Physics and control of wall turbulence for drag reduction Kim, John
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
04/2011, Volume:
369, Issue:
1940
Journal Article
Peer reviewed
Turbulence physics responsible for high skin-friction drag in turbulent boundary layers is first reviewed. A self-sustaining process of near-wall turbulence structures is then discussed from the ...perspective of controlling this process for the purpose of skin-friction drag reduction. After recognizing that key parts of this self-sustaining process are linear, a linear systems approach to boundary-layer control is discussed. It is shown that singular-value decomposition analysis of the linear system allows us to examine different approaches to boundary-layer control without carrying out the expensive nonlinear simulations. Results from the linear analysis are consistent with those observed in full nonlinear simulations, thus demonstrating the validity of the linear analysis. Finally, fundamental performance limit expected of optimal control input is discussed.
Abstract Methods The American Society of Anesthesiologists Physical Status classification system (ASA PS) is a method of characterizing patient operative risk on a scale of 1–5, where 1 is normal ...health and 5 is moribund. Every anesthesiologist is trained in this measure, and it is performed before every procedure in which a patient undergoes anesthesia. We measured the independent predictive value of ASA-PS for complications and mortality in the ACS-NSQIP database by multivariate regression. We conducted analogous regressions after standardizing ASA-PS to control for interprocedural variations in risk in the overall model and sub-analyses by surgical specialty and the most common procedures. Results For 2,297,629 cases (2005–2012; median age 55, min = 16, max>90 90 and above are coded as 90+), at increasing levels of ASA-PS (2–5), odds ratios (OR's) from 2.05 to 63.25 (complications, p < 0.001) and 5.77–2011.92 (mortality, p < 0.001) were observed, with non-overlapping 95% confidence intervals. Standardization of ASA-PS (OR = 1.426 per standard deviation above the mean ASA-PS per procedure, p < .001) and subgroup analyses yielded similar results. Discussion ASA PS was not only found to be associated with increased morbidity and mortality, but independently predictive when controlling for other comorbidities. Even after standardization based on procedure type, increases in ASA predicted significant increases in complication rates for morbidity and mortality post-operatively. Conclusions ASA PS has strong, independent associations with post-operative medical complications and mortality across procedures. This capability, along with its simplicity, makes it a valuable prognostic metric.
Retrospective multivariate analysis of a prospectively collected, multicenter database.
To identify patient characteristics and perioperative risk factors associated with postoperative infectious ...complications after single-level lumbar fusion (SLLF) surgery.
Postoperative infection is a known complication after lumbar fusion. Risk factors for infectious complications after lumbar fusion have not been investigated using select set of SLLF procedures.
Patients who underwent SLLF between 2006 and 2011 were identified from the American College of Surgeons National Surgical Quality Improvement Program database. Multivariate logistic regression analyses were performed to identify pre- and intraoperative risk factors associated with postoperative infection.
A total of 3353 patients were analyzed in this study. Overall, 173 (5.2%) patients experienced a postoperative infection, including 86 (2.6%) surgical site infections (SSIs) and 111 (3.3%) non-SSI infectious complications (pneumonia, urinary tract infection, sepsis/septic shock). Twenty-four (0.7%) patients experienced both SSI and non-SSI infectious complications. Postoperative SSI were associated with obesity (odds ratio OR, 1.628; 95% confidence interval CI, 1.042-2.544), American Society of Anesthesiologists class more than 2 (OR, 2.078; 95% CI, 1.309-3.299), and operative time more than 6 hours (OR, 2.573; 95% CI, 1.310-5.056). Risk factors for non-SSI infectious complications included age (60-69 yr; OR, 3.279; 95% CI, 1.541-6.980; and ≥70 yr; OR, 3.348; 95% CI, 1.519-7.378), female sex (OR, 1.791; 95% CI, 1.183-2.711), creatinine more than 1.5 mg/dL (OR, 2.400; 95% CI, 1.138-5.062), American Society of Anesthesiologists class more than 2 (OR, 1.835; 95% CI, 1.177-2.860), and operative time more than 6 hours (OR, 3.563; 95% CI, 2.082-6.097).
Across a wide study population, we identified that obesity, advanced American Society of Anesthesiologists classification, and longer operative time were predictive of postoperative SSI. We also demonstrated that increased age, female sex, serum creatinine more than 1.5 mg/dL, and prolonged operative duration are associated with non-SSI infectious complications after SLLF. Continued efforts to elucidate and optimize perioperative risk factors are warranted to improve outcomes in patients requiring spinal fusion.
3.
MicroRNAs (miRNAs) are major drivers of cell fate specification and differentiation. The post-transcriptional regulation of key molecular factors by microRNAs contributes to the progression of ...embryonic and postembryonic development in several organisms. Following the discovery of lin-4 and let-7 in Caenorhabditis elegans and bantam microRNAs in Drosophila melanogaster, microRNAs have emerged as orchestrators of cellular differentiation and developmental timing. Spatiotemporal control of microRNAs and associated protein machinery can modulate microRNA activity. Additionally, adaptive modulation of microRNA expression and function in response to changing environmental conditions ensures that robust cell fate specification during development is maintained. Herein, we review the role of microRNAs in the regulation of differentiation during development.
There is a paucity of data assessing the effect of increased surgical duration on the incidence of venous thromboembolism (VTE).
To examine the association between surgical duration and the incidence ...of VTE.
Retrospective cohort of 1,432,855 patients undergoing surgery under general anesthesia at 315 US hospitals participating in the American College of Surgeons National Surgical Quality Improvement Program from 2005 to 2011.
Duration of surgery.
The rates of deep vein thrombosis (DVT), pulmonary embolism (PE), and VTE within 30 days of the index operation. Surgical duration was standardized across Current Procedural Terminology codes using a z score. Outcomes were compared across quintiles of the z score. Multiple logistic regression models were developed to examine the association while adjusting for patient demographics, clinical characteristics, and comorbidities.
The overall VTE rate was 0.96% (n = 13,809); the rates of DVT and PE were 0.71% (n = 10,198) and 0.33% (n = 4772), respectively. The association between surgical duration and VTE increased in a stepwise fashion. Compared with a procedure of average duration, patients undergoing the longest procedures experienced a 1.27-fold (95% CI, 1.21-1.34; adjusted risk difference ARD, 0.23%) increase in the odds of developing a VTE; the shortest procedures demonstrated an odds ratio of 0.86 (95% CI, 0.83-0.88; ARD, -0.12%). The robustness of these results was substantiated with several sensitivity analyses attempting to minimize the effect of outliers, concurrent complications, procedural differences, and unmeasured confounding variables.
Among patients undergoing surgery, an increase in surgical duration was directly associated with an increase in the risk for VTE. These findings may help inform preoperative and postoperative decision making related to surgery.
Human acellular dermal matrix has become an increasingly used adjunct to traditional submuscular tissue expander/implant breast reconstruction, but there is no strong consensus regarding complication ...outcomes. This study stratified outcomes based on a meta-analysis of complications.
A query of the MEDLINE database for articles on human acellular dermal matrix and submuscular tissue expander breast reconstruction yielded 901 citations. Two levels of screening identified 48 relevant studies. The DerSimonian and Laird random-effects model was used to perform the meta-analysis. Risk ratios and pooled complication rates were calculated for each outcome of interest.
Nineteen studies reporting human acellular dermal matrix (n = 2037) and 35 reporting submuscular outcomes (n = 12,847) were used to estimate complication rates. Rates were generally higher in acellular dermis patients: total complications, 15.4 versus 14.0 percent; seroma, 4.8 versus 3.5 percent; infection, 5.3 versus 4.7 percent; and flap necrosis, 6.9 versus 4.9 percent. Six studies reporting both acellular dermis and submuscular outcomes were used to estimate relative risks. There was an increased risk of total complications (relative risk, 2.05; 95 percent CI, 1.55 to 2.70), seroma (relative risk, 2.73; 95 percent CI, 1.67 to 4.46), infection (relative risk, 2.47; 95 percent CI, 1.71 to 3.57), and reconstructive failure (relative risk, 2.80; 95 percent CI, 1.76 to 4.45) in acellular dermis patients.
The meta-analysis suggests that the use of human acellular dermal matrix increases complication rates vis-à-vis submuscular expander/implant reconstruction. This must be weighed against its reported advantages in enhancing cosmesis and ameliorating contracture.
: Therapeutic, III.
Operative procedural training is a key component of orthopaedic surgery residency. The influence of intraoperative resident participation on the outcomes of surgery has not been studied extensively ...using large, population-based databases.
We identified 30,628 patients who underwent orthopaedic procedures from the 2011 American College of Surgeons National Surgical Quality Improvement Program. Outcomes as measured by perioperative complications, readmission rates, and mortality within thirty days were compared for cases with and without intraoperative resident involvement.
Logistic regression with propensity score analysis revealed that intraoperative resident participation was associated with decreased rates of overall complications (odds ratio, 0.717 95% confidence interval, 0.657 to 0.782), medical complications (odds ratio, 0.723 95% confidence interval, 0.661 to 0.790), and mortality (odds ratio, 0.638 95% confidence interval, 0.427 to 0.951). Resident presence in the operating room was not predictive of wound complications (odds ratio, 0.831 95% confidence interval, 0.656 to 1.053), readmission (odds ratio, 0.962 95% confidence interval, 0.830 to 1.116), or reoperation (odds ratio, 0.938 95% confidence interval, 0.758 to 1.161). A second analysis by propensity score stratification into quintiles grouped by similar probability of intraoperative resident presence showed resident involvement to correlate with decreased rates of overall and medical complications in three quintiles, but increased rates of overall and medical complications in one quintile. All other outcomes were equivalent across quintiles.
Orthopaedic resident involvement during surgical procedures is associated with lower risk of perioperative complications and mortality in the National Surgical Quality Improvement Program database. The results support resident participation in the operative care of orthopaedic patients.
Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
Cutaneous squamous cell carcinoma (cSCC) is the second most common form of human cancer and has an increasing annual incidence. Although most cSCC is cured with office-based therapy, advanced cSCC ...poses a significant risk for morbidity, impact on quality of life, and death. This document provides evidence-based recommendations for the management of patients with cSCC. Topics addressed include biopsy techniques and histopathologic assessment, tumor staging, surgical and nonsurgical management, follow-up and prevention of recurrence, and management of advanced disease. The primary focus of these recommendations is on evaluation and management of primary cSCC and localized disease, but where relevant, applicability to recurrent cSCC is noted, as is general information on the management of patients with metastatic disease.
Basal cell carcinoma (BCC) is the most common form of human cancer, with a continually increasing annual incidence in the United States. When diagnosed early, the majority of BCCs are readily treated ...with office-based therapy, which is highly curative. In these evidence-based guidelines of care, we provide recommendations for the management of patients with BCC, as well as an in-depth review of the best available literature in support of these recommendations. We discuss biopsy techniques for a clinically suspicious lesion and offer recommendations for the histopathologic interpretation of BCC. In the absence of a formal staging system, the best available stratification based on risk for recurrence is reviewed. With regard to treatment, we provide recommendations on treatment modalities along a broad therapeutic spectrum, ranging from topical agents and superficially destructive modalities to surgical techniques and systemic therapy. Finally, we review the available literature and provide recommendations on prevention and the most appropriate follow-up for patients in whom BCC has been diagnosed.
Multicenter retrospective cohort study.
To estimate the impact of increasing surgical duration on outcomes after single-level lumbar fusion.
Lumbar fusion is a widely used practice for the treatment ...of disability and chronic low back pain. Longer operative duration is shown to correlate with increased morbidity and mortality in various surgical disciplines, but no large-scale study has been performed to validate this relationship in lumbar spine surgery.
The American College of Surgeons National Surgical Quality Improvement Program was retrospectively reviewed to identify all patients who underwent lumbar fusion procedures during 2006 to 2011. Thirty-day morbidity and mortality rates were reported on the basis of operative time, whereas multivariate logistic regression model was used to examine operative duration as an independent risk factor for outcomes.
A total of 4588 patients were included in the analysis. The mean operative duration for all patients was 197 ± 105 minutes. Our multivariate risk-adjusted regression models demonstrated that increasing operative time was associated with step-wise increase in risk for overall complications (odds ratio OR, 2.09-5.73), medical complications (OR, 2.18-6.21), surgical complications (OR, 1.65-2.90), superficial surgical site infection (OR, 2.65-3.97), and postoperative transfusions (OR, 3.25-12.19). Operative duration of 5 hours or more was also associated with increased risk of reoperation (OR, 2.17), organ/space surgical site infection (OR, 9.72), sepsis/septic shock (OR, 4.41), wound dehiscence (OR, 10.98), and deep vein thrombosis (OR, 17.22).
Our data suggest that increasing operative duration is associated with a wide array of complications. Operative duration is, therefore, an important quality metric in the performance of lumbar fusion. Strategies to reduce operative time and further research to identify risk factors that are associated with longer surgical duration are needed for improved patient outcomes.
3.
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