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Biomedical subjects

P MacDonald

Publications and source records attributed to P MacDonald.

At least 19 recordsLinked to original sources
PubMed1996

Silicon and silicone levels in patients with silicone implants.

Although a potential link between silicone gel breast implants and autoimmune connective tissue disease has been suggested, none has been proven. The potential role of silicone as an immune adjuvant remains very controversial. Currently available techniques do not easily allow precise measurements of silicone in tissues. However, all compounds containing silicon (which would include silicone) can be measured accurately. The present study was designed to measure silicon levels in the fibrous capsules of patients with silicone-gel breast implants, saline breast implants and silicone inflatable penile prostheses. Baseline control silicon levels were obtained from the breast tissue of patients undergoing breast reduction, who had no exposure to breast implants. All silicon measurements were carried out using atomic absorption spectrometry with a graphite furnace. The mean silicon levels in 16 breast tissue control samples from 8 patients undergoing breast reduction varied from 0.046 to 0.742 micrograms/g dry weight, with the median mean being 0.0927. The median silicon level in capsules from 6 patients with saline implants was 7.7 micrograms/g (range 36.6). The median silicon level in capsules from 5 patients with silicone inflatable penile prostheses was 19.5 micrograms/g (range 34.8). Although the levels of silicon in capsules of patients with saline breast prostheses and penile implants were higher than in control samples, they were much lower than those from the capsules of the 58 gel implants (median 9979 micrograms/g). Of the 58 silicone gel breast implants (from 20 patients with bilateral implant removal and 18 patients with unilateral removal) which had been inserted from 1974 to 1990, 28 were intact, 8 had pinhole leaks, and 22 were ruptured. Median capsule silicon levels and ranges for all 58 implants, for intact only, for leaking, and for ruptured were: 9979 (152,000), 10,477 (88,703), 6592 (65,396), and 9922 (152,387) micrograms/g respectively. There were no significant differences in silicon levels associated with implant status, duration in situ, or year of implantation. Capsule contracture was not associated with higher levels of capsule silicon. Capsule silicon levels were about 10(6) times higher than previously assayed blood silicon levels. This may be because silicone released from implants remains localized in capsular tissue, or because blood-borne silicone is quickly excreted. Using 29Si nuclear magnetic resonance spectroscopy, no detectable silicone was found in the blood of 7 control women and 7 women with silicone-gel implants (5 with known implant rupture).

Breast Implants↗
PubMed1996

A biomechanical analysis of joint contact forces in the posterior cruciate deficient knee.

The approach to the posterior cruciate deficient knee is controversial. The purpose of this study is to document the biomechanical changes in the static cadaveric knee model with simulated physiological loads. Nine fresh cadaveric knees from young donors (aged under 45 years) were mounted on a materials testing machine. Loading was carried out at 0 degrees, 30 degrees and 60 degrees to 1.5 kN with low-pressure sensitive Prescale film (Fuji; Tokyo, Japan) inserted through arthrotomies into the medial and lateral compartments. Computerized analysis of the imprints on the film was then carried out. Tests were then repeated after cutting the posterior cruciate ligament (PCL). Results demonstrate a statistically significant posterior subluxation of the tibia on the femur at 60 degrees flexion. This causes a significant increase in contact pressure and pressure concentration on the medial compartment of the knee after cutting the PCL. This may help explain the long-term degenerative changes observed in the medial femoral condyle after cutting the PCL.

Adult↗
PubMed1994

The core content of a generalist curriculum for general internal medicine, family practice, and pediatrics.

The authors analyzed the educational content of the curricula developed for teaching in the generalist disciplines of pediatrics, family medicine, and general internal medicine. Fifteen educational components that constitute the core content shared by the three generalist disciplines are identified, described, and referenced. Tailoring the generalist curriculum for students and residents at the different stages of learning is reviewed, along with the refinement of the curriculum to meet the special needs of each generalist discipline. The success of a generalist curriculum will ultimately be measured by generalist career choices, quality of care, and both patient and professional satisfaction. The curricular determinants of success require institutional commitment to an educational philosophy that embraces the generalist disciplines, a core curriculum that provides education and training that are correlated with the demands of clinical practice, and generalist faculty who serve as role models, mentors, and teachers.

Adult↗
PubMed1994

Preliminary experience using an optimized three-point transformation algorithm for spatial registration of coordinate systems: a method of noninvasive localization using frame-based stereotactic guidance systems.

This study describes the use of an optimized three-point transformation algorithm to spatially cross-register a volumetric computerized tomographic scan or magnetic resonance image data set with the coordinate system of a stereotactic frame. This algorithm was tested for accuracy using a scanned phantom in which calculated targets, using the Brown-Roberts-Wells (BRW) frame picket-fence algorithm as a standard, could be compared to physical targets measured using a BRW arc and phantom. These target values were then compared to target values calculated with the optimized three-point algorithm. This method was used for target localization in 21 patients. Following this noninvasive localization method, the standard BRW stereotactic system was used for guidance. The application accuracy of this frameless localization technique was within the limits of the scan slice thickness in 16 of 21 cases, with an average error of 2.11 mm in an average scan slice thickness of 3.1 mm. Intracranial targets were successfully reached in all cases without morbidity or mortality. The algorithm can be customized to cross-register image data sets with the coordinate systems of a wide variety of stereotactic guidance systems. The method increases the convenience and flexibility of frame-based stereotactic guidance by providing a means of noninvasive localization that can be accomplished electively at a separate time from the guidance part of a stereotactic operative procedure.

Aged↗
PubMed1991

Characterization of a novel erythropoiesis-inhibiting human protein.

We have isolated an erythropoiesis-inhibiting protein, DIP (differentiation-inhibiting protein), from the blood of a 60-year-old woman suffering from pure red cell aplasia. This protein inhibits the growth and differentiation of normal human and murine BFU-E, but not CFU-E, cells as well as dimethyl sulfoxide-induced hemoglobin synthesis by Friend murine erythroleukemia cells. It appears that DIP primarily affects differentiation rather than proliferation, because it does not inhibit the proliferation of untreated Friend erythroleukemia cells. DIP seems to function like a recently described 45-kDa autocrine differentiation-inhibiting protein factor (ADIF) which is secreted by tsAEV-transformed chicken erythroleukemia cells. Both proteins selectively block the differentiation of normal human and murine BFU-E cells as well as the differentiation (but not the proliferation) of Friend murine erythroleukemia cells. However, the human DIP is not an autocrine product of the patient's bone marrow cells, nor does it affect chicken erythroid cells.

Animals↗
PubMed1988

Study of relation of continuing medical education to quality of family physicians' care.

A random sample of 120 physicians in Ontario was studied to assess quality of care in primary care and test an hypothesis that quality of care was related to continuing medical education (CME) activities. The quality-of-care scores were obtained by an in-office audit of a random selection of charts. The scores were global scores for charting, prevention, the use of 13 classes of drugs, and care of a two-year period for 182 different diagnoses. There were no relationships between global quality-of-care scores based on these randomly chosen charts and either the type or quantity of the physicians' CME activities. These activities were reading journals, attending rounds, attending scientific conferences, having informal consultations, using audio and video cassettes, and engaging in self-assessment. The implications of these findings are significant for future research in CME and for planners of present CME programs.

Certification↗
PubMed1986

Caliceal diverticula developing into simple renal cyst.

Although common in adults simple cortical renal cysts are rare in children. Caliceal diverticula are rare in adults and children. A case of a caliceal diverticulum apparently sealing off and becoming an isolated simple cyst in the renal parenchyma has been reported as an unusual complication of caliceal diverticula. There have been 2 other cases of caliceal diverticula becoming sealed off reported in the literature, although neither progressed to frank cysts. We report 2 cases of definite caliceal diverticula progressing to simple renal cortical cysts.

Child↗
PubMed1986

Popliteal artery injuries: civilian experience with sixty-three patients during a twenty-four year period (1960 through 1984).

Our experience with 63 patients who had popliteal artery injuries sustained in civilian accidents is reported. Blunt injuries occurred in 53 patients and 49 had associated skeletal injuries. Eighteen patients suffered knee dislocation; six of these patients had associated fractures. Fractures of the upper third of the tibia occurred in 21 patients. Five patients had irreversible ischemia and required primary amputation. Thirteen amputations were required in 58 patients in whom arterial repair was performed, for an amputation rate of 22%. There were no amputations in 19 patients treated less than 6 hours after injury was sustained. Four deaths occurred. Fasciotomy was performed in 20 patients. Skeletal injuries were usually treated with external fixation.

Adolescent↗
PubMed1981

Hormonal induction of pulmonary maturation in the rabbit fetus: effects of maternal treatment with estradiol-17 beta on th endogenous levels of cholinephosphate, CDP-choline and phosphatidylcholine.

1. Administration of estradiol-17 beta to pregnant rabbits at 25 days gestation (term, 31 days) resulted n a significant increase in the incorporation of [14C]-choline, but not [14C]ethanolamine, into the lipids of fetal lung slices. The incorporation of [35S]methionine was not affected. 2. Enzymatic assays conducted in vitro revealed no significant effect on either the activities of several enzyme markers for subcellular organelles, the activities of the enzymes responsible for the production of phosphatidylglycerol and phosphatidylinositol, membrane-bound or aqueously dispersed phosphatidate-dependent phosphatidic acid phosphohydrolase activities or the activities of the auxiliary enzymes responsible for the synthesis of dipalmitoylphosphatidylcholine. 3. The activity of the enzymes involved in the choline pathway for the de novo biosynthesis of phosphatidylcholine were not significantly altered except for a 66% increase in the CTP:cholinephosphate cytidylyltransferase activity assayed in the cytosol. The addition of phosphatidylglycerol stimulated cholinephosphate cytidylyltransferase activity approx. 3-fold. However, in the presence of this lipid, the activities in cytosol from control and treated fetuses were similar, indicating that the increased activity noted in the absence of phosphatidylglycerol was due to an activation of existing cytidylyltransferase activity rather than an increase in total enzyme units. 4. Estrogen treatment of the does was also associated with a marked decrease in the levels of cholinephosphate in fetal lung and significant increases in the levels of CDPcholine and phosphatidylcholine. These alterations in pool size are consistent with an increase in the activity of cholinephosphate cytidyltransferase in vivo. The results suggest that cholinephosphate cytidylyltransferase may catalyse an important rate-determining reaction in the synthesis of phosphatidylcholine in fetal lung. The data also support the view that the reaction catalysed by CDPcholine:diacylglycerol cholinephosphotransferase also has a regulatory role during development.

Animals↗