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Pressure Levels (pressure + level)
Kinds of Pressure Levels Selected AbstractsBlood Pressure Level and Outcomes in Adults Aged 65 and Older with Prior Ischemic StrokeJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 9 2006Robert C. Kaplan PhD OBJECTIVES: To examine the association between blood pressure (BP) levels and long-term stroke outcomes in elderly stroke survivors. DESIGN: Observational study. SETTING: The Cardiovascular Health Study (CHS) of 5,888 community-dwelling adults. PARTICIPANTS: Two hundred fifty-four adults aged 65 and older (mean age 78.6) who sustained a nonfatal first ischemic stroke. MEASUREMENTS: BP levels assessed at prestroke and poststroke CHS visits were examined as predictors of stroke recurrence, coronary heart disease (CHD), combined vascular events (CVEs), and mortality. RESULTS: Higher poststroke BP level, assessed 261.6 days (mean) after stroke, was associated with higher risk of stroke recurrence over 5.4 years (mean) of follow-up. The multivariate-adjusted hazard ratio for stroke recurrence was 1.42 (95% confidence interval (CI)=1.03,1.99) per standard deviation (SD) of systolic BP (P=.04) and 1.39 (95% CI=1.01,1.91) per SD of diastolic BP (P=.04). Mortality was significantly greater in patients with low or high poststroke BP than in those with intermediate BP. Poststroke BP was not associated with risk of CHD or CVE, although further analyses suggested that high systolic BP predicted CHD and CVE in younger but not older subjects. Prestroke BP did not predict poststroke outcomes. CONCLUSION: In this observational study of adults aged 65 and older assessed approximately 8 months after stroke, low BP was associated with favorable risk of recurrent stroke, although high and low poststroke BP levels were associated with greater mortality. Long-term antihypertensive trials in older stroke survivors would increase knowledge about the benefits of lowering BP in this population. [source] Changes in Vein Dynamics Ranging from Low to High Pressure Levels as a Determinant of the Differences in Vein Adaptation to Arterial Hemodynamic ConditionsARTIFICIAL ORGANS, Issue 7 2007Yanina Zócalo Abstract:, The causes of the regional differences in venous grafts patency rates are partially understood. Differences in vein dynamics during physiological situations could determine differences in veins' capability to face arterial conditions and could contribute to the dissimilar performance of veins as arterial grafts. In vitro pressure and diameter were measured in four different veins during physiological and arterial (graft) pressure conditions. A diameter,pressure transfer function was designed. Compliance, viscous and inertial properties; circumferential stresses and deformation; and buffering function were calculated. Regional differences in veins' dynamics, but not in buffering function were found during physiological and arterial conditions. The back vein (femoral) showed the least changes when submitted to arterial conditions. Arterial conditions represent different changes in vein dynamics depending on the segment considered. The regional differences in vein dynamics, both at physiological and graft conditions, could contribute to explain the dissimilar results of venous grafts. [source] REVIEW: Role of adipokines in obesity-associated hypertensionACTA PHYSIOLOGICA, Issue 2 2010M. Vlasova Abstract It has been well documented that obesity is a major risk factor for the development of the hypertensive state. The correlation between body mass index and blood pressure level is well established. Nevertheless, the exact mechanisms which contribute to obesity-related hypertension remain poorly understood. In the last years, we have realized that the white adipose tissue is not just an inert organ for nutrient storage and isolation but rather depending on the body mass index the biggest endocrinological organ. Thus, the possible contribution of adipokines to the blood pressure elevation becomes an attractive hypothesis to explain the hypertensive state that often occurs in obesity. In this review, we consider direct and indirect effects of main adipokines on structural and functional changes in the cardiovascular system. [source] Single-beat estimation of the left ventricular end-systolic pressure,volume relationship in patients with heart failureACTA PHYSIOLOGICA, Issue 1 2010E. A. Ten Brinke Abstract Aim:, The end-systolic pressure,volume relationship (ESPVR) constructed from multiple pressure,volume (PV) loops acquired during load intervention is an established method to asses left ventricular (LV) contractility. We tested the accuracy of simplified single-beat (SB) ESPVR estimation in patients with severe heart failure. Methods:, Nineteen heart failure patients (NYHA III-IV) scheduled for surgical ventricular restoration and/or restrictive mitral annuloplasty and 12 patients with normal LV function scheduled for coronary artery bypass grafting were included. PV signals were obtained before and after cardiac surgery by pressure-conductance catheters and gradual pre-load reductions by vena cava occlusion (VCO). The SB method was applied to the first beat of the VCO run. Accuracy was quantified by the root-mean-square-error (RMSE) between ESPVRSB and gold-standard ESPVRVCO. In addition, we compared slopes (EES) and intercepts (end-systolic volume at multiple pressure levels (70,100 mmHg: ESV70,ESV100) of ESPVRSB vs. ESPVRVCO by Bland,Altman analyses. Results:, RMSE was 1.7 ± 1.0 mmHg and was not significantly different between groups and not dependent on end-diastolic volume, indicating equal, high accuracy over a wide volume range. SB-predicted EES had a bias of ,0.39 mmHg mL,1 and limits of agreement (LoA) ,2.0 to +1.2 mmHg mL,1. SB-predicted ESVs at each pressure level showed small bias (range: ,10.8 to +9.4 mL) and narrow LoA. Two-way anova indicated that differences between groups were not dependent on the method. Conclusion:, Our findings, obtained in hearts spanning a wide range of sizes and conditions, support the use of the SB method. This method ultimately facilitates less invasive ESPVR estimation, particularly when coupled with emerging noninvasive techniques to measure LV pressures and volumes. [source] Rationale, design and methods of the OSCAR study: observational study on cognitive function and systolic blood pressure reduction in hypertensive patientsFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 2 2007Atul Pathak Abstract Data from several recent clinical trials have suggested a beneficial effect of antihypertensive medications on preservation of cognitive function. Eprosartan, an angiotensin type-1 receptor antagonist (ARA) with dual action on both pre- and postsynaptic angiotensin type 1 receptors, may be effective in the control of SBP and the prevention of cognitive decline. The OSCAR (Observational Study on Cognitive function And SBP Reduction) study is an international longitudinal observational study with a duration of 6 months intended to examine the impact of the ARA eprosartan on cognitive function (assessed using the Mini-Mental State Examination [MMSE]) and control of systolic blood pressure (SBP) in a large international population of hypertensive patients managed in a standard primary care setting. A total of 100 000 hypertensive patients, aged ,50 years and with SBP of >140 mmHg will be recruited by more than 20 000 primary care physicians in 27 countries. These patients will receive eprosartan 600 mg once a day for 6 months. The MMSE, a globally validated cognitive screening test, will be performed at baseline, and after 6 months of treatment. After the first month of monotherapy, eprosartan treatment may, at the absolute discretion of individual investigators, be supplemented with other antihypertensive medications for the remainder of the study. The primary outcome indices are the mean relative change in MMSE score and the absolute change from baseline in SBP in the study population as a whole and in subsets of patients according to various factors among them: ethnicity, comorbidities (i.e. target organ damage, diabetes), baseline cognitive level and baseline blood pressure level. The secondary objectives are to identify factors influencing SBP and MMSE changes. The OSCAR trial is the first international observational study focusing on MMSE in a wide international cohort of hypertensive patients. The results are expected in 2007. [source] Relation of hypertension and glucose tolerance impairment in elderly people to the development of arteriosclerosis: Investigation using pulse wave velocity,GERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 1 2005Takeshi Isobe Background: The aim of the present study was to determine the correlation between the combination of hypertension and diabetes mellitus and arteriosclerosis using pulse wave velocity (PWV). Methods: The subjects were 186 men over the age of 60 years (mean age: 68.8 ± 5.8 years). PWV, systolic blood pressure (SBP), diastolic blood pressure, body mass index, fasting blood sugar (FBS), total cholesterol, triglyceride and HDL cholesterol were measured in all subjects. The subjects were divided into three groups on the basis of FBS level: a normal group (FBS < 110 mg/dL), an impaired fasting glucose group (110 , FBS < 126 mg/dL) and a diabetes mellitus group (FBS , 126 mg/dL or taking antidiabetics). The subjects were also divided into two groups on the basis of blood pressure level: a hypertension (HT) group (SBP , 140 mmHg and/or diastolic blood pressure , 90 mmHg or taking antihypertensives) and a normotension group (other subjects). Results: PWV showed positive correlations with SBP and FBS (r = 0.499 and r = 0.300, respectively). In all three groups classified by FBS level, PWV was higher in subjects with HT than in subjects with normotension (P < 0.01 in all three groups). In the HT group, PWV had already increased at the stage of impaired fasting glucose and was significantly higher in the diabetes mellitus group than in the normal FBS group (P = 0.002). In multiple regression analysis using PWV as a dependent variable, SBP and FBS were selected as independent variables. Conclusions: Even in the elderly, strict control of blood pressure and blood sugar level may be necessary in order to prevent the development of arteriosclerotic diseases. [source] Comparison of non-local and polar modelling of softening in hypoplasticityINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2004Th. Maier Abstract The paper deals with the comparison of a non-local and a polar (Cosserat) hypoplastic model. The hypoplastic constitutive law in the version of von Wolffersdorff is chosen as local reference model. For the comparison the results of biaxial tests on dense Hostun Rf sand are predicted with both enhanced models. The comparison is based on a strict separation of input data from triaxial- and oedometer tests and output data from biaxial tests. The comparison is drawn in terms of the shear band width, the load,displacement curves and the influence of the pressure level. Finally, the non-local and the polar hypoplastic model are applied on the strip foundation problem. Copyright © 2004 John Wiley & Sons, Ltd. [source] Spatial and temporal 850 hPa air temperature and sea-surface temperature covariances in the Mediterranean region and their connection to atmospheric circulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2002C. J. Lolis Abstract The spatial and temporal covariability between the lower troposphere and sea surface temperatures (SSTs) are studied in the Mediterranean basin for the period 1958,98. Monthly air temperature anomalies for the 850 hPa pressure level (T-850hPa) at 2.5° × 2.5° grid points and SST anomalies in 5° × 5° grid boxes are utilized. As a first step, factor analysis is applied on both sets of data in order to reduce their dimensionality. Then, canonical correlation analysis is applied and this leads to one statistically significant pair of canonical variates for winter and to two pairs for summer. In winter, a teleconnection (see-saw) between western Europe and the eastern Mediterranean at the 850 hPa level is revealed, and a corresponding weaker one between the areas of central-west and eastern Mediterranean for SST. The correlation between T-850hPa and SST appears higher over the eastern Mediterranean. In summer, the first pair of canonical variates reveals a covariability between T-850hPa and SST in the western Mediterranean, and the second one shows a covariability in the eastern Mediterranean, without the existence of any strong spatial teleconnection. The analysis is repeated, using time lags of 1 month, or longer, in order to detect any possible non-synchronous relation. Statistically significant results are found only when T-850hPa leads SST with a time lag of 1 month. In particular, the results are statistically significant for winter only, and the findings are similar to those of the first analysis. Therefore, the existence of a 1 month time scale SST persistence is detected for winter months. Copyright © 2002 Royal Meteorological Society. [source] The effect of high pressure treatment on rheological characteristics and colour of mango pulpINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2005Jasim Ahmed Summary The effect of high-pressure (HP) treatment (100,400 MPa for 15 or 30 min at 20 °C) on the rheological characteristics and colour of fresh and canned mango pulps was evaluated. Differences were observed in the rheological behaviour of fresh and canned mango pulps treated with HP. Shear stress,shear rate data of pulps were well described by the Herschel,Bulkley model. The consistency index (K) of fresh pulp increased with pressure level from 100 to 200 MPa while a steady decrease was noticed for canned pulp. For fresh pulp the flow behaviour index decreased with pressure treatment whereas an increasing trend was observed with canned pulp. Storage and loss moduli of treated fresh pulp with HP increased linearly with angular frequency up to 200 MPa for a treatment time of 30 min while a steady decreasing trend was found for processed pulp. No significant variation in colour was observed during pressure treatment. [source] HIGH PRESSURE INACTIVATION OF PECTIN METHYL ESTERASE IN ORANGE JUICE USING COMBINATION TREATMENTSJOURNAL OF FOOD BIOCHEMISTRY, Issue 6 2001S. BASAK ABSTRACT The contribution of several high pressure (HP) processing related factors (pressure level, 300-400 MPa; pressure cycle, 1-3, and pressure-hold time, 30,120 min) on the inactivation of pectin methyl esterase (PME) in single strength (pH 3.7 and 11.4 °Brix) and concentrated (pH 3.5 and 42 °Brix) orange juice was evaluated. A response surface methodology was employed to model the combined effects of factors on the enzyme inactivation. The main effects were described by linear or quadratic functions. For both single strength and concentrated orange juices, the effects of all three main factors and some interactions (pressure level, cycle and holding time) were statistically significant (p<0.05). The dual nature of pressure inactivation of PME (with an instantaneous inactivation due to a pressure pulse, instantaneous pressure fall, and first order rate of inactivation during the pressure hold, yielding D and z values) reported in earlier studies was confirmed. Combination models were developed to predict the residual enzyme activity as influenced by the pressure level, number of pressure cycles and pressure hold time. [source] Pasteurization of Fruit Juices by Means of a Pulsed High Pressure ProcessJOURNAL OF FOOD SCIENCE, Issue 3 2010Giorgio Donsì ABSTRACT:, The use of pulsed high hydrostatic pressure was investigated as a possible approach to stabilize foodstuffs. The objective of this article was to investigate the effect of the main processing variables (pressure [150 to 300 MPa], temperature levels [25 to 50 °C], and pulse number [1 to 10]) on the sanitation of nonpasteurized clear Annurca apple juice as well as freshly-squeezed clear orange juice. The aim of the article was the optimization of the process parameters in step-wise pressure treatment (pressure holding time of each pulse: 60 s, compression rate: 10.5 MPa/s, decompression time: 2 to 5s). The shelf life of the samples, processed at optimized conditions, was evaluated in terms of microbiological stability and quality retention. According to our experimental results, the efficiency of pulsed high pressure processes depends on the combination of pulse holding time and number of pulses. The pulsed high pressure cycles have no additive or synergetic effect on microbial count. The efficacy of the single pulses decreases with the increase of the pulse number and pressure level. Therefore the first pulse cycle is more effective than the following ones. By coupling moderate heating to high pressure, the lethality of the process increases but thermal degradation of the products can be detected. The optimization of the process condition thus results in a compromise between the reduction of the pressure value, due to the synergetic temperature action, and the achievement of quality of the final production. The juices processed under optimal processing conditions show a minimum shelf life of 21 d at a storage temperature of 4 °C. [source] Experimental and numerical research for fluidization behaviors in a gas,solid acoustic fluidized bedAICHE JOURNAL, Issue 7 2010Changqing Cao Abstract The effects of sound assistance on fluidization behaviors were systematically investigated in a gas,solid acoustic fluidized bed. A model modified from Syamlal,O'Brien drag model was established. The original solid momentum equation was developed and an acoustic model was also proposed. The radial particle volume fraction, axial root-mean-square of bed pressure drop, granular temperature, and particle velocity in gas,solid acoustic fluidized bed were simulated using computational fluid dynamics (CFD) code Fluent 6.2. The results showed that radial particle volume fraction increased using modified drag model compared with that using the original one. Radial particle volume fraction was revealed as a parabolic concentration profile. Axial particle volume fraction decreased with the increasing bed height. The granular temperature increased with increasing sound pressure level. It showed that simulation values using CFD code Fluent 6.2 were in agreement with the experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Three-dimensional variational assimilation of Special Sensor Microwave/Imager data into a mesoscale weather-prediction model: A case studyTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 626 2007C. Faccani Abstract Assimilation of data from the Special Sensor Microwave/Imager (SSM/I) is performed in order to improve the forecast of a heavy-precipitation case (IOP2b, 20,21 September 1999) of the Mesoscale Alpine Programme 1999. The three-dimensional variational data assimilation technique of the MM5 model is used. Either brightness temperatures or precipitable water and surface wind speed are assimilated. The sensitivity of the model to SSM/I data is also tested by selectively excluding SSM/I frequencies and changing the size of the thinning box. All the experiments are performed using the European Center for Medium range Weather Forecasting (ECMWF) analysis on pressure level. The new initial conditions show considerable underestimation of the surface wind component V, and, even more, of the surface water vapour mixing ratio. This last error is partially corrected by assimilation of precipitable water alone, although these data produce a large increase in the mean error of the other surface variables (U, V and T). However, the forecast with this new set of initial conditions shows a good agreement (high correlation coefficient) with the rain gauge observations for the 1 h accumulated precipitation 3 h after the initial time. With a doubled box size, there is low sensitivity to the density of the observations used. In this case, the effect of the SSM/I data is slight, and the rainfall pattern produced is comparable to that obtained without any data assimilation. The model performance is also degraded if the 22 GHz brightness temperatures are removed from the assimilated measurements: the correlation coefficient for the precipitation is lower than in the case where all the frequencies are assimilated, and it decreases over time. In general, the use of precipitable water and surface wind speed affects the early stages (3 h) of the rainfall forecast, reducing the model spin-up. Brightness temperatures affect the forecast at a longer range (10 h). Copyright © 2007 Royal Meteorological Society [source] High Pressure Processing , a Database of Kinetic InformationCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 8 2008R. Buckow Abstract Hydrostatic high pressure technology is relatively new to food industry and is more and more considered as an alternative to traditional preservation methods like heat processing. The inactivation of bacteria, spores, viruses and enzymes has been demonstrated in numerous papers, and various schemes for modelling the experimental inactivation data have been suggested. Although there are similarities to heat inactivation kinetics it is generally agreed that the heat process safety assessment with its typical indicator organisms cannot simply be transferred to high pressure treatment. In this paper a database is introduced which aims at the comparison of published kinetic high pressure inactivation data by using suitable mathematical modelling tools. For the sake of clarity, the functional associations of pressure, temperature and exposure time is presented by means of pressure-temperature diagrams (pT -diagrams), which show pressure-temperature combinations yielding to a desired reaction (e.g. inactivation) rate constant. Thus, the database software was particularly designed to enable the user to call up pressure-temperature dependent function equations for a number of micro-organisms, enzymes and food constituents and to visualize them in pT -diagrams for predetermined treatment times or as kinetics under predetermined p - T conditions. In addition, the database also features a simple calculator tool which allows the user to make an entry in three of the four process conditions (pressure level, temperature level, inactivation level, dwell time) and calculate the remaining forth process condition. The database is accessible through the internet and is continuously updated on the basis of the most recent publications and own experimental data. [source] Angiotensin receptors in the eyes of arterial hypertensive ratsACTA OPHTHALMOLOGICA, Issue 4 2010Anu Vaajanen Abstract. Purpose:, The aim of the present study was to determine whether the eye tissues of arterial hypertensive rats evince expression of angiotensin receptors (AT1 and AT2) as well as the novel Mas receptor, whose endogenous ligand is vasorelaxing Angiotensin (1,7) [Ang (1,7)]. Methods:, Enucleated eyes from spontaneously hypertensive rats (SHR) and double transgenic rats harbouring human renin and angiotensinogen genes (dTGR) and their normotensive controls were used. Half of the rats were pretreated orally with an Angiotensin II (Ang II) type 1 receptor blocker (ARB). The eyes were snap-frozen in isopentane at ,40° and stored at ,70° for subsequent reverse transcriptase polymerase chain reaction (RT-PCR) analysis or in vitro autoradiography. Results:, The mRNA expression of AT1a and AT 2 as well as the novel Mas receptor was detected in all rat groups, being markedly higher in the retina than in the ciliary body. dTGR had significantly more receptors than SHR, but no direct relation to blood pressure level was seen. According to the autoradiography, treatment with ARB blocked a part of AT1 receptors but had no clear effect on AT2 receptors. Conclusion:, The novel Mas receptor was found by RT-PCR in eye tissue for the first time. Its specific ligand, Ang (1,7), may be involved in the regulation of intraocular pressure , as recently demonstrated by us , and in the pathogenesis of retinal diseases as a counter-regulatory component for the vascular and proliferative actions of Ang II. The results suggest that the density of AT1 receptors in the eye is independent of the blood pressure level of the animal. [source] Effects of sinus lifting on voice qualityCLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2003A prospective study, risk assessment Abstract: A variety of potential complications associated with sinus lift surgery have been reported in the literature. However, potential alterations of voice quality following sinus elevation have so far not been mentioned or evaluated scientifically. For the majority of patients, slight changes of the voice pattern are of no importance. However, for voice professionals, whose voices have become part of their distinctive profession or trademark, minimal changes may have dramatic consequences. This specific group of patients, such as speakers, actors and singers, depend on the particular quality and timbre of their voice for their livelihood. Consequently, the purpose of this study was to assess the effects of sinus lifting on voice quality in the above patient group. In a collaborative interdisciplinary effort, the Departments of Oral Surgery and Otorhinolaryngology, Section of Phoniatrics and Logopedics, thoroughly evaluated a series of voice parameters of four patients undergoing sinus lifting pre- and postoperatively. The parameters analyzed included pitch, dynamic range, sound pressure level, percent jitter, percent shimmer and noise-to-harmonics ratio with special emphasis on formant analysis. No changes were detected in any of the commonly evaluated parameters. These were rated subjectively by patients and their friends or relatives and objectively with instrumental tools under isolated phoniatric lab conditions. In conclusion, sinus lift surgery appears to be a safe, predictable evidence-based method for regenerating the highly atrophic posterior maxilla, which does not jeopardize the individual characteristic voice pattern of high-profile patients critically dependent on their voices for their livelihood. Résumé Quelques complications potentielles associées à la chirurgie d'épaississement du plancher sinusal ont été rapportées dans la littérature. Les altérations potentielles de la qualité de la voix suivant l'épaississement du plancher sinusal n'ont pas encore été mentionnées et évaluées scientifiquement. Pour la majorité des patients, des petites variations dans le timbre de la voix ne sont pas importantes. Cependant, pour les professionnels de la phonation pour lesquels la voix est devenue une partie importante de leur profession, des variations même faibles peuvent entraîner des conséquences dramatiques. Ce groupe spécifique de patients, tels que les orateurs, les acteurs et les chanteurs dépendent essentiellement de la qualité et du timbre particulier de leur voix dans leur vie professionnelle. Par conséquent, le but de cette étude a été d'estimer les effets d'un épaississement du sinus sur la qualité de la voix dans ce groupe de patients. Dans un effort interdisciplinaire collaboratif, les départements de chirurgie buccale et d'otorhino-laringologie, la section de phonétique et de logopédie ont évalué de manière très précise une série de paramètres de la voix avant et après l'opération chez quatre patients ayant subi un épaississement du sinus maxillare. Les paramètres analysés contenaient la hauteur, l'étalement, le niveau de pression du son, le pourcentage de trac, le pourcentage de chatoiements et la proportion bruit-harmonie avec une insistance spéciale sur l'analyse du formant. Aucun changement n'a été détecté dans aucun des paramètres évalués couramment. Ces derniers étaient estimés subjectivement par les patients et par leurs amis ou parents, et objectivement à l'aide des instruments sous des conditions de laboratoire de phonétique isolé. En conclusion, la chirugie d'épaississement du plancher sinusal semble une méthode sûre, avec un pronostic basé sur l'évidence, permettant de regénérer les maxillaires très atrophiés qui n'empêche pas la caractéristique individuelle de la voix chez des patients avec des profils où la voix est essentielle à leur vie active. Zusammenfassung Der Einfluss einer Sinusbodenelevation auf die Stimmqualität, eine Langzeitstudie und Risikoanalyse. In der Literatur werden eine ganze Reihe von möglichen Komplikationen beschrieben, die bei dem chirurgischen Eingriff der Sinusbodenelevation auftreten können. Veränderungen der Stimme, die als Folge einer Sinusbodenelevation vorkommen können, wurden aber bis heute weder beschrieben, noch wissenschaftlich ausgewertet. Für den Grossteil der Patienten haben leichte Veränderungen der Stimme keine Bedeutung. Für Personen aber, deren Stimme bei der Ausübung ihres Berufes wichtig ist, eventuell ein Teil ihres Berufes oder gar Markenzeichen geworden ist, können kleine Veränderungen dramatische Folgen haben. Diese ausgewählte Gruppe von Patienten, wie zum Beispiel Nachrichtensprecher, Schauspieler oder Sänger, sind im täglichen Leben auf die spezifische Art und den Klang ihrer Stimme angewiesen. Daher war das Ziel dieser Studie, Einflüsse einer Sinusbodenelevation auf die Stimmqualität bei den oben erwähnten Patienten zu untersuchen. In einer interdisziplinären Zusammenarbeit untersuchten die Klinik für Oralchirurgie und Otorhinolaryngologie und die Abteilung für Phonetik und Logopädie an 4 Patienten vor und nach der Sinusbodenelevation sehr eingehend verschiedene Parameter der Stimme. Die untersuchten Parameter waren Tonhöhe, Tonvolumen, den durch den Ton erzeugten Luftdruck, Schwingungen, Vibrationen und das Verhältnis zwischen Nebengeräuschen und harmonischem Klang mit speziellem Augenmerk auf formative Analysen. Man erkannte bei keinem der oben untersuchten Parametern eine Veränderung. Sie wurden sowohl subjektiv durch die Patienten und ihre Freunde oder Verwandten, sowie objektiv mit Messinstrumenten unter absolut schallisolierten Laborbedingungen gemessen. Über die Sinusbodenelevation kann man zusammenfassend sagen, dass es sich um eine sichere, voraussagbare und auf wissenschaftlichen Grundlagen basierende Operationsmethode zum Wiederaufbau einer massiv athrophischen Maxilla im Seitenzahnbereich handelt. Sie gefährdet die individuellen Stimmcharakteristika von kritischen und sehr anspruchsvollen Patienten, die in ihrem täglichen Leben auf ihre charakteristische Stimme angwiesen sind, nicht. Resumen Se han descrito en la literatura una variedad de complicaciones asociadas con la cirugía de la elevación del seno. Pero hasta el momento no se han mencionado ni evaluado científicamente alteraciones potenciales de la calidad de voz tras la elevación del seno. Para la mayoría de los pacientes, pequeños cambios en el patrón de voz no tienen importancia. De todos modos, en los profesionales de la voz, cuyas voces se han convertido en parte distintiva de su profesión o marca, pequeños cambios pueden tener consecuencias dramáticas. Este grupo específico de pacientes, tales como locutores, actores y cantantes, dependen de la calidad particular y timbre de su voz para su sustento. Consecuentemente, el propósito de este estudio fue valorar los efectos de la elevación del seno en la calidad de voz en el anterior grupo de pacientes. En un esfuerzo de colaboración interdisciplinaria, los departamentos de Cirugía Oral y Otorrinolaringología, Sección de Foniatría y Logopedia, evaluaron e profundidad una serie de parámetros de voz de 4 pacientes que se someterían a elevación del seno pre y postoperatoriamente. Los parámetros analizados incluyeron tono, rango dinámico, nivel de presión sonoro, porcentaje de reverberación, porcentaje de tremulación y relación ruido a harmónicos con especial énfasis en el análisis formante. No se detectaron cambios en ninguno de los parámetros evaluados comúnmente. Estos se valoraron subjetivamente por los pacientes y sus amigos o parientes y objetivamente por herramientas instrumentales bajo condiciones de laboratorio de aislamiento foniátrico. En definitiva, la cirugía de elevación del seno parece ser un método seguro, predecible basado en la evidencia para regenerar el maxilar posterior altamente atrófico, que no pone en peligro las características del patrón de voz de los pacientes de características especiales dependientes de manera crítica de sus voces para su sustento. [source] Single-beat estimation of the left ventricular end-systolic pressure,volume relationship in patients with heart failureACTA PHYSIOLOGICA, Issue 1 2010E. A. Ten Brinke Abstract Aim:, The end-systolic pressure,volume relationship (ESPVR) constructed from multiple pressure,volume (PV) loops acquired during load intervention is an established method to asses left ventricular (LV) contractility. We tested the accuracy of simplified single-beat (SB) ESPVR estimation in patients with severe heart failure. Methods:, Nineteen heart failure patients (NYHA III-IV) scheduled for surgical ventricular restoration and/or restrictive mitral annuloplasty and 12 patients with normal LV function scheduled for coronary artery bypass grafting were included. PV signals were obtained before and after cardiac surgery by pressure-conductance catheters and gradual pre-load reductions by vena cava occlusion (VCO). The SB method was applied to the first beat of the VCO run. Accuracy was quantified by the root-mean-square-error (RMSE) between ESPVRSB and gold-standard ESPVRVCO. In addition, we compared slopes (EES) and intercepts (end-systolic volume at multiple pressure levels (70,100 mmHg: ESV70,ESV100) of ESPVRSB vs. ESPVRVCO by Bland,Altman analyses. Results:, RMSE was 1.7 ± 1.0 mmHg and was not significantly different between groups and not dependent on end-diastolic volume, indicating equal, high accuracy over a wide volume range. SB-predicted EES had a bias of ,0.39 mmHg mL,1 and limits of agreement (LoA) ,2.0 to +1.2 mmHg mL,1. SB-predicted ESVs at each pressure level showed small bias (range: ,10.8 to +9.4 mL) and narrow LoA. Two-way anova indicated that differences between groups were not dependent on the method. Conclusion:, Our findings, obtained in hearts spanning a wide range of sizes and conditions, support the use of the SB method. This method ultimately facilitates less invasive ESPVR estimation, particularly when coupled with emerging noninvasive techniques to measure LV pressures and volumes. [source] Pressure-independent cardiac effects of angiotensin II in pigsACTA PHYSIOLOGICA, Issue 2 2004M. Broomé Abstract Background:, Angiotensin II (Ang II) is a potent vasoconstrictor with an important role in the development of cardiovascular disease. Earlier results have shown a positive acute inotropic effect of Ang II in anaesthetized pigs together with significant vasoconstriction. This investigation was designed to study cardiac effects of Ang II, when blood pressure was maintained constant by experimental means. Methods:, Ang II (200 ,g h,1) was infused in anaesthetized pigs (n = 10) at two different arterial blood pressures, the first determined by the effects of Ang II alone, and the second maintained at baseline blood pressure with nitroprusside. Cardiac systolic and diastolic function was evaluated by analysis of left ventricular pressure,volume relationships. Results:, Heart rate, end-systolic elastance (Ees) and pre-load adjusted maximal power (PWRmax EDV,2) increased at both blood pressure levels, although less when blood pressure was kept constant with nitroprusside. The time constant for isovolumetric relaxation (,1/2) was prolonged with Ang II alone and shortened with Ang II infused together with nitroprusside. Conclusion:, Ang II infusion in the pig has inotropic and chronotropic properties independent of arterial blood pressure levels, although the effects seem to be blunted by pharmacological actions of the nitric oxide donor nitroprusside. [source] Self glucose monitoring and physical exercise in diabetesDIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue S1 2009G. Pugliese Abstract Cardiorespiratory fitness, which is determined mainly by the level of physical activity, is inversely related to mortality in the general population as well as in subjects with diabetes, the incidence of which is also increased by low exercise capacity. Exercise is capable of promoting glucose utilization in normal subjects as well as in insulin-deficient or insulin-resistant diabetic individuals. In diabetic subjects treated with insulin or insulin secretagogues, exercise may also result in complications, with too much insulin causing hypoglycaemia and not enough insulin leading to hyperglycaemia and possibly ketoacidosis; both complications may also occur several hours after exercise. Therefore, self-monitoring of blood glucose before, during (for exercise duration of more than 1 h) and after physical exercise is highly recommended, and also carbohydrate supplementation may be required. In the Italian Diabetes Exercise Study (IDES), measurement of blood glucose and systolic and diastolic blood pressure levels before and after supervised sessions of combined (aerobic + resistance) exercise in type 2 diabetic subjects with the metabolic syndrome showed significant reductions of these parameters, though no major hypoglycaemic or hypotensive episode was detected. The extent of reduction of blood glucose was related to baseline values but not to energy expenditure and was higher in subjects treated with insulin than in those on diet or oral hypoglycaemic agents (OHA). Thus, supervised exercise training associated with blood glucose monitoring is an effective and safe intervention to decrease blood glucose levels in type 2 diabetic subjects. Copyright © 2009 John Wiley & Sons, Ltd. [source] Treatment of diabetic nephropathy in its early stagesDIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 2 2003Giacomo Deferrari Abstract Diabetic nephropathy is one of the most frequent causes of end-stage renal disease (ESRD), and, in recent years, the number of diabetic patients entering renal replacement therapy has dramatically increased. The magnitude of the problem has led to numerous efforts to identify preventive and therapeutic strategies. In normoalbuminuric patients, optimal glycemic control (HbA1c lower than 7.5%) plays a fundamental role in the primary prevention of ESRD [weighted mean relative risk reduction (RRR) ,37% for metabolic control versus trivial renoprotection for intensive anti-hypertensive therapy or ACE-inhibitors (ACE-I)]. In the microalbuminuric stage, strict glycemic control probably reduces the incidence of overt nephropathy (weighted mean RRR ,50%), while blood pressure levels below 130/80 mmHg are recommended according to the average blood pressure levels obtained in various studies. In normotensive patients, ACE-I markedly reduce the development of overt nephropathy almost regardless of blood pressure levels; in hypertensive patients, ACE-I are less clearly active (weighted mean RRR ,23% versus other drugs), whereas angiotensin-receptor blockers (ARB) appear strikingly renoprotective. Once overt proteinuria appears, it is uncertain whether glycemic control affects the progression of nephropathy. In type 1 diabetes, various anti-hypertensive treatments, mainly ACE-I, are effective in slowing down the progression of nephropathy; in type 2 diabetes, two recent studies demonstrate that ARB are superior to conventional therapy or calcium channel blockers (CCB). In clinical practice, pharmacological tools are not always used to the best benefit of the patients. Therefore, clinicians and patients need to be educated regarding the renoprotection of drugs inhibiting the renin-angiotensin system (RAS) and the overwhelming importance of achieving target blood pressure. Copyright © 2003 John Wiley & Sons, Ltd. [source] Short Daily Dialysis (SDHD) Efficacy : Pilot Multicentric Study with Nine Patients from MadridHEMODIALYSIS INTERNATIONAL, Issue 1 2003G. Barril Interest in quotidian (daily) hemodialysis (HD) seems to be growing. Clinical data consistently showed improved quality of life, better control of blood pressure, less need for medications including erythropoietin (EPO) and better nutrition. We evaluate the SDHD efficacy in 9 patients in conventional HD (3 weekly sesions/4 hours), mean age 57,78 years range (33,75), 6 males and 3 females who needed increased dialysis efficiency by different medical indications: 5 cases with hypertensive miocardiopathy and severe LVH, 2 of them with EFLV 26% and 27%. 2 cases with ischemic cardiopathy symptoms, one of them with anger and restless dysnea with a non resvascularizable coronary lesion, and other with cardiac insufficiency episodes requiring hospitalization once a month. 1 patient with big body surface area and elevated phosphorus levels although without control, with conventional three times/week HD. 1 patient indication was made by 12 years on HD with multiple vascular accesses failed needing a Tessio cathéter being into infradialysis regimen for his malnutrition status. The schedule in all of them was 6 days per week sessions between 2.15 hrs till 3 hours depending of body surface area to obtain a weekly kt/v nearest to 4. HD session were realized in the Hospital (4 pts) or in satellite unit (5 pts) due to the characteristics of the patients. The time remaining in this schedule was between 5 months to 2 years and 9 months. All the patients showed clinical improvement, subjective and objective, since the first weeks of starting SDHD. Sleep symptoms were the first to improve. All patients showing good coping with this HD alternative. Blood pressure levels were controlled without need for antihypertensive drugs, although the dry weight increased significantly in all cases. Albumin serum levels increased as nutrition parameter, controlling also the osteodystrophy and phosphorus. In a patient the EFLV was normalized from 6 months (26%,50%) improving in other. Two patients could be included in Tx waiting list. Again, anemia improved and decreasing EPO was required. No vascular access (autologous AVF) malfunction was detected in relation to daily procedure. Conclusion: Our pilot experience shows a clinical and biochemical improvement in the patients and quality of life as well. Prospective studies to demonstrate the financial benefits of these modalities are needed. [source] A field-based investigation to examine underwater soundscapes of five common river habitats,HYDROLOGICAL PROCESSES, Issue 22 2010Diego Tonolla Abstract Aquatic river habitat types have been characterized and classified for over five decades based on hydrogeomorphic and ecological variables. However, few studies considered the generation of underwater sound as a unique property of aquatic habitats, and therefore as a potential information source for freshwater organisms. In this study, five common habitat types along 12 rivers in Switzerland (six replicates per habitat type) were acoustically compared. Acoustic signals were recorded by submerging two parallel hydrophones and were analysed by calculating the energetic mean as well as the temporal variance of ten octave bands (31·5 Hz,16 kHz). Concurrently, each habitat type was characterized by hydraulic and geomorphic variables, respectively. The average relative roughness, velocity-to-depth ratio, and Froude number explained most of the variance of the acoustic signals created in different habitat types. The average relative roughness predominantly affected middle frequencies (63 Hz,1 kHz), while streambed sediment transport increased high-frequency sound pressure levels (2,16 kHz) as well as the temporal variability of the recorded signal. Each aquatic habitat type exhibited a distinct acoustic signature or soundscape. These soundscapes may be a crucial information source for many freshwater organisms about their riverine environment. Copyright © 2010 John Wiley & Sons, Ltd. [source] Bayesian analysis of changes in Radiosonde Atmospheric TemperatureINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2009Christoph Schleip Abstract This paper describes long-term changes of global atmospheric temperature, using a strict Bayesian approach which considers three different models to describe the time series: the constant model, the linear model and a change point model. The change point model allows the description of nonlinear annual rates of change with associated confidence intervals. We calculate the probabilities of each of the three models and average finally over these models to obtain the expected functional behaviour and rate of change in temperature with annual resolution. We apply this procedure to a new homogenized Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC-A) data set. Annual mean temperature for 13 pressure levels from the surface to 30 hPa is examined. Residual sums of squares reveal that Bayesian-model-averaged function descriptions and rates of changes are especially useful and informative for the surface, troposphere and tropopause and less appropriate for the stratosphere. From the surface up to the tropopause (200,100 hPa), the results reveal that the change point model provides the best data fit. Despite the occurrence of two volcanic eruptions El Chicón (1982) and Mt. Pinatubo (1991), the stratosphere (70,30 hPa) shows a preference for the linear model (60%). The near surface changes exhibit comparatively high change point probability around 1985 and 1995, whereas those at the tropopause level are highest between 1995 and 2000. For the surface and troposphere the model-averaged functional behaviour increases quite constantly, whereas the model-averaged functional behaviour for the tropopause decreases until the end of the 1990s and increases from 2000 onwards. The limitations of the currently used radiosonde data render interpretation of the observed changes difficult. Additionally undetected change points may result from our limited model space. In future it should be tested whether a multiple change point model provides a better data description for the stratosphere. Copyright © 2008 Royal Meteorological Society [source] Global atmospheric energetics from NCEP,Reanalysis 2 and ECMWF,ERA40 ReanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2009Carlos A. F. Marques Abstract The global atmospheric energy cycle is estimated on an annual basis using Reanalysis 2 data from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR), and ERA 40 Reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1979,2001. A formalism to avoid belowground data on pressure levels intercepted by topography is adopted. No appreciable differences were found between the two datasets from the energetics point of view. The so-called ,, and v·grad z formulations were both used for the conversions from zonal available potential energy into zonal kinetic energy (CZ) and from eddy available potential energy into eddy kinetic energy (CE). Results with both formulations are comparable only when using the formalism preventing belowground data to enter into the computations. Atmospheric energetics are also computed using ECMWF Reanalyses for the period 1958,1978. A significant increase was found in the eddy kinetic and eddy available potential energies from the early period to the later period, likely related to the assimilation in the reanalyses of satellite data after 1979. The conversion rate, CZ, was found to change its sign throughout the years. The atmospheric energy cycle using the ECMWF Reanalyses data is compared with five previous estimates. Differences in the direction of the conversion rate, CZ, between the various estimates may be explained by the different time periods chosen for averaging. Owing to the omission of belowground data, the conversion from zonal available potential energy into eddy available potential energy (CA) was somewhat smaller in ECMWF Reanalyses than in the previous estimates. Despite those differences, an overall agreement may be found between the various estimates for the atmospheric energy cycle. Copyright © 2008 Royal Meteorological Society [source] Retro-active skill of multi-tiered forecasts of summer rainfall over southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2001Willem A. Landman Abstract Sea-surface temperature (SST) variations of the oceans surrounding southern Africa are associated with seasonal rainfall variability, especially during austral summer when the tropical atmospheric circulation is dominant over the region. Because of instabilities in the linear association between summer rainfall over southern Africa and SSTs of the tropical Indian Ocean, the skilful prediction of seasonal rainfall may best be achieved using physically based models. A two-tiered retro-active forecast procedure for the December,February (DJF) season is employed over a 10-year period starting from 1987/1988. Rainfall forecasts are produced for a number of homogeneous regions over part of southern Africa. Categorized (below-normal, near-normal and above-normal) statistical DJF rainfall predictions are made for the region to form the baseline skill level that has to be outscored by more elaborate methods involving general circulation models (GCMs). The GCM used here is the Centre for Ocean,Land,Atmosphere Studies (COLA) T30, with predicted global SST fields as boundary forcing and initial conditions derived from the National Centres for Environmental Prediction (NCEP) reanalysis data. Bias-corrected GCM simulations of circulation and moisture at certain standard pressure levels are downscaled to produce rainfall forecasts at the regional level using the perfect prognosis approach. In the two-tiered forecasting system, SST predictions for the global oceans are made first. SST anomalies of the equatorial Pacific (NIÑO3.4) and Indian oceans are predicted skilfully at 1- and 3-month lead-times using a statistical model. These retro-active SST forecasts are accurate for pre-1990 conditions, but predictability seems to have weakened during the 1990s. Skilful multi-tiered rainfall forecasts are obtained when the amplitudes of large events in the global oceans (such as El Niño and La Niña episodes) are described adequately by the predicted SST fields. GCM simulations using persisted August SST anomalies instead of forecast SSTs produce skill levels similar to those of the baseline for longer lead-times. Given high-skill SST forecasts, the scheme has the potential to provide climate forecasts that outscore the baseline skill level substantially. Copyright © 2001 Royal Meteorological Society [source] The value of a specialist lipid clinicINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 6 2008S. C. Martin Summary Aims:, To establish the value of the first 3 years of a cardiovascular risk factor clinic in tackling the major risk factors for cardiovascular disease (CVD). Methods:, A database review of all 339 patients referred to the clinic. Results:, Blood pressure levels in the hypertensive patients were significantly reduced and 9% of the smokers managed to quit for 12 months, half of them subsequently relapsing. Ninety-eight oral glucose tolerance tests were performed and 40% were abnormal yielding 10 patients with hitherto unsuspected diabetes and 29 with impaired glucose tolerance. Sixty-four of the 97 referrals of patients in the primary prevention group (no evidence of CVD) were found to have calculated Framingham coronary heart disease risk estimates of < 15% per decade, the lowest being 0.3%. Lipid levels were significantly reduced in both the hypercholesterolaemic (n = 290) and hypertriglyceridaemic (n = 49) patient groups through the use of more potent statins, extensive use of combination therapy and appropriate use of fibrates and omega-3 fish oil supplements. The annual drug cost per patient treated only increased from £310.72 to £398.08, yet there was a 3.5-fold increase in the number of patients achieving the General Medical Services 2 target of a total cholesterol < 5 mmol/l and a 4.5-fold increase in patients achieving the Joint British Societies 2 target of a low-density lipoprotein (LDL) cholesterol < 2 mmol/l. Conclusion:, The need for a specialist clinic was demonstrated by the 66% of primary prevention referrals who did not meet the current NICE treatment threshold. Additionally, the clinic was able to diagnose and treat 39 patients with undiagnosed diabetes mellitus/impaired glucose tolerance and 12 with hypothyroidism. LDL cholesterol was reduced overall by 36% implying a greater than one-third reduction in future cardiovascular events before the improvements in blood pressure control and smoking cessation are included and this was achieved at marginal extra cost to the mean drug bill at referral. [source] Management of advanced chronic kidney disease in primary care , current data from GermanyINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 8 2006S. HERGET-ROSENTHAL Summary The quality of chronic kidney disease (CKD) care and the control of CKD progression factors and of comorbid conditions according to current recommendations in primary care were investigated in this retrospective cohort study of 127 consecutive CKD patients. CKD was advanced (glomerular filtration rate 21 ± 10 ml/min). Fifty-seven per cent of patients had been evaluated to clarify CKD aetiology. Blood pressure was substantially elevated (148 ± 20/83 ± 11 mmHg) and only 39% of patients achieved target blood pressure levels. At a mean HbA1c of 6.5 ± 1.1%, glycaemic control was good in 63% of diabetics. Mean haemoglobin was 10.8 ± 1.8 g/dl, and anaemia was adequately controlled in 49%. In 42% the management of bone disease and in 80% the nutritional status was sufficient. Angiotensin converting enzyme inhibitors or angiotensin-2-receptor blockers was used in 59% of patients with diabetic nephropathy or proteinuria above 1 g/day. High-total quality of care was only achieved in 35% which suggests that the management of advanced CKD in primary care is suboptimal. [source] Comparison of low temperature mixed refrigerant cycles for separation systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2009M. Mafi Abstract Numerous mixed refrigerant cycles (MRCs) were developed in the past several decades in different applications. In this paper, two sets of low temperature MRCs are developed and simulated for a typical olefin plant utilizing a mixture of methane, ethane, propane and nitrogen as cycle working fluid to replace the pure ethylene refrigeration cycle that is used in conjunction with propylene refrigeration cycle in conventional plants. The key parameters of the cycles including mixture compositions and operating pressure levels are optimized to meet the objective of minimum shaftwork in compressor. The results show that different cycle configuration has different optimal mixture composition and low and high operating pressures. The results of exergy analysis reveal that the main location of the exergy loss in the cycles is the heat exchanger system. Also, the Carnot factor versus heat flow diagram is provided to identify the distribution of inefficiencies in the heat exchangers for each cycle. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system using the optimal working fluid mixture composition, optimal high and low operating pressures and optimal arrangement of the cycle components. Copyright © 2008 John Wiley & Sons, Ltd. [source] Transient thermal modelling of heat recovery steam generators in combined cycle power plantsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2007Sepehr Sanaye Abstract Heat recovery steam generator (HRSG) is a major component of a combined cycle power plant (CCPP). This equipment is particularly subject to severe thermal stress especially during cold start-up period. Hence, it is important to predict the operational parameters of HRSGs such as temperature of steam, water, hot gas and tube metal of heating elements as well as pressure change in drums during transient and steady-state operation. These parameters may be used for estimating thermal and mechanical stresses which are important in HRSG design and operation. In this paper, the results of a developed thermal model for predicting the working conditions of HRSG elements during transient and steady-state operations are reported. The model is capable of analysing arbitrary number of pressure levels and any number of elements such as superheater, evaporator, economizer, deaerator, desuperheater, reheater, as well as duct burners. To assess the correct performance of the developed model two kinds of data verification were performed. In the first kind of data verification, the program output was compared with the measured data collected from a cold start-up of an HRSG at Tehran CCPP. The variations of gas, water/steam and metal temperatures at various sections of HRSG, and pressure in drums were among the studied parameters. Mean differences of about 3.8% for temperature and about 9.2% for pressure were observed in this data comparison. In the second kind of data verification, the steady-state numerical output of the model was checked with the output of the well-known commercial software. An average difference of about 1.5% was found between the two latter groups of data. Copyright © 2007 John Wiley & Sons, Ltd. [source] The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stentJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Tré R. Welch Abstract We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L -lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62°C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] | |||||||||||||||||||||||||||||||||||||