Influence of age and of desmotropic drugs on the step phenomenon observed in rat skin

Summary Comprehensive analysis of the mechanical properties of rat skin revealed the step phenomenon. This particular observation was made after constant strain rate (analysis of stress strain curves) as well as after constant load (creep experiments). Relative low extensions or low loads were necessary to provoke the steps. In most cases two, sometimes three steps were observed. The step phenomenon was found mainly in skin strips punched out perpendicularly to the body axis. Probably some bonds in the fibrous network are broken giving way to additional elongation whereafter stronger links take over the stress. Since earlier studies demonstrated a pronounced influence of age and of desmotropic drugs on mechanical properties at ultimate load, e.g., tensile strength, ultimate modulus of elasticity, and ultimate strain, also the step phenomenon was studied under these conditions. In stress-strain experiments most of the steps were found at the ages of 2 and 4 months. Total stress loss and total work loss due to the steps were the highest at the age of 4 months. If, however, these values were calculated as percentage of ultimate values, the highest figures were found in young animals. Elongation gain due to the steps also showed a maximum at time of maturation, e.g., 4 months. Similar findings were achieved in creep experiments at medium load (200 g). After treatment with prednisolone acetate more steps and after treatment with d-penicillamine fewer steps were observed. In stress-strain experiments total stress loss and total work loss due to steps were more than twice as high than controls after prednisolone treatment and only one half after d-penicillamine. If calculated as percentage of ultimate stress or percentage of work input, these changes disappeared because of similar changes at ultimate load. However, elongation gain due to steps, which was not significantly influenced by prednisolone acetate but significantly decreased by d-penicillamine, showed the same changes when calculated as percentage of ultimate strain. Under all conditions the step phenomenon mainly influenced the extension parameters. The data presented here confirm earlier observations that mechanical properties at low loads or low and medium extensions show at least to some extent a different pattern under the influence of maturation and age and after treatment with desmotropic drugs compared to the mechanical parameters at ultimate load.     

Modeling lipid uptake in expanded polytetrafluoroethylene vascular prostheses and its effects on mechanical properties

The radial transport across the wall of expanded polytetrafluoroethylene (ePTFE) arterial prostheses has a significant effect on lipid uptake observed in prostheses implanted in humans, which has been postulated to be one of the causes associated with implant failure. The goal of this study was to stimulate radial transport on a lipidic dispersion across the wall of an ePTFE prosthesis and investigate its effects on the circumferential mechanical properties of the prosthesis. An in vitro model was developed to simulate the lipidic radial transport across the wall. Lipids contained in a phosphatidylcholine dispersion were used as the transported molecules. Lipid concentration profiles were obtained after exposing commercial ePTFE prostheses to various transmural pressure and/or lipidic concentration gradients. Phospholipids gradually accumulated up to the external reinforcing wrap of the prosthesis, which clearly acted as a rigid barrier against lipid infiltration. Tensile tests performed on the virgin samples showed that the wrap was much more rigid than the microporous part of the prosthesis. After the lipid simulation, the rigidity of the wrap decreased with respect to what was observed for the virgin prosthesis. Finally, some clinical implications of this phenomena are discussed.     

Design and test of a vascular access device

Transarterial left ventricular assist devices (LVADs), such as the Hemopump, IABP, and PUCA-pump, are meant to be introduced into the body via the femoral or axillary artery without major surgery. For certain applications, introduction is performed directly into the aorta via an open thorax procedure. A prototype of a vascular access device has been realized that allows direct access into the aorta as an alternative for the common surgical graft anastomosis suturing technique. The device consists of a metal tube acting as a circular knife to cut a hole in the aortic wall, a screw to store the removed part of the aortic wall, and a plastic tube that is introduced through the hole and tightly connected to the aortic wall. The device could be placed without aortic clamping. The device has been tested on a slaughterhouse porcine aorta. A low-pressurized aorta appeared to be the worst case; thus, two animal experiments in the low-pressurized pulmonary artery were performed. No leakage occurred for pressures between 40 and 300 mm Hg.     

Is Avoidance of Air Contact Necessary for the In Vitro Evaluation of Thrombogenicity in Mechanical Circulatory Assist Devices?

An effective in vitro protocol for the investigation of thrombogenicity can provide many advantages in the development of mechanical circulatory assist devices. Strict avoidance of air contact with blood recently was proposed for reliable in vitro evaluation. This study was performed to confirm the necessity of avoidance of air contact for the in vitro test of thrombogenicity in a rotary pump. Two sets of mock circuits with the same rotary blood pumps, reservoirs, and connecting tubes were made. In one system, blood came in contact with air while the other did not. The test blood was heparinized at the dose of 1 IU per 1 ml of blood. The tests were terminated at an activated coagulation time of 1.5 times the control value. The levels of hematocrit, platelet, factors VIII and XII, fibrinogen, thromboxane B2, and plasma-free hemoglobin were measured during the procedures. After the experiments, the thrombi formed were observed, measured, and compared with those formed in in vivo circumstances. The tests were repeated 12 times. There were no statistically significant differences between the 2 groups in hematologic parameters and the amounts of thrombi formed. The thrombi observed in both groups showed the same pathologic findings as those formed in vivo with the exception of intermittent multiple air bubbles found in thrombi of the air-contact group. In conclusion, the effect of air contact in the in vitro investigation of thrombogenicity was negligible while the proposed in vitro test models of thrombogenesis in the mechanical circulatory assist device proved to be reliable.     

氧气驱动雾化吸入肾上腺素在减轻新生儿机械通气拔管后喉水肿中的应用

目的观察氧气驱动吸入肾上腺素对减轻新生儿机械通气拔管后喉水肿的疗效。方法88例机械通气的新生儿随机分为两组,对照组43例,在拔管前1h静脉注射地塞米松0.5mg/kg,拔管后予以地塞米松2mg加生理盐水2ml,用6L/min氧气驱动雾化吸入,2h1次。治疗组45例,拔管后立即予以肾上腺素1mg加生理盐水2ml,用6L/min氧气驱动雾化吸入,2h1次,雾化4~5次后改用常规雾化吸入。两组均予以吸氧、吸痰、抗感染等处理。结果治疗组总有效率86.6%,明显优于对照组(总有效率67.4%)(P<0.05)。结论氧气驱动雾化吸入肾上腺素对减轻新生儿机械通气拔管后喉水肿效果明显,值得临床推广应用。     

Risk factors for respiratory syncytial virus associated apnoea

Respiratory syncytial virus (RSV) infections are characterized by upper or lower respiratory tract symptoms including bronchiolitis and pneumonia. Apnoea may be the first sign of disease in children with RSV infection. The aims of this study were the identification of independent risk factors for RSV associated apnoea and the prediction of the risk for mechanical ventilation in children with RSV associated apnoea. Medical records of children younger than 12 months of age admitted with RSV infection between 1992 and 1995 to the Sophia Children's Hospital, were reviewed. Demographic parameters, clinical features and laboratory parameters (SaO₂, pCO₂ and pH) were obtained upon admission and during hospitalization. Children with and without apnoea were compared using univariate and multivariate logistic and linear regression analysis. One hundred and eighty-five patients with RSV infection were admitted of whom 38 (21%) presented with apnoea. Patients with apnoea were significantly younger, had a significantly lower temperature, higher pCO₂ and lower pH and had on chest radiographs also more signs of atelectasis. The number of patients admitted to the ICU because of mechanical ventilation and oxygen administration was significantly higher in children with RSV associated apnoea. Apnoea at admission was a strong predictor for recurrent apnoea. The relative risk for mechanical ventilation increased with the number of episodes of apnoea: 2.4 (95% CI 0.8 – 6.6) in children with one episode of apnoea (at admission) versus 6.5 (95% CI 3.3 – 12.9) in children with recurrent episodes of apnoea. Conclusions Age below 2 months is the strongest independent risk factor for RSV associated apnoea. Apnoea at admission increases the risk for recurrent apnoea. The risk for mechanical ventilation significantly increases in children who suffer from recurrent apnoea. Received: 12 May 1997 / Accepted in revised form: 22 August 1997     

修复贝尔克血透机同一报警编码不同故障原因的故障

重庆市中医研究院医疗器械维修小组在维修贝尔克(Bellco)公司的formula(tm)型血液透析机压力传感器的不同故障中的心得体会.     

长期机械通气的老年患者医院内肺部感染的调查

目的调查和分析长期应用机械通气的老年患者医院内常见的肺部感染。方法对2002年1月~2005年6月住院期间中长期应用机械通气的69例患者进行回顾性分析;对其中普通肺炎的相关危险因素进行Logistic回归分析。结果69例患者中发生普通肺炎53例,肺结核7例,结核性胸膜炎1例,非结核分枝杆菌3例,卡氏肺囊虫8例;引发普通肺炎的相关危险因素是应用通气机的时间和误吸。结论缩短用通气机时间和防止误吸是预防普通细菌性肺炎的重要措施;对长期机械通气的老年患者,还要警惕结核分枝杆菌、非结核分枝杆菌以及卡氏肺囊虫引起的肺部感染。     

机械通气治疗腹部外伤术后成人呼吸窘迫综合征

目的探讨机械通气对腹部外伤术后成人呼吸窘迫综合征(ARDS)的治疗作用。方法对24例本病患者采用A/C、SIMV、PEEP、正比呼吸模式及综合治疗。结果抢救成功14例,死亡10例,分别死于心、肾、脑等脏器功能衰竭。结论早期和及时有效的机械通气是救治腹部外伤术后ARDS的重要手段。     

机械通气下极低出生体重儿颅内出血相关因素分析

目的:探讨机械通气下极低出生体重儿(VLBW I)发生颅内出血的相关因素。方法:以NICU收治的机械通气治疗的VLBW I为研究对象,分为颅内出血组和无出血组进行对比分析。结果:颅内出血发生率为47.2%,两组VLBW I孕周越小,上机时间越早,持续时间越长者,越易发生颅内出血。而两组患儿出生体重、1分钟及5分钟Apgar评分均无显著差别(P>0.05);两组的最高FIO2、PIP、PEEP均无显著差别(P>0.05);两组患儿上机前后血气分析PCO2最高及最低值均无显著差别(P>0.05)。结论:在VLBW I需机械通气治疗时,除严格掌握机械通气的指征外,应尽早使用外源性肺表面活性物质,以延迟开始上机时间,缩短用机持续时间,并采取肺保护性通气策略,可减少机械通气下的VLBW I发生颅内出血。