Virginia Commonwealth University

About: Virginia Commonwealth University is a education organization based out in Richmond, Virginia, United States. It is known for research contribution in the topics: Population & Health care. The organization has 23822 authors who have published 49587 publications receiving 1787046 citations. The organization is also known as: VCU.

Reducing Transformation Bias in Curve Fitting

Abstract: (1984). Reducing Transformation Bias in Curve Fitting. The American Statistician: Vol. 38, No. 2, pp. 124-126.

A developmental examination of amygdala response to facial expressions

Abstract: Several lines of evidence implicate the amygdala in face-emotion processing, particularly for fearful facial expressions. Related findings suggest that face-emotion processing engages the amygdala within an interconnected circuitry that can be studied using a functional-connectivity approach. Past work also underscores important functional changes in the amygdala during development. Taken together, prior research on amygdala function and development reveals a need for more work examining developmental changes in the amygdala's response to fearful faces and in amygdala functional connectivity during face processing. The present study used event-related functional magnetic resonance imaging to compare 31 adolescents (9--17 years old) and 30 adults (21--40 years old) on activation to fearful faces in the amygdala and other regions implicated in face processing. Moreover, these data were used to compare patterns of amygdala functional connectivity in adolescents and adults. During passive viewing, adolescents demonstrated greater amygdala and fusiform activation to fearful faces than did adults. Functional connectivity analysis revealed stronger connectivity between the amygdala and the hippocampus in adults than in adolescents. Within each group, variability in age did not correlate with amygdala response, and sex-related developmental differences in amygdala response were not found. Eye movement data collected outside of the magnetic resonance imaging scanner using the same task suggested that developmental differences in amygdala activation were not attributable to differences in eye-gaze patterns. Amygdala hyperactivation in response to fearful faces may explain increased vulnerability to affective disorders in adolescence; stronger amygdala-hippocampus connectivity in adults than adolescents may reflect maturation in learning or habituation to facial expressions.

Older males secrete luteinizing hormone and testosterone more irregularly, and jointly more asynchronously, than younger males

Abstract: New statistical perspectives on the secretory patterns of both luteinizing hormone (LH) and testosterone (T) may prove useful in further understanding the aging process, and possibly ultimately in improving the diagnosis and treatment of spermatogenetic failure and loss of sexual interest. We examined serum concentration time-series for LH and T in 14 young (21-34 years of age) and 11 aged (62-74 years of age) healthy men. For each subject, blood samples were obtained at 2.5-min intervals during a sleep period, with an average sampling duration of 7 hr. For each of LH and T, we used the model-independent statistic approximate entropy (ApEn) to quantify the irregularity of the serum concentration time-series; to quantify joint LH-T secretory asynchrony, we employed the recently introduced cross-ApEn. Although mean (and SD) LH and T concentrations were indistinguishable in the two age groups (P > 0.25), for LH, aged subjects had greater ApEn values (1.525 +/- 0.221) than younger individuals (1.207 +/- 0.252), P < 0.003, indicating more irregular secretion in the older cohort. For T, aged subjects also had greater ApEn values (1.622 +/- 0.120) than younger counterparts (1.384 +/- 0.228), P < 0.004. In young, but not older men, ApEn(T) significantly exceeded ApEn(LH), P < 0.02. Aged subjects had greater cross-ApEn values (1.961 +/- 0.121) than younger subjects (1.574 +/- 0.249), P < 10(-4), with nearly 100% sensitivity and specificity, indicating greater LH-T asynchrony in the older group. In conjunction with previous findings of greater irregularity of growth hormone release with increasing age, we propose that increased secretory irregularity with advancing age may be a widespread hormonal phenomenon. Finally, theoretically, we clarify the need for quantifications such as ApEn and cross-ApEn via a study of a "variable lag" pulsatile process, and empirically note the potential wide applicability of cross-ApEn to quantify asynchrony in interconnected (hormonal) networks.

Predictors of Mortality and Outcomes of Therapy in Low-Flow Severe Aortic Stenosis A Placement of Aortic Transcatheter Valves (PARTNER) Trial Analysis

Abstract: Background—The prognosis and treatment of patients with low-flow (LF) severe aortic stenosis are controversial. Methods and Results—The Placement of Aortic Transcatheter Valves (PARTNER) trial randomized patients with severe aortic stenosis to medical management versus transcatheter aortic valve replacement (TAVR; inoperable cohort) and surgical aortic valve replacement versus TAVR (high-risk cohort). Among 971 patients with evaluable echocardiograms (92%), LF (stroke volume index ≤35 mL/m2) was observed in 530 (55%); LF and low ejection fraction (<50%) in 225 (23%); and LF, low ejection fraction, and low mean gradient (<40 mm Hg) in 147 (15%). Two-year mortality was significantly higher in patients with LF compared with those with normal stroke volume index (47% versus 34%; hazard ratio, 1.5; 95% confidence interval, 1.25–1.89; P=0.006). In the inoperable cohort, patients with LF had higher mortality than those with normal flow, but both groups improved with TAVR (46% versus 76% with LF and 38% versus 53...

Quantifying the predictability of diaphragm motion during respiration with a noninvasive external marker.

Abstract: The aim of this work was to quantify the ability to predict intrafraction diaphragm motion from an external respiration signal during a course of radiotherapy. The data obtained included diaphragm motion traces from 63 fluoroscopic lung procedures for 5 patients, acquired simultaneously with respiratory motion signals (an infrared camera-based system was used to track abdominal wall motion). During these sessions, the patients were asked to breathe either (i) without instruction, (ii) with audio prompting, or (iii) using visual feedback. A statistical general linear model was formulated to describe the relationship between the respiration signal and diaphragm motion over all sessions and for all breathing training types. The model parameters derived from the first session for each patient were then used to predict the diaphragm motion for subsequent sessions based on the respiration signal. Quantification of the difference between the predicted and actual motion during each session determined our ability to predict diaphragm motion during a course of radiotherapy. This measure of diaphragm motion was also used to estimate clinical target volume (CTV) to planning target volume (PTV) margins for conventional, gated, and proposed four-dimensional (4D) radiotherapy. Results from statistical analysis indicated a strong linear relationship between the respiration signal and diaphragm motion (p<0.001) over all sessions, irrespective of session number (p=0.98) and breathing training type (p=0.19). Using model parameters obtained from the first session, diaphragm motion was predicted in subsequent sessions to within 0.1 cm (1 sigma) for gated and 4D radiotherapy. Assuming a 0.4 cm setup error, superior-inferior CTV-PTV margins of 1.1 cm for conventional radiotherapy could be reduced to 0.8 cm for gated and 4D radiotherapy. The diaphragm motion is strongly correlated with the respiration signal obtained from the abdominal wall. This correlation can be used to predict diaphragm motion, based on the respiration signal, to within 0.1 cm (1 sigma) over a course of radiotherapy.