Differential response to frequency-dependent interactions: an experimental test using genotypes of an invasive grass.

Positive feedbacks have been suggested as a means for non-indigenous species to successfully invade novel environments. Frequency-dependent feedbacks refer to a species performance being dependent on its local abundance in the population; however, frequency dependence is often described as a monolithic trait of a species rather than examining the variation in response for individual genotypes and fitness traits. Here, we investigate frequency-dependent outcomes for individual genotypes and fitness-related traits for the invasive grass Phalaris arundinacea. We tested for competition-mediated frequency dependence by establishing hexagonal arrays with the center target plant surrounded by either same, different or no genotype neighbors to determine how changing the small-scale frequency neighborhood-influenced invasion success. We used a Bayesian ANOVA approach which allowed us to easily accommodate our non-normal dataset and found that same neighbor plots had greater biomass production than different neighbor plots. Target plants also had greater stem height and aboveground biomass when surrounded by same genotype neighbors. A greenhouse experiment did not support the hypothesis that increased mycorrhizal associations were the cause of positive frequency dependence. We devised a frequency-dependent metric to quantify the extent of fitness-related differences for individual genotypes and found that individual genotypes showed a range of both positive and negative responses to different frequency treatments; however, only positive responses were statistically significant. The small-scale genotypic neighborhood had no effect for the fitness-related traits of leaf number, belowground biomass and total biomass. We demonstrate that individual invasive genotypes respond differently to changing frequency neighborhoods and that growth responses do not respond with the same direction and magnitude. A range of frequency-dependent responses may allow genotypes to invade a wide range of environments.

Uncorrected total anomalous pulmonary venous drainage in pregnancy.

Total anomalous pulmonary venous drainage is a rare form of congenital heart disease. It usually presents in the neonatal period, although later presentation, including in adulthood, is known to occur. We could not find any accounts of adult survivors with the undiagnosed disease becoming pregnant. We describe the case of a 19-year-old Bengali primiparous woman who arrived in the UK at 27 weeks' gestation and needed an urgent caesarean section for intrauterine growth restriction at 34 weeks' gestation. Uncorrected congenital heart disease was diagnosed at this time although the exact nature of the pathology was not clear. She underwent an uncomplicated caesarean section using a combined spinal-epidural technique with invasive monitoring. Intrathecal 0.5% hyperbaric bupivacaine 0.7 mL and fentanyl 25 microg were sufficient for surgery. She remained cardiovascularly stable throughout the procedure and a female infant was successfully delivered. She underwent corrective cardiac surgery 14 months after delivery. To our knowledge, this is the first report of caesarean section in a patient with uncorrected total anomalous pulmonary venous drainage. In this case, regional anaesthesia was successfully used.

Impact study of the introduction of low-dose epidural (bupivacaine 0.1%/fentanyl 2 microg . mL(-1)) compared with bupivacaine 0.25% for labour analgesia.

We conducted a retrospective analysis of the obstetric effects of introducing a low-dose epidural regimen for epidural analgesia in labour. Before this, all women in our unit requesting epidural analgesia for labour received intermittent boluses (10 mL) of 0.25% bupivacaine. After the introduction of the low-dose service in March 2000, intermittent boluses (10 mL) of 0.1% bupivacaine with fentanyl 2 microg . mL(-1) were given. The records of 300 women were examined, 150 who had received the standard regimen before the introduction of the new service and 150 women afterwards. The groups were compared for outcome of labour, quality of analgesia and any adverse events related to the epidural analgesia. There was a significant reduction in the low-dose group in the number of women requiring instrumental delivery (41% vs. 29%, P = 0.04). The need for indwelling bladder catheters was also reduced in the patients receiving the low-dose regimen (21.3% vs. 4.7%, P < 0.001). Duration of analgesia was longer in patients receiving bupivacaine 0.25% (mean minimum time between boluses 42.25 +/- 33.8 vs. 24.37 +/- 19.8 min, P < 0.001). The need for further anaesthetic intervention was higher with the low-dose regimen (24% vs. 34%, P = 0.037). Maternal satisfaction was high in both groups (95 and 97%, respectively). We conclude that the introduction of a low-dose regimen of epidural analgesia for labour reduces the incidence of instrumental deliveries. It also decreases the incidence of bladder catheterisation during labour, but the need for anaesthetic intervention may be greater.

A pattern classification approach to characterizing solitary pulmonary nodules imaged on high resolution CT: preliminary results.

The purpose of this research is to characterize solitary pulmonary nodules as benign or malignant based on quantitative measures extracted from high resolution CT (HRCT) images. High resolution CT images of 31 patients with solitary pulmonary nodules and definitive diagnoses were obtained. The diagnoses of these 31 cases (14 benign and 17 malignant) were determined from either radiologic follow-up or pathological specimens. Software tools were developed to perform the classification task. On the HRCT images, solitary nodules were identified using semiautomated contouring techniques. From the resulting contours, several quantitative measures were extracted related to each nodule's size, shape, attenuation, distribution of attenuation, and texture. A stepwise discriminant analysis was performed to determine which combination of measures were best able to discriminate between the benign and malignant nodules. A linear discriminant analysis was then performed using selected features to evaluate the ability of these features to predict the classification for each nodule. A jackknifed procedure was performed to provide a less biased estimate of the linear discriminator's performance. The preliminary discriminant analysis identified two different texture measures--correlation and difference entropy--as the top features in discriminating between benign and malignant nodules. The linear discriminant analysis using these features correctly classified 28/31 cases (90.3%) of the training set. A less biased estimate, using jackknifed training and testing, yielded the same results (90.3% correct). The preliminary results of this approach are very promising in characterizing solitary nodules using quantitative measures extracted from HRCT images. Future work involves including contrast enhancement and three-dimensional measures extracted from volumetric CT scans, as well as the use of several pattern classifiers.

CT of pulmonary thromboembolism.

Conventional incremental CT has for many years been useful in the fortuitous diagnosis of pulmonary thromboembolic disease, allowing for visualization of both the central occluding thrombus and the pleuroparenchymal sequelae. Unfortunately, the slow data acquisition times precluded the inclusion of conventional CT in diagnostic algorithms for the diagnosis of this disease. The development and increasing availability of fast scanning techniques, namely helical (spiral) CT and electron-beam CT, now provide a noninvasive means of consistently and accurately demonstrating acute and chronic pulmonary arterial thrombus to the segmental level. CT has the added advantage over ventilation-perfusion scanning and pulmonary angiography of depicting unsuspected intrathoracic disease that may account for the patient's presenting illness.

Risk factors for higher cost in congenital heart operations.

BACKGROUND: For many congenital heart defects, hospital mortality is no longer a sensitive parameter by which to measure outcome. Although hospital survival rates are now excellent for a wide variety of lesions, many patients require expensive and extensive hospital-based services during the perioperative period to enable their convalescence. These services can substantially increase the cost of care delivery. In today's managed care environment, it would be useful if risk factors for higher cost could be identified preoperatively so that appropriate resources could be made available for the care of these patients. The focus of this retrospective investigation is to determine if risk factors for high cost for repair of congenital heart defects can be identified. METHODS: We assessed financial risk by tracking actual hospital costs (not charges) for 144 patients undergoing repair of atrial septal defect (58 patients), ventricular septal defect (48 patients), atrioventricular canals (14 patients), or tetralogy of Fallot (24 patients) at Duke University Medical Center between July 1, 1992, and September 15, 1995. Furthermore, we were able to identify where the costs occurred within the hospital. Financial risk was defined as a large (> 60% of mean costs) standard deviation, which indicated unpredictability and variability in the treatment for a group of patients. RESULTS: Cost for atrial septal defect repair was predictably consistent (low standard deviation) and was related to hospital length of stay. There were factors, however, for ventricular septal defect, atrioventricular canal, and tetralogy of Fallot repair that are identifiable preoperatively that predict low- and high-risk groups using cost as an outcome parameter. Patients undergoing ventricular septal defect repair who were younger than 6 months of age at the time of repair, who required preoperative hospital stays of longer than 7 days before surgical repair, or who had Down's syndrome had a less predictable cost picture than patients undergoing ventricular septal defect repair who were older than 2 years, who had short (< 4 days) preoperative hospitalization, or who did not have Down's syndrome ($48,252 +/- $42,539 versus $15,819 +/- $7,219; p = 0.008). Patients with atrioventricular canals who had long preoperative hospitalization (> 7 days), usually due to pneumonia (respiratory syncytial virus) with preoperative mechanical ventilation had significantly higher cost than patients with atrioventricular canals who underwent elective repair with short preoperative hospitalization ($83,324 +/- $60,138 versus $26,904 +/- $5,384; p = 0.05). Patients with tetralogy of Fallot had higher costs if they had multiple congenital anomalies, previous palliation (combining costs of both surgical procedures and hospital stays), or severe "tet" spells at the time of presentation for operation compared with patients without these risk factors ($114,202 +/- $88,524 versus $22,241 +/- $7,071; p = 0.0005). One patient (with tetralogy of Fallot) with multiple congenital anomalies died 42 days after tetralogy of Fallot repair of sepsis after a gastrointestinal operation. Otherwise, hospital mortality was 0% for all groups. CONCLUSIONS: Low mortality and good long-term outcome for surgical correction of congenital heart defects is now commonplace, but can be expensive as some patients with complex problems receive the care necessary to survive. This study demonstrates that it is possible to identify factors preoperatively that predict financial risk. This knowledge may facilitate implementation of risk adjustments for managed care contracting and for strategic resource allocation.

Detection of simulated lung nodules with computed radiography: effects of nodule size, local optical density, global object thickness, and exposure.

RATIONALE AND OBJECTIVES: We quantified differences in the detection of simulated lung nodules on computed radiographs on the basis of variations in nodule size, local contrast, body habitus (global contrast), and exposure. METHODS: A step-wedge phantom was developed to simulate the attenuation ranges of the lung, retrocardiac, and subdiaphragmatic regions of the adult human chest. Additional Lucite wedges were used to simulate two different body thicknesses and to provide variable structural noise. Soft-tissue-equivalent nodules of 3-mm and 5-mm diameter that resulted in 10% differences in attenuation from lung equivalence were embedded in lung-equivalent material. By superimposing the sheets in various positions, 84 unique nodule configurations containing eight nodules per image were exposed on a computed radiography system. Computed radiographs were acquired at two different exposures approximating standard exposure and underexposure. For each resulting phantom image, seven observers scored the presence or absence of a nodule within individual cells of a 5 x 5 grid matrix. RESULTS: True-positive fractions for 3-mm-diameter nodules were very low across all conditions. True-positive fractions for 5-mm-diameter nodules varied from 0.23 to 0.98. Significant differences in the conspicuity of 5-mm nodules depended on differences in phantom thickness and differences in the locations of nodules within lung-, retrocardiac-, or subdiaphragmatic-equivalent regions. Accuracy in detecting nodules was significantly lower at lower exposures when nodules were located in the subdiaphragmatic-equivalent region. CONCLUSION: On computed radiographs, small nodules (5-mm diameter) can be reliably detected when they are located in areas of high or moderate surrounding local contrast, such as the lung or mediastinal regions. Detection of nodules decreases in regions of lower optical density corresponding to the subdiaphragmatic regions of the chest. The decrease in nodule detectability is greatest under conditions that simulate large body thickness and underexposure.

Pulmonary thromboembolism: spectrum of findings on CT.

CT has emerged as a potentially important diagnostic technique in pulmonary thromboembolism that can provide direct visualization of the obstructing embolus and its associated vascular and pleuroparenchymal sequelae. Although the role of contrast-enhanced CT in the diagnostic algorithm of pulmonary embolism has not been defined, patients at risk for pulmonary embolism frequently undergo thoracic CT as part of the assessment for other cardiopulmonary conditions. As such, CT may provide the first indication of clinically significant pulmonary embolic disease. This essay reviews the vascular, pleural, and parenchymal features of pulmonary thromboembolism observed on CT scans, describes the limitations of CT, and discusses the imaging features of pulmonary embolism that overlap other clinical conditions.

Effects of reduced exposure on computed radiography: comparison of nodule detection accuracy with conventional and asymmetric screen-film radiographs of a chest phantom.

OBJECTIVE: Radiographic exposure has been thought to have little impact on the diagnostic quality of chest computed radiography because of automatic digital control of global optical density. The objectives of this study were to compare images obtained with two different exposures in computed radiography with conventional and asymmetric screen-film images of the chest for the detection of simulated lung nodules by use of receiver operating characteristic analysis and to relate differences in observer performance to parameters of image noise measured for each receptor condition. MATERIALS AND METHODS: At 110 kVp (fixed), exposures for the two screen-film systems were those necessary to achieve adequate optical densities over the lung and mediastinal regions of an anthropomorphic phantom. The two exposures used for the computed radiographs corresponded to the exposure used for the conventional chest screen-film system and an exposure 22% lower. An anthropomorphic phantom constructed of materials matched to the muscle, lung, and bone attenuation of a muscular adult man was used. Soft-tissue-equivalent plastic nodules of various sizes were secured at multiple sites on the phantom to simulate lung nodules. The chest phantom was imaged in 50 configurations with a total of 70 superimposed nodules. The perceptual performances of five radiologists were compared by use of receiver operating characteristic analysis. The signal-to-noise ratio in the mediastinum and the coefficient of variation of noise were measured for all four image conditions by use of a step wedge technique to provide an explanation for differences in diagnostic accuracy. RESULTS: We found no significant differences in the detection of lung nodules between the two screen-film systems or between the conventional screen-film images and the standard-exposure computed radiographs. However, there was a significant decrease in nodule detection on computed radiographs obtained at a reduced exposure; this result was associated with a 21% decrease in the signal-to-noise ratio. CONCLUSION: Our results show that underexposure of computed radiographs decreases the detection of low-contrast objects such as lung nodules. Although consistent global optical density on computed radiographs is achieved over a wide range of exposures, the alterations in signal-to-noise ratio that result from underexposure can reduce the diagnostic quality of computed radiographs.

Psychosocial concerns of adults with congenital heart disease. Employability and insurability.

Addressing the psychosocial concerns of the growing population of adults with congenital heart disease presents a unique challenge to health care providers. These patients frequently need information about their disease with emphasis on how it may affect their sexuality, childbearing, and risk of having children with congenital heart disease. These patients also face problems in securing employment that will provide health insurance coverage for their cardiac conditions.