Biomedical subjects

Richard J Davies

Publications and source records attributed to Richard J Davies.

5 recordsLinked to original sources

PubMed2006

From macro- to nanoscopic templating with nanographenes.

A hexa-peri-hexabenzocoronene carrying six long, branched alkyl chains has been processed in nano- and macroscopic pore templates. An extraordinary self-organization of this material was observed within macroscopically large glass capillaries after cooling from the isotropic phase. Thereby, the columnar structures were long-range aligned along the capillary axis over several centimeters. This behavior was explained by the pronounced directional self-assembly of the molecules, whereby the curvature effect of the capillary was negligible. The processing in nanoscopic pores of an inorganic membrane yielded an improved supramolecular organization. It was possible to remove the inorganic template and to obtain bundles and single nanorods. The templating over different dimensions opens a variety of potential applications.

Journal Article↗

PubMed2005

Studying morphological variations across single fibres using an X-ray waveguide.

Waveguide and glass capillary optics have been used to study morphological variations across single as-spun poly(p-phenylene benzobisoxazole) (PBO) fibres. The waveguide provides a beam with a submicrometre dimension perpendicular to the fibre axis. The glass capillary optics provide a beam of a few micrometres in diameter. By directly comparing results obtained with both optics it is possible to assess the influence of beam size on experimental observations. The study demonstrates that submicrometre beams are invaluable for detailed morphological studies across single fibres. The greater morphological averaging inherent to data collected using glass capillary optics reduces the variation between skin and core measurements, as well as obscuring other important features. Crystalline domain orientation, (200) crystal plane spacings and reflection intensities can be determined from data generated using a submicrometre beam. All parameters are found to vary significantly across the diameter of single PBO fibres. In terms of orientation, both skin and core regions exhibit a lower degree of crystalline domain orientation than an intermediate zone. In terms of (200) crystal plane spacing, the observed variations suggest residual stresses within the fibre structure following manufacture.

Journal Article↗

PubMed2005

The learning curve measured by operating times for laparoscopic and open gastric bypass: roles of surgeon's experience, institutional experience, body mass index and fellowship training.

BACKGROUND: Surgeons must overcome a substantial learning curve before mastering laparoscopic Roux-en-Y gastric bypass (LRYGBP). This learning curve can be defined in terms of mortality, morbidity or length of surgery. The aim of this study was to compare the learning curves in terms of surgical time for the first 3 surgeons performing LRYGBP in our hospital with the length of surgery for open gastric bypass (CONTROLS). METHODS: We compared 494 primary LRYGBPs performed by 3 surgeons (393 by 1st SURGEON, 57 by 2nd SURGEON and 44 by 3rd SURGEON) to 159 open vertical banded gastroplasty-Roux-en-Y gastric bypasses (CONTROLS). Data for LRYGBP patients were prospectively obtained. Factors that significantly affected the length of surgery were identified by univariate and multivariate linear regression analysis. RESULTS: LRYGBP and CONTROL patients were similar in age, height, weight and BMI, although more CONTROLS were male. Median time for the 1st SURGEON performing LRYGBP dropped for each subsequent 100 operations: 1st 100 - 190 min, 2nd 100 - 135 min, 3rd 100 - 110 min and 4th 100 - 100 min. Median time for 2nd SURGEON performing LRYGBP was 120 min, 3rd SURGEON 173 min and CONTROLS 64 min. Length of surgery significantly correlated with surgical experience in terms of numbers of operations and BMI of patient. Times for 2nd SURGEON, a fellowship trained laparoscopic surgeon, started significantly faster than 1st SURGEON's, but did not significantly improve with experience. 3rd SURGEON's initial times were similar to 1st SURGEON's, but his times improved more rapidly with experience. Times for CONTROLS were significantly faster than all laparoscopic groups and did not correlate with operation number or patient BMI. CONCLUSIONS: The length of surgery for LRYGBPs continued to shorten beyond 400 operations for the first surgeon performing LRYGBP in our hospital. Previous fellowship training in LRYGBP shortened surgical times during initial clinical experience as an attending for the second surgeon. The learning curve was truncated because of the already established LRYGBP program.

Adult↗

PubMed2004

Predictors of prolonged hospital stay following open and laparoscopic gastric bypass for morbid obesity: body mass index, length of surgery, sleep apnea, asthma, and the metabolic syndrome.

BACKGROUND: The number of weight reduction operations performed for type II and type III obesity is rapidly escalating. Risk of surgery has been infrequently stratified for patient subgroups. The purpose of this study was to identify patient characteristics that increased the odds of a prolonged hospital length of stay (LOS) following open or laparoscopic Roux-en-Y gastric bypass (RYGBP). METHODS: The hospital records of 311 patients who underwent RYGBP in a 6-month period were retrospectively reviewed. Patient characteristics including the presence of significant obesity-related medical conditions were recorded. Analysis was based on intent to treat. Univariate and step-wise logistic regression analysis was used to identify the odds ratio (OR) and adjusted odds ratio (AOR) for predictors of an increased hospital LOS. RESULTS: Datasets for 311 patients were complete.159 patients underwent open vertical banded gastro-plasty-Roux-en-Y gastric bypass (VBG-RYGBP) and152 laparoscopic RYGBP (LRYGBP). 78% of patients were female. Median age was 40 years (range 18-68). Median BMI was 49 kg/m2 (range 35-82). 17% of patients had sleep apnea, 18% asthma, 19% type 2 diabetes, 13% hypercholesterolemia and 44% hypertension. Median length of surgery for open VBG-RYGBP (64 minutes) was significantly faster than forLRYGBP (105 minutes). Median length of stay was significantly shorter for LRYGBP (2 days) than openVBG-RYGBP (3 days). Univariate logistic regression analysis identified 6 predictors of increased LOS:open surgery (0.4 OR); increasing BMI (60 kg/m2 0.38 OR; BMI 70 kg/m2 0.53 OR); increasing length of surgery (120 min 0.33 OR; 180 min 0.48 OR); sleep apnea (2.25 OR); asthma (3.73 OR); and hypercholesterolemia (3.73 OR). Subset analysis identified patients with the greatest odds for a prolonged hospital stay: women with asthma (2.47 AOR) or coronary artery disease (8.65 AOR); men with sleep apnea (5.54 OR) or the metabolic syndrome (6.67-10.20 OR); and patients undergoing a laparoscopic operation with sleep apnea (11.53 AOR) or coronary artery disease(12.15 AOR). CONCLUSIONS: Open surgery, BMI, length of surgery,sleep apnea, asthma and hypercholesterolemia all increased the odds of a prolonged LOS. Patients with the greatest odds of long LOS were women with asthma or coronary disease, men with sleep apnea or the metabolic syndrome, and patients undergoing laparoscopic surgery with sleep apnea or coronary artery disease. Patients at high-risk for prolonged hospital stay can be identified before undergoingRYGBP. Surgeons may wish to avoid high-risk patients early in their bariatric surgery experience.

Adolescent↗

PubMed2002

Short-term results of laparoscopic gastric bypass in patients with BMI > or = 60.

BACKGROUND: Laparoscopic Roux-en-Y gastric bypass (LRYGBP) has been shown to be safe and effective. Little information is available about the subgroup of patients with BMI > or = 60. The goal of this study was to evaluate the feasibility and safety of LRYGBP for patients with BMI > or = 60. METHODS: The study consisted of the first 300 attempted LRYGBPs performed by one surgeon (HJS). This population was analyzed as 2 groups of patients: those with BMI < 60 and those with BMI > or = 60. Outcome variables included mortality, complications, conversion, and operative time. RESULTS: Of the first 300 LRYGBP patients, 261 had BMI < 60 and 39 had BMI > or = 60. Age, comorbidity rate, and gender distribution were similar in both BMI groups. Conversion rates were < 3% in both groups. Mean operative time for the BMI > or = 60 group was 156 minutes vs 139 minutes in the lighter group (P = 0.04). Major complications occurred more commonly in the BMI > or = 60 group (10% vs 6%) but this difference was not significant. The types of complications differed between the 2 groups, with infectious complications and gastrointestinal leak occurring more frequently in the heavier group. The mortality rate was higher in the heavier group (5% vs 0.4%, P = 0.055). CONCLUSION: LRYGBP is feasible for patients with BMI > or = 60. Our data suggest that these patients are at a higher risk for GI leak, postoperative infection, and death.

Adult↗