Biomedical subjects
Publications and source records attributed to P Eng.
Tissue hypoxia is an important cause for the development of multisystem organ failure in the critically ill. Achieving adequate haemodynamic support of oxygen demand is the mainstay of treatment in these patients. Controversies regarding therapeutic end-points do exist but in general maintaining oxygen delivery by ensuring adequate cardiac output, oxygen saturation and haemoglobin is important in the critically ill.
Chylothorax is a relatively uncommon condition. We report a case of a 53-year-old Chinese man with chylothorax who presented with cough, breathlessness, loss of weight and generalised lymphadenopathy. He was initially diagnosed as having tuberculosis based on histology and cultures of the cervical lymph node. However, immunophenotyping of the pleural fluid by flow cytometry showed the presence of a monoclonal B cell population with Kappa light chain expression suggesting an underlying lymphoproliferative disorder. A repeat lymph node biopsy showed malignant lymphoma (follicular small cleaved type). In spite of aggressive measures which included bilateral tube thoracostomy drainage, a low fat diet, medium chain triglyceride diet, total parenteral nutrition, chemotherapy and mediastinal irradiation, his chylothorax persisted. Hence, we report a patient with persistent chylothorax and generalised lymphadenopathy who was subsequently diagnosed to have concurrent tuberculosis and malignant lymphoma. The literature on chylothorax is reviewed.
Vocal cord dysfunction is an uncommon condition characterised by adduction of vocal cords that can masquerade as or coexists with bronchial asthma. The glottic dysfunction is due to a functional (non-organic) cause. If unrecognised, incorrect diagnosis may result in patients being unnecessarily treated as refractory or severe asthma with high doses of corticosteroid. This may result in unwarranted steroid toxicity. Clues that should raise clinical suspicion to the diagnosis of vocal cord dysfunction include lack of response to bronchodilators, poor reproducibility of spirometric indices due to inconsistent effort and truncation of the inspiratory limb of the flow-volume loop. Definitive diagnosis is made by direct visualisation of the vocal cords during an attack. We report two patients with vocal cord dysfunction and review the literature on this disorder.
Ventilator-associated pneumonia (VAP) is a common problem in the intensive care unit (ICU). It is associated with a distinct spectrum of pathogens and its pathogenesis involves microaspiration of oropharyngeal organisms. Clinical and radiographic criteria have been shown to be unreliable in diagnosing VAP, and it remains a challenge for intensivists to utilise the array of diagnostic procedures at their disposal to optimise diagnostic accuracy (improve specificity) and guide in therapy. These procedures and guided antibiotic therapy may not always improve the outcome and therefore simple preventive measures should be employed to reduce the incidence.
The ideal position of the endotracheal tube (ETT) within the trachea is 5 +/- 2 cm from the carina with the head and neck in neutral position (Goodman's criteria). We assessed the possibility of achieving ideal placement of ETTs in our population by positioning them at reference marks of 23 cm in men and 21 cm in women. From January 1995 to April 1995, 105 intubated patients in the Medical Intensive Care Unit, Singapore General Hospital were studied. The mean distance of the ETT tip from the carina was 4.02 cm +/- 3.90. The ETT tip was < 3 cm from the carina in 30 cases (28.6%) with one case resulting in endobronchial intubation. These 30 patients were significantly shorter in height when compared to the rest of the study population (P = 0.01). Five cases (4.8%) had ETT tip > 7 cm from the carina. Adopting the above-mentioned reference marks did not result in ideal positioning of ETTs in a significant proportion of cases (33.4%). We postulate that this is because our Asian population is generally shorter than those in previous studies which had achieved ideal ETT positioning using similar reference marks.
The main advantage of noninvasive ventilation over conventional mechanical ventilation is in the avoidance of endotracheal intubation and its related complications. Currently, the role of noninvasive ventilation in the management of patients with acute respiratory failure is still not firmly established. We conducted a prospective study to evaluate the efficacy of nasal positive pressure ventilation in patients with acute respiratory failure. Thirty-three consecutive patients with acute failure in whom intubation and mechanical ventilation were strongly considered were included in the study. They received ventilatory support by means of BiPAP ventilatory support system and nasal mask. Physical findings and laboratory measurements were documented before and at specific intervals after initiation of support. Eighty per cent (24/30) of patients were successfully supported. Successfully supported patients tolerated the device with improved gas exchange, hence avoiding endotracheal intubation. The mean duration of support was 19.2 hours. There were major associated complications, e.g. gastric distention or aspiration.
The goal of this chapter is to demonstrate the role of integrated biomechanical analyses in complex movements such as gait in alerting researchers of the goals and synergies of the CNS. Because of the large number of segments involved and the potential for the CNS to take advantage of inter-limb coupling it is only through appropriate biomechanical analyses that such collaboration can be identified. Examples from normal, perturbed, elderly and pathological gait are presented to demonstrate the principles of total limb and total body analysis to pinpoint the goals of the CNS and to identify total limb or body synergies and adaptations in the elderly and in gait pathologies. Such findings reinforce the generalizations made many years ago by Bernstein [2] when he postulated several simplifying principles of CNS control. Also, evident from these analyses are the precision and accuracy of biomechanical variables that make these measures particularly sensitive to small changes within an individual or across a population group.
1. INTRODUCTION TO DEPARTMENTAL PACS. Full or partial Departmental PACS is generally taken to mean an image management system focused on serving the needs of a specific modality or modality application. It will provide a modality specific means of image acquisition, specialized redisplay of images, distribution, and local long term storage of images. A Departmental PACS can be considered in isolation or as a component in a distributed Radiology PACS which consists of one or more departmental work groups on a back bone, potentially with shared resources. 2. DEPARTMENTAL PACS Issues Implementation of a Departmental PACS requires an in-depth knowledge of departmental clinical practice and work flow in all affected areas in the department, including patient intake, image collection, data routing, retrieval of previous image data, reporting, and long term data management and storage. Optimization of modality specific image display systems requires significant involvement from representative physician users. System architectures and user interfaces must be flexible enough to support the span of variation in clinical practice encountered in the site. A departmental PACS should offer a variety of "open" communications interfaces, both local and wide area, recognizing that outreach efforts are often driven by specific imaging departments. Interfaces to other departmental PAC systems and other information systems must be considered in order to facilitate institutions developing "Best of Breed" PACS systems. As hospitals move toward the integrated electronic medical record, means need to exist for a client process launched from a physician desktop to acquire images and/or reports from a departmental system. At minimum, HIS/RIS interfaces need to be considered to minimize re-keying of data and reduce data entry errors. 3. DESIGN OBJECTIVES FOR ALI ULTRAPACS. The key objectives were to design a product which could function either as a free standing PACS or as a departmental subnet on a larger PACS backbone, one which could function in a local or mixed local and wide area environment and one which could provide a cost effective implementation based on currently available technologies. 4. IMPLEMENTATION STRATEGIES. In order to attain the product design objectives, ALI made the following critical implementation decisions: 1) to build the UltraPACS application as a suite of separable UNIX processes based on a message passing client server model; 2) to host the application and operating system on a Digital Equipment Corporation PC using an Intel microprocessor because of the competition and broad variety of suppliers in the PC arena; and 3) to use NEXTSTEP as the UNIX variant of choice because of NEXTSTEPUs strong object orientation, superb development tools, and the excellent integration between the Graphical User Interface level and the underlying operating system layers. 5. CONCLUSION. ALI is convinced that a departmental approach to PACS offers significant advantages over monolithic PACS in several key areas including: optimization for modality specific clinical practice and workflow, cost effectiveness, the potential for an institution to implement PACS in a stepwise fashion, starting with the department with the potential for the greatest savings, and the capability for an institution to build a "best of breed" solution for large scale PACS.
Major changes have occurred in the epidemiology of community-acquired pneumonia recently. The emergence of new pathogens emphasises the need for continued vigilance in the diagnosis of pneumonia while changes in the microorganism or in the host have resulted in exciting new aspects of several old pathogens. Clinical and radiologic signs are unreliable in predicting the infecting organisms. Thus initial therapy is nearly always empiric. This approach often requires good clinical judgement and a knowledge of local epidemiological patterns in choosing an appropriate regimen. State-of-the-art invasive diagnostic procedures are usually reserved for pneumoniae that fail to resolve with initial treatment. Non-specific measures like stabilisation of underlying medical conditions, adequate nutrition and cessation of smoking or alcohol may help prevent the development of community-acquired pneumonia. On a larger scale, influenza and pneumococcal vaccinations are cost-effective preventive measures.
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High-frequency ultrasound biomicroscopy is a new method of examining subsurface anterior segment structures of the eye at microscopic resolution. The sclera has a high internal reflectivity and can be differentiated from the cornea, and overlying and underlying tissue. Using this modality, we examined 18 patients with various manifestations of scleral disease. Localized anterior staphyloma could be differentiated from other causes of a black spot on the scleral surface. Episcleral thickening could be differentiated from involvement of the sclera itself. Different patterns of scleral involvement could be imaged including diffuse low-reflective mottling, low-reflective nodules extending into the scleral substance, and scleral thinning. Scleral thinning could be assessed and quantified. Underlying changes in the vitreous could be detected. Ultrasound biomicroscopy was a useful adjunct to clinical examination in the assessment of anterior scleral disease.
UNLABELLED: Continuous warm blood cardioplegia has recently been recommended as an alternative to multidose cold blood cardioplegia for myocardial protection during coronary bypass operations. Cardioplegia may have to be interrupted in order to provide a bloodless operating field during coronary anastomosis. To determine the effects of ischemia at normothermia on myocardial oxygen consumption and lactate production we randomized 17 dogs to receive either warm blood cardioplegia (37 degrees C) or cold blood cardioplegia combined with systemic and topical cooling. After initiating arrest, cardioplegia was interrupted for periods of 1, 2, 3, 4, 5, 6, and 10 min. Myocardial oxygen debt occurred after 3.5 min of ischemia in the 9 animals receiving warm blood cardioplegia. In contrast, myocardial oxygen consumption never exceeded oxygen availability during cold blood cardioplegia (P less than 0.001). Lactate production increased linearly in both groups but was much greater in those animals receiving warm blood cardioplegia (P less than 0.001). Spontaneous electromechanical activity was much more common during warm blood cardioplegia which required frequent infusions of cardioplegia to maintain cardiac arrest (P less than 0.0003). CONCLUSIONS: (1) Oxygen debt occurred after 3.5 min of warm ischemia; (2) spontaneous electromechanical activity is more common during warm heart protection which necessitates the use of larger volumes of cardioplegia to maintain cardiac arrest.
Respiratory infections occur commonly in patients with advanced human immunodeficiency virus (HIV) infection. Prompt accurate diagnosis is essential as many of the various available therapies have significant toxicities. We describe a patient previously diagnosed with the acquired immunodeficiency syndrome (AIDS) who was found to have cytomegalovirus (CMV) pneumonitis on bronchoscopy. His pneumonitis responded to treatment with the nucleoside analogue ganciclovir. Our patient is the first documented CMV pneumonitis in the Singapore HIV seropositive population.
Tuberculosis is a common cause of cavitating pneumonia in Singapore. In patients with the human immunodeficiency virus (HIV), cavitary pneumonias mimicking tuberculosis can mislead the clinician, delaying diagnosis, resulting in increased morbidity. We describe a HIV seropositive patient with cavitating pneumonia in whom the diagnosis of Pneumocystis carinii pneumonia (PCP) was ultimately established only on bronchoscopy.
UNLABELLED: The effects of high-volume cardioplegia on the presence of small-amplitude electrical activity during cardioplegia arrest were investigated in 19 mongrel dogs. The animals were randomly assigned to receive either high-volume crystalloid cardioplegia (HV-plege) or crystalloid cardioplegia guided by continuous electrical monitoring (V-plege). Cardiac index, left ventricular stroke work index dp/dt, and myocardial oxygen consumption were measured before bypass and following 90 min ischemia and 45 min reperfusion. Biopsies were taken for measurement of adenosine triphosphate (ATP) and examination of myocardial ultrastructure. Nine animals received HV-plege, while the remaining 10 animals received cardioplegia guided by voltage criteria. Small-amplitude electrical potentials were recorded within 10-15 min after the infusion of cardioplegia in all animals receiving cardioplegia guided by voltage criteria. Electrical activity, however, was immediately abolished by reinfusion of cardioplegia. HV-plege reduced the incidence of small-amplitude electrical activity during cardioplegia arrest but did not prevent electrical activity. Left ventricular function and myocardial ultrastructure were better preserved when cardioplegia was guided by electrical monitoring. ATP decreased similarly in both groups following cardioplegic arrest, but myocardial oxygen consumption was significantly higher following the arrest in the V-plege group. CONCLUSIONS: HV-plege does not prevent small-amplitude electrical activity and may have adverse effects on myocardial metabolic and functional recovery.
Pneumocystis carinii pneumonia is extremely common in patients with the acquired immunodeficiency syndrome (AIDS). Diagnostic techniques vary between different institutions depending on availability of expertise. We have limited experience in the workup and evaluation of patients with human immunodeficiency virus infection because we have at present only 56 reported cases of HIV positive individuals. We report here two cases where Pneumocystis carinii pneumonia was the index illness and the diagnosis was confirmed by bronchoscopy.
Through collaboration of surgeons, pathologists and bioengineers at five centers in Canada and France, this study analyzed the late pathology and structural changes in 73 expanded PTFE arterial prostheses harvested from patients at autopsies and reoperations. The degree of tissue encapsulation increased with the duration of implantation but was reduced by the presence of infection. In several cases, the fibrous tissue penetrated the wall of the prosthesis and partitioned off the thin outer layer, thus disrupting the delicate microporous structure of the wall. The presence of aneurysms was observed in models that had no external reinforcing layer and among grafts that apparently suffered from surgical trauma. Wrinkling of grafts was noted at areas of flexion and was often associated with thickening of the external capsule and reduced luminal diameters. Endothelialization was found within only a few millimeters of the anastomoses. The luminal surfaces were generally not well healed. The PTFE structure was usually readily visible under a thin covering of loosely adhering thrombotic deposits. Bacteria were observed in 46% of the cases, even though only 29% were considered clinically infected. The incidence of lipid or cholesterol deposits was high. Avoiding iatrogenic trauma to the external wall of the prosthesis during implantation is important. Those features where design improvements are required to provide longer term structural integrity and dimensional stability in future models of expanded PTFE prostheses should be identified.
One of the early diamond crimped knitted polyester (Dacron) grafts was surgically excised after implantation for 25 years in the aorto-biiliac position because of false aneurysm formation at the three anastomotic sites. The sutures were no longer visible. While the areas around the false aneurysm were poorly incorporated, the graft limbs were well encapsulated with some endothelial-like cells on the luminal surface. The integrity of the graft was well preserved despite mild fraying and the disruption of one stitch.