Search PubMed⌕ Search

Biomedical subjects

C Pereira

Publications and source records attributed to C Pereira.

At least 73 records · Page 4Linked to original sources
PubMed1996

Semi-automated thresholding technique for measuring lesion volumes in multiple sclerosis: effects of the change of the threshold on the computed lesion loads.

Quantitative evaluation of lesion load in multiple sclerosis (MS) from magnetic resonance imaging (MRI) scans is becoming important in understanding and monitoring the progression of the disease. Methods of MS lesion segmentation based on intensity thresholding offer one of the most robust and easily-implemented means of computing the total lesion volume. This study evaluated the effects of slight changes in the choice of intensity threshold on computed lesion volumes in 20 patients with MS using such a technique. After judging the optimum choice of threshold value, the threshold value was increased and decreased by 3% in 1% steps around this value; we observed a mean change of 15% in computed lesion volumes for 1% changes of threshold value. Larger changes in lesion volume were found when the threshold was changed by larger amounts. On the other hand, the amount of time required for manual review decreased, and the confidence with which manual review could be performed increased when using lower thresholds. This study shows that the choice of threshold is a crucial factor in measuring lesion volumes in MS when using intensity-based techniques. It also suggests that in multicenter and/or longitudinal studies, criteria for choosing the threshold should be developed whereby the threshold level should be set such that all MR visible lesions are above it, in order to minimise the human interaction and, consequently, the reproducibility of the results.

Brain↗
PubMed1996

Prenatal and postpartum pharmacokinetics of stavudine (2',3'-didehydro-3'-deoxythymidine) and didanosine (dideoxyinosine) in pigtailed macaques (Macaca nemestrina).

Stavudine (5 mg/kg of body weight; n = 7) or didanosine (3.2 mg/kg; n = 4) was administered as an intravenous bolus to pregnant pigtailed macaques (Macaca nemestrina) near term and 4 to 5 weeks postpartum. No significant differences were found between the prenatal and postpartum total plasma drug clearance, steady-state volume of distribution, terminal plasma drug half-life, mean body residence time, or recovery of unchanged drug in urine. These data indicate that pregnancy does not affect the pharmacokinetics of stavudine or didanosine in M. nemestrina.

Animals↗
PubMed1996

Uterine evacuation by vaginal misoprostol after second trimester pregnancy interruption.

BACKGROUND: The purpose was to study the capacity of vaginal misoprostol in combination with methylergometrine to achieve complete evacuation of the uterus without ensuing surgical evacuation of the uterine cavity. METHODS: We performed this trial on 228 women seeking pregnancy interruption. Vaginal misoprostol was given in a dosage of 800 micrograms in early second trimester. All women received concomitant treatment with peroral methlyergometrine from the moment of misoprostol application every 8 hours until uterine evacuation. Follow-up was continued until the first menstruation after interruption. RESULTS: Complete uterine evacuation was achieved in 173/228 cases (76%) [group 1]. The remaining 55 women [group 2] underwent manual evacuation of placental remnants trapped in the cervix. In seven of these women a conventional curettage was carried out due either to ultrasound evidence of placental remnants or due to uterine bleeding. The interval between misoprostol application and fetal expulsion averaged 14.9 hours (s.d. 9.6) in group 1 and 21.0 hours (s.d. 14.5) in group 2 (p=0.006). CONCLUSIONS: Misoprostol, in combination with methylergometrine, is a remarkably efficient drug in achieving uterine evacuation also in the absence of surgical evacuation of the uterine cavity. The present study provides justification for a more expectant attitude after vaginal misoprostol treatment for pregnancy interruption. The avoidance of close to 80% of otherwise conventional curettages would seem to represent a major advantage, particularly in settings where manpower and material resources are scarce.

Abortion, Induced↗
PubMed1995

The nitric oxide transduction pathway in Trypanosoma cruzi.

A nitric oxide synthase was partially purified from soluble extracts of Trypanosoma cruzi epimastigote forms. The conversion of L-arginine to citrulline by this enzyme activity required NADPH and was blocked by EGTA. The reaction was activated by Ca2+, calmodulin, tetrahydrobiopterin, and FAD, and inhibited by N omega-methyl-L-arginine. L-Glutamate and N-methyl-D-aspartate stimulated in vivo conversion of L-arginine to citrulline by epimastigote cells. These stimulations could be blocked by EGTA, MK-801, and ketamine and enhanced by glycine. A sodium nitroprusside-activated guanylyl cyclase activity was detected in cell-free, soluble preparations of T. cruzi epimastigotes. L-Glutamate, N-methyl-D-aspartate, and sodium nitroprusside increased epimastigote cyclic GMP levels. MK-801 bound specifically to T. cruzi epimastigote cells. This binding was competed by ketamine and enhanced by glycine or L-serine. Evidence thus indicates that in T. cruzi epimastigotes, L-glutamate controls cyclic GMP levels through a pathway mediated by nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1995

Dietary chlorophyllin is a potent inhibitor of aflatoxin B1 hepatocarcinogenesis in rainbow trout.

Epidemiological and experimental evidence indicates a strong relationship between diet and cancer. The purpose of this study was to examine the potential of chlorophyllin (CHL), a food-grade derivative of the ubiquitous green plant pigment chlorophyll, to inhibit experimental carcinogenesis. We report that CHL is a potent, dose-responsive inhibitor of aflatoxin B1 DNA adduction and hepatocarcinogenesis in the rainbow trout model when fed with carcinogen. CHL neither promoted nor suppressed carcinogenesis with chronic postinitiation feeding. By molecular dosimetry analysis, reduced aflatoxin B1-DNA adduction accounted quantitatively for reduced tumor response up to 2000 ppm dietary CHL, but an additional protective mechanism was operative at 4000 ppm CHL. The finding of potent inhibition (up to 77%) at CHL levels well within the chlorophyll content of some green leafy vegetables may have important implications in intervention and dietary management of human cancer risks.

Aflatoxin B1↗
PubMed1995

Resolution-dependent estimates of lesion volumes in magnetic resonance imaging studies of the brain in multiple sclerosis.

In this study, we investigated the relationship between multiple sclerosis lesion volumes measured from magnetic resonance imaging scans and image-slice thickness. The lesion volume was computed using a semiautomated thresholding technique from axial scans of the brain of varying slice thickness. Ten patients were studied, and in all cases the computed lesion volume increased with decreasing slice thickness (p = 0.01). Linear extrapolation from our data allowed the lesion volume at very small slice thickness to be estimated; this was found to be on average 20% greater than that obtained using a slice thickness of 5 mm. Furthermore, there were considerable differences in the percentage of change in lesion volume from patient to patient, and it would appear that there is a larger variation with slice thickness for patients with smaller lesions and higher lesion loads.

Adult↗
PubMed1995

Transitional progressive multiple sclerosis: MRI and MTI findings.

Transitional progressive multiple sclerosis (MS) is quite an unusual form of presentation and course of the disease. A case with this progressive form is presented and brain MRI and MTI findings are discussed in relation to the possible insight they may provide for understanding the mechanisms that determine progressive disability in MS.

Adult↗
PubMed1994

Why Africa said no.

Explore the source record for details and available documents.

Academies and Institutes↗
PubMed1994

Quantitative carcinogenesis and dosimetry in rainbow trout for aflatoxin B1 and aflatoxicol, two aflatoxins that form the same DNA adduct.

Two exposure protocols were used to establish complete dose-response relationships for the hepatic carcinogenicity and DNA adduction in vivo of aflatoxin B1 (AFB1) and aflatoxicol (AFL) in rainbow trout. By passive egg exposure, AFL was taken up less well than AFB1, but was more efficiently sequestered into the embryo itself, to produce an embryonic DNA binding curve that was linear with carcinogen dose and with a DNA binding index three-fold greater than AFB1. Both aflatoxins produced the same phenotypic response, predominantly mixed hepatocellular/cholangiocellular carcinoma. Tumor responses as logit [incidence] vs. In [dose] were parallel-offset, non-linear responses showing a three-fold greater carcinogenic potency for AFL at all doses examined (i.e. 3 times more AFB1 than AFL required to produce an equivalent liver tumor incidence). By molecular dosimetry analysis (logit [incidence] vs. In [DNA adducts]), the two data sets were coincident, indicating that, per DNA adduct formed in vivo in total embryonic DNA, these two aflatoxins were equally efficient in tumor initiation. By dietary fry exposure, both carcinogens produced linear DNA binding dose responses in liver, but with an AFL target organ DNA binding index only 1.14 times that of AFB1 by this exposure route. The tumor dose-response curves also did not exhibit the three-fold difference shown by embryo exposure, but were closely positioned non-linear curves. Since the DNA binding indices differed by only 14%, the resulting molecular dosimetry curves for AFL and AFB1 by dietary exposure were similar to the tumor response curves. These results indicate that differing exposure routes produced differing relative carcinogenicity estimates based on doses applied, as a result of protocol-dependent differences in AFL and AFB1 pharmacokinetic behaviors, but that potency comparisons based on molecular dose received were similar for the two protocols. By comparison with standard DNA adducts produced in vitro using the dimethyloxirane-produced 8,9-epoxides of AFB1 and AFL, we conclude that > 99% of AFL-DNA adducts produced in vivo were identical to those produced by AFB1. Thus similar molecular dosimetry responses should be expected under all exposure protocols in which the two parent carcinogens do not exhibit differing toxicities to the target organ.

Aflatoxin B1↗
PubMed1994

A long-term follow-up of hepatitis B vaccination in patients with congenital clotting disorders.

All patients with congenital clotting disorders attending our centre routinely receive hepatitis B vaccination. We have assessed retrospectively the vaccine responses in 167 such individuals, with a follow-up period of up to 7.5 years. The initial postvaccine anti-HBs response was lower in older patients (p = 0.001), those infected with human immunodeficiency virus (HIV) (p = 0.05), and those who received intradermal rather than subcutaneous administration of vaccine (p = 0.08). It was estimated that the median time for anti-HBs levels to fall to 100 IU l-1 was between 36 and 42 months, with a shorter period for older or HIV-infected patients. Although the persistence of protective antibody levels can be predicted to some extent from the absolute levels of initial postvaccine anti-HBs, the wide variation in antibody decline between individuals precludes recommendation of the timing of vaccine booster doses solely based on this value.

Adolescent↗
PubMed1994

Obstetric implications of rhesus antigen distribution in Mozambican and Swedish women.

AB0 and Rhesus phenotypes were analyzed in 199 Mozambican women and the gene frequencies were calculated. The frequencies of the K and Fya antigens were also investigated. The findings were interpreted against the background of the corresponding phenotype distribution of a Swedish population. D- and Du-positive women amounted to 97.0%, which is significantly more than in Sweden (p < 0.001). Among AB0 groups it was found that blood group 0 is significantly more predominant in Mozambican than in Swedish women (p < 0.001). The reverse is true for blood group A (p < 0.001). Blood group B has a similar prevalence in Mozambican and Swedish women. The obstetric implication of the low prevalence of D-negative women is that the Rhesus alloimmunization problem may be of a much smaller magnitude than would be expected.

ABO Blood-Group System↗
PubMed1994

[Intracranial cavernous angioma].

Clinical, radiological and histopathological features of eight cases of symptomatic cavernous angioma are presented. Five patients were being evaluated for seizure, two for mass lesions and one for intracranial hemorrhage. CT and/or MRI detected the lesion in all cases, but there is not a characteristic image for cavernous angioma. Good results were obtained by microsurgical approach to these malformations in seven patients with only one patient suffering a worsening of neurological status after surgery.

Adolescent↗
PubMed1992

Parity-related prevalence of rhesus antigens among Mozambican parturients.

The potential risk of rhesus alloimmunization and the ensuing risk of fetal death with increasing parity were investigated in two groups of parturients; primiparous and grand multiparous (para > or = 5) women with liveborns. It was hypothesized that significantly fewer women of the latter than of the former group would be rhesus negative, since grand multiparity would be expected to be associated with an increased risk of late fetal death in rhesus-negative parturients. Primiparous (n = 390) and grand multiparous (n = 755) parturients with liveborns were studied in order to identify D- and Du-negative individuals. Sixteen out of 390 primiparas (4.10%) and 28/755 (3.71%) grand multiparas were D and Du negative. The difference did not reach statistical significance. It appears that being a D- and Du-negative grand multiparous parturient, in the absence of anti-D prophylaxis, is not a significant reproductive disadvantage to being primipara in terms of an increased risk of having stillborn babies.

ABO Blood-Group System↗
PubMed1992

Role of rhesus alloimmunization in the etiology of late fetal death in Maputo.

Grand multiparous parturients with unexplained late fetal death (n = 70) and with surviving newborns (n = 755) were analyzed and compared regarding blood group in general and presence of D and Du antigens in particular. In the stillbirth group, none of the parturients had any signs of disease (syphilis, preeclampsia, placental abruption, severe anemia or fever) that could be associated with the fetal death. It was found that none of the parturients with stillbirth were D- and Du-negative while 28/755 (3.71%) of parturients with liveborn babies were D- and Du-negative. It is concluded that, among grand multiparous parturients with otherwise unexplained late fetal death, the risk of having fetomaternal rhesus incompatibility as stillbirth etiology is insignificant. The advantage of introducing anti-D immunoglobulin for prophylaxis against rhesus alloimmunization would presumably be insignificant.

Developing Countries↗
PubMed1992

Phase II trial of cisplatin and alpha-interferon in advanced malignant melanoma.

PURPOSE: To evaluate the antitumor activity of combination cisplatin (CDDP) and alpha-interferon (alpha-IFN) in advanced, measurable metastatic melanoma. PATIENTS AND METHODS: Adult patients with metastatic melanoma were required to have bidimensionally measurable lesions and a Karnofsky performance status > or = 60%. Serum creatinine < or = to 1.5 mg/dL, creatinine clearance > or = 60 mL/min, adequate organ and bone marrow function, and radiologic proof of the absence of brain metastases were required. CDDP 40 mg/m2 intravenously (IV) on day 1 and day 8, and alpha-IFN 3 million units/m2 subcutaneously on days 1 to 5 and 8 to 12 were administered every 3 to 4 weeks. RESULTS: Forty-two patients were entered onto this phase II trial and were assessable for response and toxicity. Three patients achieved complete responses (CRs) that lasted 31+, 5, and 8+ months. Seven patients had partial responses (PRs) and a median response duration of 4.4 months. The overall objective response rate was 24% (95% confidence interval, 12% to 39%). Toxicities were mild. Only 11% of the courses required dose reduction of alpha-IFN, and three of 128 courses required CDDP dose reduction for reversible nephrotoxicity. CONCLUSION: The combination of moderate-dose CDDP and alpha-IFN as administered in this schedule is well tolerated and possesses encouraging activity in metastatic melanoma.

Adult↗
PubMed1991

Hepatitis C virus.

Explore the source record for details and available documents.

Blood Donors↗