Biomedical subjects
Publications and source records attributed to S J Thomas.
A case report of a bilateral traumatic amputee who underwent a cross leg flap to preserve a knee disarticulation level amputation is presented. Salvage of amputated parts in the lower extremities to preserve stamp length provided our patient with better stability and decreased energy expenditure with ambulation.
BACKGROUND: Thyroid hormone has many effects on the cardiovascular system. During and after cardiopulmonary bypass, serum triiodothyronine concentrations decline transiently, which may contribute to postoperative hemodynamic dysfunction. We investigated whether the perioperative administration of triiodothyronine (liothyronine sodium) enhances cardiovascular performance in high-risk patients undergoing coronary-artery bypass surgery. METHODS: We administered triiodothyronine or placebo to 142 patients with coronary artery disease and depressed left ventricular function. The hormone was administered as an intravenous bolus of 0.8 microgram per kilogram of body weight when the aortic cross-clamp was removed after the completion of bypass surgery and then as an infusion of 0.113 microgram per kilogram per hour for six hours. Clinical and hemodynamic responses were serially recorded, as was any need for inotropic or vasodilator drugs. RESULTS: The patients' preoperative serum triiodothyronine concentrations were normal (mean [+/- SD] value, 81 +/- 22 ng per deciliter [1.2 +/- 0.3 nmol per liter]), and they decreased by 40 percent (P < 0.001) 30 minutes after the onset of cardiopulmonary bypass. The concentrations in patients given intravenous triiodothyronine became supranormal and were significantly higher than those in patients given placebo (P < 0.001). However, the concentrations were once again similar in the two groups 24 hours after surgery. The mean postoperative cardiac index was higher in the triiodothyronine group (2.97 +/- 0.72 vs. 2.67 +/- 0.61 liters per minute per square meter of body-surface area, P = 0.007), and systemic vascular resistance was lower (1073 +/- 314 vs. 1235 +/- 387 dyn.sec.cm-5, P = 0.003). The two groups did not differ significantly in the incidence of arrhythmia or the need for therapy with inotropic and vasodilator drugs during the 24 hours after surgery, or in perioperative mortality and morbidity. CONCLUSIONS: Raising serum triiodothyronine concentrations in patients undergoing coronary-artery bypass surgery increases cardiac output and lowers systemic vascular resistance, but does not change outcome or alter the need for standard postoperative therapy.
OBJECTIVE: A history of stillbirth is universally accepted as an indication for antepartum fetal heart rate testing. Our goal was to examine when fetal testing should begin in an otherwise healthy patient with a history of stillbirth. STUDY DESIGN: This is a nonconcurrent cohort study of patients who were seen for antepartum surveillance from January 1979 to December 1991 with a history of stillbirth as the only indication for testing. Subsequent pregnancies were evaluated for adverse outcomes and abnormal antepartum test results. RESULTS: There was one case of recurrent stillbirth among the 300 study patients. Nineteen patients (6.4%) had one or more positive antepartum surveillance tests (positive contraction stress test or biophysical profile < or = 4). Three patients (1%) had positive tests before 32 weeks, all of whom were subsequently delivered without incident at term. Three patients were delivered for positive tests at < 36 weeks, one by cesarean section for fetal distress. We could not detect a relationship between the gestational age of the previous stillborn and the incidence of abnormal tests or fetal distress in subsequent pregnancies. CONCLUSION: Antepartum surveillance should begin at > or = 32 weeks in the healthy pregnant woman with a history of stillbirth.
If the jaws of a linear accelerator are moved under computer control during irradiation, dose distributions similar to those with wedge filters can be produced. Varian linear accelerators utilize this effect to give a 'dynamic wedge', using segmented treatment tables (STTs). An algorithm is described to generate the dose per monitor unit at any point in a beam, using the STT values. Dynamically wedged beams are modelled as the superposition of static asymmetric beams, using an algorithm based on beam data measured for symmetric beams. Predictions of wedge factors, depth doses and profiles generated using the algorithm are compared with measurements. Good agreement is found between predictions and measurements. The calculation time is typically 5 ms/dose point on a PC with a 486DX processor.
When the geometry of an implant does not exactly follow a system of dosimetry problems arise in choosing a treatment dose rate. This study has investigated the use of natural dose-volume histograms (DVHs) as a means for choosing the treatment dose level in these cases. A number of ideal geometrical cases have been investigated. For these, where appropriate, the Paris or Manchester dose rates have been calculated and compared with the peak position of the natural DVH. The dose rate at the peak of the DVH was found to agree with the basal dose rate calculated according to the Paris rules. For implants that completely obeyed the Paris rules the mean ratio was 1.009 +/- 4%. A series of clinical implants was also examined. For these the mean ratio was 1.002 +/- 2.5%. It is concluded that the peak position of a DVH can be used to predict the Paris basal dose rate of an implant. There was no systematic relationship found between the Manchester dose rate and the peak position of the DVH. The mean ratio between the Manchester dose rate and the peak dose rate position of the DVH was 0.82 +/- 13% for a series of implants.
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Linear accelerator based stereotactic radiotherapy or radiosurgery is usually performed with small collimated circular beams. The penumbral shape of these beams is caused by geometric penumbra and radiation penumbra; the former is affected by collimator position and focal spot size, the latter by energy and field size. This note reports measurements of penumbral width as collimator position, size and energy are varied. Radiation penumbra is a much greater effect than geometric penumbra at the distances used. The profile can also be changed by adding flattening filters to the external collimator. Adding a shaped filter to increase the primary radiation at the edges of the beam improves the shape of the profiles. What is of clinical importance is not the penumbral shape itself, but the effect it has on the three-dimensional dosage distributions. Cumulative dose-volume histograms (DVHS) have been used to compare treatment plans produced by beams with different penumbral shapes. None of the aforementioned factors changes the DVH as much as a change in the field radius of a few mm. Ensuring that sufficient collimators are made, and reducing the interval between successive field sizes, is the single most important thing that can be done to avoid irradiating unnecessarily large volumes of tissue.
Lymphoblasts of the normal embryonic follicles of the chicken bursa of Fabricius undergo rapid apoptosis when exposed to gamma-radiation or when cell-cell contacts are disrupted by mechanical dispersion in short term culture. We have observed previously that overexpression of v-myc sensitizes preneoplastic bursal lymphoblasts to induction of cell death, whereas resistance to induced cell death is acquired during progression to neoplasia. In this study we observed extensive DNA degradation in the large majority of the lymphoblast population within the first hour after dispersion-induced apoptosis. Paradoxically these cells continued to progress into S-phase with the bulk of DNA cleavage and death occurring in S-phase cells (i.e., in cells with more than 2C and less than 4C DNA content). We confirmed the S phase status of apoptotic cells by determining that detection of nuclear cyclin A in individual cells also corresponded with detection of DNA breakage. Levels of cyclin E, cyclin E-dependent H1 histone kinase, and p53 proteins were maintained during dispersion-induced DNA cleavage. gamma-radiation failed either to inhibit cell cycle progression or to raise p53 levels in dispersed bursal lymphoblasts. In intact bursal follicles low doses of gamma-radiation induced p53 whereas higher, apoptosis-inducing doses failed to induce p53 or prevent G1 to S-phase progression. These results suggest that normal DNA damage-induced cell cycle checkpoint controls are lost or overridden when apoptosis is induced in bursal lymphoblasts.
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OBJECTIVE: The objective of this study was to compare perinatal outcomes of hypertensive and normotensive women experiencing abruptio placentae. Our hypothesis is that hypertensive women have a less favorable perinatal outcome than do normotensive women. STUDY DESIGN: Women with the diagnosis of abruptio placentae delivered between July 1, 1988, and May 31, 1992, composed the study group (n = 226) in this case-control study. The incidence of abruptio placentae was 0.7% during this time. Those women with either multifetal gestations (n = 4) or delivery before 20 weeks' gestation (n = 2) were excluded from data analysis. The remaining 220 patients were divided according to their hypertensive (n = 29) or normotensive (n = 191) status. Maternal and neonatal medical records were reviewed and abstracted for demographic variables, antepartum complications, delivery route, abruptio placentae grade, neonatal gender, birth weight, Apgar score, cord pH, and perinatal mortality. These perinatal outcome variables were compared between the hypertensive and normotensive patient groups. RESULTS: Black women with abruptio placentae were significantly more likely to be hypertensive (p = 0.0078). Hypertensive women with abruptio placentae had the antepartum complication diabetes mellitus significantly more often than did normotensive women (p = 0.032). However, they were similar to normotensive women with regard to the frequency of positive urine drug screen and trauma. Hypertensive women were no more likely to be delivered before 32 or 37 weeks' gestation, have neonates weighing < 1500 or 2500 gm, or to be delivered by cesarean section. Abruptio placentae grades 2 and 3 occurred more often in hypertensive women (p = 0.053), as did significantly lower umbilical cord artery (p = 0.005) and venous (p = 0.003) pH values. Neonates from hypertensive women were no more likely to have low 5-minute Apgar scores or to die than those from normotensive women. CONCLUSION: Although hypertensive women experiencing abruptio placentae are more likely to have higher-grade abruptio placentae and lower umbilical cord pH values, the overall perinatal outcome was not significantly different from that of normotensive women experiencing abruptio placentae.
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Oral squamous cell cancer is the most common malignant tumour in Papua New Guinea. We have found that oral cancer in this region is concentrated at the corner of the mouth and cheek, by striking contrast with western populations, and corresponds precisely with the site of application of lime in 77% of 169 cases. Powdered slaked lime applied to the chewed Areca nut with Piper betle inflorescence at the corner of the mouth causes the mean pH to rise to 10, at which reactive oxygen species are generated from betel quid ingredients in vitro. Reactive oxygen species, together with sustained lime-induced cell proliferation, suggest a possible mechanism of carcinogenesis for this tumour.
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The lymphoid cells of embryonic bursal follicles are engaged in rapid growth and preimmune diversification of immunoglobulin genes. Disruption of follicular architecture by mechanical dispersion of these cells in short-term tissue culture was accompanied by continued cell division and extensive cell death by apoptosis. Apoptosis was suppressed in parallel cultures of intact follicles. gamma Radiation also triggered extensive apoptosis in embryonic bursal follicles within a few hours. Preneoplastic bursal stem cell populations induced by a v-myc oncogene were hypersensitive to induction of apoptosis by follicular dispersion and radiation. In contrast, tumor progression in v-myc- and v-rel-initiated bursal neoplasms was accompanied by development of resistance to induction of apoptosis. A programmed cell death pathway can be activated during normal B-cell development in the bursa, and alterations in the expression of this pathway accompany neoplastic change in this system.
Temporomandibular joint pain and dysfunction is a common complaint and a frequent cause of referral to oral and maxillofacial surgeons. The importance of considering malignant disease in the differential diagnosis is illustrated by the following cases of parotid gland neoplasia which were referred as temporomandibular joint dysfunction.
Cesarean delivery has become the most frequently performed major operation in the United States. Widespread use of vaginal birth after previous cesarean delivery could potentially eliminate up to one-third of cesareans. However, many physicians have been reluctant to adopt this policy without large studies conclusively demonstrating its safety. This study evaluated the maternal and perinatal outcomes of over 5000 cases of labor after previous cesarean delivery. This multicenter study began in 1984 and initially included nine California hospitals. During the first 2 years, there were 1776 trials of labor resulting in 1314 vaginal births. In January 1986 two additional hospitals joined the collaborative project. Over the next 3 years, there were 3957 trials of labor resulting in 2977 vaginal births at the 11 participating hospitals. During the entire study period, 5733 patients opted for a trial of labor and 4291 (75%) delivered vaginally. There were no maternal deaths in the trial-of-labor group, and perinatal mortality was not significantly different from that of the general obstetric population. These results support the findings of numerous smaller studies that have concluded that the policy of routine repeat cesarean delivery should be abandoned.