Centralized PI controllers for interacting multivariable processes by synthesis method.

In this article, two methods of designing a centralized control system for multi-input, multi-output (MIMO) processes are presented. Centralized proportional-integral (PI) controllers are designed based on a direct synthesis method. The inverse of the process transfer function matrix in the direct synthesis method is approximated based on the relative gain array concept. The method is further improved by using a relative normalized gain array, and an equivalent transfer function for each element in the process transfer function matrix is derived for the closed-loop control system. The transpose of the effective transfer function is used to approximate the inverse of the process transfer function matrix. The simulation studies demonstrate the effectiveness of this method. The proposed centralized controllers reduce the interactions better than recently reported decentralized controllers do. A centralized controller designed based on a relative normalized gain array (RNGA) gives a better performance than a centralized controller designed based on a relative gain array (RGA).

Comparison of circumferential resection margin clearance criteria with survival after surgery for cancer of esophagus.

BACKGROUND: Circumferential resection margin (CRM) is widely recognized as an important prognostic factor in esophageal cancer. The aim of this study was to evaluate the clinical significance of CRM according to the current criteria of the Royal College of Pathologists (RCP) and the College of American Pathologists (CAP). METHODS: Patients (115) who underwent esophagectomy between 2000 and 2006 were included in this retrospective study. Factors such as neo-adjuvant therapy, site, histological type, size, and lymph node involvement were tested to determine predictability of CRM involvement. Along with these, age, sex, CRM, and adjuvant therapy were analyzed to determine influence on survival. RESULTS: On the basis of CRM, patients were divided into three groups (involved, 0.1-1 mm and >1mm). Size (T) was the only factor strongly predictive of CRM involvement (P < 0.001). Size (T; P = 0.04) and lymph node involvement (N; P = 0.0003) were found to significantly influence overall survival (OS). When patients with CRM (involved and 0.1-1mm) were compared with those with CRM > 1 mm, OS was significantly prolonged in the latter (P = 0.02). CONCLUSION: This study appears to lend credence to the RCP criteria for definition of CRM over the CAP criteria.

Unusual presentation of gastric perforation by foreign body: a case report.

Perforation of the gastrointestinal tract by ingested foreign body is rare. The majority of patients do not recall ingestion of the foreign body, and dietary foreign bodies are most commonly involved. We present an interesting case where the offending foreign body gave rise to a diagnostic dilemma masquerading as a pancreatic mass. A high index of suspicion is indicated especially when dealing with atypical presentation and nonspecific symptoms as highlighted in this case.

The 'modified triple staple' technique: a variant stapling technique for anastomosis after low anterior resection.

INTRODUCTION: Stapled techniques of coloanal anastomosis in anterior resection have gained widespread acceptance over hand anastomosis. We believe a modification of the 'triple staple technique' has ergonomic advantages over existing stapling methods and present our technique and experience here. METHODS: Fifty consecutive patients underwent anterior resection with a concomitant defunctioning ileostomy in 44 (86%) patients. A modified triple staple technique of side to end coloanal anastomosis was performed without the need of a purse string suture on the proximal and the distal segments. RESULTS: There were no major intra-operative complications. 2/50 (4%) clinical leaks and 2/37 (5.4%) radiological leaks were noted. A combined leak rate of 4/50 (8%) was reported. The incidence of anastomotic stricture encountered was 1/50 (2%). CONCLUSION: The modified triple staple technique for side to end anastomosis in anterior resection has ergonomic advantages and comparable safety to the existing techniques of stapling coloanal anastomosis. We believe this technique can be widely adopted as an added alternative to the current techniques of stapled anastomosis after anterior resection.

Set point weighted modified Smith predictor for integrating and double integrating processes with time delay.

A simple method of designing the controllers for a modified form of Smith predictor is proposed for integrating and double integrating processes with time delay. The modified Smith predictor has two controllers, namely, a set point tracking controller and a load disturbance rejection controller for obtaining good set point tracking and load disturbance rejection, respectively. The set point tracking controller is designed using the classical direct synthesis method based on the process model without considering the time delay. The disturbance rejection controller is considered as a proportional-derivative (PD) controller and is designed using optimal gain and phase margin approaches. Set point weighting is considered for reducing undesirable overshoots and settling times in the modified Smith predictor. Guidelines are provided for selection of the desired closed loop tuning parameter in the direct synthesis method and the set point weighting parameter. The method gives significant load disturbance rejection performances. Illustrative examples are considered to show the performances of the proposed method. A significant improvement in control performance is obtained when compared to recently reported methods.

Potential prognostic and therapeutic roles for cytokines in breast cancer (Review).

Cytokines are known to have both stimulatory and inhibitory effects on breast cancer growth depending on their relative concentrations and the presence of other modulating factors in the tumour microenvironment. Certain cytokines appear to prevent an effective immune response being mounted, permitting cancer growth, whereas others promote the immune system's anti-tumour capability. Furthermore, the systemic levels of certain cytokines, e.g. IL-6 and IL-18, independently show promising correlations with disease stage and progression. With advances in methods for delivery of cytokines to a tumour site, the enhanced induction of anti-tumour immunity by targeted cytokine release is becoming a realistic option. Here, we review the role of cytokines in the immune response against breast cancer and assess their potential as prognostic indicators and/or use in immune therapy. A literature search was conducted using Medline, restricted to articles published in the English language, using combinations of the following MeSH terms: cytokines, breast cancer, immunology, immunotherapy and interleukins. Focused searches using keywords relevant to the role of cytokines in breast cancer immunology yielded >200 references.

Endoscopic laser ablation of advanced rectal carcinoma--a DGH experience.

BACKGROUND: Patients with inoperable advanced rectal carcinoma require palliation for local symptoms. Endoscopic Nd-Yag laser ablation is a valid palliative treatment option in patients with advanced rectal carcinoma who are poor operative risks due to coexistent multiple comorbidities. METHODS: All patients who cannot undergo radical surgery due to various factors such as tumour size, poor risk patients, distant metastasis and refusal to undergo surgery were offered palliation with endoscopic Nd-YAG laser ablation. Indications included troublesome bleeding, local recurrence, mucous discharge and impending obstruction. Patients were admitted on the day of treatment, phosphate enema given for bowel preparation and endoscopic ablation done through a flexible sigmoidoscope under intravenous sedation with midazolam. All patients were discharged the next day after overnight observation. Patients were reviewed every 3 months and laser ablation repeated if deemed necessary. RESULTS: Eleven patients (7 males, 4 females; mean age 83.6 years, range 77-90 years) underwent endoscopic laser ablation in a District General Hospital --8 for rectal carcinoma, 2 for rectosigmoid tumour and 1 for recurrent tubulovillous adenoma. The number of treatment episodes varied from 1 to 12 with symptom free interval from 2 to 18 months between treatment episodes. There were 3 failures, one patient required defunctioning colostomy, one patient was referred for radiotherapy due to persistent symptoms and in one patient laser treatment had to be abandoned due to local extent. There were no immediate post-treatment complications, but one patient developed incontinence after 5 episodes which might be attributable to tumour infiltration. DISCUSSION: Endoscopic laser ablation is a practical and feasible alternative to other palliative treatment modalities in the management of this unfortunate category of patients due to low morbidity and mortality, short hospitalization and low complication rates.

Comparison of rigid vs flexible sigmoidoscopy in detection of significant anorectal lesions.

OBJECTIVE: Sigmoidoscopy is an essential tool in colorectal clinics in the detection of anorectal lesions including rectosigmoid adenomas and carcinomas. However, rigid sigmoidoscope (RS) is still more widely used than flexible sigmoidoscope (FS) as the primary investigation, despite the fact that the latter is more comfortable to the patient and has greater diagnostic yield. Hence we wanted to compare the two modalities in terms of diagnostic use for picking up significant anorectal lesions. METHODS: A retrospective review of all patients referred to the colorectal clinic who had undergone both rigid and flexible sigmoidoscopy for investigation of colorectal symptoms in 2001 was done. Findings recorded during rigid and flexible sigmoidoscopy including depth of insertion, site of lesion and complications were analysed. RESULTS: 152 patients underwent both rigid and flexible sigmoidoscopy as part of investigation of colorectal symptoms. Of the 115 (75.6%) declared normal by RS, 39 (33.9%) had significant lesions including 7 polyps and 4 malignant lesions within 20 cm of the anal verge during FS. Of the 31 patients (20.4%) in whom RS was not helpful due to faecal loading, 15 (48.4%) had significant lesions including 4 malignancies and 1 polyp --all within 20 cm of the anal verge during FS. Only 2 polyps and 1 malignant lesion were picked up by both flexible and rigid sigmoidoscopy. There were no complications in both procedures. CONCLUSION: Since flexible sigmoidoscopy is superior to rigid sigmoidoscopy in terms of patient comfort, diagnostic value and ease of doing procedures like biopsy and polypectomy; it can be used as a front line investigation to exclude colorectal pathology in out patient clinics. The utility of rigid sigmoidoscope is in question and in view of obvious shortcomings, may be replaced by flexible sigmoidoscopy, though obvious resource constraints need to be considered.

Radioresistance in carcinoma of the breast.

Radiotherapy plays an important role in the management of breast cancer. Whilst its role in achieving local control following surgery in patients with early stage cancer is well established, there is still unclear evidence to explain the factors governing radioresistance in patients who develop recurrences both in the breast and axilla. Radiotherapy induces damage to the DNA. Various cell cycle damage check points and DNA damage repair pathways have been demonstrated. Ataxia telangiectasia mutant (ATM) kinase, which is a member of phosphatidylinositol-3 kinase (PI-3K) family appears to play a central role in DNA damage check point pathways. Over-expression of Insulin like growth factor-I receptor (IGF-IR), Human Epidermal Growth factor receptors (HERS), Vascular Endothelial growth factor (VEGF) on the cell surface and increased concentration of Epidermal Growth factor in the extracellular fluid have been associated with radioresistance. Specific genes such as p53, BRCA, Bcl-2 and chromosomal characteristics like telomere lengths have also been identified as playing significant roles in radiation responsiveness of a cell. This article reviews the current data on general principles of radiotherapy, the cellular mechanisms that operate in response to radiation damage and various molecular markers, intranuclear and extranuclear which have been demonstrated to influence radiation sensitivity in breast cancer cells.

Gynaecomastia and the plant product "Tribulis terrestris".

Gynaecomastia is the commonest benign breast condition seen in men. It is well recognised that certain drugs that alter the normal sex hormonal profile in the body can induce gynaecomastia. Recently, an increasing use of androgenic-anabolic steroids among young men especially body-builders has increased the incidence of gynaecomastia. We report a case of a young weight-trainer who developed gynaecomastia due to oral intake of a herbal tablet which he used as a steroid alternative for body-building.