Effects of mild hypothermic cardiopulmonary bypass on blood viscoelasticity in coronary artery bypass grafting patients

The purpose of this study was to determine the changes in blood viscoelasticity during and after coronary artery bypass grafting (CABG) and to identify correlations between blood viscoelasticity and patients' age, duration of cardiopulmonary bypass (CPB), and cross-clamp time. After Institutional Review Board approvals, patients (n = 10) who were subjected to mild hypothermic CPB were included in this study. Viscosity and elasticity were measured at strains of 0.2, 1, and 5 using a Vilastic-3 Viscoelasticity Analyzer. Arterial blood samples were collected pre-CPB, on normothermic CPB, hypothermic CPB, after rewarming, and after CPB. Viscosity and elasticity at strains of 0.2 and 1 were altered significantly during and after CPB compared to the pre-CPB (p < 0.01). In particular, elasticity of blood was diminished during normothermic bypass and could not be recovered after CPB (p < 0.01). Although there were strong correlations between blood viscoelasticity, duration of CPB, and cross-clamp time on normothermic CPB, only the patients' age showed a positive correlation between viscosity (r = 0.61, p = 0.05), and elasticity (r = 0.89, p < 0.001) after CPB. These results suggest that mild hypothermic CPB alters the blood viscoelasticity during and after CABG.     

先天性心脏病患儿的全血粘弹特性

本文采用Low Shear-30流变测定仪,测定了52例青紫型先天性心脏病(CCHD)患儿,51例非青紫型先天性心脏病(ACHD)患儿)以及CCHD组中3例有严重并发症患儿的全血粘弹性参数。按年龄和性别分别与相应对照组比较。结果表明:(1)CCHD组的Hb、RBC、HCT、η_(0.512)、η_(5.96)、η_(51.2)、η、η″G、AI明显增高;OD明显降低,而Fib、ηp则无明显变化。(2)ACHD组仅有Hb、OD明显增高,其余全血粘弹性参数无明显变化。(3)3例有严重并发症的CCHD患儿的全血粘弹参数,除ηp、Fib、OD明显降低外,其余指标均明显增高。其升高幅度明显大于无并发症的CCHD患儿。本文所提出的CCHD并发症患儿全血粘弹性参数变化的临界值,可为临床早期诊断和防治并发症提供参考资料。     

年龄变化与性别对血液粘弹特性的影响

用Low Shear-30流变仪测定了350例健康成年人（男178名,女172名）和211名健康儿童（男108名,女103名）于血细胞压积自然状态下的血液粘弹性参数和有关流变参数:复粘度的粘性分量q’和弹性分量n”、剪切弹性模量G’、在0石125-‘和51.ZS-‘下全血表观粘度（n。。;。、n。;。）、释氧系数（OD）、纤维蛋白原和血浆粘度（n。）。将男女受试者按年龄分成9组:I组,新生儿（生后1—7天）;I组,l--x岁;互组,5—9岁;N组,10—15岁;v组,17—29岁;v组,30—39岁;w组,40—49岁;贝组;50-59岁;辽组,大于60岁。探讨年龄对全血粘弹特性参数和其他流变参数的影响。结果征明新生儿组处于血液高粘滞状态,He丁,n。。;:,儿;.1,丫、丫、0’明显高于其他各组;而刀、巨组处于血液低粘滞状态,上述各参数低于其他各组;I-互组血液粘弹性参数无性别差异;w组才出现男女性别差异;在卜亚组,男性血液的丫、门”、G’、n。。;。、n。;.:明显高于女性组,女性组血液的ODk于男性组,纤维蛋白原和＊。男女两组间无差异。纤维蛋白原和nP随年龄增长而增高;HCT、n。。;:、门s:。在男子第伍组比 V-w组明显降低,在女子第可组这些参数高于第R组。OD在第卜皿组均无慑别差异,在第可组达闻峰,且女子组OD值高于男子组而后随年龄增长几乎平行地降低。n’在男     

高脂血症患者血液粘弹特性改变

为研究高脂血症患者血液粘弹特性的改变，对３０名平均年龄５５．９岁（３８－７５岁）的男性高脂血症患者的空腹血，用低剪切－３０流变测定仪进行了规范的备注流变学测定。结果证明观察组和对照组的ＨＣＴ无显著性差异，但观察组的血浆粘度（ηｐ），切变率分别为０．５１２秒＾－１和５１．２秒＾－１时的表观粘度η０．５１２和η５１．２，红细胞聚集指数（ＡＩ），复粘度的粘性分量（η＇）和弹性分量（η＾ｎ），剪切弹性模量     

Entanglement Locking in the Unique Elasticity of Polydimethylsiloxane Rubbers

The viscoelasticity behavior of the polydimethylsiloxane (PDMS) rubber blends of high molecular weight polymers modified by low molecular weight agents is studied in compression mode by stress–strain curves, the creep and step‐strain, and dynamic‐mechanical experiments. The strain spectra highlight the dynamics of active chains at high frequencies and of dangling ends in the low frequencies field. At low deformation, the blending agent enhances the elastic properties by increasing the density of the active chains in the rubber network, in agreement with the classical theories of elasticity. At high deformation, in analogy with the rheological studies on similar liquid blends, the Entanglement Locking model is proposed: the short chains of the blending agent are adsorbed on entanglement sites of long dangling chains, giving effective crosslinks via high entropy dynamics. In this way, the long‐term entanglement locking enhances the density of active chains and elastic behavior. At high deformation, the entanglement locking model enriches the rubber elasticity theories according to the tube network model and Mooney–Rivlin equation. The models herein and the possibility they offer for improving rubber viscoelasticity are valuable for the development of polymer physics and technology.     

Compliance of Resilient Denture Liners Immersed in Effervescent Denture Cleansers

PURPOSE: Six resilient denture liners (RDL) were exposed to two immersion effervescent denture cleansers to evaluate change in compliance over a simulated 1 year time interval. MATERIALS AND METHODS: Ten samples of each material, Molloplast B, Mollosil, MPDS-SL, Permasoft, Softline, and Sofreliner were exposed to either Fixodent or Efferdent denture cleanser. A cyclic load was applied in a squarewave fashion to derive a load displacement curve to measure compliance at 0, 7, 30, 180, and 360 simulated days. RESULTS: All 12 of the material/cleanser combinations demonstrated a significant change in compliance at each time interval relative to baseline. Mollosil had the greatest increase in flexibility from baseline, and MPDS-SL had the smallest increase in flexibility. In general, chairside materials demonstrated greater change in compliance from baseline compared to laboratory materials. Materials subjected to Fixodent cleanser, when averaged over time, were significantly more flexible than materials exposed to Efferdent cleanser. CONCLUSIONS: Exposure of resilient soft liners to two common cleansers resulted in a significant increase in flexibility. This change in flexibility depended slightly, though significantly, on the type of cleanser, and appeared to be more significant with time. In general, chairside materials seemed to change more than laboratory-processed liners. The exception was Permasoft that was fabricated as a laboratory material but behaved like a chairside material. CLINICAL SIGNIFICANCE: The initiator of the polymerization reaction rather than the mode of polymerization may be more important in predicting a change in the flexibility of RDLs. Constituents within the oral environment may be more responsible for changes in RDL flexibility than denture cleansers.     

Predictive value of measurements of respiratory mechanics in preterm infants with HMD

Conventional methods for measuring respiratory mechanics model the respiratory system as a single compartment. The interrupter technique allows the respiratory system to be considered as a two compartment model with “flow resistance” of the conducting airways (Pinit), calculated from the initial pressure drop (Pinit), considered separately from Pdiff, as a measure of the viscoelastic properties of the lung and chest wall and any pendelluft present. The pulmonary mechanics of 50 intubated and mechanically ventilated preterm infants (≤1500 g) were studied during the first week of life using conventional methods and the interrupter technique to determine whether it was possible to predict which infants would develop bronchopulmonary dysplasia (BPD). Pulmonary mechanics of preterm infants intubated and ventilated for apnea of prematurity were also studied. The dynamic compliance of the respiratory system (C_rsdyn) was significantly lower on day 1 (P<0.001) and during the first week of life in the infants with HMD who developed BPD (ANOVA, P<0.0001). There was no significant difference in the respiratory system resistance (R_rs), Rinit, or Pdiff between BPD and no-BPD groups. However, Pdiff was significantly higher in infants with HMD, regardless of the outcome, when compared to the infants ventilated for apnea of prematurity. This suggests that the pathology of HMD is distal to the conducting airways and significantly alters the viscoelastic properties of the lung on day 1. Using stepwise logistic regression, C_rsdum on day 1 and birth weight or gestational age were significant independent predictors of the development of BPD, correctly classifying 92% of infants. Due to the correlation between birth weight and gestational age (r = 0.72, P<0.0001). only one of these variables was necessary in the prediction model. In conclusion, C_rsdyn is a better independent predictor of the development of BPD in preterm infants with HMD than gestational age or birth weight. Pediatr Pulmonol. 1993; 16:116–123. © 1993 Wiley-Liss, Inc.     

The role of neural tension in hamstring flexibility

Resistance to stretch, electromyographic (EMG) response to stretch, stretch discomfort and maximum range of motion (ROM) were measured during passive hamstring stretches performed in the slump test position (neural tension stretch) and in the upright position (neutral stretch) in eight healthy subjects. Stretches were performed on an isokinetic dynamometer at 5°/s with the test thigh flexed 40° above the horizontal, and the seat back at 90° to the horizontal. Surface EMG signals were recorded from the medial and lateral hamstrings during stretches. Knees were passively extended to maximum stretch tolerance with test order (neural tension vs neutral) alternated between legs. For neural tension stretches, the cervical and thoracic spine were manually flexed. Maximum ROM was 8° less for the neural tension stretch vs the neutral stretch (P<0.01). Resistance to stretch was 14–15% higher for the neural tension stretch vs the neutral stretch (P<0.001) at common joint angles in the final third of ROM. Stretch discomfort and EMG response were unaffected by neural tension. In conclusion, an increased passive resistance to stretch with the addition of neural tension during passive hamstring stretch despite no change in the EMG response indicates that passive extensibility of neural tissues can limit hamstring flexibility.     

A Numerical Model for Investigating the Effect of Viscoelasticity on the Partial Slip Solution

To investigate the effects of viscoelasticity on the stick-slip behaviour, a new model reproducing the partial slip of viscoelastic materials under fully coupled conditions is developed in this paper. The ratio of retardation time to relaxation time is employed to characterize the rheological property of a viscoelastic material. It is found that materials with higher ratios exhibit more fluid-like behaviours while those with lower ratios perform more like solid. As long as the contact input (load or displacement) is constant, the stick ratio (ratio of stick area to contacting area) is found to be insensitive to the viscoelasticity of materials. However, the separation pattern of the stick and slip regions varies with time when different contact phenomena (creep or stress relaxation) are encountered in the lateral and normal directions. The transition process from partial slip to gross sliding of viscoelastic materials, unlike the elastic response, tends to be abrupt when fully coupled conditions between shear tractions and pressure are introduced. When identical contact parameters are specified for different viscoelastic materials, the more fluid-like material always experiences a quicker transition from partial slip to gross sliding.