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Biomedical subjects

R Loewen

Publications and source records attributed to R Loewen.

10 recordsLinked to original sources
PubMed2004

Advanced electronics for the CTF MEG system.

Development of the CTF MEG system has been advanced with the introduction of a computer processing cluster between the data acquisition electronics and the host computer. The advent of fast processors, memory, and network interfaces has made this innovation feasible for large data streams at high sampling rates. We have implemented tasks including anti-alias filter, sample rate decimation, higher gradient balancing, crosstalk correction, and optional filters with a cluster consisting of 4 dual Intel Xeon processors operating on up to 275 channel MEG systems at 12 kHz sample rate. The architecture is expandable with additional processors to implement advanced processing tasks which may include e.g., continuous head localization/motion correction, optional display filters, coherence calculations, or real time synthetic channels (via beamformer). We also describe an electronics configuration upgrade to provide operator console access to the peripheral interface features such as analog signal and trigger I/O. This allows remote location of the acoustically noisy electronics cabinet and fitting of the cabinet with doors for improved EMI shielding. Finally, we present the latest performance results available for the CTF 275 channel MEG system including an unshielded SEF (median nerve electrical stimulation) measurement enhanced by application of an adaptive beamformer technique (SAM) which allows recognition of the nominal 20-ms response in the unaveraged signal.

Cluster Analysis↗
PubMed2000

The Food Situations Questionnaire: a measure of children's willingness to try novel foods in stimulating and non-stimulating situations.

This paper reports the development and validation of a self-report measure of food neophobia for children. Items described hypothetical situations in which novel foods might be encountered and asked children to report how they would feel about tasting or eating them. Ten items, representing two correlated subscales, were selected from among a larger number, using standard item selection measures with a total of 335 children, aged 7-12 years. The two subscales represent willingness to try novel foods in highly stimulating circumstances and willingness to try novel foods in non-stimulating circumstances. The test was shown to significantly predict actual willingness to taste novel foods in a laboratory situation. In addition, it was shown to predict such willingness better than parents' reports of the children's neophobia. Finally, the test was shown to have satisfactory internal and test-retest reliabilities.

Age Factors↗
PubMed1999

Effects of prior exposure to palatable and unpalatable novel foods on children's willingness to taste other novel foods.

In two studies, 7- to 9-year-old and 10- to 12-year-old children received taste exposure to four good-tasting familiar, four good-tasting novel or four bad-tasting novel foods. Following this exposure phase, they saw a series of different foods, familiar and novel, and rated their willingness to taste them. For older children, exposure to the novel-good foods increased willingness to taste novel foods in comparison to the familiar-good control, while exposure to the novel-bad foods had no effect. For younger children, exposure to both novel-good and novel-bad foods decreased willingness to taste novel foods. The studies were originally framed in terms of children's schemas about novel foods and how exposure to good- and bad-tasting novel foods constituted provision of schema-inconsistent (novel-good) or schema-consistent (novel-bad) information. While such a framework accounted well for the results for the older children, it did not account for those for the younger children. The behaviour of the younger children was tentatively explained in terms of their attempt to regulate arousal produced by the initial exposure to the novel foods.

Child↗
PubMed1997

Cytotoxic therapy-induced D-xylose malabsorption and invasive infection during remission-induction therapy for acute myeloid leukemia in adults.

PURPOSE: To study the sequential changes in the intestinal absorption of an oral pentose probe, D-xylose, in patients receiving therapy for untreated acute myeloid leukemia (AML), and to correlate these changes to infectious morbidity. PATIENTS AND METHODS: Serial D-xylose absorption studies were conducted in 110 consecutive adult patients admitted to a university-affiliated tertiary care hospital for remission-induction therapy for untreated newly diagnosed AML. Serial serum D-xylose levels were obtained 1 hour after a 5-g oral dose of D-xylose at baseline and weekly for 4 weeks until marrow recovery. These results were correlated with invasive infection using multivariate techniques. RESULTS: The mean (+/- SEM) serum D-xylose levels were 0.88 +/- 0.03, 0.69 +/- 0.03, 0.58 +/- 0.02, 0.53 +/- 0.02, and 0.73 +/- 0.02 mmol/L at baseline and weeks 1 to 4, respectively (P < .0001, analysis of variance [AN-OVA]). Time to malabsorption varied with induction regimen (P = .007, log-rank test). Bloodstream infections during week 2 correlated with malabsorption (P = .007). Neutropenic enterocolitis correlated independently with induction regimen (P = .009), malabsorption at week 2 (P = .02), and the development of candidemia (P = .005). Hepatosplenic fungal infection correlated with induction regimen (P = .03), malabsorption at week 2 (P = .02), and fever at diagnosis (P = .003). Malabsorption was unrelated to the duration of severe neutropenia and the administration of parenteral nutrition. CONCLUSION: Serial D-xylose absorption studies in subjects with AML produced a characteristic profile of cytotoxic therapy-related damage to the functional integrity of the intestinal epithelium that was regimen dependent, myelosuppression independent, and predictive for invasive infectious complications. Further study to validate these observations appears warranted.

Adolescent↗
PubMed1995

Reduced requirement for antibiotic therapy targeting gram-negative organisms in febrile, neutropenic patients with cancer who are receiving antibacterial chemoprophylaxis with oral quinolones.

An open, nonrandomized, phase 2 study of 53 adult patients who had 60 neutropenic episodes was conducted to determine if quinolone antibacterial prophylaxis could reduce the need during febrile episodes for parenteral therapy directed at gram-negative organisms. Suspected infections among recipients of quinolones were treated empirically with vancomycin and ceftazidime; therapy with the latter was discontinued after 24-48 hours in the absence of infection due to gram-negative organisms. In five neutropenic episodes, patients had no fever or infection. An aerobic gram-negative bacillus was isolated during only 1 (1.8%) of 55 febrile episodes. Febrile episodes occurred at a median of day 15 of cytotoxic therapy. Vancomycin monotherapy was successful in 22 (50%) of 44 evaluable cases. Modification of the vancomycin regimen by the addition of metronidazole or rifampin increased the response rate to 40 (91%) of 44. Response occurred after a median of 4.5 days. Parenteral empirical therapy with amphotericin B was required in only 3 (7%) of 44 cases. The study strategy safely permitted a reduction in the amount and duration of antibiotic therapy directed against gram-negative organisms in febrile neutropenic patients.

Administration, Oral↗
PubMed1995

Invasive fungal disease in adults undergoing remission-induction therapy for acute myeloid leukemia: the pathogenetic role of the antileukemic regimen.

Using multivariate techniques, we studied the relationships of cytotoxic regimen, intestinal mucosal damage, and fungal colonization in the pathogenesis of invasive fungal disease in 138 patients undergoing induction therapy for untreated acute myeloid leukemia (AML) according to three institutional protocols: AML-84 (cytarabine/daunorubicin), AML-87 (high-dose cytarabine/etoposide/daunorubicin), and AML-88 (mitoxantrone/etoposide). Invasive fungal disease occurred in 36%, 6%, and 2.6% of patients participating in protocols AML-87, AML-84, and AML-88, respectively (chi 2 = 23.465; P < .0001). Protocol AML-87 was the strongest independent predictor in the multivariate model (RR = 26.7; P < .0001). Cytotoxic therapy-related epithelial damage in the gut, as measured by D-xylose malabsorption, correlated with invasive fungal disease and protocol AML-87. Fungal colonization, a predictor of invasive fungal disease, correlated with frequent modifications of antibiotic regimens. These results demonstrate the role of cytotoxic regimen-related gut epithelial damage, antibiotic-prescribing behavior, and fungal colonization in the pathogenesis of invasive fungal disease in patients with leukemia.

Adolescent↗
PubMed1989

Sex differences in small-magnitude heart-rate responses to sexual and infant-related stimuli: a psychophysiological approach.

Small-magnitude (2-3 beats per minute) heart-rate responses can show sex differences if assessed with a psychophysiological approach in which temporally fine-grained methods are used to determine topographical differences. Such differences emerged when 15 males and 37 females were shown videosegments depicting emotional scenes. Specifically, males accelerated to erotic segments (couples making love), while females accelerated to segments showing babies crying. In addition, the peak development of baby-cry-elicited accelerations occurred about 1 second before that of erotic segment-elicited accelerations. The results are consistent with a preparatory-response interpretation, but more research is needed both to investigate the generality of these sex differences in heart-rate responses, and to determine the role of experiential and psychosocial factors.

Adult↗
PubMedDate not supplied

Crystalloid structures in retroperitoneal paragangliomas: a light and electron microscopic study.

Samples from three clinically functional retroperitoneal paragangliomas were studied by light and electron microscopy. The tumors exhibited a Zellballen pattern histologically, and ultrastructurally all three neoplasms consisted of cells containing catecholamine granules. Prominent cytoplasmic crystalloids were present in all cases. The crystalloids were identified in routine histologic sections, demonstrated eosinophilia, and stained with periodic acid-Schiff, Giemsa, phloxine-tartrazine, and azan stains. Ultrastructurally the crystalloids were osmiophilic, often appeared as slender needles, were membrane bound, and demonstrated a periodicity of 9 nm. The crystalloids, unlike the catecholamine granules, were negative for catecholamine fluorescence. X-ray microanalysis, however, revealed the selective presence of chromium in both catecholamine granules and crystalloids.

Adult↗