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Biomedical subjects

D Ayers

Publications and source records attributed to D Ayers.

25 records · Page 2Linked to original sources
PubMed1993

Relation of tumor-cell ploidy to survival in children with medulloblastoma.

PURPOSE: To assess the value of tumor-cell ploidy as a predictor of survival in medulloblastoma. PATIENTS AND METHODS: Ploidy determinations were based on the flow-cytometric analysis of cellular DNA content in fresh tumor specimens taken from 34 consecutively treated children with newly diagnosed medulloblastoma. Patients were assigned a high or low risk of failure depending on tumor size and invasiveness, and the presence or absence of metastatic disease. Treatment consisted of radiotherapy, with or without chemotherapy, according to institutional or cooperative group protocols. RESULTS: Univariate analysis of candidate prognostic factors showed that only tumor-cell ploidy and clinical risk group had a statistically significant influence on survival. Patients with hyperdiploid stem lines (n = 9) had significantly longer survival times (P = .04) than did those with diploid lines (n = 20). The estimated 5-year survival probabilities (+/- SE) for these two subgroups were 89% +/- 11% and 48% +/- 13%, respectively. Although clinical risk status (high v low) showed essentially the same predictive strength as ploidy, the two features identified largely nonoverlapping subgroups. Thus, within the clinical high-risk group, it was possible to distinguish hyperdiploid patients whose 5-year survival rate (83% +/- 15%) was comparable to that of patients with localized, low-risk tumors. CONCLUSION: This prospective study indicates that both ploidy and clinical risk group are important prognostic factors in medulloblastoma. Their combined use at diagnosis would distinguish patients who require more aggressive therapeutic intervention (diploid, clinical high-risk group) from those who could be expected to benefit most from standard treatment.

Adolescent↗
PubMed1991

Mephenytoin phenotyping: lack of haematologic effect and timing of urine collections.

Mephenytoin is the prototype substrate for the genetically regulated, polymorphically distributed cytochrome P450, mephenytoin hydroxylase. Mephenytoin is an anticonvulsant which has been associated with leukopenia when used chronically. The haematologic effects of a single dose of oral mephenytoin, as is typically used to determine drug metabolism phenotype for this polymorphism, have not been reported. We administered 100 mg oral racemic mephenytoin to 30 healthy male volunteers and measured complete blood count three times weekly for 23 days. The time dependency of the urinary ratio of S to R mephenytoin in five serial urine samples (0-4, 4-8, 8-16, 16-24 and 24-32 h after the dose) was evaluated. There were no significant decreases from baseline in any subject in leukocyte count, haematocrit or platelet count. Two of the 30 subjects both of Indian extraction, were poor metabolizers of mephenytoin. The S:R ratio decreased with time (p = 0.001). Using the 0-4 h urine, one subject would have been misphenotyped as a poor metabolizer; phenotype assignments were in agreement with each other based on all subsequent urine collections. We conclude that there is no evidence that single dose mephenytoin is associated with haematologic toxicity in healthy male volunteers, and that the 4-8 h post-dose urine is as reliable as the 24-32 h collection for assignment of phenotype.

Adult↗
PubMed1991

Accuracy of pulse oximeters in estimating heart rate at rest and during exercise.

Pulse oximeters are being widely used for non-invasive, simultaneous assessment of haemoglobin oxygen saturation. They are reliable, accurate, relatively inexpensive and portable. Pulse oximeters are often used for estimating heart rate at rest and during exercise. However, at present the data available to validate their use as heart rate monitors are not sufficient. We evaluated the accuracy of two oximeters (Radiometer, ear and finger probe; Ohmeda 3700, ear probe) in monitoring heart rate during incremental exercise by comparing the pulse oximeters with simultaneous ECG readings. Data were collected on eight men (713 heart rate readings) during graded cycle ergometer and treadmill exercise to volitional fatigue. Analysis by linear regression revealed that general oximeter readings significantly correlated with those of ECG (r = 0.91, P less than 0.0001). However, comparison of heart rate at each level of work showed that oximeter readings significantly (P less than 0.05) under-estimated rates above 155 beats/min. These results indicate that the use of pulse oximeters as heart rate monitors during strenuous exercise is questionable. This inaccuracy may well originate from the instability of the probes, sweating, other artefacts during exercise, and measurement of different components in the cardiovascular cycle.

Adult↗
PubMed1991

Physiological correlates to 800 meter running performance.

Much of the previous research efforts aimed at determining those physiological characteristics that contribute to distance running success have centered around distances greater than 1500 meters with little attention to events such as the 800 meter run. Therefore, this investigation examined the relationship between selected physiological and body composition, characteristics and performance in an 800 meter run. Measurements of body composition, VO2max, running economy, and performance times for 100 and 300 meter dashes were obtained on 11 male track athletes. Stepwise multiple regression analysis was performed using 800 meter race time as the dependent variable. Although the combination of 300 and 100 meter run times, percent body fat, running economy and VO2 max as independent variables accounted for the greatest amount of total variance (r2 = .89), the additional variance explained by the model did not increase significantly (p greater than 0.05), when VO2max, percent body fat, and running economy were added to a model which contained 300 and 100 meter run time (r2 = .85) as the explanatory variables. These data offer additional support for the notion that much of the intramuscular ATP produce and utilized during an 800 meter run comes from anaerobic metabolic pathway.

Adult↗
PubMed1991

Joint and systemic distribution of dialysis amyloid.

Deposition of beta 2-microglobulin amyloid in the joints of dialysis patients is common and begins early in the course of treatment, but its pathogenic significance in the production of dialysis arthropathy is uncertain. The joints (hip, knee, shoulder, elbow, wrist, cervical and lumbar spine, sacroiliac joint) and systemic tissues of 19 autopsied patients who had undergone haemodialysis for between 6 and 231 months were examined histopathologically for the presence of beta 2-microglobulin amyloid; it was present in all joints examined, including those unassociated with radiological changes and those of patients who had been on haemodialysis alone for only 24 months. Osteoarticular beta 2-microglobulin amyloid deposits were also found in patients who had been treated mainly by continuous ambulatory peritoneal dialysis. Systemic amyloid deposition was only seen in patients who had been haemodialysed for more than 13 years and consisted of sparse tiny deposits in blood vessel walls.

Aged↗