Fatigue Analysis and Defect Size Evaluation of Filled NBR including Temperature Influence

The fatigue behavior of a filled non-crystallizing elastomer was investigated on axisymmetric dumbbell specimens. By plotting relevant Wöhler curves, a power law behavior was found. In addition, temperature increases due to heat build-up were monitored. In order to distinguish between initiation and crack growth regimes, hysteresis curves, secant and dynamic moduli, dissipated and stored energies, and normalized minimum and maximum forces were analyzed. Even though indications related to material damaging were observed, a clear trend to recognize the initiation was not evident. Further details were revealed by considering a fracture mechanics. The analysis of the fracture surfaces evidenced the presence of three regions, associated to initiation, fatigue striation, and catastrophic failure. Additional fatigue tests were performed with samples in which a radial notch was introduced. This resulted in a reduction in lifetime by four orders of magnitude; nevertheless, the fracture surfaces revealed similar failure mechanisms. A fracture mechanics approach, which considered the effect of temperature, was adopted to calculate the critical defect size for fatigue, which was found to be approximately 9 μm. This value was then compared with the particle size distribution obtained through X-ray microcomputed tomography (μ-CT) of undamaged samples and it was found that the majority of the initial defects were indeed smaller than the calculated one. Finally, the evaluation of J-integral for both unnotched and notched dumbbells enabled the assessment of a geometry-independent correlation with fatigue life.     

呼吸科常见疾病肠内营养的选择

目的:探讨呼吸科常见疾病肠内营养(EN)支持治疗的合理选择方案. 方法:临床药师对我院呼吸科住院病人进行营养状况筛查,分析其EN的使用情况,并对目前几种常用EN制剂的特点进行分析. 结果:呼吸科EN使用率较低,建议不同呼吸科疾病应分别选择EN制剂. 结论:EN支持治疗是呼吸科病人治疗方案中的重要组成部分.     

Clinical Characteristics and Risk Factors for Mortality in Critical Coronavirus Disease 2019 Patients 50 Years of Age or Younger During the Delta Wave: Comparison With Patients > 50 Years in Korea

BackgroundNumerous patients around the globe are dying from coronavirus disease 2019 (COVID-19). While age is a known risk factor, risk analysis in the young generation is lacking. The present study aimed to evaluate the clinical features and mortality risk factors in younger patients (≤ 50 years) with a critical case of COVID-19 in comparison with those among older patients (> 50 years) in Korea.MethodsWe analyzed the data of adult patients only in critical condition (requiring high flow nasal cannula oxygen therapy or higher respiratory support) hospitalized with PCR-confirmed COVID-19 at 11 hospitals in Korea from July 1, 2021 to November 30, 2021 when the delta variant was a dominant strain. Patients’ electronic medical records were reviewed to identify clinical characteristics.ResultsDuring the study period, 448 patients were enrolled. One hundred and forty-two were aged 50 years or younger (the younger group), while 306 were above 50 years of age (the older group). The most common pre-existing conditions in the younger group were diabetes mellitus and hypertension, and 69.7% of the patients had a body mass index (BMI) > 25 kg/m². Of 142 younger patients, 31 of 142 patients (21.8%, 19 women) did not have these pre-existing conditions. The overall case fatality rate among severity cases was 21.0%, and it differed according to age: 5.6% (n = 8/142) in the younger group, 28.1% in the older group, and 38% in the ≥ 65 years group. Age (odds ratio [OR], 7.902; 95% confidence interval [CI], 2.754–18.181), mechanical ventilation therapy (OR, 17.233; 95% CI, 8.439–35.192), highest creatinine > 1.5 mg/dL (OR, 17.631; 95% CI, 8.321–37.357), and combined blood stream infection (OR, 7.092; 95% CI, 1.061–18.181) were identified as independent predictors of mortality in total patients. Similar patterns were observed in age-specific analyses, but most results were statistically insignificant in multivariate analysis due to the low number of deaths in the younger group. The full vaccination rate was very low among study population (13.6%), and only three patients were fully vaccinated, with none of the patients who died having been fully vaccinated in the younger group. Seven of eight patients who died had a pre-existing condition or were obese (BMI > 25 kg/m²), and the one remaining patient died from a secondary infection.ConclusionAbout 22% of the patients in the young critical group did not have an underlying disease or obesity, but the rate of obesity (BMI > 25 kg/m²) was high, with a fatality rate of 5.6%. The full vaccination rate was extremely low compared to the general population of the same age group, showing that non-vaccination has a grave impact on the progression of COVID-19 to a critical condition. The findings of this study highlight the need for measures to prevent critical progression of COVID-19, such as vaccinations and targeting young adults especially having risk factors.     

利多卡因过敏性休克伴呼吸循环骤停急救1例报告

报告1例6岁女孩在局麻注射利多卡因时,即刻发生过敏性休克伴呼吸循环骤停的抢救经过和体会。利多卡因过敏反应虽十分罕见,但可能发生速发型过敏性休克甚至呼吸循环骤停而致死。普鲁卡因过敏或过敏性体质者可改用利多卡因,但应先做皮试,并备好氧气和急救药品,以防不测。抢救成功的关键是及时正确的诊断和急救,首选药物是肾上腺素。     

cAMP and voltage modulate rat auditory mechanotransduction by decreasing the stiffness of gating springs

Hair cells of the auditory and vestibular systems transform mechanical input into electrical potentials through the mechanoelectrical transduction process (MET). Deflection of the mechanosensory hair bundle increases tension in the gating springs that open MET channels. Regulation of MET channel sensitivity contributes to the auditory system’s precision, wide dynamic range and, potentially, protection from overexcitation. Modulating the stiffness of the gating spring modulates the sensitivity of the MET process. Here, we investigated the role of cyclic adenosine monophosphate (cAMP) in rat outer hair cell MET and found that cAMP up-regulation lowers the sensitivity of the channel in a manner consistent with decreasing gating spring stiffness. Direct measurements of the mechanical properties of the hair bundle confirmed a decrease in gating spring stiffness with cAMP up-regulation. In parallel, we found that prolonged depolarization mirrored the effects of cAMP. Finally, a limited number of experiments implicate that cAMP activates the exchange protein directly activated by cAMP to mediate the changes in MET sensitivity. These results reveal that cAMP signaling modulates gating spring stiffness to affect auditory sensitivity.

Hair cells of the auditory and vestibular systems convert mechanical input from sound and head movement into an electrical current through a process termed mechanoelectrical transduction (MET). At the apical surface of each hair cell is a specialized mechanosensitive organelle called the hair bundle, composed of a collection of actin-filled stereocilia arranged in graded height. The tips of the shorter rows house MET channels (1), nonspecific cation channels hypothesized to be comprised of TMC1/2, TMIE, and a number of other accessory proteins (2–4). MET channels are gated by a tension force imparted by a gating spring, which is part of or connected with the filamentous tip links that span adjacent rows of stereocilia (5–9). Positive stimuli directed along the sensitive axis of the hair bundle (10) result in displacement toward the tallest row and increase tension in the gating spring, increasing the open probability of the MET channel.Mechanisms that regulate the sensitivity of the MET channel are hypothesized to contribute to the wide dynamic range and frequency selectivity of the auditory system, with MET adaptation being the most widely studied (11–14). Based on the gating spring theory, changes in gating spring stiffness alter the setpoint and the sensitivity of the MET channel (5, 6). The second messenger cyclic adenosine monophosphate (cAMP) has been proposed to modulate the sensitivity of the MET channel in turtle and bullfrog hair cells. In turtle auditory hair cells, cAMP shifts the operating point of the MET channel after a period of minutes, extending the dynamic range of the channel (15). In bullfrog hair cells, pharmacological up-regulation of cAMP reduced the frequency of spontaneous hair bundle oscillations (16). Furthermore, in humans, a loss of function mutation in adenylyl cyclase 1 (ADCY1, an enzyme that catalyzes cAMP production) is associated with hearing loss (17) and zebrafish carrying an equivalent mutation (adcy1b morphants) exhibited significantly reduced fn1-43 dye uptake in lateral line hair cells, indicating dysfunctional MET. These studies indicate a potential role for cAMP in modulating MET channel sensitivity in mammals.In this study, we determine the mechanism of cAMP modulation of the MET channel in a mammalian cochlear hair cell model. We first characterized the cAMP effect in rat outer hair cells (OHCs). Second, we describe a long depolarization manipulation (LDM), which we found mirrored the effects of cAMP up-regulation. Third, by measuring the mechanical changes of the hair bundle, we confirmed that cAMP and long depolarization-induced effects on channel sensitivity are due to a reduction in gating spring stiffness. Finally, we find that cAMP targets the exchange protein directly activated by cAMP (EPAC) rather than protein kinase A (PKA) for modulating MET sensitivity. This cAMP regulation of gating spring stiffness provides a cell signaling means for controlling the sensitivity of MET channels.     

小剂量多巴胺对高原老年慢性肺心病患者呼吸肌疲劳治疗作用的研究

目的 :观察多巴胺对高原地区老年肺心病患者呼吸肌功能的影响。方法 :4 8例老年肺心病患者随机分为观察组 (A组 )和对照组 (B组 ) ,每组 2 4例。A组用多巴胺 6 0mg加入 10 %葡萄糖溶液 15 0ml,以 5 μg·kg-1·min-1的速度静滴作为治疗。B组用等量 10 %葡萄糖溶液 ,以同样速度静滴作为对照。用药前、后测定肺功能、呼吸肌功能和心功能。结果 :用药前 ,两组一秒钟用力呼气容积占预计值百分比 (FEV1%预计值 )、动脉血氧分压 (PaO2 )、二氧化碳分压 (PaCO2 )、最大吸气压 (PImax)、最大呼气压 (PEmax)、最大跨膈压 (Pdimax)、呼吸肌力量指数 (RMS)、心脏指数 (CI )和心搏指数 (SI)差异无显著性。用药后 ,A组PI max、PEmax、Pdimax、RMS、CI、SI显著高于用药前 (P均 <0 .0 1) ,B组各项指标无显著性变化。A组用药后PImax、PEmax、Pdimax、RMS与CI呈显著正相关 (r=0 .6 74、0 .5 4 1、0 .6 6 9、0 .6 2 9,P均 <0 .0 1)。结论 :小剂量多巴胺有显著增强呼吸肌功能的作用 ,可作为高原肺心病的辅助治疗。     

Passive expiratory flow-volume curve is not an accurate method to measure the respiratory time constant in rabbits

BACKGROUND: In mechanically ventilated patients, inspiration is forced by an externally applied positive pressure whereas expiration remains passive and depends on the time constant of the total respiratory system (tau), which constitutes an important determinant of mechanical ventilation. The end-inspiratory occlusion technique is one of the easiest methods to obtain tau values in ventilated patients, especially infants, but its accuracy is not well established. The aim of this study was to compare in anesthetized, paralyzed rabbits tau values given by the end-inspiratory occlusion technique (tau(rs)) to tau values obtained by references methods for measurements (i.e. the product of static lung compliance by airway resistance: tau(ref)) during carbachol-induced bronchospasm eliciting marked modifications of the respiratory mechanics. METHODS: Comparisons were made in the basal state and after carbachol-induced bronchoconstriction in seven New Zealand adult rabbits. This procedure resulted in a wide range of expiratory time constants. A pneumotachograph was used to measure expiratory flow and volume before and after end-inspiratory occlusion. The slope of the flow volume curve gave tau(rs). Then tau(rs) was compared with tau(ref) (which ranged from 0.30 to 1.96 s). RESULTS: Statistical analysis revealed a weak correlation between the two methods, and a size-dependent bias of tau(rs) measurements. CONCLUSIONS: The end-inspiratory occlusion technique leads to a systemic bias in measurements of respiratory time constant, especially when the resistance of the respiratory system is elevated.     

机械通气对ICU肺动脉高压伴呼吸衰竭患者血浆脑钠肽水平的影响

目的 :探讨机械通气对ICU肺动脉高压伴呼吸衰竭患者血浆脑钠肽(BNP)水平的影响。方法 :挑选82名需要进行机械通气的肺动脉高压伴呼吸衰竭患者,随机分成两组,每组41名成员。无创组在常规治疗的基础上提供面罩呼吸机辅助呼吸,有创组在常规治疗的基础上提供气管切开或气管插管呼吸机辅助呼吸。分别统计治疗前及治疗24h后两组患者血气分析结果、血浆BNP含量及肺动脉压的变化。结果 :治疗24h后两组患者动脉血气分析指标均较治疗前有显著改善,此外有创机械通气组较无创机械通气组动脉血气分析指标略低,同时两者血浆BNP含量及肺动脉压力均明显降低,有创机械通气组患者较无创机械通气组患者下降明显。结论 :有创机械通气治疗ICU肺动脉高压伴呼吸衰竭患者较无创机械通气治疗效果显著。机械通气可以降低BNP浓度,其浓度变化有创机械通气效果优于无创机械通气。     

涂覆草酸钇薄膜改善氮化铝粉耐水性及其机理

研究了表面涂覆草酸钇薄膜对氮化铝（ＡｌＮ）粉耐水性的影响。结果显示：涂膜后ＡｌＮ粉在１００℃沸水中回流４５ｍｉｎ不与水反应，温度降至７８℃时可耐水３ｈ以上；耐水时间随涂覆量增加而增加，随温度升高而下降。水分子通过薄膜的扩散过程是影响ＡｌＮ耐水性的决定因素。用Ｘ光电子能谱（ＸＰＳ）和红外光谱测定了表面草酸钇与ＡｌＮ界面形成的化学键。