Biomedical subjects
D Burr
Publications and source records attributed to D Burr.
On inconsistency of Breslow's estimator as an estimator of the hazard rate in the Cox model.
In the Cox proportional hazards model, Breslow's estimator of the cumulative hazard function is well known. This estimator is sometimes presented in such a way that it appears to offer a method of estimating the hazard rate function as well. We state and prove an asymptotic result for this estimator of the hazard rate, which shows that the estimator is inconsistent, and that it is asymptotically unbiased.
Enterotoxigenic Escherichia coli and other causes of infectious pediatric diarrheas in Jakarta, Indonesia.
A hospital stool survey of Indonesian children less than 5 years of age determined the prevalence of diarrhea caused by enterotoxigenic Escherichia coli (ETEC) and other bacterial enteropathogens, compared to non-diarrheic control patients. ETEC were the second most frequent cause of diarrhea, isolated from 16 of 194 (8.2%) of patient's stools compared to 2 of 97 (2.1%) of control stools. The highest prevalence was in infants 12 to 23 months of age (17.9%).
Diagnosis of typhoid fever by detection of Salmonella typhi antigen in urine.
A monoclonal antibody specific for group D Salmonella antigen 9 was used in an indirect enzyme-linked immunosorbent assay (ELISA) for detecting the antigen in urine specimens collected from patients with clinical typhoid fever in Jakarta, Indonesia. The ELISA had a sensitivity of 95% in identifying patients in whom Salmonella typhi was isolated from hemocultures, 73% in patients in whom S. typhi was isolated from stool specimens, and 40% in patients in whom the organism was isolated from bone marrow cultures. Among patients in whom S. typhi was isolated from blood cultures, the ELISA had a sensitivity of 65% when a single urine specimen was examined and 95% when serially collected urine specimens were examined. A dot blot immunoassay performed on a nitrocellulose filter in parallel had a sensitivity of 85%, versus 83% for the plate ELISA in which S. typhi was isolated from blood, bone marrow, and/or stool specimens. Since S. typhi antigen is intermittently excreted in the urine of patients with typhoid fever, serially collected urine from patients with typhoid should be tested for antigen 9.
Osteoarthritic changes in canine articular cartilage, subchondral bone, and synovium fifty-four months after transection of the anterior cruciate ligament.
Anterior cruciate ligament transection (ACLT) in the dog results in osteophyte formation and in morphologic, metabolic, biochemical, and biomechanical changes in the articular cartilage of the unstable knee that mimic those of human osteoarthritis (OA). However, in dogs studied up to 2 years after ACLT, the changes have appeared to be self-limiting, which has led to the suggestion that this is a model of cartilage damage and repair, rather than of OA. To ascertain whether changes in articular cartilage and subchondral bone of dogs subjected to ACLT lead to progressive changes of OA, we studied 3 dogs for 54 months after ACLT. Arthrotomy was performed in the dogs to visualize and then transect the anterior cruciate ligament. When the dogs were killed, full-thickness ulceration of the articular cartilage was seen on the medial femoral condyle and tibial plateau of the unstable knee, while cartilage in other regions was thicker than that of the contralateral knee, consistent with hypertrophic cartilage repair. Synovial infiltration by mononuclear cells was not more severe than that seen in dogs killed at earlier intervals after ACLT, although gross fibrotic thickening of the capsule was apparent in each dog. Histomorphometric studies revealed a marked increase in subchondral bone volume and active bone formation. These findings show that the changes that develop in the canine knee joint after ACLT are progressive and are unambiguously those of OA.
Rapid diagnosis of typhoid fever through identification of Salmonella typhi within 18 hours of specimen acquisition by culture of the mononuclear cell-platelet fraction of blood.
Detection of Salmonella typhi in blood by culture of the mononuclear cell-platelet layer was compared with other methods currently used for the diagnosis of typhoid fever. Colonies of S. typhi were present in all mononuclear cell-platelet layer-positive cultures within 18 h of plating and were identified within an additional 10 min by a coagglutination technique. In contrast, identification of all positive cultures by conventional blood culture required 3 days.
The effect of adenosine on respiratory chemosensitivity in the awake rat.
The effect of adenosine on respiration and respiratory chemosensitivity in awake animals was studied in rats, intact and chemodenervated, before and after intra-peritoneal injection of L-phenylisopropyladenosine (PIA). Respiration was measured by barometric plethysmography. The administration of PIA depressed respiration substantially, in a dose-related manner, the maximum effect occurring after 30-80 min; PIA also depressed body temperature but over a slower time course. In both intact and chemodenervated animals, the characteristic responses to hypoxia were maintained after the administration of PIA, but at depressed respiratory levels. There was no interaction between effects. Administration of PIA produced enhancement of the ventilatory response to hypercapnia, in both intact and peripherally chemodenervated animals. The results do not support the hypothesis that hypoxic effects on respiration are related to the accumulation of adenosine in brain tissues. Enhancement of the hypercapnic response represents evidence for disinhibition of the mechanism concerned.
Alkaline phosphatase-conjugated oligonucleotide probes for enterotoxigenic Escherichia coli in travelers to South America and West Africa.
Several studies have demonstrated the usefulness of 32P-labeled recombinant DNA probes for identifying enterotoxigenic Escherichia coli (ETEC). The use of radioisotopes and X-ray development, however, severely handicaps the utility of DNA probes in most clinical laboratories. In this study, enzyme-labeled oligonucleotide probes for ETEC LT (heat-labile toxin) and ST (heat-stable toxin) genes were compared with the standard Y1 adrenal cell and suckling mouse assays for their ability to identify ETEC in a population of American adults experiencing acute episodes of diarrhea in South America and West Africa. The LT probe hybridized with 12% (64 of 529) of the E. coli colonies tested, whereas 11% (57 of 529) were positive by Y1 adrenal cell assay. DNA from 9% (47 of 529) of the E. coli colonies tested hybridized with the ST probe, whereas only 5% (28 of 529) produced ST as measured by the suckling mouse bioassay. For the patient samples tested, correlation between probe and bioassay for LT was 97%, or three discrepancies in 111 patients tested. Overall concordance of the ST probe and bioassay was 95%, or five discrepancies in 111 patients. Enzyme-labeled oligonucleotide probes represent a major advance in the diagnosis of ETEC-associated diarrheal disease and may be used in laboratories with minimal equipment.
Selective association and transport of Campylobacter jejuni through M cells of rabbit Peyer's patches.
M cells in the Peyer's patches may facilitate transport of pathogens such as Campylobacter jejuni from the intestine. We evaluated this hypothesis by using electron microscopy to examine Peyer's patches in ligated adult rabbit ileal loops inoculated with 5-mL suspensions of 10(9) cfu/mL of Campylobacter jejuni. Peyer's patches taken at intervals from 15 min to 2 h after inoculation of loops in anaesthetized rabbits provided evidence that Campylobacter jejuni selectively adhered to M cells as opposed to absorptive epithelial cells and was transported, apparently intact, into the M cell follicle. Although intercellular organisms were seen within the follicle, many others were phagocytosed by lymphoid cells. The proximity of the lymphatic and blood circulatory systems to the M cell follicle makes this a probable route for systemic spread of Campylobacter jejuni.
Comparison of the characteristics of children with multiple admissions to hospital for asthma with those with a single admission.
Hospital admission rates in children for asthma have increased strikingly and part of this increase is due to an increase in the readmission rate. The study compared the characteristics of European children with multiple admission to hospital for asthma with those having their first admission for asthma. The number and magnitude of the differences found were small. Differences found included asthma drug management in the 24 hours prior to the index admission and six months later and days lost from school. Twenty-four percent of study population were readmitted within six months. The number of parents who smoked and the number of pets in the home are of concern and the lack of difference between the multiple and single admission groups suggest our education efforts are ineffectual at altering parental behaviour.
Intra-cortical inhibition prevents simple cells from responding to textured visual patterns.
Evidence is presented that simple cells in the cat striate cortex (area 17) fail to respond to two dimensional random patterns but respond vigorously to one dimensional patterns with identical power at the preferred orientation of the cell. Further observations suggest that complex cells inhibit simple cells so as to permit them to respond selectively to one-dimensional stimuli. Implications for the role of this inhibition in visual analysis are discussed.
Motion smear.
It is well known that the visual system summates signals over time, about 120 ms in daylight. Although this summation has the obvious advantage of enhancing visual sensitivity, it creates the potential problem of motion smear when viewing moving targets, whose images are also summated over time. Here I report some measurements which reveal that provided the moving target is exposed for long enough to elicit a clear sensation of motion, the amount of smear is far less than may be expected. This suggests that the visual mechanisms which signal motion are also responsible for signalling a clear unsmeared perception of the target in motion.
Suprascapular entrapment neuropathy: a clinical, anatomical, and comparative study. Part 2: anatomical study.
Two hundred eleven adult scapulae were examined and quantitative data pertaining to the dimensions of the suprascapular notch were obtained. Six types of suprascapular notch were observed. Transitions tended to occur between Types II, III, and IV. A classification function was developed utilizing the measured values of the dimensions of the suprascapular notch, which might help in assigning the scapulae to these transitional types. Dissections of the suprascapular area were performed in 15 cadavers. Static and dynamic relationships of the suprascapular nerve to the suprascapular foramen were examined.
Suprascapular entrapment neuropathy: a clinical, anatomical, and comparative study. Part 3: comparative study.
The suprascapular ligament seems to serve no defined function in the human. A comparative study was undertaken to elucidate its function. The suprascapular region was dissected in species representing seven existing primate families and six subprimate families. A striking dichotomy of pattern was observed. In the New World primates, the suprascapular ligament appeared to be continuous with the coracoclavicular ligament; the former merely served to increase the area of bony attachment of the coracoclavicular ligament. In the Old World monkeys and subprimate mammals, the suprascapular ligament was entirely absent. The human anatomy was comparable to that found in the New World primates. This dichotomy of pattern seems to be related to the function of the upper extremity in the different classes of mammals.
Human resources for the energized lab.
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