Search PubMed⌕ Search

Biomedical subjects

D Charles

Publications and source records attributed to D Charles.

At least 19 recordsLinked to original sources
PubMed1998

Resistance to interference in human associative learning: evidence of configural processing.

In 4 experiments the authors used 2-stage designs to study susceptibility to interference in human discrimination learning. The experiments used a food allergy task. In Experiment 1, participants were presented with a discrimination in Stage 1 in which Food A predicted an allergy outcome (A-->O). In Stage 2, when combined with Food B, Food A predicted the absence of the allergy (B-->O, AB-->no O). In the test phase, Food A was found to have retained its Stage 1 association with the allergy despite the potentially interfering Stage 2 trials. In Experiment 2, a discrimination between 2 compounds (AB-->O, CD-->no O) remained intact despite subsequent complete reevaluation of the elements, (A-->no O, B-->no O, C-->O, D-->O); in Experiments 3 and 4, a discrimination between 2 pairs of elements (A-->O, B-->O, C-->no O, D-->no O) remained intact despite subsequent complete reevaluation of the AB and CD compounds, (AB-->no O, CD-->O). These experiments yielded evidence of remarkable resistance to interference in human discrimination learning. The results are at variance with the predictions of J. M. Pearce's (1987, 1994a) configural theory of associative learning.

Association Learning↗
PubMed1998

Modelling multiple-cause structure using rectification constraints.

We present an artificial neural network which self-organizes in an unsupervised manner to form a sparse distributed representation of the underlying causes in data sets. This coding is achieved by introducing several rectification constraints to a PCA network, based on our prior beliefs about the data. Through experimentation we investigate the relative performance of these rectifications on the weights and/or outputs of the network. We find that use of an exponential function on the output to the network is most reliable in discovering all the causes in data sets even when the input data are strongly corrupted by random noise. Preprocessing our inputs to achieve unit variance on each is very effective in helping us to discover all underlying causes when the power on each cause is variable. Our resulting network methodologies are straightforward yet extremely robust over many trials.

Animals↗
PubMed1996

[Etiopathogenic, ultrasonographic and prognostic features of postpartum cardiomyopathy].

Peripartum cardiomyopathy is a classic but uncommon entity in African women about which there is little etiologic understanding. From January 1990 to March 1996 a series of 30 cases of peripartum cardiomyopathy was collected at the Principal Hospital in Dakar, Senegal. Peripartum cardiomyopathy was defined as the occurrence of cardiac insufficiency in a woman with no previous history of heart disease, during the period between the second and twentieth weeks after delivery confirmed by ultrasound evidence of dilated cardiomyopathy. The overall incidence of peripartum cardiomyopathy during the study period was 30 out of 1200 deliveries. The mean age of the women in the study was 34 years and mean parity was 5.2. In 13.3% of cases births involved twins. There were no predisposing socio-economic or climatic factors. The clinical picture was severe cardiac failure in 80.3% of cases and left ventricular insufficiency in 16.6%. In all cases ultrasound findings were typical of dilated cardiomyopathy. Serum selenium and vitamin B1 levels were normal. Measurements of T CD4 and CD8 in eight patients were normal. Conversion enzyme inhibitors were administered to twenty patients. Complete remission was achieved in 14 patients, three patients died, and thirteen patients presented ultrasonic evidence of persistent dilated cardiomyopathy. One patient relapsed after a subsequent delivery. These findings are in agreement with previous reports concerning the clinical and prognostic features of peripartum cardiomyopathy in Africa.

Adolescent↗
PubMed1995

A comparison of percutaneous and operative tracheostomies in intensive care patients.

The aim of our study was to compare the complication rate of convenional surgical and percutaneous dilational tracheostomies performed under general anaesthesia in critically ill patients. Fifty-three consecutive patients whose lungs were mechanically ventilated and who required tracheostomy were randomised to undergo either conventional surgical tracheostomy (n = 28) in the operating room or percutaneous dilational tracheostomy (n = 25) in the intensive care unit under general anaesthesia. All of the procedures were successfully completed. No deaths were related to the performance of either tracheostomy technique. Three patients in each group required a dressing change for minor bleeding at the tracheostomy site. There was no major bleeding requiring blood transfusion. One patient in each group developed atelectasis detected on chest x-ray post-operatively. In the surgical tracheostomy group, there were two patients with cuff leaks, one with a stomal infection and one with a pneumothorax. None of these complications occurred after percutaneous, dilational tracheostomy. We conclude that the low incidence of complications in both groups indicates that percutaneous dilational tracheostomy can be performed as safely in the intensive care unit with general anaesthesia as surgical tracheostomy can be performed in the operating room.

Adult↗
PubMed1994

Angiographic embolization for the treatment of epistaxis: a review of 108 cases.

Ninety-seven patients were referred to the Toronto Hospital (Western Division) between January 1984 and January 1992 for selective angiographic embolization (108 embolizations, including repeat procedures) to control intractable or recurrent severe epistaxis. Eighty-one patients (comprising 94 embolizations) were referred on an emergent basis because of failure of conventional conservative therapy, consisting of anterior and posterior packing. The remaining 16 patients (14 embolizations) were referred electively for recurrent epistaxis. A retrospective review of these cases was performed, with long-term telephone follow-up achieved in over 95% of cases. Embolization safely controlled active hemorrhage in 88% of the emergent cases. The success rate increased to 90% when two cases in which the source of epistaxis was found to be from the internal carotid artery were excluded (because these vessels could not be safely embolized). Of the patients whose epistaxis was initially controlled by embolization, 82% had no further nosebleeds (follow-up time ranged from 2 to 82 months; average, 26.8 months). More than half of the long-term failures were seen in patients with Osler-Weber-Rendu disease. Overall, the mortality rate was 0% and the long-term morbidity rate was 2% (one cerebral vascular accident and one case of skin slough in the territory of the superficial temporal artery.

Adolescent↗
PubMed1994

[Difficulties in diagnosing idiopathic hypereosinophilic syndrome in Black Africa. A case report observed in Senegal].

A combination of febrile malaise with adenopathy, massive hypereosinophilia (62678 components/mm3) and visceral, cutaneous, central nervous and digestive infiltration suggesting essential hypereosinophilic syndrome was observed in a 42-year-old male Senegalese. Diagnosis was confirmed after excluding all other possible causes in particular parasitic infection and by the rapidly fatal outcome. To our knowledge, this is the first reported case of essential hypereosinophilic syndrome in West Africa. Because of the high incidence of parasitic hypereosinophilia in this region and the non-specific nature of the symptoms, diagnosis of this syndrome can be difficult. In Africa more than elsewhere, diagnosis must be made after elimination of all other possible causes based on the criteria of Chusid. Although uncommon, essential hypereosinophilic syndrome has an unfavorable prognosis even when immunosuppressor therapy is administered.

Adult↗
PubMed1994

[Vitamin deficiency pancytopenia].

Eight patients with vitamin deficiency pancytopenia were admitted, within a year, in a department of internal medicine. Folic acid and vitamin B12 metabolism and the clinical and haematological symptoms are discussed. These vitamin deficiencies are frequent in underdeveloped countries and are responsible of megaloblastic anaemia. Such deficiencies may also influence the granulocyte and platelet lines and may be mistaken for leukaemia. A therapeutic test may be undertaken, giving rapid diagnosis and avoiding high mortality.

Adult↗
PubMed1993

Determination of sensitivity to antifungal drugs: evaluation of an API kit.

Evaluation of a commercial kit method for testing sensitivity of yeasts to antifungal drugs was performed employing agar gel dilution as the reference method. For the cidal drugs amphotericin B and flucytosine, results were closely comparable. For the three azole drugs tested, miconazole, econazole and ketoconazole, the discrepant results obtained probably relate to a number of factors affecting the end-point when testing these agents. Although easy to perform, the kit method is relatively expensive and the newer antifungal agents (e.g. fluconazole and itraconazole) are not included. Though showing promise, the kit method has limitations in its present format.

Antifungal Agents↗
PubMed1992

An improved method of in vivo wound disruption and measurement.

Biomechanical studies of wound strength are important because of new investigations in growth factors, cytokines, and fetal wounds. We compared two traditional methods of wound disruption measurement with a novel computerized model designed for in vivo experiments. An Instron tensiometer (INSTS) and an air insufflated positive pressure device (AIPPD) were compared with a vacuum-controlled wound chamber device (VCWCD). The VCWCD produced vacuum at the wound site and wound disruption was monitored with two video camera/recorders. Rats were marked with a template guide for a 2.5 cm, full-thickness, abdominal incisional wound. Rats were divided into three groups and studied at 2, 7, or 14 days after wounding. The recorded images were computer digitalized to generate wound strength curves from a three-dimensional model. A comparison of the wound disruption curves demonstrated that the VCWCD was comparable to the INST or AIPPD in normal wound healing (P greater than .40). The VCWCD provided data with less standard error at 2 days after wounding (P less than 05). In separate series of experiments, VCWCD was tested in the early phases of healing and was found to be sensitive to change at intervals of 48 hr after wounding (P less than .005). The INST or AIPPD methods could not perform this task because of an unacceptable level of random error after tissue manipulation. The VCWCD system was considered superior for evaluating early wound healing because it was an in vivo method which required minimal wound manipulation.

Animals↗
PubMed1992

[Slow ventricular tachycardia caused by naftidrofuryl overdose (naftidrofuryl and ventricular tachycardia)].

Treatment with intravenous naftidrofuryl may be complicated by ventricular arrhythmias. A case of slow ventricular tachycardia occurring in a 65-year-old man with a dilated cardiomyopathy following an accidental overdose of naftidrofuryl (2 x 200 mg ampules in 250 ml of 5% glucose solution in 2 hours) prescribed for complicated arterial disease of the lower limbs is reported. This sustained ventricular tachycardia converted spontaneously after several hours. This case emphasises the risk of arrhythmogenic effects of this drug and indicates the need for careful monitoring when it is used intravenously in patients with underlying heart disease.

Aged↗
PubMed1992

Prevalence & pathogenesis of hypophosphatemia in ventilated patients.

Hypophosphatemia was found in 12 (43%) patients within 24-36 h of mechanical ventilation in a group of 28 patients in an intensive care unit. The hypophosphatemic patients had a significant lowering of renal phosphorus threshold (P = 0.005) and inappropriate phosphaturia. These abnormalities resolved once ventilation was discontinued. Serum parathyroid hormone (PTH) levels were unaltered in this group of patients suggesting that some factor other than PTH was responsible for hypophosphatemia. This study has demonstrated that abnormalities of renal phosphate handling can cause hypophosphatemia in ventilated patients.

Adolescent↗