203 research outputs found
Instantaneous force-velocity-length relationship in diaphragmatic sarcomere
No full text Coirault, Catherine, Denis Chemla, Jean-Claude Pourny, Francine Lambert, and Yves Lecarpentier. Instantaneous force-velocity-length relationship in diaphragmatic sarcomere. J. Appl. Physiol. 82(2): 404–412, 1997.—The simultaneous analysis of muscle force, length, velocity, and time has been shown to precisely characterize the mechanical performance of isolated striated muscle. We tested the hypothesis that the three-dimensional force-velocity-length relationship reflects mechanical properties of sarcomeres. In hamster diaphragm strips, instantaneous sarcomere length (S L) and muscle length were simultaneously measured during afterloaded twitches. S L was measured by means of laser diffraction. We also studied the influence of initial S L, abrupt changes in total load, and 2 × 10−7 M dantrolene. Baseline resting S L at the apex of the length-active tension curve was 2.2 ± 0.1 μm, whereas S L at peak shortening was 1.6 ± 0.1 μm in the preloaded twitch and 2.1 ± 0.1 μm in the “isometric” twitch. Over the whole load continuum and at any given level of isotonic load, there was a unique relationship between instantaneous sarcomere velocity and instantaneous S L. Part of this relationship was time independent and initial S L independent and was markedly downshifted after dantrolene. When five different muscle regions were considered, there were no significant variations of S L and sarcomere kinetics along the muscle. These results indicate that the time- and initial length-independent part of the instantaneous force-velocity-length relationship previously described in muscle strips reflects intrinsic sarcomere mechanical properties. </jats:p
Echocardiography-based score to predict outcome after renal transplantation
No full textBackground: Given the high cardiac mortality of renal transplant recipients, identification of high-risk patients is important to offer appropriate treatment before transplantation.Aim: To determine patients with high mortality after renal transplantation despite selection according to current criteria.Methods: Preoperative parameters were collected from 203 renal transplant recipients over a follow-up time of 3.6 (1.9) years. The primary end point was all-cause mortality.Results: 22 deaths (11%) and 12 cardiac failures (6%) were observed. Non-survivors were older (p0.001), had larger left ventricular end-systolic diameter (LVSD) (p0.001) and end-diastolic diameter (p = 0.002), and lower ejection fraction (p0.001). Left ventricular mass index (p = 0.001), maximal wall thickness (p = 0.006) and the proportion with mitral annular calcification (p = 0.001) were significantly higher in the non-survivors. The risk factors for ischaemic heart disease and exercise test data were not significantly different between the two groups. Four independent predictors of mortality after renal transplantation were identified: age 50 years (p = 0.002), LVESD 3.5 cm (p = 0.002), maximal wall thickness 1.4 cm (p = 0.014) and mitral annular calcification (p = 0.036). The 5-year survival estimates for 0, 1, 2 and 3 prognostic factors were 96%, 86%, 69% and 38%, respectively. No patient had four prognostic factors. In patients 50 years, the 5-year survival estimates for 0, 1 and 2 additional prognostic factors were 73%, 45% and 18%, respectively.Conclusion: In addition to selection according to current guidelines, age and three conventional echocardiography parameters may further improve risk stratification before renal transplantation.Abbreviations: LVEF, left ventricular ejection fraction; LVESD, left ventricular end-systolic diamete
Hemodynamic correlates of effective arterial elastance in mitral stenosis before and after balloon valvotomy
No full textColin, Patrice, Michel Slama, Alec Vahanian, Yves Lecarpentier, Gilbert Motté, and Denis Chemla. Hemodynamic correlates of effective arterial elastance in mitral stenosis before and after balloon valvotomy. J. Appl. Physiol. 83(4): 1083–1089, 1997.—This study had the purpose of documenting the hemodynamic correlates of effective arterial elastance (Ea; i.e., an accurate estimate of hydraulic load) in mitral stenosis (MS) patients. The main hypothesis tested was that Ea relates to the total vascular resistance (R)-to-pulse interval duration ( T) ratio (R/ T) in MS patients both before and after successful balloon mitral valvotomy (BMV). High-fidelity aortic pressure recordings were obtained in 10 patients (40 ± 12 yr) before and 15 min after BMV. Ea value was calculated as the ratio of the steady-state end-systolic aortic pressure (ESAP) to stroke volume (thermodilution). Ea increased after BMV (from 1.55 ± 0.63 to 1.83 ± 0.71 mmHg/ml; P < 0.05). Throughout the procedure, there was a strong linear relationship between Ea and R/ T: Ea = 1.09R/ T − 0.01 mmHg/ml, r = 0.99, P = 0.0001. This ultimately depended on the powerful link between ESAP and mean aortic pressure [MAP; r = 0.99, 95% confidence interval for the difference (MAP − ESAP) from −18.5 to +4.5 mmHg]. Ea was also related to total arterial compliance (area method) and to wave reflections (augmentation index), although to a lesser extent. After BMV, enhanced and anticipated wave reflections were observed, and this was likely to be explained by decreased arterial compliance. The present study indicated that Ea depended mainly on the steady component of hydraulic load (i.e., R) and on heart period (i.e., T) in MS patients.</jats:p
Couplage contraction-relaxation myocardique: etude in vitro et in vivo
No full textSIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 81396 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Changing mathematical cultures, conceptual history and the circulation of knowledge. A case study based on mathematical sources from ancient China
No full textInternational audienceThis chapter is devoted to the conceptual history of “quadratic equation” in China between the first and the eleventh century. It argues that conceptual history must rely on a description of how practitioners worked with various elements used in their mathematical activity —here mainly problems, algorithms, computational tools, and diagrams. The uses of these elements establish connections between and among them, forming complexes of practices to which the author refers as “mathematical cultures.” She argues that describing the mathematical cultures in the context in which practitioners actually operated provides essential tools for interpreting sources. The author identifies different mathematical cultures in China during the timespan considered that display both continuities and transformations in mathematical practice. In each of these contexts, the concept of equation identified correlates with both computational tools and ways of working with diagrams. This approach highlights material dimensions of conceptual history
A systematic review of invasive, high-fidelity pressure studies documenting the amplification of blood pressure from the aorta to the brachial and radial arteries
No full textInternational audienc
(corresponding author)
No full textChemla for their comments and suggestions. All remaining errors are ours. 1 Abstract: Financial crises are often associated with an endogenous credit reversal, followed by a fall in asset prices and serious disruptions in the …nancial sector. To account for this sequence of events, this paper constructs a model where excessive risk-taking by investors leads to a bubble in asset prices, and where the supply of credit to these investors is endogenous. We show that the interplay between excessive risk-taking and the endogeneity of credit may give rise to multiple equilibria associated with di¤erent levels of lending, asset prices, and output. Stochastic equilibria lead, with positive probability, to an ine ¢ cient liquidity dry-up, a market crash, and widespread failures by borrowers. The possibility of multiple equilibria and self-ful…lling crises is shown to be related to the severity of the risk-shiftin
Pression artérielle pulmonaire moyenne et pulsée ; relations pression débit dans l'hypertension artérielle pulmonaire
No full textLE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF
The Dangers and Promises of Comparative History of Science
No full textInternational audienceJoseph Needham (1900-1995) is well-known for many essay-articles as well as for being the author, or rather the editor, of Science and Civilisation in China, a multi-volume encyclopaedia whose publication began in 1954 and which deals with virtually every aspect of the history of science and technology in China. However, this is not the sum of Needham’s career and broader activities. To evoke a few other dimensions of this multi-faceted man, Christian-Socialist Needham began his scientific life as a biochemist, specializing in embryology. He experienced and denounced the rise of fascism and National Socialism in Europe, later contributing to the war effort as the Director of the Sino-British Cooperation Office in Chongqing between 1942 and 1946. This position was his first significant engagement for a worldwide scientific cooperation, a task he carried on while being, from 1946 to 1948, the first head of UNESCO’s Natural Sciences Section. The article interprets against this background Needham’s suspicion towards the comparative method in the history of science. It seeks to identify the origins of Needham’s standpoint on this topic, suggesting that the historian Lucien Febvre and his project of a history of mankind in the context of immediate post-war UNESCO might have had a deep influence on Needham in this respect. Finally, the chapter outlines a suggestion for carrying out comparative method in ways that could avoid the traps Needham identified
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