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Biomedical subjects

S Dubé

Publications and source records attributed to S Dubé.

At least 37 records · Page 2Linked to original sources
PubMed1994

Visual search asymmetry for viewing direction.

In visual search experiments, we examined the existence of a search asymmetry for the direction with which three-dimensional objects are viewed. It was found that an upward-tilted target object among downward-tilted distracting objects was detected faster than when the orientation of target and distractors was reversed. This indicates that the early visual process regards objects tilted downward with respect to the observer as the situation that is more likely to be encountered. That is, the system is set up to expect to see the tops of these objects. We also found a visual field anisotropy, in that the asymmetry was more pronounced in the lower visual field. These findings are consistent with the idea that the tops of objects are usually situated in the lower visual field and less often in the upper field. Examination of the conditions under which the asymmetry and the anisotropy occur demonstrated the importance of the three-dimensional nature of the stimulus objects. Early visual processing thus makes use of heuristics that take into account specific relationships between the relative locations in space of the observer and 3-D objects.

Attention↗
PubMed1994

[Factors of recurrence in Crohn disease].

The surgical treatment of complications of Crohn's disease is often postponed, because of the threat of short gut and high recurrence rates. We reviewed retrospectively 286 cases of intestinal resection to evaluate factors influencing the recurrence of Crohn's disease after surgery. Recurrence was defined as the need for reoperation. Risk factors used as independent variables are all subject of controversy in recent literature. These factors included: smoking, blood transfusion, contamination, localisation of the disease, length of resection, microscopic margins and the duration of follow-up. A logistic regression model was calculated, using recurrence as the dependent variable. The mean follow-up is 55 months. Kaplan Meier was used to measure the recurrence rate. Duration of follow-up is the most important variable. The length of resection and the positive margins can statistically predict recurrence (p = 0.046 et p = 0.016), both having a predictive value of 72%. A resection with clear margins decreases the recurrence rate significantly (15%) (p = 0.0025).

Adolescent↗
PubMed1993

Ambiguous plaids: switching between coherence and transparency.

A plaid pattern consisting of two differently oriented moving gratings can be seen as two alternative percepts: transparency, in which the two gratings are seen to slide over each other in their respective directions, or coherence, in which one integrated pattern (the plaid) is seen to move in a new direction. With prolonged inspection, an observer switches between these two alternatives. It was found here that adaptation to unambiguous coherence reduces the time that coherence is seen with an ambiguous test stimulus. Similarly, adaptation to transparency reduces the time transparency is seen. Analysis of the duration of consecutive episodes revealed that the underlying processes are adapted independently. Control experiments confirmed that adaptation occurred to the coherent plaid and not to the intersections, and that this adaptation was not simply a directional motion aftereffect. It is concluded that switching occurs between motion processes at different cortical levels that can be adapted independently.

Adaptation, Ocular↗
PubMed1993

The effect of disparity on motion coherence.

Many moving plaid stimuli are ambiguous, and perception switches between a coherent plaid pattern and two transparent gratings. Here, experiments are reported that examined the effect of stereodepth between the two gratings of the moving plaid stimulus on the perception of coherence or motion transparency. Increasing disparity increased the percentage of time that two independently drifting transparent gratings were perceived. This was studied for plaids with various levels of intersection luminance. Using intersection luminances beyond conditions of physical transparency increased the percentage of time that one coherent plaid was seen. These two opposing influences could be pitted against each other to achieve constant levels of coherence. An adaptation paradigm was also used in which observers adapted to a stationary stimulus with either zero, crossed or uncrossed disparity between the gratings, and then indicated the occurrence of coherence and motion transparency in test stimuli of drifting plaids with zero, crossed or uncrossed disparity. Adaptation to crossed and uncrossed stereo-depth increased relative perceived coherence equally, especially for zero test disparity. An analysis of the length of the episodes of coherence and motion transparency indicated that the effect of adaptation was to decrease the length of motion transparency episodes, while the length of coherence episodes did not change. It is concluded that mechanisms involved in the processing of stereo-depth must have an input to the integration stage of the motion channel and that pattern and component motion mechanisms can operate quite independently.

Adaptation, Ocular↗
PubMed1992

Comparing local and remote motion aftereffects.

A new method, using phase-reversing sinusoidal gratings to cancel perceived motion, was developed to measure the motion aftereffect (MAE). This technique was used to show the existence of a remote MAE, i.e. an MAE in areas that were not directly stimulated during adaptation. In several experiments, this remote MAE was compared to the local MAE. The remote effect was generally weaker and of shorter duration. It showed no directional tuning within the investigated range, as compared to a tuning of +/- 60 deg of the local MAE. There was no adaptation effect to the component gratings of a plaid, indicating that the plaid was treated as a coherent pattern. The local MAE showed clear spatial frequency tuning, whereas the remote MAE varied little with spatial frequency difference, although there was a tendency towards frequencies lower than the adaptation frequency. The possibility is considered that both local and remote MAEs are generated in extrastriate areas.

Adaptation, Ocular↗
PubMed1990

Pouchitis and gastric hyposecretion: cause or effect?

Pouchitis is a well recognized entity but its aetiology is still controversial. The aim of this study is to determine if gastric acidity has a role in the physiopathology of this problem. In a series of 70 consecutive patients with pelvic reservoir (65 mucosal ulcerative colitis (UC), 5 familial adenomatous polyposis (FAP], 15 patients developed pouchitis. Ten patients responded favourably to metronidazole. Five patients had several episodes of resistant pouchitis. Two of these (with FAP) developed recurrent bouts of pouchitis while on cimetidine therapy for severe peptic disease. Both patients were improved on sucralfate and symptoms did not recur after highly selective vagotomy. The other three patients began to complain of pouchitis one to six years after the fabrication of the reservoir. Gastric studies were undertaken to determine the fasting gastric pH. The values were high in all three cases despite normal stimulation tests and normal gastric biopsy. After pouch removal for toxic dilatation (without obstruction) in one of these patients, the gastric pH returned to normal. From these preliminary results, it seems that pouchitis might be associated with hypochlorhydria. It might also be possible that certain physiologic properties of the reservoir reduce gastric acidity and so create recurrent bouts of pouchitis. Further studies are needed to evaluate the physiologic consequences of the pelvic ileal reservoir on gastric physiology.

Adenomatous Polyposis Coli↗
PubMed1990

Postoperative myocardial infarction and cardiac death. Predictive value of dipyridamole-thallium imaging and five clinical scoring systems based on multifactorial analysis.

Sixty-six patients unable to complete a standard preoperative exercise test because of physical limitations were studied to determine the predictive value of individual clinical parameters, of clinical scoring systems based on multifactorial analysis, and of dipyridamole-thallium imaging before major general and vascular surgery. Study endpoints were limited to postoperative myocardial infarction or cardiac death before hospital discharge. There were nine postoperative cardiac events (seven deaths and two nonfatal infarctions). There was no statistical correlation between cardiac events and preoperative clinical descriptors, including individual clinical parameters, the Dripps-American Surgical Association score, the Goldman Cardiac Risk Index score, the Detsky Modified Cardiac Risk Index score, Eagle's clinical markers of low surgical risk, and the probability of postoperative events as determined by Cooperman's equation. There were no cardiac events in 30 patients with normal dipyridamole-thallium scans or in nine patients with fixed myocardial perfusion defects. Of 21 patients with reversible perfusion defects who underwent surgery, nine had a postoperative cardiac event (sensitivity, 100%; specificity, 43%). In the six other patients with reversible defects, preoperative angiography showed severe coronary disease or cardiomyopathy. Thus in patients unable to complete a standard exercise stress test, postoperative outcome cannot be predicted clinically before major general and vascular surgery, whereas dipyridamole-thallium imaging successfully identified all patients who sustained a postoperative cardiac event.

Aged↗
PubMed1990

Dietary habits after ileal pouch-anal anastomosis.

Dietary habits of patients who had undergone ileal pouch-anal anastomosis were assessed and correlated with bowel function. Twenty-four well-adapted patients (11 women, 13 men; mean age 32 years) voluntarily entered the study 30 +/- 4 months after closure of the diverting ileostomy. A standardized questionnaire on 108 food items and a 3-day food journal were used in the assessment. Twenty-one patients had no difficulty in selecting an appropriate diet. Caloric intake was adequate. Specific symptoms associated with several foods were as follows: increased stool frequency (beer, spirits, chinese food), decreased stool consistency (beer, wine, fried fish), perianal irritation (spicy foods), undigested particles (grapefruit, lettuce), odours (eggs). Pasta and bananas were associated with increased stool consistency. The authors believe that these observations may help in dietary counselling after ileal pouch-anal anastomosis.

Adult↗
PubMed1990

Pyloromyotomy of Ramstedt: experience of a nonspecialized centre.

In a general hospital over a period of 6 years 57 infants with congenital hypertrophic stenosis underwent a Ramstedt pylorotomy. In most cases a surgical resident-in-training performed the operation under the direct supervision of a general surgeon. There were no complications of anesthesia, no deaths and no substantial morbidity. The majority of infants left the hospital within 48 hours. The results in this series compared favourably with those reported from more specialized centres.

Clinical Protocols↗
PubMed1988

Glycosylation at specific sites of erythropoietin is essential for biosynthesis, secretion, and biological function.

The glycoprotein hormone erythropoietin (Ep), the primary regulator of erythropoiesis, is synthesized by the kidney and secreted as the mature protein with three N-linked and one O-linked oligosaccharide chains. To investigate the role(s) of each carbohydrate moiety in the biosynthesis and function of Ep, we have used oligonucleotide-directed mutagenesis of a cDNA for human Ep to alter the amino acids at each of the carbohydrate attachment sites. Each mutated cDNA construct was expressed in stably transfected sublines of a kidney cell line, baby hamster kidney. We show, by preventing attachment of N-linked carbohydrate at asparagines 38 or 83, or preventing O-linked glycosylation at serine 126, that glycosylation of each of these specific sites is critical for proper biosynthesis and secretion of Ep. Fractionation of cellular extracts demonstrated that the mutant proteins lacking glycosylation at each of these three sites, (38, 83, and 126) were associated mainly with membrane components or were degraded rapidly. Less than 10% of these three mutant proteins were processed properly and secreted from the cells. The Ep protein lacking N-linked glycosylation at asparagine 24 is synthesized and secreted as efficiently as native Ep. The carbohydrates at positions 24 and 38 may be involved in the biological activity of Ep, since the absence of either of the oligosaccharide side chains at these positions reduced the hormone's biological activity.

Animals↗
PubMed1988

Cholinergic REM sleep induction by arecoline in normal subjects: relation to thyroid function.

Serum thyroid hormones and the speed of rapid eye movement (REM) sleep induction by the central muscarinic agonist arecoline were measured in 21 normal volunteers. The arecoline-REM induction latencies had a modestly significant negative correlation with free thyroxine index. This finding is discussed in the light of observations in animal studies that thyroid hormones stimulate central cholinergic neuronal function.

Adult↗
PubMed1987

Quantitative assessment of pelvic ileal reservoir emptying with a semisolid radionuclide enema. A correlation with clinical outcome.

Fecal stasis in an ileal reservoir may lead to overgrowth of bacteria and changes in mucosal morphology that are of future concern. Moreover, improper evacuation may lead to increased stool frequency and reduced continence. The aims of this study were: to compare the functional results of two types of ileal reservoirs constructed with an ileoanal anastomosis, to compare their emptying to a normal rectum as assessed by a radionuclide enema, and to correlate functional results with emptying. The reservoirs were made of two (J) or three (S) limbs of terminal ileum. Thirty-three patients (16 with J-pouch and 17 with S-pouch) and ten healthy controls were included in the study. There was no difference in the mean age of patients or interval following diverting ileostomy closure. Functional results were obtained by written questionnaire assessing stool frequency, and soiling, use of medication, need for intubation, and episodes of pouchitis. Emptying was measured with instillation per anus of a semisolid medium labeled with 1.0 mCi of Tc-99. Ileal pouch counts were measured using a scintillation camera and computer before and after spontaneous evacuation. The emptying was defined as the difference in counts divided by preevacuation counts. The functional results were similar in the two groups. Nocturnal soiling occurred more frequently in the S-pouch group. Pouchitis occurred in seven patients. Emptying of the two types of reservoir was similar (J: 72 +/- 4%, S: 67 +/- 5%), but it was less efficient than a normal rectum (90 +/- 3%, P less than 0.004). No correlation was established between age, sex, number of stools, pouchitis, and the efficacy of emptying. The clinical outcome of two patients who emptied less than 30%, however, was greatly improved by intermittent intubation. In conclusion, a semisolid radionuclide enema can be useful to identify patients who would benefit from intubation. No persistent defect in emptying was detected in patients with pouchitis.

Adult↗
PubMed1987

Determining gastric contents during general anaesthesia: evaluation of two methods.

Two methods used to measure the volume of gastric contents were evaluated in 24 supine anaesthetized adults. Methods compared were: (1) aspiration of stomach contents through a large, vented, multi-orificed gastric tube, and (2) indirect determination by a dye dilution method using polyethylene glycol (PEG) as the marker. The volumes determined by these methods (Vasp and Vpeg respectively) were compared to the total volume (Vtot) present in the stomach, determined by direct inspection of the gastric pouch by the surgeon at the beginning of surgery. The results show that the volume of aspirated gastric fluid, using this type of tube, is a very good estimate of the total volume of gastric residue. The PEG dilution method yields similar results. However, correlation between Vpeg and Vtot was not as close-fitting as the correlation between Vasp and Vtot. PEG dilution is more complicated, time-consuming and offers no advantage over aspiration.

Anesthesia, General↗
PubMed1986

Toxic megacolon. An analysis of 70 cases.

The clinical features and outcome of 70 patients treated for toxic megacolon between 1970 and 1984 in five university-affiliated hospitals were determined. There were 35 women and 35 men with a mean age of 39 +/- 0.2 years. Toxic megacolon occurred at the initial episode of colitis in 43 patients (61 percent). Only five patients had a specific colitis: salmonellosis, two; ischemic, two; and pseudomembranous, one. Of the 65 remaining patients with nonspecific colitis, six had to be operated on without delay because of peritonitis. In the remaining 59 patients, toxic megacolon was cured with intensive medical management in nine (15 percent), improved temporarily in 14 (24 percent), and remained unchanged in 36 (61 percent). The postoperative mortality rate was 11 percent for all patients (6/56), 4 percent for patients without perforation (2/50) compared with 27 percent for patients with perforation (4/15). None of the patients who underwent surgery within five days of medical treatment died. When toxic megacolon was complicated by hemorrhage (nine patients) or peritonitis (eight patients), the mortality rate increased to 33 percent and 27 percent, respectively. A one-stage proctocolectomy was performed in 19 patients (32 percent). Of 32 patients in whom the rectum was retained, successful restoration of continuity was possible in only seven (22 percent) within 12 months after surgery. In well-selected patients, a plea is made for rectal preservation to offer an alternative to permanent ileostomy.

Adolescent↗
PubMed1986

Interface of panic and depression: clinical and sleep EEG correlates.

Four groups of subjects were compared with respect to their clinical and demographic status and electroencephalographic (EEG) characteristics, namely: primary major depressive disorder (PRI MDD); panic disorder (Panic); "Mixed" group comprising patients meeting full syndromal criteria for MDD and panic occurring concomitantly; and normal controls. The "Mixed" (MDD + Panic) patients were characterized by earlier age of onset of psychiatric illness, longer duration of current episode, greater intensity of symptoms, higher impairment of functioning, increased miscellaneous psychopathology, and greater objective stress and anger. With respect to sleep EEG variables, PRI MDD patients were clearly different from the other three groups. The sleep profile of the "Mixed" group occupies an intermediate position between the "pure" Panic and MDD groups. Classification of the "Mixed" patients based on the discriminant function coefficients of the Schedule for Affective Disorders and Schizophrenia and sleep analysis of the "pure" groups (PRI MDD and Panic) reveals that some patients are classified as true PRI MDD while others are classified as falling somewhere along the PRI-MDD/Panic spectrum. The separation of the PRI MDD from Panic and Normals, however, is clear, suggesting that sleep can be successfully used as a physiological marker in the separation of these conditions.

Adult↗
PubMed1985

Cholinergic REM induction response: separation of anxiety and depression.

Five groups of subjects underwent EEG sleep recordings, arecoline rapid eye movement (REM) induction response testing, and Schedule for Affective Disorders and Schizophrenia (SADS) interview. Group I: 20 patients with primary major depressive disorder (MDD) (endogenous) without any coexisting anxiety disorder; Group II: 19 primary MDD (endogenous) patients with secondary panic, GAD, or phobic disorders; Group III: 18 patients with primary anxiety disorder without coexisting MDD; Group IV: 14 patients with primary anxiety plus secondary MDD; Group V: 26 normal controls. Modified Research Diagnostic Criteria (RDC) were used for diagnosis, based on the SADS interview. There was considerable overlap of SADS scaled scores between patient groups, which is consistent with a heterogeneous clinical presentation of depressive and anxiety states. REM latency was significantly shorter in patients with primary MDD (without anxiety) as compared with that in patients with primary anxiety (no MDD) and normals. Arecoline REM induction response time was significantly shorter in both primary affective groups (I and II) as compared with primary anxiety (no MDD) patients and normal controls. REM latency and arecoline REM induction time was not significantly different between the primary anxiety groups (III and IV) and normals. The study highlights the use of biological markers in differentiating between clinical syndromes confounded by mixed or overlapping phenomenology.

Adult↗
PubMed1985

The fate of human umbilical vein grafts as an infrarenal aortic substitute in monkeys.

The literature contains conflicting reports about the potential value of the processed human umbilical vein graft as an arterial substitute. With a view to a better understanding of the ultimate fate of this device, a series of long-term implantation was undertaken with a nonhuman primate model. Dardik Biografts were implanted as an infrarenal aortic substitute in 13 monkeys. Nine were put to death following complications after post-operative periods ranging from 3 months to 3 years, while four animals remain alive. No calcification or lipid infiltration was found, presumably because the animals were healthy. The patency rate was poor because of complications associated with thrombotic deposits and thinning of the graft wall after implantation, which led to stenosis and fibrous hyperplasia along the anastomoses. The external polyester mesh was found to encourage external tissue proliferation, which could not prevent the graft from dilating since it contained neither elastin nor smooth muscle cells. Because the places where the graft had been damaged before or during processing were the sites of thrombotic accumulation and initial collagen degeneration, it is essential to use only defect-free material. As a consequence the long-term durability of this graft continues to be questioned.

Animals↗