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Biomedical subjects

A Hamilton

Publications and source records attributed to A Hamilton.

At least 19 recordsLinked to original sources
PubMed1997

The use of stereotactic radiosurgical boost in the treatment of medulloblastomas.

PURPOSE: Starting in 1992, we began using a stereotactic radiosurgical (SRS) boost for the treatment of medulloblastomas. Four patients ranging in age from 7 to 42 years old have since been treated and are the subject of this retrospective study. METHODS AND MATERIALS: All patients were initially treated with a maximally debulking surgery and external beam radiotherapy, which were then followed by a stereotactic radiosurgical boost using a modified 6 MeV linear accelerator. Radiosurgical boost doses ranged from 4.50 to 10.0 Gy. Target volumes ranged from 1.1 to 8.1 cc. The procedure was well tolerated with minimal acute toxicities. RESULTS: All four patients are alive without evidence of recurrence (at 8 to 35 months). Acute nausea and vomiting was elicited during the radiosurgical procedure in the first patient treated. We have since begun premedicating patients with antiemetics or treating under general anesthesia. Late complications consisted of panhypopituitarism in one patient, which was thought to be attributable to the previous course of whole-brain radiotherapy. We have not observed any incidence of radionecrosis in this small cohort of patients. CONCLUSIONS: Our preliminary results with the use of radiosurgery for medulloblastomas are optimistic, and we would like to suggest the inclusion of a radiosurgery boost in future clinical trials for treatment of this disease.

Adult↗
PubMed1997

Anaesthesia for phaeochromocytoma in pregnancy.

PURPOSE: Phaeochromocytoma in pregnancy is a rare occurrence. Details of the anaesthetic are even more rarely reported. Our purpose is to describe our management with reference to previous reports. CLINICAL FEATURES: A 31-yr-old woman underwent resection of a phaeochromocytoma at seven weeks gestation. Preoperative preparation included 2 mg prazosin p.o. bid and 40 mg propranolol p.o. bid. A balanced anaesthetic technique including 5 mg midazolam, 1500 micrograms alfentanil, 35 micrograms sufentanil, nitrous oxide and isoflurane was used. Blood pressure was controlled with 3.4 g magnesium and 2437 micrograms nitroglycerin. There were no episodes of hypertension intraoperatively. The patient made an uneventful recovery and delivered a normal baby at 37 wk gestation by caesarean section. CONCLUSION: Anaesthesia for resection of a phaeochromocytoma in early pregnancy can be successfully managed with preoperative alpha and beta sympathetic blockade and a balanced anaesthetic technique using magnesium as the main intraoperative hypotensive agent.

Adrenal Gland Neoplasms↗
PubMed1996

Synthesis and properties of DNA-PNA chimeric oligomers.

Adenine, thymine and cytosine PNA monomers have been prepared using 3-amino-1,2-propanediol as a starting material. The benzoyl group was used to protect the exocyclic amines of the heterocyclic bases of A and C PNA monomers and the backbone primary amine was protected with the monomethoxytrityl group. The thymine and cytosine PNA monomers were used in conjunction with standard DNA synthesis monomers to produce chimeric PNA DNA (PDC) oligomers. Ultraviolet melting studies confirmed that these oligomers form stable hybrids with complementary DNA strands and that mismatches in the DNA but more so in the PNA sections lead to duplex destabilisation.

Chemistry, Organic↗
PubMed1996

Animal model for thoracoscopic laser ablation of emphysematous pulmonary bullae.

BACKGROUND AND OBJECTIVE: Thoracoscopic laser techniques have been described for treatment of pulmonary bullae. Clinical application of this procedure has proliferated despite limited data regarding efficacy or optimal techniques. The objective of this study was to develop an animal model for investigating laser treatment of bullous lung disease. STUDY DESIGN/MATERIALS AND METHODS: Sixty-two New Zealand White rabbits (3-5 kg) were injected intravenously with 0.35 cc sterile-filtered Sephadex G-100 beads (1 g/100 cc suspension). Three hours later, rabbits were anesthetized, intubated, and 10 cc 0.7% heat-treated or 1% untreated carrageenan solution was instilled endotracheally into a catheter wedged in a mainstem bronchus. RESULTS: Bullae formed over 4-6 weeks in 33% of the animals treated with 0.7% heat-treated carrageenan, and 90% of animals receiving 1% untreated carrageenan (P < 0.005) as demonstrated by serial thoracoscopy. Thoracoscopy was performed at 6-8 weeks using 5 mm trocars under general anesthesia and mechanical ventilatory support. Animals developed pulmonary bullae ranging in size from 0.5 to 2 cm. Bullae were ablated under thoracoscopic visualization using a CO2 laser with a 4 mm OD rigid probe and short focal length in a defocused mode, or an Nd:YAG laser with a 0.4 mm diameter flexible fiberoptic probe. Animals recovered quickly following thoracoscopy. CONCLUSION: We have successfully developed an animal model for thoracoscopic laser ablation of emphysematous pulmonary bullae. This animal model should be useful in investigating treatment of bullous lung disease in humans.

Animals↗
PubMed1996

Comparison of continuous versus pulsed CO2 and Nd:YAG laser-induced pulmonary parenchymal lung injury in a rabbit model.

BACKGROUND AND OBJECTIVE: Laser techniques have recently been described for treatment of patients with emphysema and bullous lung disease. Laser exposure of the pulmonary parenchyma during these procedures is complicated by laser-induced lung injury with substantial associated morbidity. Animal investigations are needed to develop methods that reduce lung injury. We hypothesized that the depth of injury could be reduced by pulsing laser exposures, with the goal of limiting thermal effects to more superficial tissue levels. In this study, we compared acute and chronic histologic injury resulting from pulsed- versus continuous-mode CO2 and Nd:YAG laser pulmonary parenchymal exposures in rabbits. STUDY DESIGN/MATERIALS AND METHODS: A total of 40 New Zealand White (NZW) rabbits underwent thoracotomy followed by exposure with CO2 laser (n = 10 continuous vs. n = 10 pulsed at 250 Hz with duty cycle 0.15 ms) or ND:YAG laser (n = 10 continuous vs. n = 10 pulsed at 10 Hz with duty cycle 0.10 sec) to the visceral pleural surface using 1 minute of laser exposure (5 watts, defocused to 70 W/cm2 power density) to the exposed lung surface. Rabbits were sacrificed at 4 and 21 days post-injury, and lungs were examined histologically. RESULTS: CO2 and Nd:YAG laser treatment resulted in substantial pulmonary parenchymal injury. While CO2 laser-induced damage was distinct from Nd:YAG histologically, pulsed-mode laser exposures did not reduce lung injury for either laser. Acute edema occurred to depths of 1180 +/- 338 microns for continuous-mode CO2 laser exposures compared to 1,340 +/- 430 microns in pulsed mode (p = .77). For Nd:YAG laser exposure, acute edema depth was 750 +/- 748 microns continuous versus 1120 +/- 367 microns pulsed mode (p = .65). Chronic lung fibrosis depth was 450 +/- 164 microns for CO2 continuous mode compared to 575 +/- 170 microns in pulsed mode (p = .61). Lung fibrosis depth for Nd:YAG was 550 +/- 96 microns, continuous versus 484 +/- 180 microns pulsed mode (p = .76). CONCLUSION: The similarity in injury between pulsed- and continuous-mode exposures suggests that thermal relaxation times are long relative to the selected pulse frequencies in intact living rabbit lungs. Alternatively, brief high-energy pulsations may increase focal temperatures with a tendency to increase injury depth relative to the penetration of the laser light. Thus, pulsed laser modes in these settings appear to be ineffective in reducing laser-induced lung injury in clinical settings.

Animals↗
PubMed1996

Spinal cord infarct after arterial switch associated with an umbilical artery catheter.

Paraplegia after an open heart operation in a neonate is a rare complication. We report a case of a infant in whom paraplegia developed after a successful arterial switch operation for transposition of the great arteries. The infant was monitored and resuscitated in the preoperative period with umbilical arterial and venous catheter tips located in the midthoracic region. He likely suffered a clinically silent thromboembolic event predisposing him to a localized hemorrhagic infarction during the repair.

Cardiopulmonary Bypass↗
PubMed1996

CO2 and Nd:YAG laser-induced pulmonary parenchymal lung injury in a rabbit model.

Laser exposure of the pulmonary parenchyma during treatment of emphysema and other clinical indications causes acute lung injury. Animal investigations are needed to understand and control laser-induced lung injury. We hypothesized that lung injury is deeper from Nd:YAG laser exposures than CO2 exposures because of deeper penetration of Nd:YAG wavelength light. We compared the temporal evolution of histologic injury in rabbits resulting from continuous mode shallow CO2 and Nd:YAG laser pulmonary parenchymal exposures applied in rabbits. Forty-six New Zealand white (NZW) rabbits underwent treatment with CO2 laser (n=18), Nd:YAG laser (n=18), or sham thoracotomy control (n=10) to the visceral pleural surface using 1 min of exposure (5 watts, defocused to 70 W/cm2 power density for both lasers). Animals were killed at 0, 4, 7, 21, and 49 d after exposure. Lung injury, similar to that seen clinically in humans, developed in all laser-treated animals. Injury progressed from ischemia and vascular congestion, to edema and necrosis, followed by pleural and parenchymal fibrosis. The acute injury was qualitatively distinct and slightly deeper in CO2 than Nd:YAG-treated animals (p<0.02) despite the shallower depth of penetration of the CO2 laser. These findings may imply that higher absorption coefficient for CO2 laser energy results in greater focal temperatures and injury in the areas of direct exposure, and suggest that Nd:YAG laser exposure at these settings may cause shallower injury than CO2 lasers in humans undergoing clinical treatment.

Absorption↗
PubMed1995

Stereotactic radiosurgery as an adjunct to surgery and external beam radiotherapy in the treatment of patients with malignant gliomas.

PURPOSE: To evaluate the efficacy and toxicity of a stereotactic radiosurgery boost as part of the primary management of a minimally selected population of patients with malignant gliomas. METHODS AND MATERIALS: Between June, 1991 and January, 1994 a stereotactic radiosurgery boost was given to 30 patients after completion of fractionated external beam radiotherapy. The study population consisted of 22 males and 8 females, with a range in age at treatment from 5 to 74 years (median: 54 years). Tumor volume ranged from 2.1 to 115.5 cubic centimeters (cc) (median: 24 cc). Histology included 17 with glioblastoma multiforme, 10 with anaplastic astrocytoma, 1 with a mixed anaplastic astrocytoma-oligodendroglioma, and 2 with a gliosarcoma. A complete resection was performed in 9 (30%) patients, while 18 (60%) underwent a subtotal resection, and 3 (10%) received a biopsy only. Fractionated radiation dose ranged from 44 to 62 Gy, with a median of 59.4 Gy. Prescribed stereotactic radiosurgery dose ranged from 0.5 to 18 Gy (median: 10 Gy), and the volume receiving the prescription dose ranged from 2.1 to 158.7 cc (median: 46 cc). The volume of tumor receiving the prescription dose ranged from 70-100% (median: 100%). One to four (median: 2) isocenters were used, and collimator size ranged from 12.5 to 50 mm (median size: 32.5 mm). The median minimum stereotactic radiosurgery dose was 70% of the prescription dose and the median maximum dose was 200% of the prescription dose. RESULTS: With a minimum follow-up of 1 year from radiosurgery, 7 (23%) of the patients are still living and 22 (73%) have died of progressive disease. One patient died of a myocardial infarction 5 months after stereotactic radiosurgery. Follow-up for living patients ranged from 12 to 45 months, with a median of 30 months. The 1- and 2-year disease-specific survival from the date of diagnosis is 57 [95% confidence interval (CI) 39 to 74%] and 25% (95% CI 9 to 41%), respectively (median survival: 13.9 months). No significant acute or late toxicity has been observed. CONCLUSION: Stereotactic radiosurgery provides a safe and feasible technique for dose escalation in the primary management of unselected malignant gliomas. Longer follow-up and a randomized prospective trial is required to more thoroughly evaluate the role of radiosurgery in the primary management of malignant gliomas.

Adolescent↗
PubMed1995

Non-11p constitutional chromosome abnormalities in Wilms' tumor patients.

The incidence in Wilms' tumor patients of constitutional chromosome defects other than those involving the short arm of chromosome 11 was examined using data on 5,854 patients registered in the National Wilms Tumor Study. Trisomy 18 and Turner syndromes were found to occur at higher rates than expected based on chromosome surveys of newborns. Four patients were reported to have trisomy 18; all of these patients were over 5 years of age at the time of diagnosis of Wilms' tumor and none survived longer than six months. Four patients were reported to have Turner syndrome; these patients are currently doing well and have all survived at least 3 years following diagnosis. Two of the Turner patients and one of the trisomy 18 patients had horse-shoe kidneys; we speculate that this renal anomaly may contribute to the higher rates of tumor in these patients. No clear pattern was found among patients with other chromosome defects, although two patients had defects involving 2q37.

Adolescent↗
PubMed1995

Magnesium sulfate prophylaxis after cardiac operations.

One hundred patients undergoing elective cardiac operations were randomized into placebo (n = 54) and magnesium (n = 46) groups. The magnesium group received six doses of 2.4 g (19.2 mEq) magnesium sulfate intravenously in the first 24 hours after the cardiac operation. The magnesium group had higher serum magnesium concentrations postoperatively (1.09 +/- 0.20 versus 0.75 +/- 0.13 mmol/L; p < 0.0001), postoperative day 1 (1.49 +/- 0.34 versus 0.70 +/- 0.12 mmol/L; p < 0.0001) and postoperative day 2 (0.96 +/- 0.19 versus 0.76 +/- 0.07 mmol/L; p < 0.0001). Patients in the magnesium group had a lower incidence of ventricular tachyarrythmias (VTs) (17.3% versus 51.9%; p = 0.0006), less need for treatment (6.5% versus 20.3%; p < 0.0001), fewer VT episodes/patient (0.3 +/- 0.8 versus 1.39 +/- 1.9; p < 0.0001), and a reduction in the severity of VTs as measured by the modified Lown grade (p = 0.0002). No differences were demonstrated with respect to supraventricular tachyarrythmias. The magnesium group had reduced absolute creatine kinase-MB levels (5.3 +/- 4.2 versus 28.4 +/- 28 IU/L; p = 0.001) as well as creatine kinase-MB fraction (0.01 +/- 0.02 versus 0.05 +/- 0.04; p = 0.001) on postoperative day 1. Serum magnesium concentrations were lower during VTs than during periods of sinus rhythm (0.75 +/- 0.75 versus 1.02 +/- 0.35 mmol/L; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Brain maturation estimation using neural classifier.

Quantitative electroencephalographic (EEG) signal analysis has revealed itself as an important diagnostic tool in the last few years. Through the use of signal processing techniques, new quantitative representations of EEG data are obtained. To automate the diagnosis, a problem of supervised classification must be solved on these. Artificial Neural Networks provide an alternative to more traditional classifier systems for this task. The objective of this paper is to perform a comparison between several classifiers in a particular problem, the brain maturation prediction. The data preprocessing/feature extraction process and the methodology for making the comparison are described. Performance of the methods is evaluated in terms of estimated percentage of correctly classified subjects.

Adolescent↗
PubMed1994

Interstitial irradiation versus interstitial thermoradiotherapy for supratentorial malignant gliomas: a comparative survival analysis.

PURPOSE: To compare the survival of two groups of patients with supratentorial malignant gliomas who were treated on two sequential protocols with either interstitial thermoradiotherapy or with interstitial irradiation without hyperthermia. METHODS AND MATERIALS: Between 1988-1992, patients with anaplastic astrocytoma or glioblastoma multiforme were treated at the University of Arizona on a Phase I/II protocol of interstitial thermoradiotherapy with ferro-magnetic seeds. The treatment protocol consisted of debulking surgery, a course of external beam radiotherapy and hyperthermia given immediately before and after brachytherapy. The survival of patients so treated was compared with that of a similar group of patients treated with interstitial brachytherapy alone at the Barrows Neurological Institute between 1982-1990. RESULTS: Twenty-five patients with primary tumors treated at the time of initial presentation with thermoradiotherapy were compared with a control group of 37 patients treated with interstitial brachytherapy alone. All primary patients were followed for a minimum of 34 months post implant. Multivariate analysis based on proportional hazards models showed that hyperthermia (p = 0.027), patient age (p < or = 0.00001) and histology (anaplastic astrocytoma vs. glioblastoma multiforme, p = 0.0017) were the only factors significantly associated with survival in this data set. From the fitted model, the hazard of dying when treated with hyperthermia was .53 times (95% confidence intervals 0.29-0.94) than that of the control group. In addition, we treated a small group of patients with recurrent tumors (13 with brachytherapy alone, and eight with thermoradiotherapy) and found no survival difference (p = 0.62). CONCLUSION: Within the constraints of the selection factors and the different treatment parameters used in these studies, we conclude that an interstitial thermoradiotherapy boost confers a statistically significant survival benefit to patients with primary high grade gliomas when compared to interstitial brachytherapy alone.

Adult↗
PubMed1994

A comparison of survival between radiosurgery and stereotactic implants for malignant astrocytomas.

The purpose of this paper is to compare the survival of three groups of patients with high grade supratentorial gliomas who were treated on three sequential protocols with surgical resection, external beam fractionated radiotherapy and a boost to the residual contrasting enhancing mass by either interstitial brachytherapy (IB, n = 33), by interstitial thermoradiotherapy (IT, n = 25) or by stereotactic radiosurgery (SRS, n = 19). The primary aim of this study was to evaluate the role of different boosting techniques in the initial management of primary brain tumors. External beam radiotherapy doses were escalated from one study to the next so that the median doses given to the IB, the IT, and the SRS groups were 41.4 Gy, 48.4 Gy, and 59.4 Gy, respectively. The median dose of interstitial irradiation or stereotactic radiosurgery, were 40 Gy, 32.2 Gy and 10 Gy, respectively, for the same groups. Follow-up was such that all living patients had been followed for a minimum of 30, 27, 4 months in the IB, IT, and SRS groups, respectively; hence, twelve-month survival was 52% (95% CI: 34%-69%), 80% (95% CI: 64%-96%), and 51% (95% CI: 24%-78%) in the same respective groups. Using a multivariate Cox proportional hazards model, treatment with IT conferred a survival advantage over IB (p = 0.029). Furthermore, survival of patients treated with SRS did not significantly differ from that of patients treated with an implant with or without hyperthermia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Immunochemical studies of heat-shock protein 80 of Histoplasma capsulatum.

A monoclonal antibody (MAb) of the IgG1 subclass, with greater activity to the yeast than the mycelial phase of Histoplasma capsulatum was raised and was found to predominantly recognize a molecule of 80 kDa by immunoblot. Enzymatic deglycosylation and chemical degradation, followed by reaction with MAb 69F on Western blots showed the molecule to be O-glycosylated, and immunofluorescence studies showed it to be heat-inducible and its distribution to be cytoplasmic and possibly cell membraneous. There was no apparent staining of the cell wall. Culture filtrate was positive by ELISA and Western blot when reacted with MAb 69F. In addition, ELISA and Western blot demonstrated that a similar epitope was present in other fungal species. The glycoprotein had a pI of approximately 4.7. N-terminal amino acid sequencing revealed this molecule to be homologous to members of the heat-shock protein 70 family and to a recently described antigen from H. capsulatum.

Amino Acid Sequence↗
PubMed1994

Immunohistochemical detection of a novel 22- to 25-kilodalton glycoprotein of Paracoccidioides brasiliensis in biopsy material and partial characterization by using species-specific monoclonal antibodies.

Two murine monoclonal antibodies (MAbs) specific to Paracoccidioides brasiliensis (as determined by enzyme-linked immunosorbent assay [ELISA] and Western blot [immunoblot]) were produced by using a modification of standard hybridization protocols, with cyclophosphamide included as an immunomodulator to abolish responses to highly cross-reactive immunodominant epitopes. MAbs PS14 and PS15 are two different clones which exhibit similar characteristics by ELISA and Western blot. They are directed against a 22- to 25-kDa antigen which is present in P. brasiliensis and which could not be identified in other dimorphic fungi by ELISA or Western blot. Partial purification of the antigen was accomplished by isoelectric focusing, and deglycosylation studies suggested that the 22- to 25-kDa antigen is a glycoprotein with a pI of between 4.5 and 5 and that O-linked sugars may be part of the recognized epitope. The MAbs stained the cytoplasm of P. brasiliensis yeast and hyphal cells in cryostat sections of fresh cultures of the fungus. In addition, the MAbs stained the wall of paracoccidioidomycotic granulomas, as well as the cytoplasm of the fungus, as determined by the use of immunofluorescence, immunoperoxidase, and immuno-alkaline phosphatase staining techniques in paraffin-embedded sections of human biopsy material, and they failed to stain granulomas resulting from other clinical conditions. These findings suggest that these MAbs have potential use in the immunohistochemical identification of P. brasiliensis.

Adrenal Glands↗
PubMed1994

Cost reduction in cardiac surgery.

OBJECTIVE: To reduce surgical waiting lists at the University of Alberta Hospitals. A cost reduction program was initiated, allowing more cases to be performed on the same budget. Reducing the cost of delivering health care services has become necessary as demands upon the system increase. METHODS: Data were retrospectively gathered on patients having open heart surgery at the University of Alberta Hospitals between March 1, 1991 and February 29, 1992. Group 1 were patients operated on before the start of the cost reduction program (September 1, 1991) and group 2 were those operated on after. Student's t test and logistic regression were use to compare population characteristics and to correlate dependent variables. RESULTS: Demographic features and severity indices were not different. Operating time decreased from 4.5 +/- 1.5 to 4 +/- 1 h, P < 0.002. Preoperative, intensive care unit (ICU) and postoperative ward length of stay were reduced (P < 0.002). Total length of stay went from 19.3 +/- 22.7 to 13.8 +/- 10.7 days, P < 0.001. Operating room, nursing and x-ray costs decreased, P < 0.002. Hospital costs declined from $14,182 +/- 16,464 to $10,710 +/- 7,332, P < 0.001. Multiple regression showed hospital stay, ICU, operating room time, severity of illness and age to be significant determinants of cost, P < 0.03 for each. Waiting time and number of patients on the waiting list declined significantly as surgical lists increased. Mortality and rate of readmission following discharge were not different between the two groups. CONCLUSIONS: Substantial cost savings can be made by changing practice patterns, without adverse consequences. ICU and hospital length of stay are the most important cost determinants.

Alberta↗