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Biomedical subjects

R Labbé

Publications and source records attributed to R Labbé.

13 recordsLinked to original sources
PubMed2002

Finite size scaling in the two-dimensional XY model and generalized universality.

In recent works [S. T. Bramwell, P. C. W. Holdsworth, and J.-F. Pinton, Nature (London) 396, 552 (1998); S. T. Bramwell et al., Phys. Rev. Lett. 84, 3744 (2000)], a generalized universality has been proposed, linking phenomena as dissimilar as two-dimensional (2D) magnetism and turbulence. To test these ideas, we performed Monte Carlo simulations of the 2D XY model. We found that the shape of the probability distribution function for the magnetization M is non-Gaussian and independent of the system size-in the range of the lattice sizes studied-below the Kosterlitz-Thoules temperature. However, our results suggest that in the full 2D XY model the shape of these distributions has a slight dependence on temperature-for finite volume-below the lattice-shifted critical temperature T*(L). This behavior can be explained by using renormalization group arguments and an extended finite-size scaling analysis, and by the existence of bounds for M.

Journal Article↗
PubMed1999

Power fluctuations in a closed turbulent shear flow.

We study experimentally the power consumption P of a confined turbulent flow at constant Reynolds number Re. We analyze in details its temporal dynamics and statistical properties, in a setup that covers two decades in Reynolds numbers. We show that nontrivial power fluctuations occur over a wide range of amplitudes and that they involve coherent fluid motions over the entire system size. As a result, the power fluctuations do not result from averaging of independent subsystems and its probability density function Pi(P) is strongly non-Gaussian. The shape of Pi(P) is Reynolds number independant and we show that the relative intensity of fluctuations decreases very slowly as Re increases. These results are discussed in terms of an analogy with critical phenomena.

Journal Article↗
PubMed1999

Psychological factors associated with emergency room visits among asthmatic patients.

This study was designed to investigate physiological and psychological characteristics of subjects with high-frequency emergency room (ER) visits. Asthma status, psychological functioning and predispositions, psychosocial adaptation to asthma, and health behaviors were measured for 30 patients who had two or more ER visits during the last 2 years. These subjects were matched for age, sex, and corticosteroid use with 30 subjects who had no unscheduled ER visits for the same period. No significant differences were found for measures of asthma status. Among the asthma-specific variables, the number of hyperventilation-bronchoconstriction symptoms did not distinguish between the groups. High attenders reported more panic-fear symptoms, lower self-efficacy, and more perceived interference. There were no differences for measures of anxiety/depression, self-focused attention, or health locus of control. However, these variables were found to be significant predictors of panic-fear symptoms, lower self-efficacy, and more perceived interference.

Adult↗
PubMed1998

A completely biological tissue-engineered human blood vessel.

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.

Animals↗
PubMed1997

Fully thoracoscopic pulmonary lobectomy and specimen extraction through rib segment resection. Preliminary report.

BACKGROUND: A technique of fully thoracoscopic pulmonary lobectomy with rib-segment resection for specimen extraction is described, and preliminary results in 18 patients are presented. METHODS: Surgery is performed through four 15-mm ports. For all lobes except one, the surgeon operates in front of the patient, where the rib spaces are widest and rib-space trauma is less. When lobar dissection is complete, specimen extraction is performed after resection of a rib segment proportional to tumor size. Muscle section is kept to a minimum. There is no rib retraction. RESULTS: There were no deaths, three conversions to open surgery, and three major complications. Average postoperative stay was 5.4 days for patients without complications and 9.6 days for patients with complications. In total six patients presented with some degree of air leaks, and two had post-thoracotomy pain (>2 month's duration). The literature is reviewed to analyze current techniques and to define parameters of a truly minimally invasive pulmonary lobectomy. CONCLUSIONS: This technique is safe and promising; however, thoracoscopic lobectomy still needs refining. Before valid randomized studies comparing thoracoscopic lobectomy and muscle-sparing thoracotomy or posterolateral thoracotomy can be credible, technical issues related to the production of a truly minimally invasive procedure should be resolved.

Cohort Studies↗
PubMed1993

Erythromycin-associated ergotamine intoxication: arteriographic and electrophysiologic analysis of a rare cause of severe ischemia of the lower extremities and associated ischemic neuropathy.

Vasospasm associated with ergotamine is a well-known phenomenon. In this case report we present a rare drug interaction between erythromycin and ergotamine at normal doses causing lower extremity ischemia in a 36-year-old woman. Nitroprusside proved to be the treatment of choice. The response was dramatic and took place in a matter of hours in this patient. Ischemic monomelic neuropathy is a recently described entity in which axonal necrosis is caused by a loss of distal extremity blood flow. The association between erythromycin and ergotamine may be a dangerous pharmacologic combination; drugs that have a hepatic cycle with ergotamine derivatives must be used with caution.

Adult↗
PubMed1993

In vitro construction of a human blood vessel from cultured vascular cells: a morphologic study.

PURPOSE: The purpose of this study was to create a tubular vascular model exclusively made of human cells and collagen. METHODS: The blood vessel equivalent was constructed with the three following human cell types: vascular smooth muscle cells, endothelial cells, and fibroblasts. A tissuelike structure was obtained from the contraction of a tubular collagen gel (human origin) by vascular smooth muscle cells, which created a media-like structure. An adventitia-like tissue was added around the media-like structure by embedding fibroblasts into a collagen gel. An endothelium was established within the tubular structure after intraluminal cell seeding. RESULTS: Cell orientation and gel contraction were followed up over time. Vascular smooth muscle cells developed a complex tridimensional network and were oriented in a circular fashion around the tube's axis. In contrast, fibroblasts were randomly oriented. A viable, homogeneous, and well-characterized endothelium was observed. These endothelial cells showed a slightly elongated structure and were oriented parallel to this vascular equivalent axis. CONCLUSION: An in vitro tridimensional vascular model that exhibits some phenotypic characteristics of in vivo vascular cells could be useful in the study of events that lead to atherosclerotic plaque formations.

Cells, Cultured↗
PubMed1993

[Percutaneous angioplasty in iliac obstructions. Immediate and long-term results].

During the last 35 months, mechanical recanalisation was obtained in 25 (19 men, 6 women, aged 39 to 92 years, average 59 years) out of 30 patients admitted for percutaneous andovascular management, associating angioplasty and endovascular stents, of iliac artery occlusion of over 5 months duration. Forty-three balloon-expandable stents (27 Palmaz, 16 Strecker) were implanted in 29 iliac arteries (15 external, 14 common iliac arteries) with occlusions 2 to 7 cms long (average: 4.6 cm) either after balloon angioplasty (22 cases) or without angioplasty (7 cases) because of a suspected fresh thrombus suggested by easy recanalisation by the guide wire and with the aim of avoiding fragmentation and embolisation of the thrombotic material. In this type of case, a Strecker stent was preferred, a choice also justified by an "obligatory" contro-lateral approach (5 cases). With the exception of these cases, the treatment of first intention was to insert one or more Palmaz stents by a homo-lateral approach. Two haematomas with no complications and 1 reocclusion at the 24th hour, revascularised by urokinase with a good 6 months result, were observed. After the insertion of one Palmaz stent in one patient, a non-occlusive thrombus, probably due to embolism, was observed straddling the homolateral superficial and profunda femoral arteries, but it was of no clinical consequence. After thromboaspiration and angioplasty by a contro-lateral approach, the arterial lumen was recanalized with a sustained result at 18 months. Clinical Doppler and angiographic (digitised intravenous angioplasty) controls were obtained every 6 months in 22 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1991

[Ruptured abdominal aortic aneurysm: long-term survival].

Despite technological improvement, surgery for ruptured aortic abdominal aneurysm (AAA) only gets about 50% of patients to survive past the operative period. This series addresses the long-term outcome of those survivors. Eighty consecutive patients operated on for ruptured AAA between January 1983 and June 1990 at l'hôpital du Saint-Sacrement by three vascular surgeons, were studied and compared to 279 patients submitted to elective aneurysm surgery during the same period. The operative mortalities were respectively of 45% (ruptured) and 6.1% (elective). Five year survivals added up to 30 and 68%. When the 5 year survivals were recalculated, including only patients who were discharged from hospital, we found no statistically significant difference (p greater than 0.05) between the ruptured (55%) and the elective groups (68%). Data from this series demonstrate that long-term survival of patients undergoing ruptured AAA surgery is good and compares with that of AAA elective surgery. Therefore, aggressive treatment of ruptured AAA remains justified.

Actuarial Analysis↗
PubMed1989

Arterial reconstruction to the foot vessels: is it worth the trouble?

Between 1974 and 1988, 32 patients with severe rest pain and ischemic ulcerations of lower extremities underwent 34 arterial reconstructions to the foot vessels, using, in the majority of cases, the in-situ vein technique. There were 10 early graft failures, resulting in the loss of five extremities. The indication for surgery, presence of diabetes and type of bypass were not predictive of early thrombosis. Five-year primary and secondary patency rates were 52.8% and 62.6%, with a foot salvage rate of 74%. Although a number of these long bypass grafts fail early because of the severity of tibial disease, this procedure appears to be durable in a selected group of patients.

Adult↗
PubMed1986

Characterization of a parasporal inclusion body from sporulating, enterotoxin-positive Clostridium perfringens type A.

Inclusion bodies (IB) synthesized during sporulation and enterotoxin formation by Clostridium perfringens NCTC 8239 and 8798 were isolated and characterized. IB were isolated by disruption of sporangia by sonication in the presence of tetrasodium EDTA and phenylmethylsulfonyl fluoride. Fractionation was carried out in a linear gradient of sodium bromide, sucrose, or diatrizoate sodium. Denaturing and reducing agents were necessary to solubilize the IB. An alkylating agent was required to prevent reaggregation of the subunits. Molecular weight, compositional, and serological analyses and peptide mapping revealed strong similarities between the IB subunits and the enterotoxin synthesized during sporulation by C. perfringens. IB appear to represent the structural component where overproduced enterotoxin accumulates intracellularly. Enterotoxin-like subunits in the IB appeared to be held together by noncovalent and disulfide bonds, which were generally resistant to the action of intracellular proteases of C. perfringens, trypsin, or trypsin plus bile salts.

Amino Acids↗
PubMedDate not supplied

Chronic effects of the novel glucocorticosteroid RPR 106541 administered to beagle dogs by inhalation.

The preclinical safety of RPR 106541, a novel 17-thiosteroid, was evaluated in young adult and mature dogs by inhalation exposure for 26 weeks and 52 weeks, respectively. A dry powder formulation of RPR 106541 in lactose was administered to young adult dogs (approximately 6 months of age at initiation) at doses of 0 (air and placebo controls), 10, 100, or 1,000 microg/kg/d for 26 weeks. A solution-based aerosol formulation was administered to mature dogs (approximately 10 months at initiation) from a pressurized metered dose inhaler at 0 (air and placebo controls), 10, 50, and 150 microg/kg/d for 52 weeks. Clinical evidence of glucocorticosteroid-induced immunosuppression was observed by weeks 20-26 following relatively high dose exposures (100 microg/kg/d and 1,000 microg/kg/d) in young dogs receiving the dry powder formulation for 26 weeks. Classic glucocorticosteroid effects were observed, including adrenocortical atrophy, reduced bone mass with retention of epiphyseal growth plates in long bones, prominence of stromal adipose tissue in bone marrow, and atrophy of lymphoid tissues. Inhalation administration of RPR 106541 to sexually mature dogs facilitated more definitive characterization of endocrine affects of RPR 106541 as compared with administration in younger, sexually immature animals. Significant effects in female reproductive organs included absence of corpora lutea in association with atresia of vesicular follicles within the ovaries, endometrial hyperplasia, and lobular development of mammary tissue. Discordant development of mammary tissue, accumulation of secretory material within hyperplastic endometrial glands, and hypertrophy of uterine lining epithelium in absence of ovulation were consistent with a secondary progestin effect by a potent glucocorticosteroid.

Administration, Inhalation↗