Publications by authors named "David J Willis"

12 Publications

  • Page 1 of 1

Percutaneous drainage of colonic diverticular abscess: is colon resection necessary?

Dis Colon Rectum 2013 May;56(5):622-6

Division of Colon and Rectal Surgery, Department of Surgery, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Background: Recurrent diverticulitis has been reported in up to 30% to 40% of patients who recover from an episode of colonic diverticular abscess, so elective interval resection is traditionally recommended.

Objective: The aim of this study was to review the outcomes of patients who underwent percutaneous drainage of colonic diverticular abscess without subsequent operative intervention.

Design: This was an observational study.

Settings: This investigation was conducted at a tertiary care academic medical center and a single-hospital health system.

Patients: Patients treated for symptomatic colonic diverticular abscess from 2002 through 2007 were included.

Main Outcome Measures: The primary outcomes measured were complications, recurrence, and colectomy-free survival.

Results: Two hundred eighteen patients underwent percutaneous drainage of colonic diverticular abscesses. Thirty-two patients (15%) did not undergo subsequent colonic resection. Abscess location was pelvic (n = 9) and paracolic (n = 23), the mean abscess size was 4.2 cm, and the median duration of percutaneous drainage was 20 days. The comorbidities of this group of patients included severe cardiac disease (n = 16), immunodeficiency (n = 7), and severe pulmonary disease (n = 6). Freedom from recurrence at 7.4 years was 0.58 (95% CI 0.42-0.73). All recurrences were managed nonoperatively. Recurrence was significantly associated with an abscess size larger than 5 cm. Colectomy-free survival at 7.4 years was 0.17 (95% CI 0.13-0.21).

Limitations: This study was limited by its retrospective, nonexperimental design and short follow-up.

Conclusion: In selected patients, observation after percutaneous drainage of colonic diverticular abscess appears to be a safe and low-risk management option.
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http://dx.doi.org/10.1097/DCR.0b013e31828545e3DOI Listing
May 2013

Movie making as a cognitive distraction for paediatric patients receiving radiotherapy treatment: qualitative interview study.

BMJ Open 2013 Jan 16;3(1). Epub 2013 Jan 16.

Centre for Program Evaluation, University of Melbourne, Melbourne, Victoria, Australia.

Objectives: To establish the outcomes achieved by using an innovative movie-making programme designed to reduce fear of radiotherapy among paediatric patients.

Design: Qualitative descriptive evaluation based on semistructured, qualitative interviews with purposeful sampling and thematic analysis.

Setting: Tertiary Cancer Centre.

Participants: 20 parents of paediatric patients who had produced a movie of their radiation therapy experience and were in a follow-up phase of cancer management.

Results: Participants attributed a broad range of outcomes to the movie-making program. These included that the programme had helped reduce anxiety and distress exhibited by paediatric patients and contributed to a willingness to receive treatment. Other outcomes were that the completed movies had been used in school reintegration and for maintaining social connections.

Conclusions: Allowing children to create a video of their experience of radiotherapy provided a range of benefits to paediatric patients that varied according to their needs. For some patients, movie-making offered a valuable medium for overcoming fear of the unknown as well as increasing understanding of treatment processes. For others, the development of a personalised video offered an important cognitive/attentional distraction through engaging with an age-appropriate activity. Together these outcomes helped children maintain self-control and a positive outlook.
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http://dx.doi.org/10.1136/bmjopen-2012-001666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549231PMC
January 2013

A coupled kinematics-energetics model for predicting energy efficient flapping flight.

J Theor Biol 2013 Feb 16;318:173-96. Epub 2012 Oct 16.

Physics Department, University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7.

A new computational model based on an optimal power, wake-only aerodynamics method is presented to predict the interdependency of energetics and kinematics in bird and bat flight. The model is divided into offline, intermediate and online modules. In the offline module, a four-dimensional design space sweep is performed (lift, thrust, flapping amplitude and flapping frequency). In the intermediate stage, the physical characteristics of the animal are introduced (wing span, mass, wing area, aspect ratio, etc.), and a series of amplitude-frequency response surfaces are constructed for all viable flight speeds. In the online component, the amplitude-frequency response surfaces are mined for the specific flapping motions being considered. The method is applied to several biological examples including a medium sized fruit bat (Cynopterus brachyotis), and two birds: a thrush nightingale (Luscinia luscinia) and a budgerigar (Melopsittacus undulatus). For each of these animals, the power and kinematics predictions are compared with available experimental data. These examples demonstrate that this new method can reasonably predict animal flight energetics and kinematics.
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http://dx.doi.org/10.1016/j.jtbi.2012.10.008DOI Listing
February 2013

Whole-body kinematics of a fruit bat reveal the influence of wing inertia on body accelerations.

J Exp Biol 2011 May;214(Pt 9):1546-53

Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA.

The center of mass (COM) of a flying animal accelerates through space because of aerodynamic and gravitational forces. For vertebrates, changes in the position of a landmark on the body have been widely used to estimate net aerodynamic forces. The flapping of relatively massive wings, however, might induce inertial forces that cause markers on the body to move independently of the COM, thus making them unreliable indicators of aerodynamic force. We used high-speed three-dimensional kinematics from wind tunnel flights of four lesser dog-faced fruit bats, Cynopterus brachyotis, at speeds ranging from 2.4 to 7.8 m s(-1) to construct a time-varying model of the mass distribution of the bats and to estimate changes in the position of their COM through time. We compared accelerations calculated by markers on the trunk with accelerations calculated from the estimated COM and we found significant inertial effects on both horizontal and vertical accelerations. We discuss the effect of these inertial accelerations on the long-held idea that, during slow flights, bats accelerate their COM forward during 'tip-reversal upstrokes', whereby the distal portion of the wing moves upward and backward with respect to still air. This idea has been supported by the observation that markers placed on the body accelerate forward during tip-reversal upstrokes. As in previously published studies, we observed that markers on the trunk accelerated forward during the tip-reversal upstrokes. When removing inertial effects, however, we found that the COM accelerated forward primarily during the downstroke. These results highlight the crucial importance of the incorporation of inertial effects of wing motion in the analysis of flapping flight.
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http://dx.doi.org/10.1242/jeb.037804DOI Listing
May 2011

Feasibility of measuring gastric emptying time, with a wireless motility device, after subjects consume fiber-matched liquid and solid breakfasts.

Appetite 2011 Aug 22;57(1):38-44. Epub 2011 Mar 22.

Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108, USA.

To explore the feasibility and sensitivity of a new technology for measuring gastric emptying time (GET) in appetite research, and also to compare appetite after subjects consumed macronutrient- and fiber-matched liquid and solid meals. Fourteen women (BMI of 21.2 ± 0.3) participated in this randomized, crossover study. On two separate days, fasted subjects consumed liquid (fruit juices and skim milk) and solid (oatmeal, blueberries, and apples) breakfasts. Both meals had 10 g of fiber and 410 kcal. GET was assessed with the SmartPill GI Motility System®, appetite was assessed with visual analog scales, and food intake was measured at lunch. Despite the same amount of fiber, GET was about 1h longer after the oatmeal than after the liquids. Subjects were less hungry after the oatmeal than after the liquids. Satisfaction and fullness were marginally improved with the oatmeal compared to the liquids. There was a negative association between GET and hunger. Lunchtime food and beverage intake did not differ between treatments. The SmartPill appears feasible and sensitive in appetite research, but has limitations. A solid meal with naturally occurring fiber from oatmeal and whole fruits increased GET and decreased hunger more than a liquid meal with added fiber.
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http://dx.doi.org/10.1016/j.appet.2011.03.006DOI Listing
August 2011

An optimized online verification imaging procedure for external beam partial breast irradiation.

Med Dosim 2011 26;36(2):171-7. Epub 2010 May 26.

Division of Radiation Oncology, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia.

The purpose of this study was to evaluate the capabilities of a kilovoltage (kV) on-board imager (OBI)-equipped linear accelerator in the setting of on-line verification imaging for external-beam partial breast irradiation. Available imaging techniques were optimized and assessed for image quality using a modified anthropomorphic phantom. Imaging dose was also assessed. Imaging techniques were assessed for physical clearance between patient and treatment machine using a volunteer. Nonorthogonal kV image pairs were identified as optimal in terms of image quality, clearance, and dose. After institutional review board approval, this approach was used for 17 patients receiving accelerated partial breast irradiation. Imaging was performed before every fraction verification with online correction of setup deviations >5 mm (total image sessions = 170). Treatment staff rated risk of collision and visibility of tumor bed surgical clips where present. Image session duration and detected setup deviations were recorded. For all cases, both image projections (n = 34) had low collision risk. Surgical clips were rated as well as visualized in all cases where they were present (n = 5). The average imaging session time was 6 min, 16 sec, and a reduction in duration was observed as staff became familiar with the technique. Setup deviations of up to 1.3 cm were detected before treatment and subsequently confirmed offline. Nonorthogonal kV image pairs allowed effective and efficient online verification for partial breast irradiation. It has yet to be tested in a multicenter study to determine whether it is dependent on skilled treatment staff.
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http://dx.doi.org/10.1016/j.meddos.2010.02.010DOI Listing
September 2011

Online kidney position verification using non-contrast radiographs on a linear accelerator with on board KV X-Ray imaging capability.

Med Dosim 2009 26;34(4):293-300. Epub 2008 Dec 26.

Division of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.

The kidneys are dose-limiting organs in abdominal radiotherapy. Kilovoltage (kV) radiographs can be acquired using on-board imager (OBI)-equipped linear accelerators with better soft tissue contrast and lower radiation doses than conventional portal imaging. A feasibility study was conducted to test the suitability of anterior-posterior (AP) non-contrast kV radiographs acquired at treatment time for online kidney position verification. Anthropomorphic phantoms were used to evaluate image quality and radiation dose. Institutional Review Board approval was given for a pilot study that enrolled 5 adults and 5 children. Customized digitally reconstructed radiographs (DRRs) were generated to provide a priori information on kidney shape and position. Radiotherapy treatment staff performed online evaluation of kidney visibility on OBI radiographs. Kidney dose measured in a pediatric anthropomorphic phantom was 0.1 cGy for kV imaging and 1.7 cGy for MV imaging. Kidneys were rated as well visualized in 60% of patients (90% confidence interval, 34-81%). The likelihood of visualization appears to be influenced by the relative AP separation of the abdomen and kidneys, the axial profile of the kidneys, and their relative contrast with surrounding structures. Online verification of kidney position using AP non-contrast kV radiographs on an OBI-equipped linear accelerator appears feasible for patients with suitable abdominal anatomy. Kidney position information provided is limited to 2-dimensional "snapshots," but this is adequate in some clinical situations and potentially advantageous in respiratory-correlated treatments. Successful clinical implementation requires customized partial DRRs, appropriate imaging parameters, and credentialing of treatment staff.
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http://dx.doi.org/10.1016/j.meddos.2008.11.002DOI Listing
January 2010

Quantifying the complexity of bat wing kinematics.

J Theor Biol 2008 Oct 25;254(3):604-15. Epub 2008 Jun 25.

Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA.

Body motions (kinematics) of animals can be dimensionally complex, especially when flexible parts of the body interact with a surrounding fluid. In these systems, tracking motion completely can be difficult, and result in a large number of correlated measurements, with unclear contributions of each parameter to performance. Workers typically get around this by deciding a priori which variables are important (wing camber, stroke amplitude, etc.), and focusing only on those variables, but this constrains the ability of a study to uncover variables of influence. Here, we describe an application of proper orthogonal decomposition (POD) for assigning importances to kinematic variables, using dimensional complexity as a metric. We apply this method to bat flight kinematics, addressing three questions: (1) Does dimensional complexity of motion change with speed? (2) What body markers are optimal for capturing dimensional complexity? (3) What variables should a simplified reconstruction of bat flight include in order to maximally reconstruct actual dimensional complexity? We measured the motions of 17 kinematic markers (20 joint angles) on a bat (Cynopterus brachyotis) flying in a wind tunnel at nine speeds. Dimensional complexity did not change with flight speed, despite changes in the kinematics themselves, suggesting that the relative efficacy of a given number of dimensions for reconstructing kinematics is conserved across speeds. By looking at subsets of the full 17-marker set, we found that using more markers improved resolution of kinematic dimensional complexity, but that the benefit of adding markers diminished as the total number of markers increased. Dimensional complexity was highest when the hindlimb and several points along digits III and IV were tracked. Also, we uncovered three groups of joints that move together during flight by using POD to quantify correlations of motion. These groups describe 14/20 joint angles, and provide a framework for models of bat flight for experimental and modeling purposes.
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http://dx.doi.org/10.1016/j.jtbi.2008.06.011DOI Listing
October 2008

Aeromechanics in aeroecology: flight biology in the aerosphere.

Integr Comp Biol 2008 Jul 18;48(1):85-98. Epub 2008 Jun 18.

Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA; Division of Engineering, Brown University, Providence, RI 02912, USA; Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge MA 02139, USA.

The physical environment of the aerosphere is both complex and dynamic, and poses many challenges to the locomotor systems of the three extant evolutionary lineages of flying animals. Many features of the aerosphere, operating over spatial and temporal scales of many orders of magnitude, have the potential to be important influences on animal flight, and much as marine ecologists have studied the relationship between physical oceanography and swimming locomotion, a subfield of aeroecology can focus attention on the ways the biology of flight is influenced by these characteristics. Airflows are altered and modulated by motion over and around natural and human-engineered structures, and both vortical flow structures and turbulence are introduced to the aerial environment by technologies such as aircraft and wind farms. Diverse aspects of the biology of flight may be better understood with reference to an aeroecological approach, particularly the mechanics and energetics of flight, the sensing of aerial flows, and the motor control of flight. Moreover, not only does the abiotic world influence the aerospheric conditions in which animals fly, but flying animals also, in turn, change the flow environment in their immediate vicinity, which can include the air through which other animals fly, particularly when animals fly in groups. Flight biologists can offer considerable insight into the ecology of the aerial world, and an aeroecological approach holds great promise for stimulating and enriching the study of the biology of flight.
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http://dx.doi.org/10.1093/icb/icn054DOI Listing
July 2008

Numerical integration techniques for curved-element discretizations of molecule-solvent interfaces.

J Chem Phys 2007 Jul;127(1):014701

Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Surface formulations of biophysical modeling problems offer attractive theoretical and computational properties. Numerical simulations based on these formulations usually begin with discretization of the surface under consideration; often, the surface is curved, possessing complicated structure and possibly singularities. Numerical simulations commonly are based on approximate, rather than exact, discretizations of these surfaces. To assess the strength of the dependence of simulation accuracy on the fidelity of surface representation, here methods were developed to model several important surface formulations using exact surface discretizations. Following and refining Zauhar's work [J. Comput.-Aided Mol. Des. 9, 149 (1995)], two classes of curved elements were defined that can exactly discretize the van der Waals, solvent-accessible, and solvent-excluded (molecular) surfaces. Numerical integration techniques are presented that can accurately evaluate nonsingular and singular integrals over these curved surfaces. After validating the exactness of the surface discretizations and demonstrating the correctness of the presented integration methods, a set of calculations are presented that compare the accuracy of approximate, planar-triangle-based discretizations and exact, curved-element-based simulations of surface-generalized-Born (sGB), surface-continuum van der Waals (scvdW), and boundary-element method (BEM) electrostatics problems. Results demonstrate that continuum electrostatic calculations with BEM using curved elements, piecewise-constant basis functions, and centroid collocation are nearly ten times more accurate than planar-triangle BEM for basis sets of comparable size. The sGB and scvdW calculations give exceptional accuracy even for the coarsest obtainable discretized surfaces. The extra accuracy is attributed to the exact representation of the solute-solvent interface; in contrast, commonly used planar-triangle discretizations can only offer improved approximations with increasing discretization and associated increases in computational resources. The results clearly demonstrate that the methods for approximate integration on an exact geometry are far more accurate than exact integration on an approximate geometry. A MATLAB implementation of the presented integration methods and sample data files containing curved-element discretizations of several small molecules are available online as supplemental material.
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http://dx.doi.org/10.1063/1.2743423DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3495009PMC
July 2007

Temporal gene expression following prosthetic arterial grafting.

J Surg Res 2004 Jul;120(1):27-36

Department of Surgery, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02115, USA.

Background: Following prosthetic arterial grafting, cytokines and growth factors released within the perianastomotic tissues stimulate smooth muscle cell proliferation and matrix production. While much in vitro work has characterized this response, little understanding exists regarding the sequential up- and down-regulation of genes following prosthetic arterial grafting. This study evaluates temporal gene expression at the distal anastomosis of prosthetic arterial grafts using microarray analysis.

Methods: Expanded polytetrafluoroethylene (ePTFE) carotid interposition grafts (n = 12) were surgically implanted into mongrel dogs. Distal anastomotic segments were harvested at 7, 14, 30, or 60 days. Contralateral carotid artery served as control. Total RNA was isolated from the anastomotic tissue and paired controls. Samples were probed with oligonucleotide microarrays consisting of approximately 10000 human genes to analyze differential gene expression at each time point.

Results: Forty-nine genes were found to be up-regulated and 37 genes were found to be down-regulated at various time points. Six genes were found to be consistently up-regulated at all time intervals, including collagen type 1 alpha-1 and alpha-2, 80K-L protein (MARCKS), and osteopontin. Six genes were found to be consistently down-regulated, including smoothelin and tropomyosin 2. RT-PCR and immunohistochemistry confirmed the microarray data.

Conclusions: This study uses microarray analysis to identify genes that were temporally up- and down-regulated after prosthetic arterial grafting. Genes with similar patterns of expression have been identified, providing insights into related cellular pathways that may result in the formation of anastomotic intimal hyperplasia.
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http://dx.doi.org/10.1016/j.jss.2003.12.014DOI Listing
July 2004

Temporal genomics of vein bypass grafting through oligonucleotide microarray analysis.

J Vasc Surg 2004 Mar;39(3):645-54

Department of Surgery, Division of Vascular Surgery, Beth Israel Deacones Medical Center, Boston, MA 02115, USA.

Objective: Autologous vein is the conduit of choice for small artery reconstruction. Despite excellent patency, these conduits undergo remodeling over time. The purpose of this study was to identify temporal gene expression in vein grafts versus control veins through microarray analysis.

Method: Cephalic vein grafts (n = 12) were used to bypass femoral arteries in canines. Vein grafts were harvested after 1, 7, 14, and 30 days. Normal contralateral cephalic vein served as control. Total RNA was isolated; its quantity and quality were confirmed with spectrophotometry and gel electrophoresis. Affymetrix U133A GeneChips, comprising approximately 15,000 genes, were used to analyze differential gene expression at each time point. Statistical analysis was performed with Affymetrix and dChip software to identify consistently upregulated and downregulated genes. Real-time, quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and immunohistochemistry were used to validate microarray data.

Results: Statistical analysis revealed that 49 genes were consistently upregulated and 31 genes were consistently downregulated in all three animals at various time points. qRT-PCR to quantitatively assess messenger RNA expression was performed on specific genes to validate the microarray data. Immunohistochemistry to qualitatively assess protein expression was used for further validation. Hierarchical clustering with dChip identified additional genes with similar temporal or functional expression patterns.

Conclusions: This is the first study to use microarray analysis with confirmatory qRT-PCR to identify altered genes after vein bypass grafting. Oligonucleotide microarrays and hierarchical clustering are powerful tools to generate hypotheses as the basis for additional research on gene expression in vein graft remodeling. Ultimately, identification of a temporal sequence of differential gene expression may provide insights not preferred into the molecular mechanisms of vein graft remodeling, but also into the pathways leading to intimal hyperplasia.
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http://dx.doi.org/10.1016/j.jvs.2003.10.049DOI Listing
March 2004