task as during cognitive paradigms. Low-LR individuals processed both types of information in a manner that might contribute to an impaired ability to recognize modest levels of alcohol intoxication in a range of life situations.

Trajectories of change in sagebrush steppe vegetation communities in relation to multiple wildfires

Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems, including changes in state. Sagebrush steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering them. Despite these issues, the majority of studies of fire effects in systems dominated by Artemisia tridentata wyomingensis have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (U.S.A.), was one of the largest contiguous areas of sagebrush steppe habitat in the state until large wildfires burned the majority of it in 2000 and 2007. We analyzed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent postfire restoration efforts, affected communities' successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Low-elevation communities, previously dominated by obligate seeders, moved furthest from their initial composition and were dominated by weedy, early-successional species in 2009. Higher-elevation sites with resprouting shrubs, native bunchgrasses, and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, although there was some recovery where communities were dominated by resprouters. Bromus tectorum dominance was reduced by herbicide application in areas where it was previously abundant, but it increased significantly in untreated areas. Several resprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant B. tectorum. Our results suggest that community dynamics can be understood through a state and transition model with two axes (shrub/grass and native/invasive abundance), although such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop a conceptual model that will be validated with further research.

Acute ethanol effects on brain activation in low- and high-level responders to alcohol

BACKGROUND

A low level of response (LR) to alcohol is an important endophenotype associated with an increased risk of alcoholism. However, little is known about how neural functioning may differ between individuals with low and high LRs to alcohol. This study examined whether LR group effects on neural activity varied as a function of acute alcohol consumption.

METHODS

A total of 30 matched high- and low-LR pairs (N = 60 healthy young adults) were recruited from the University of California, San Diego, and administered a structured diagnostic interview and laboratory alcohol challenge followed by two functional magnetic resonance imaging (fMRI) sessions under placebo and alcohol conditions, in randomized order. Task performance and blood oxygen level-dependent response contrast to high relative to low working memory load in an event-related visual working memory (VWM) task were examined across 120 fMRI sessions.

RESULTS

Both LR groups performed similarly on the VWM task across conditions. A significant LR group by condition interaction effect was observed in inferior frontal and cingulate regions, such that alcohol attenuated the LR group differences found under placebo (p < 0.05). The LR group by condition effect remained even after controlling for cerebral blood flow, age, and typical drinking quantity.

CONCLUSIONS

Alcohol had differential effects on brain activation for low- and high-LR individuals within frontal and cingulate regions. These findings represent an additional step in the search for physiological correlates of a low LR and identify brain regions that may be associated with the low LR response.

Comparing structural equation models that use different measures of the level of response to alcohol

BACKGROUND

The two measures of a low level of response (LR) to alcohol, an alcohol challenge and the retrospective Self-Report of the Effects of Alcohol questionnaire (SRE), each identify individuals at high risk for heavy drinking and alcohol problems. These measures also perform similarly in identifying subjects with unique functional brain imaging characteristics. However, few data are available regarding whether alcohol challenge-based and SRE-based LRs operate similarly in structural equation models (SEMs) that search for characteristics, which help to mediate how LR impacts alcohol outcomes.

METHODS

Two hundred and ninety-four men from the San Diego Prospective Study were evaluated for their LR to alcohol using alcohol challenges at approximately age 20. At approximately age 35, the same subjects filled out the SRE regarding the number of drinks needed for effects 15 to 20 years earlier. The two different LR scores for these men were used in SEM analyses evaluating how LR relates to future heavy drinking and to drinking in peers (PEER), alcohol expectancies (EXPECT), and drinking to cope (COPE) as potential mediators of the LR to drinking pattern (ALCOUT) relationships.

RESULTS

While the 2 LR measures that were determined 15 years apart related to each other at a modest level (r = 0.17, p < 0.01), the SEM results were similar regardless of the LR source. In both alcohol challenge-based and SRE-based LR models, LR related directly to ALCOUT, with partial mediation from PEER and COPE, but not through EXPECT in these 35-year-old men.

CONCLUSIONS

Consistent with the >60% overlap in prediction of outcomes for the 2 LR measures, and with results from functional brain imaging, alcohol challenge- and SRE-based LR values operated similarly in SEM models in these men.

Relative contributions of multiple determinants to bone mineral density in men

SUMMARY

Focus on individual risk factors for osteoporosis could allocate disproportionate attention to trivial relationships. We tested many recognized risk factors of osteoporosis for their association with bone mineral density (BMD) in multivariate models among men. Lean mass accounted for the most variance, with substantially less accounted for by demographic, strength, and health factors.

INTRODUCTION

Osteoporosis in men has gained recognition as a public health problem, generating an interest in the search for risk factors. Isolation of individual risk factors could allocate disproportionate attention to relationships that may be of limited consequence.

METHODS

The Boston Area Community Health/Bone (BACH/Bone) Survey is a population-based study of randomly selected community-dwelling men (age, 30-79 years). BMD and lean mass were measured by dual X-ray absorptiometry. Socioeconomic status, health history, and lifestyle factors were obtained via interview. Hormone levels and markers of bone turnover were obtained from non-fasting blood samples. Multivariate analyses measured relative contributions of covariates to femoral neck (hip), one-third distal radius (wrist), and lumbar spine BMD.

RESULTS

Factors positively associated with BMD in multivariate models at the three sites were black race and appendicular lean mass. Asthma was consistently negatively associated. Various other risk factors also contributed significantly to each of the individual sites. R (2) values for the hip, wrist, and spine were 41%, 30%, and 24%, respectively. Lean mass accounted for the most explained variance at all three sites.

CONCLUSIONS

These data emphasize the limitation of focusing on individual risk factors and highlight the importance of potentially modifiable lean mass in predicting BMD.

Litter and dead wood dynamics in ponderosa pine forests along a 160-year chronosequence

Disturbances such as fire play a key role in controlling ecosystem structure. In fire-prone forests, organic detritus comprises a large pool of carbon and can control the frequency and intensity of fire. The ponderosa pine forests of the Colorado Front Range, USA, where fire has been suppressed for a century, provide an ideal system for studying the long-term dynamics of detrital pools. Our objectives were (1) to quantify the long-term temporal dynamics of detrital pools; and (2) to determine to what extent present stand structure, topography, and soils constrain these dynamics. We collected data on downed dead wood, litter, duff (partially decomposed litter on the forest floor), stand structure, topographic position, and soils for 31 sites along a 160-year chronosequence. We developed a compartment model and parameterized it to describe the temporal trends in the detrital pools. We then developed four sets of statistical models, quantifying the hypothesized relationship between pool size and (1) stand structure, (2) topography, (3) soils variables, and (4) time since fire. We contrasted how much support each hypothesis had in the data using Akaike's Information Criterion (AIC). Time since fire explained 39-80% of the variability in dead wood of different size classes. Pool size increased to a peak as material killed by the fire fell, then decomposed rapidly to a minimum (61-85 years after fire for the different pools). It then increased, presumably as new detritus was produced by the regenerating stand. Litter was most strongly related to canopy cover (r2 = 77%), suggesting that litter fall, rather than decomposition, controls its dynamics. The temporal dynamics of duff were the hardest to predict. Detrital pool sizes were more strongly related to time since fire than to environmental variables. Woody debris peak-to-minimum time was 46-67 years, overlapping the range of historical fire return intervals (1 to > 100 years). Fires may therefore have burned under a wide range of fuel conditions, supporting the hypothesis that this region's fire regime was mixed severity.

Assessment of aortic regurgitation by transesophageal color Doppler imaging of the vena contracta: validation against an intraoperative aortic flow probe

OBJECTIVES

This study was performed to validate the accuracy of color flow vena contracta (VC) measurements of aortic regurgitation (AR) severity by comparing them to simultaneous intraoperative flow probe measurements of regurgitant fraction (RgF) and regurgitant volume (RgV).

BACKGROUND

Color Doppler imaging of the vena contracta has emerged as a simple and reliable measure of the severity of valvular regurgitation. This study evaluated the accuracy of VC imaging of AR by transesophageal echocardiography (TEE).

METHODS

A transit-time flow probe was placed on the ascending aorta during cardiac surgery in 24 patients with AR. The flow probe was used to measure RgF and RgV simultaneously during VC imaging by TEE. Flow probe and VC imaging were interpreted separately and in blinded fashion.

RESULTS

A good correlation was found between VC width and RgF (r = 0.85) and RgV (r = 0.79). All six patients with VC width >6 mm had a RgF >0.50. All 18 patients with VC width <5 mm had a RgF <0.50. Vena contracta area also correlated well with both RgF (r = 0.81) and RgV (r = 0.84). All six patients with VC area >7.5 mm2 had a RgF >0.50, and all 18 patients with a VC area <7.5 mm2 had a RgF <0.50. In a subset of nine patients who underwent afterload manipulation to increase diastolic blood pressure, RgV increased significantly (34 +/- 26 ml to 41 +/- 27 ml, p = 0.042) while VC width remained unchanged (5.4 +/- 2.8 mm to 5.4 +/- 2.8 mm, p = 0.41).

CONCLUSIONS

Vena contracta imaging by TEE color flow mapping is an accurate marker of AR severity. Vena contracta width and VC area correlate well with RgF and RgV obtained by intraoperative flow probe. Vena contracta width appears to be less afterload-dependent than RgV.

Detection of myocardial perfusion defects by contrast echocardiography in the setting of acute myocardial ischemia with residual antegrade flow

Although myocardial contrast echocardiography accurately demarcates area at risk during total coronary occlusion, the ability of MCE to delineate area at risk in the presence of residual antegrade flow is unknown. We hypothesized that perfusion defects in myocardial segments supplied by severe coronary stenoses with residual antegrade flow could be detected by MCE using intravenous FS069. We studied 13 open-chest dogs using an intravenous injection of FS069 during intermittent harmonic imaging. Images were collected at baseline, during acute ischemia with residual antegrade flow, physiologic hyperemia (release of stenosis), and total coronary occlusion. Regional myocardial blood flow was assessed using colored microspheres. MCE risk area during acute ischemia with residual antegrade flow and total occlusion was planimetered and compared with pathologic risk area (area unstained by monastral blue). Background-subtracted peak videointensity in the risk area was assessed for all flow states. Regional myocardial blood flow confirmed expected flow states, being significantly greater during physiologic hyperemia (4.16 +/- 1.22 ml/min/g) than at baseline (0.71 +/- 0.19 ml/min/g) and significantly diminished during coronary stenosis with residual antegrade flow (0.20 +/- 0.16 ml/min/g) and total occlusion (0.09 +/- 0.06 ml/min/g; p < 0.0001). Myocardial risk area by MCE during coronary stenosis with residual antegrade flow correlated well with pathologic risk area determined by monastral blue staining (r = 0.86). Peak videointensity during coronary stenosis (111 +/- 27) was significantly less than at baseline (157 +/- 50) but greater than during total occlusion (81 +/- 34; p < 0.0001). In conclusion, intravenous FS069 in conjunction with intermittent harmonic imaging delineates area at risk in ischemic myocardium supplied by a coronary stenoses with residual antegrade flow. The presence of a perfusion defect on MCE does not necessarily imply that the coronary artery is totally occluded.

Comparison of vena contracta width by multiplane transesophageal echocardiography with quantitative Doppler assessment of mitral regurgitation

Mitral regurgitation (MR) severity is routinely assessed by Doppler color flow mapping, which is subject to technical and hemodynamic variables. Vena contracta width may be less influenced by hemodynamic variables and has previously been shown to correlate with angiographic estimates of MR severity. This study was performed to compare mitral vena contracta width by multiplane transesophageal echocardiography (TEE) with simultaneous quantitative Doppler echocardiography in 35 patients with MR. The vena contracta width was measured at the narrowest portion of the MR jet as it emerged through the coaptation of the leaflets; it was identified in 97% of the patients. Vena contracta width correlated well with regurgitant volume (R2 = 0.81) and regurgitant orifice area (R2 = 0.81) by quantitative Doppler technique. A vena contracta width > or = 0.5 cm always predicted a regurgitant volume >60 ml and an effective regurgitant orifice area > or = 0.4 cm2 in all patients. A vena contracta width < or = 0.3 cm always predicted a regurgitant volume <45 ml and a regurgitant orifice area < or = 0.35 cm2. Thus, vena contracta width by multiplane TEE correlates well with mitral regurgitant volume and regurgitant orifice area by quantitative Doppler echocardiography and provides a simple method for the identification of patients with severe MR.

Safety and efficacy of QW7437, a new fluorocarbon-based echocardiographic contrast agent

The aim of this study was to evaluate the safety and efficacy of QW7437, a new fluorocarbon-based transpulmonary myocardial echocardiographic contrast agent. QW7437 is an anionically charged 2% dodecafluoropentane emulsion molecule, similar to EchoGen, a contrast agent previously shown to be efficacious in providing myocardial opacification by means of venous injection. This new agent has theoretical potential to provide greater safety and efficacy as a result of (1) reduced adherence to the negatively charged vascular endothelium and (2) reduced microbubble coalescence. Myocardial contrast echocardiography was performed in 10 dogs to evaluate the safety and efficacy of this agent. QW7437 (0.05 ml/kg) was injected as an intravenous bolus during intermittent harmonic epicardial imaging. Hemodynamic variables including heart rate, blood pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, and arterial blood gases were determined at baseline and serially after contrast administration. Left ventricular fractional area shortening the regional myocardial blood flow at rest and during hyperemia (adenosine 140 micrograms/kg/min) were measured before and after contrast echocardiography. QW7437 provided dense myocardial opacification which persisted for more than 2 minutes in all subjects. This prolonged contrast effect did not result in significant changes in any hemodynamic variables, left ventricular function, or myocardial blood flow. Future studies should address the potential of this agent for human use.

Does digoxin provide additional hemodynamic and autonomic benefit at higher doses in patients with mild to moderate heart failure and normal sinus rhythm?

OBJECTIVES

This study sought to examine the hemodynamic and autonomic dose response to digoxin.

BACKGROUND

Previous studies have demonstrated an increase in contractility and heart rate variability with digitalis preparations. However, little is known about the dose-response to digoxin, which has a narrow therapeutic window.

METHODS

Nineteen patients with moderate heart failure and a left ventricular ejection fraction < 0.45 were studied hemodynamically using echocardiography and blood pressure at baseline and after 2 weeks of low dose (0.125 mg daily) and 2 weeks of moderate dose digoxin (0.25 mg daily). Loading conditions were altered with nitroprusside at each study. Autonomic function was studied by assessing heart rate variability on 24-h Holter monitoring and plasma norepinephrine levels during supine rest.

RESULTS

Low dose digoxin provided a significant increase in ventricular performance, but no further increase was seen with the moderate dose. Low dose digoxin reduced heart rate and increased heart rate variability. Moderate dose digoxin produced no additional increase in heart rate variability or reduction in sympathetic activity, as manifested by heart rate, plasma norepinephrine or low frequency/high frequency power ratio. In addition, we did not find that either low or moderate dose digoxin increased parasympathetic activity.

CONCLUSIONS

We conclude that moderate dose digoxin provides no additional hemodynamic or autonomic benefit for patients with mild to moderate heart failure over low dose digoxin. Because higher doses of digoxin may predispose to arrhythmogenesis, lower dose digoxin should be considered in patients with mild to moderate heart failure.

Assessment of mitral regurgitation severity by Doppler color flow mapping of the vena contracta

BACKGROUND

Although Doppler color flow mapping is widely used to assess the severity of mitral regurgitation (MR), a simple, accurate, and quantitative marker of MR by color flow mapping remains elusive. We hypothesized that vena contracta width by color flow mapping would accurately predict the severity of MR.

METHODS AND RESULTS

We studied 80 patients with MR. Vena contracta width was measured in multiple views with zoom mode and nonstandard angulation to optimize its visualization. Flow volumes across the left ventricular outflow tract and mitral annulus were calculated by pulsed-Doppler technique to determine regurgitant volume. Effective regurgitant orifice area was calculated by dividing the regurgitant volume by the continuous-wave Doppler velocity-time integral of the MR jet. The cause of MR was ischemia in 24, dilated cardiomyopathy in 34 mitral valve prolapse in 12, endocarditis in 2, rheumatic disease in 2, mitral annular calcification in 1, and uncertain in 5. Regurgitant volumes ranged from 2 to 191 mL. Regurgitant orifice area ranged from 0.01 to 1.47 cm2. Single-plane vena contracta width from the parasternal long-axis view correlated well with regurgitant volume (r = .85, SEE = 20 mL) and regurgitant orifice area (r = .86, SEE = 0.15 cm2). Biplane vena contracta width from apical views correlated well with regurgitant volume (r = .85, SEE = 19 mL) and regurgitant orifice area (r = .88, SEE = 0.14 cm2). A biplane vena contracta width > or = 0.5 cm was always associated with a regurgitant volume > 60 mL and a regurgitant orifice area > 0.4 cm2. A biplane vena contracta width < or = 0.3 cm predicted a regurgitant volume < 60 mL and a regurgitant orifice area < 0.4 cm2 in 24 of 29 patients. No other parameter, including jet area, left atrial size, pulmonary flow reversal, or semiquantitative MR grade, correlated significantly with regurgitant volume or regurgitant orifice area in a multivariate analysis.

CONCLUSIONS

Our results demonstrate that careful color flow mapping of the vena contracta of the MR jet provides a simple quantitative assessment of MR that correlates well with quantitative Doppler techniques.

An analysis of dilemmas posed by prehospital DNR orders

This article briefly recounts the development of the prehospital do-not-resuscitate (DNR) order and indicates certain situations, such as a choking episode or a suicide attempt, in which the presence of a DNR order may provoke a moral dilemma for the emergency medical technician as to whether or not the patient should be treated. An ethical analysis of this question is performed and concludes that resuscitative treatment is ethical and mandatory.

Time course of improvement in left ventricular function, mass and geometry in patients with congestive heart failure treated with beta-adrenergic blockade

OBJECTIVES

We examined the time course of ventricular functional improvement in patients with dilated cardiomyopathy who received beta-blockade and the long-term effects of beta-blockade on ventricular mass and geometry in these patients.

BACKGROUND

Previous studies have shown that beta-adrenergic blocking agents when administered long term improve ventricular function in patients with heart failure. However, the time course of improvement in ventricular function and the long-term effects of beta-blockade on ventricular mass and geometry are not known.

METHODS

Twenty-six men with dilated cardiomyopathy underwent serial echocardiography on days 0 and 1 and months 1 and 3 of either metoprolol (n = 16) or standard therapy (n = 10). At 3 months all patients on standard therapy were crossed over to metoprolol, and late echocardiograms were obtained after 18 +/- 5 (mean +/- SD) months of metoprolol therapy. All echocardiograms were read in blinded manner.

RESULTS

Patients treated with metoprolol had an initial decline (day 1 vs. day 0) in ventricular function (increase in end-systolic volume and decrease in ejection fraction). Ventricular function improved between months 1 and 3 (p = 0.013, metoprolol vs. standard therapy). Left ventricular mass regressed at 18 months (333 +/- 85 to 275 +/- 53 g, p = 0.011) but not at 3 months. Left ventricular shape became less spherical and assumed a more normal elliptical shape by 18 months (major/minor axis ratio 1.5 +/- 0.2 to 1.7 +/- 0.2, p = 0.0001).

CONCLUSIONS

Patients with heart failure treated with metoprolol do not demonstrate an improvement in systolic performance until after 1 month of therapy and may have a mild reduction in function initially. Long-term therapy with metoprolol results in a reversal of maladaptive remodeling with reduction in left ventricular volumes, regression of left ventricular mass and improved ventricular geometry by 18 months.

Transperineal palladium 103 prostate brachytherapy: analysis of morbidity and seed migration

OBJECTIVES

To evaluate the early morbidity of palladium 103 (103Pd) prostate brachytherapy.

METHODS

Thirty-two patients with Stage A or B prostate carcinoma were implanted transperineally with 103Pd using transrectal ultrasound and fluoroscopy between May 1990 and December 1992. Patients were subsequently followed to evaluate for morbidity and possibility of migration of the implanted seeds into the lungs.

RESULTS

The median follow-up time was 20 months (range, 2 to 45 months). The major acute toxicity of the procedure, dysuria, was seen in 88% of the patients. Although this was generally grade 1 or 2 and transient, grade 3 or 4 toxicity occurred in 18% of patients. Mild rectal symptoms (transient diarrhea, rectal bleeding) occurred in 19% of patients. Sexual functions could not be evaluated. Seven of the 3213 total seeds implanted (0.2%) were found to have migrated to the lung in 6 of 30 (20%) patients having a postoperative chest radiograph. This did not cause any clinical problems.

CONCLUSIONS

103Pd prostate brachytherapy is generally associated with only mild or moderate urinary and rectal symptoms, and the incidence of severe complications is low. Further follow-up is required to evaluate the efficacy.

Chicxulub Multiring Impact Basin: Size and Other Characteristics Derived from Gravity Analysis

The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.

Should public health respect autonomy?

This paper suggests that public health, due to its community orientation, may be ignoring certain ethical principles--namely the rights of individuals and communities to self-determination. The expectation of individual rights as a member of a community is reviewed and the additional right of a community for self-determination is proposed. The influences on ethical evaluations by the legal and economic environments are suggested, using US examples. The conclusion argues that as the focus of health-care delivery changes, it will become more important to consider these questions of group ethics.