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Biomedical subjects

R C Chan

Publications and source records attributed to R C Chan.

At least 109 records · Page 6Linked to original sources
PubMed1984

Adherence of cervical, vaginal and distal urethral normal microbial flora to human uroepithelial cells and the inhibition of adherence of gram-negative uropathogens by competitive exclusion.

The adherence of the normal flora to human uroepithelial cells was examined using scanning and transmission electron microscopy and an in vitro adhesion assay. The normal flora were isolated from human cervical, vaginal and distal urethral surfaces. Human uroepithelial cells were obtained from healthy females (controls) and from female patients with recurrent urinary tract infection. The results indicate that: 1) there was no significant difference between the mean adherence of the normal flora to the uroepithelial cells from controls or patients, but there were quantitative differences between different bacterial species of the normal flora attaching to uroepithelial cells; 2) bacterial species isolated from the distal urethral and vaginal surfaces attached in larger numbers to uroepithelial cells from controls than from patients at day 10 of the menstrual cycle (peak value of adherence); 3) the adherence patterns of the cervical and vaginal microbial flora were bicyclic and appeared to be related to the human menstrual cycle; 4) complete or partial inhibition of adherence of several Gram-negative uropathogens was achieved by preincubating the uroepithelial cells with several bacterial species of the normal flora. Results from this study suggest that the normal flora of the urinary tract may play an important protective role against attachment of uropathogens to the surfaces of uroepithelial cells, and that the blocking capacity of these organisms may vary over the menstrual cycle.

Cervix Uteri↗
PubMed1984

Abnormal response of tumor vasculature to vasoactive drugs.

The effects of the vasoconstrictor phenylephrine and the vasodilator hydralazine on blood flow to tumor were studied and compared to those on blood flow to normal tissues in vivo. Regional blood flow and cardiac output were measured with the use of radioactive microspheres in 150- to 250-g inbred Harlan F344 rats bearing subcutaneous nodules of two types of transplantable carcinoma ("hard" and "soft") with microscopically different vascular patterns. Three groups of rats were treated with hydralazine, saline, or phenylephrine, and regional blood flow was determined at the time of maximum blood pressure response. Results were correlated with quantitative morphometric analysis of arteriolar and capillary wall thickness in tumor and normal tissue. Phenylephrine decreased and hydralazine increased normal tissue perfusion as indicated by cardiac output. Tumor blood flow remained low and was not significantly influenced by drug treatment, except for the phenylephrine effect on hard tumors. Histologic study of tumor vessel walls revealed an absence of smooth muscle capable of responding to the vasoactive drugs by constriction or dilation. Evidently, by their selective action on normal vessels, vasoactive drugs can change the ratio of tumor:normal tissue perfusion. In particular, the increase of normal tissue: tumor blood flow by vasodilator drugs may enhance the selectivity of local heat therapy.

Animals↗
PubMed1984

Microbial colonization of human ileal conduits.

Morphological and microbiological techniques were used to locate and identify the microorganisms that colonized the human ileal conduits in 17 different patients from 5 days after surgery up to as many as 16 years of service as a urine conduit. The ecological sequence of this colonization assumes some practical importance because the ascending growth of pathogenic organisms in this essentially open, unvalved urinary tract diversion system leads to the development of life-threatening pyelonephritis. Extensive examination of the microvillus surfaces of the ilea of five accident victims by both transmission and scanning electron microscopy showed that these tissue surfaces were not colonized by bacteria, even in the absence of prophylactic antibiotic therapy, and that these surfaces were not occupied by adherent microorganisms after several years of service as a urine conduit, even when the skin surface stoma and the conduit contents were heavily colonized by bacteria and yeasts. During the initial period (10 days) of postoperative antibiotic therapy, the mucus and urine within the conduit were largely colonized by yeasts. A mixed population of yeasts and gram-positive cocci subsequently developed in the conduit itself, and gram-positive cocci were seen to be avidly adherent to epidermal cells at the stoma. As antibiotic protection was gradually withdrawn, gram-negative organisms became a part of the mixed microbial flora of the conduit contents, and some of the potentially pathogenic organisms of this group (e.g., Escherichia spp., Proteus spp., Pseudomonas spp., etc.) were isolated from patients with pyelonephritis that appeared to come from the ileal conduit.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗
PubMed1984

Ischemic necrosis of the scalp after preoperative embolization of meningeal tumors.

The authors report two patients who suffered ischemic necrosis of their scalps after preoperative therapeutic embolic occlusion of the external carotid artery and its terminal branches for highly vascular meningeal tumors. Local anesthesia, selective catheterization of the external carotid artery, and radiopaque polyvinyl alcohol and Gelfoam as embolic agents were used. The various complications of external carotid artery embolization are reviewed. The importance of preserving normal branches of the external carotid artery (especially the superficial temporal artery) during embolization and of careful design of the scalp flap to avoid ischemic necrosis is emphasized.

Adult↗
PubMed1984

Morbidity, mortality, and quality of life following surgery for intracranial meningiomas. A retrospective study in 257 cases.

The authors report 257 patients who underwent 338 craniotomies for the removal of meningiomas. The average duration of observed survival was 9.0 years, while that with acceptable quality of life was 8.3 years. Multiple factors including the size and location of tumors, the degree of tumor excision, the histological features, and the preoperative condition of the patients are important in both duration of survival and quality of life following surgery for intracranial meningiomas. Computerized tomography permits early diagnosis and is invaluable in follow-up assessment. It allows for recognition of small recurrent tumors, and offers a better opportunity for complete removal and, subsequently, a longer duration of reasonable survival. Radiation therapy may prolong survival time in patients with malignant meningiomas, but it fails to delay further tumor recurrences following its delivery to patients with recurrent tumors. There are multiple predisposing factors responsible for the development of postoperative seizures. These include tumor recurrence involving highly functional anatomical areas of the brain, history of preoperative seizures, and intraoperative factors such as excessive brain retraction and the sacrifice of major draining or bridging veins. Intraoperative complications may be decreased by using osmotic diuretics and subarachnoid drains, meticulous dissection, and with the increased awareness and preservation of the important venous structures.

Adult↗
PubMed1984

Delayed onset of Lhermitte's sign following head and/or neck injuries. Report of four cases.

The authors report four patients who suffered the delayed onset of Lhermitte's sign following head and/or neck trauma with no significant neurological deficits. The average onset from the time of the injury was 2 1/2 months. In all patients, there was a full range of movement of the cervical spine with no tenderness and no neurological deficits. Myelography was performed in three of the four patients and was normal. The duration of Lhermitte's sign ranged from 4 months to 1 year (mean 8 months). Complete recovery occurred in all cases. The pathogenesis, differential diagnosis, and management of patients with Lhermitte's sign are discussed.

Adult↗
PubMed1984

The role of the prostacyclin-thromboxane system in cerebral vasospasm following induced subarachnoid hemorrhage in the rabbit.

Subarachnoid hemorrhage (SAH) was induced in 50 rabbits by injecting 1.25 cc/kg of autologous, well heparinized, fresh arterial blood into the cisterna magna, followed by suspending the animals in a head-down position at 30 degrees for 15 minutes. The animals were evenly divided into five groups: a control group, or groups receiving post-SAH prostacyclin (PGI2), carbacyclin, thromboxane A2 (TXA2) synthetase inhibitor (OKY-1581), or nutralipid. Radiographic vertebrobasilar arterial spasm was demonstrated on the 3rd day post-SAH in the control animals. This was decreased in the prostacyclin and the carbacyclin groups and was absent in the OKY-1581 and the nutralipid groups. Cerebral blood flow (CBF) measurements on the 4th day post-SAH using the xenon-133 technique failed to reveal any significant difference between the prostacyclin, the carbacyclin, and the control groups, but flows in the nutralipid and the OKY-1581 groups were significantly higher. There was a good correlation between the clinical status and the CBF. Intracytoplasmic vacuolation and detachment of the vascular endothelium, seen ultrastructurally, may account for the impaired synthesis of prostacyclin. Exogenous prostacyclin and carbacyclin decreased vasospasm but failed to improve cerebral perfusion. OKY-1581 blocked the synthesis of the potent vasoconstrictor, TXA2, which is not only formed during platelet aggregation but also induces platelet aggregation. Nutralipid contains linolenic acid, a precursor of eicosapentaenoic acid (EPA), which is more potent in inhibiting platelet aggregation and in blocking TXA2 production. The various fatty acid constituents of nutralipid bind to albumin and thereby shorten the half-life of TXA2.

Acrylates↗
PubMed1983

Third ventricular colloid cysts presenting with acute neurological deterioration.

Colloid cysts may be found in any part of the third ventricle. The authors report that four out of 12 patients with colloid cysts of the third ventricle suffered acute neurological deterioration, and unilateral ventriculostomy resulted in dramatic recovery in two patients. Unilateral ventriculostomy followed by clinical assessment and computed tomographic scanning is an acceptable approach in emergency situations; computed tomographic scanning allows early detection of third ventricular colloid cysts. Ventriculoperitoneal shunting provides a laternative measure to surgical removal of the cyst. Definitive management soon after diagnosis and before acute neurological deterioration is recommended. The cases presenting with sudden death in the literature are reviewed.

Acute Disease↗
PubMed1983

Simple methods for determining the accuracy of tumor blood flow measurements using radioactive microspheres in rats.

Two simple methods are presented which allow positive identification of the accuracy and precision of the microsphere technique and a quick verification of sphere entrapment in tumor vessels. A known flow of Ringer's solution from a motor-driven syringe is perfused through the rat's isolated systemic circulation from left ventricle to right atrium and collected in a funnel. Using this preparation, total blood flow in rats measured with radioactive microspheres injected into the left ventricle was 97% of actual flow. The coefficient of variation (standard deviation/mean) of the microsphere measurements was 0.22. In the same preparation, nonentrapment of microspheres in subcutaneous tumor nodules grown on a hind limb could be measured from the difference in counts collected in venous effluent before and after placement of a tourniquet proximal to the tumor. For example, in two types of transplantable carcinoma, we found nonentrapment of less than 0.1% of the injected microspheres. Such a shunt would correspond to less than 10% of microspheres entering a typical tumor nodule and, in turn, less than 10% underestimation of true flow to the tumor. These two techniques may be helpful to other investigators in testing the accuracy of microsphere methods in various small animal tumor models.

Animals↗
PubMed1983

Adherence of gram-negative uropathogens to human uroepithelial cells.

The adherence of several gram-negative uropathogens to human uroepithelial cells was examined with scanning and transmission electron microscopy, and in vitro adhesion assays. The bacteria studied demonstrated different extracellular structures: fimbria and glycocalyx. Human uroepithelial cells were obtained from a bladder tumor cell line (T-24) and from different groups of patients, including those with no history of urinary tract infection (controls), recurrent urinary tract infection, acute cystitis and bladder tumors before and after bacillus Calmette-Guerin therapy. Results from these comparative studies showed that bacteria with extracellular structures adhered better than those bacteria without extracellular structures. It also was shown that uroepithelial cells obtained from patients with recurrent urinary tract infection and with acute cystitis were more susceptible to bacterial adherence than the uroepithelial cells of the controls (there were significant increases of 2 to 5-fold in mean adherence in the former 2 groups, p equals 0.015 and 0.002). There was no significant difference in bacterial adherence between the T-24 cells and the bladder tumor cells before bacillus Calmette-Guerin treatment. However, in both groups after treatment with bacillus Calmette-Guerin the mean adherence increased 2 to 4-fold (p equals 3 times 10(-5)). A survey of 29 bladder tumor patients also showed a 5-fold increase in the incidence of acquired urinary tract infection after bacillus Calmette-Guerin therapy. These results reveal a correlation between bacterial adherence and urinary tract infection, and suggest that bacterial adherence to uroepithelial cells depends upon the bacterial extracellular structures and the source of the uroepithelial cells.

BCG Vaccine↗
PubMed1983

The influence of growth media on the morphology and in vitro adherence characteristics of gram-negative urinary pathogens.

We studied the adherence of 3 groups of gram-negative urinary pathogens, grown in different culture media, to human uroepithelial cells obtained from healthy females (controls) and from female patients with recurrent urinary tract infection, using an in vitro adhesion assay and electron microscopy. Morphologic examination and mannose sensitivity testing of the uropathogens grown in urine showed that they expressed extracellular structures similar to those found in infected urine in vivo. However, the production of various bacterial extracellular structures responsible for adhesion can be enhanced or decreased when the same uropathogens are grown in media other than urine, resulting in an alteration of the mean adherence of the uropathogens to uroepithelial cells. Brain Heart Infusion broth enhances the production of fimbriae, Modified Vogel and Bonner's Medium enhances the production of exopolysaccharides, and yeast nitrogen base decreases the production of both. These studies suggest that bacterial extracellular structures should be examined morphologically prior to in vitro adhesion assays and that urine is the medium of choice for studying the adherence characteristics of various urinary pathogens in vitro.

Adhesiveness↗
PubMed1983

Primary choroid plexus papilloma of the cerebellopontine angle.

A case of choroid plexus papilloma of the cerebellopontine angle, extending from the upper cervical region to the level of the tentorial notch, in a 50-year-old woman is presented. The differential diagnosis of tumors in the cerebellopontine angle and the role of surgical treatment vs. radiation therapy are discussed.

Cerebellar Neoplasms↗
PubMed1983

Halo-thoracic brace immobilization in 188 patients with acute cervical spine injuries.

The authors report 188 patients with acute cervical spine injury with fracture who underwent Halo-thoracic brace immobilization. The majority of the fractures were considered unstable. Early neurological assessment revealed 24 patients without neurological deficit. There were 164 patients with associated cervical cord injury; 84 patients with incomplete, and 80 patients with complete tetraplegia. Management consisted of skull traction and application of the Halo-thoracic brace about 1.3 weeks after admission. The average radiological union time was 11.5 weeks following a mean of 10.2 weeks of immobilization in a Halo apparatus. Satisfactory restoration of bone and ligament stability, with no significant posttreatment neck pain, was obtained in 168 cases (89%). This is comparable to the fusion rate achieved for cervical fractures in the literature. The follow-up periods range from 1 month to 6 years, with a mean of 10.8 months. The management and results in 73 patients with unilaterally and bilaterally locked facets with or without fractures are discussed. Complete tetraplegia is not considered a contraindication to Halo apparatus immobilization. The multiple factors responsible for overcoming the barrier of anesthetic skin are elucidated. Use of the Halo apparatus offers early mobilization and rehabilitation without neurological deterioration. Complications are few and insignificant.

Acute Disease↗
PubMed1982

Theoretical feasibility of vasodilator-enhanced local tumor heating.

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action which can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma and canine transmissible venereal tumor while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, clearly demonstrate improved selective heating for spheroidal tumors over 2 cm in diameter. In the presence of vasodilator drug effect, steady-state center tumor temperatures of 45-50 degrees C can be achieved by increased power input, while surrounding normal tissues remain below 42 degrees C.

Animals↗
PubMed1982

Solitary cerebral metastasis: the effect of craniotomy on the quality and the duration of survival.

The authors report 57 patients in whom craniotomies for solitary intracranial metastatic tumor were performed in Vancouver General Hospital between 1970 and 1980. The median survival after craniotomy varied between 3.5 and 10 months depending upon the types of primary tumors. Patients with metastatic central nervous system (CNS) tumor from breast, kidney, or an unknown primary site had longer periods of survival than those with bronchogenic carcinoma. The outcome for metastatic melanoma was poor. Eighty-two per cent of the patients were able to enjoy home life and were self-dependent at the time of discharge from the hospital. A long latent interval between the primary tumor diagnosis and secondary CNS metastasis favored longer survival for patients with bronchogenic carcinoma, but not for those with melanoma. The presence of systemic metastases was an adverse factor. There was no significant difference in the duration of survival between patients with right- or left-sided cerebral lesions, but those with right hemispheric involvement had a better quality of survival. The use of computed tomographic scanning improved both the duration and the quality of postoperative survival.

Brain Neoplasms↗
PubMed1980

Bladder carcinoma: results with preoperative radiation therapy and radical cystectomy.

The records of 159 patients treated with preoperative radiotherapy and radical cystectomy were reviewed to ascertain the influence on survival rates and disease-free intervals of tumor stage, tumor grade, tumor appearance, lymphatic permeation, history of previous bladder tumors, and downstaging (pathologic stage < clinical stage). Knowledge of grade, tumor appearance, lymphatic invasion, and history of previous bladder tumors did not make possible an accurate prediction of response to integrated therapy. However, both downstaging and the absence of muscle invasion were associated with significantly improved survival rates and disease-free intervals.

Carcinoma↗
PubMed1980

Ulnar neuropathy at the elbow: comparison of simple decompression and anterior transposition.

The authors report 235 cases of ulnar neuropathy at the elbow. The treatment was simple decompression in 115 cases and anterior transposition in 120 cases. Men were affected 3 times as often as women. The average age of presentation was 54.5 years. The nondominant arm was involved more frequently. The etiology of ulnar neuropathy was diverse, but one-third of the cases fell into the idiopathic category. Numbness and paresthesia were the most common complaints. Examination revealed hypalgesia of the little finger and the medial half of the ring finger, with weakness and wasting of the intrinsic muscles of the hand. Electromyography and nerve conduction studies are important for early diagnosis. Young men with a symptom duration of 1 year or less have a better chance of improvement after the operation. Both simple decompression and anterior transposition result in improvement in 82% of the cases; however, a higher percentage of full recovery was seen in the cases treated by simple decompression. This is explained by the facts that the nerve is not handled and its vital blood supply is left intact.

Adult↗